2007
May 3
Title : When Should Lactating Dairy Cows Reach Positive Energy Balance?
Source : University of Wisconsin
Author : Grummer, Rastani
Date :  
Content :  

When Should Lactating Dairy Cows Reach Positive Energy Balance?

Energy Balance (EB)

EB = Energyconsumed- Energyrequired

Energyrequired=Energymaintenance+Energygrowth+ Energypregnancy+ Energyproduction

Energy Balance

  • Positive EB = cow stores energy, primarily in adipose tissue and gains weight
  • Negative EB = cow mobilizes energy, primarily fat, as an energy source and looses weight

Severe or Prolonged Negative Energy Balance May Cause

  • Metabolic disorders
  • Compromised immune system
  • Greater postpartum interval to ovulation
  • Lower conception rate
  • Poor lactation performance

Energy Requirement for

Factors Affecting EB

  • Maintenance requirements for energy are related to body weight and are relatively constant among cows.
  • Energy requirements for fetal growth and growth of immature cows is relatively small compared to energy requirements for milk production.
  • Energy intake and energy output in milk are the two most likely candidates to affect EB!

Objectives

  • To survey the scientific literature to determine:
    • When do cows typically return to positive energy balance following parturition
    • If there are factors that are likely to influence when a cow returns to positive energy balance

Literature Survey

  • Twenty studies published in peer-reviewed journals between 1988 and 2001
  • 52 dietary treatments
  • Data collected:
    • Days to positive energy balance
    • Days to peak milk yield
    • Peak milk yield
    • Energy density of diet

Days to Positive Energy Balance

For 90% of treatments, cows reached energy balance by 63 d postpartum

A Recent Research Trial-Univ. of Wisconsin

  • 24 primi-and 49 multiparous cows
  • Fed diets ranging from 1.70 -1.74 Mcal NEl/kg DM
  • Weekly means for EB, FCM yield (kg/d), NEl intake (Mcal/d)

Correlations Between Weekly Means for Daily EB and FCM Yield or NEl intake

  FCM NEI Intake
r P r P
All Cows -.26 <.0001 .58 <.0001
Primiparous -.15 .001 .75 <.0001
Multiparous -.33 <.0001 .69 <.0001

Estimating EB on Farm??

  • Essentially impossible
  • Can not use milk yield!
  • BCS is not the answer
    • Too insensitive
    • Takes a minimum of approximately 3 wk to accurately measure change in BCS
    • Does not measure inter-muscular and abdominal fat where fat storage begins

Conclusions

  • There is little evidence to indicate level of milk production is a predictor of the amount of time to reach positive EB
  • At any snapshot in time, energy intake is more closely related to EB than milk yield

Conclusions

  • However, energy intake (at any time) was not a good predictor of the amount of time to reach positive EB
  • Avoiding high milk yield is not a logical approach to avoid negative EB and problems associated with negative EB

Source: University of Wisconsin
Author: Rastani Grummer

History of Bovine Somatotropin

Posted by admin on Sep 15th, 1999
1999
Sep 15

Bovine somatotropin (BST)

Institute Of Food Science & Technology
September 1999

Summary

[Special Note: Having regard to the current conflict of interpretation of evidence, this Information Statement represents an IFST overview of the present position in relation to this topic, and does not imply that IFST has adopted a position in relation to the continuing controversy].

The effects of BST treatment of cows in relation to human health and animal health have been re-evaluated by the Food and Drug Administration (FDA) in USA, and have been evaluated by independent assessments for the Canadian authorities, by Codex Alimentarius and by scientific committees of the European Union.

The US and Canadian assessments both concluded that products from BST-treated cows present no hazard to human health, and this is supported by the Codex assessment. However, the EU assessment is inconclusive, while drawing attention to potential hazards requiring more research.

The US reassessment reaffirmed that BST treatment is not harmful to animal health, but both the Canadian and EU assessments concluded that it is harmful to animal health.

Background

BST is, confusingly, referred to variously as BST or rbST, or, rbST or rBGH). Here the term BST is used except where quoting from the relevant documents, in which case the term used in a particular document has been retained, and when directly comparing “natural” BST with recombinant BST.

Somatotropin is a proteinaceous hormone produced by the anterior pituitary gland situated at the base of the brain. After its discovery in the 1930’s, it was found that rats in the growth phase when injected with a crude rat pituitary extract underwent increased growth rate. In the 1950’s, it was discovered that certain types of human dwarfism were due to an inadequate pituitary production of somatotropin. However, clinical trials involving the injection of these patients with BST demonstrated that BST was not biologically active in humans.

BST is produced naturally by all cows and has direct and indirect effects in coordinating the metabolism of various body organs and tissues to the requirements of milk production, In particular by promoting production of the hormone IGF-1, which stimulates glands in the cow’s udder. Small quantities of BST are found in all cows’ milk. More recently, high-yielding dairy cows were found to have higher circulating levels of naturally occurring BST, and it was discovered that the injection of BST could increase the milk yield of cows by minimising the rate of yield decline after peak lactation (BST can only produce a biological effect by injection - the oral route leads to its breakdown under acidic conditions by proteases in the digestive system).

The early experiments, many conducted in the UK, were carried out with BST extracted from the pituitary glands of slaughtered cows, not a supply suitable for extensive agricultural use. The application of modern biotechnology has resulted in the development of recombinant BST (referred to variously as rbST, or, rbST or rBGH), identical in activity to natural BST. This is done by taking, from the DNA of cows, the specific gene sequence that carries the instructions for making BST, and inserting it into E coli, which can then produce large amounts of recombinant BST.

The amino acid sequence of BST, which gives it its three-dimensional shape, differs by about 35% from that of human somatotropin (HST) - the bearing of this on human health is discussed below. BST can either be 190 or 191 amino acids long; in addition, there can be either of two different amino acids (leucine or valine) at position number 126 in the sequence. Thus, four different variants of BST are produced naturally. rbST may differ slightly, in that a few extra amino acids may be attached at the N-terminal end of the BST molecule in the manufacturing process. The additional amino acids on the end of the protein do not alter its biological activity because the three-dimensional shape of the active part of the molecule which binds to the tissue receptors is not changed. They are solely present as a result of the additional base-pairs on the BST gene which have been added to aid the bacteria to express the gene in the most efficient manner during production of rbST. However, they confer on rbST an increased molecular weight over that of natural BST.

Recent developments in electro-spray mass spectrometry analysis have made it possible to use the difference in molecular weight to distinguish between them. This technique has been used to determine the differences in molecular weight between the natural BST and one of the recombinant products (Somagrebove®). Purified preparations of bovine pituitary BST and rbST were used (Scippo et al, 1997).

BST Application

Treatment of cows with BST was approved in February 1994 by the Food and Drug Administration (FDA) for use in USA , and has been extensively used over the ensuing period. In addition, regulatory agencies in 34 countries have reached similar conclusions with respect to food safety, 24 of which have actually given approval for use of BST, namely Algeria, Brazil, Bulgaria, Columbia, Costa Rica, Czech Republic, Honduras, Hungary, Jamaica, Kenya, Korea, Malaysia, Mexico, Namibia, Pakistan, Peru, Romania, Russia, Slovakia, South Africa, Turkey, UAE, Ukraine and Zimbabwe.

In use, the product is presented in filled syringes, for subcutaneous administration, at the tailhead, once every 14 or 28 days to cattle to increase milk production and improve the efficiency of feed use. It is normally applied only to certain lower-yielding cows within a herd, and only during the later period of their lactation, Because of the bulking of milk from a herd, in such herds segregation of milk from BST treated cows is impracticable.

At present BST treatment is not permitted in in the European Union (EU), where there has been a moratorium on its use since 1993, initially intended to give time to study the situation and prompted mainly by the regime of milk quotas to avoid over-production. In 1994 the moratorium was extended to 31 December 1999. If its use were to be considered in the UK or EU, BST would fall within the legal definition of a medicinal product, requiring a licence for marketing. Applications for a licence are considered in the UK by the VPC, the independent scientific body established under the Act to advise the Health and Agriculture Ministers on applications for product licences and certificates. Its members are drawn from various fields of animal and human health, including veterinary science, toxicology, pharmacology and human medicine, statistics and environmental sciences. A company applying for approval of a product is required to provide all relevant scientific data (including the full range of comparative analyses of milk composition, toxicological studies, and the results of investigations into how recombinant BST is metabolised during human digestion) for assessment by the Committee. Unless these data indicate that the product meets the licensing criteria of safety, quality and efficacy, the company is asked to undertake further work if it wishes to proceed with its application. Safety in this respect also covers the welfare of treated animals.

In 1993 the EU Committee on Veterinary Medicinal Products (CVMP) stated that, if permitted, BST should only be available within the Community on veterinary prescription, and also recommended that systematic and clearly defined procedures should be established for the collection and evaluation of any adverse drug reaction reports associated with the use of the products. Successful use of the product would require a high quality nutritional regime for treated animals, good hygiene at the injection site, ongoing monitoring of somatic cell counts of milk obtained from treated animals, and the inclusion of detailed instructions for use on product labels and all product-related literature. These requirements are normal for such products. To derive the maximum benefits from the use of BST, veterinary advice would be needed as to the cows to which it should be administered, the appropriate timing of such administration, and the nutritional and reproductive management of animals to which it has been administered. The CVMP considered that appropriate advice should be included on the packaging stating that BST should not be used on first lactation heifers and should not be used in other dairy cows until pregnancy is confirmed. The CVMP concluded that it was important to verify that the overall level of risk to the health and welfare of the target animal is not increased when BST is used under commercial conditions. It therefore recommended that, if licensed, a wide ranging structured study of at least two years duration should be undertaken under veterinary supervision to determine the effects of BST on the incidence of mastitis and associated metabolic disorders under practical conditions of use. Interim reports would be required to be presented to Member States and the CVMP at the end of the first and second years of the study. In addition a structured programme of adverse reaction reporting should also be established, and consolidated reports, including information about sales and the number of doses sold, would be required to be presented to Member States and the CVMP every six months in the first two years following authorisation, and annually thereafter until the 5 yearly renewal becomes due. Suspected adverse reaction reports would include possible effects on both animals and humans.

Evaluations and Debate

There has been, and continues to be, controversy about the use of BST, originating with opponents of its approval before and after its approval by the FDA in the USA in February 1994, but spilling over into the rest of the world and especially Europe and Canada. Expressed concerns have centred on four main aspects, human health, animal health and welfare, labelling and socio-economic aspects. Objective assessment has been clouded by media-amplified fears generated by organisations and individuals opposed to any use of modern biotechnology, and confusion caused by trade-motivated use of selectively emphasised evidence.

In USA the FDA has maintained its position that milk from BST-treated cows is not significantly different from milk from untreated cows, and as regards animal health points to its post-approval monitoring program (PAMP). The PAMP was the most extensive post-approval study ever conducted on any animal product in USA. Special drug experience reports were submitted to FDA’s Center for Veterinary Medicine (CVM) every 90 days, including the status reports, units of product distributed, etc, The herd component involved 28 commercial herds representing 1213 cows in key dairy States to reflect the health of dairy cattle given POSILAC 1 STEP® (the trade name used by Monsanto for its BST product) for a single lactation under commercial conditions. Stringent requirements were placed on the participants regarding data collection, record-keeping, veterinary consultation, daily observations, etc. Information provided from the State tracking programme showed that there had been no changes in the percentage of milk discarded due to violative residues attributable to the use of POSILAC. Based upon the results of the 28 herd study and summarisation of Adverse Drug Experience Reports, CVM concluded that the effects of POSILAC on animal safety and effectiveness were in close agreement with the effects observed in pre-clearance studies. During public hearings held on 29 May and 20 November 1996, FDA’s Veterinary Medicine Advisory Committee also concluded from the PAMP that the labelling for POSILAC provides adequate pack directions for actual conditions of use and that POSILAC is safe and has no adverse effect on the milk supply. Published scientific studies in USA (e.g. White et al, 1994; Judge et al, 1997) also supported the earlier conclusions.

In February 1999, FDA’s Center for Veterinary Medicine (CVM) issued an Update, in which it reported that it had conducted a review of the human safety aspects of the use of rbST, stimulated by the product’s review for approval in Canada (see below). The CVM review upheld the FDA’s original conclusion that milk from cows treated with rbST is safe for human consumption.

In 1998, FAO/WHO revisited BST in the light of the most up-to-date research evidence. The Joint FAO/WHO Expert Committee on Food Additives (JECFA), met at FAO in Rome from 17 to 26 February 1998. JECFA’s work on the safety of residues of veterinary drugs in food includes establishing acceptable daily intakes (ADIs) and maximum residue limits (MRLs) for certain drugs when they are administered to food-producing animals in accordance with good animal husbandry practices. In the area of maximum residue limits (MRL) for BST, JECFA found that available data on the identity and concentration of residues in animal tissues provide a wide margin of safety for consumption of residues in food when the drug is used according to good practice in the use of veterinary drugs. The Committee concluded that the presence of drug residues in animal products does not present any human health concerns.

JECFA also considered possible problems such as the likelihood of a possible increase in the udder disease mastitis in BST-treated cows which could lead to contamination of milk with antibiotics used to treat mastitis. It concluded that the use of BST will not result in a higher risk to human health due to the use of antibiotics to treat mastitis and that the increased potential for drug residues in milk could be managed by practices currently in use by the dairy industry and by following label directions for use.

The Codex Committee on Residues of Veterinary Drugs in Food (CCRDVF), acting on the advice of JECFA, recommended that the Codex Alimentarius Commission should adopt a Maximum Residue Limit (MRL) for BST in food. The European Commission opposed the advancement of an MRL for rbST to Step 8 of the procedure for Elaboration of a Codex Standard which would mean a recommendation for acceptance by Codex. The EU wished to retain the proposal at Step 7 until a full JECFA report was available and the outcome of the Codex Committee on General Principles. Nevertheless, the Chairman of the CCRDVF decided to take the proposal forward for discussion in the Codex Commission in June 1999, where, however, the matter was withdrawn from the agenda.

Although the use of BST has been under review in Canada since 1990, Canadian examination of the issues was brought to a head in 1998 following a company’s application for approval. The Canadian Health Department (Health Canada) referred the matter to two independent committees set up at its request in 1998 “to review the adequacy of scientific data and broader issues related to the use of bovine growth hormone in Canada”. The two committees were the Expert Panel on Human Safety of rbST , set up by the Royal College of Physicians and Surgeons of Canada, and the Expert Panel on rbST set up by the Canadian Veterinary Medical Association (CVMA). The Expert Panel on Human Safety “found no significant risk to human safety through ingestion of products from rbST-injected animals”. However, the Panel of the CVMA found that rbST “presents a sufficient and unacceptable threat to the safety of dairy cows”.. Health Canada concluded in January 1999 that “The findings of the animal safety committee, when combined with our own assessment, made it quite clear that Health Canada had to reject the request for approval to use rbST in Canada, as it presents a sufficient and unacceptable threat to the safety of dairy cows’ (an animal health finding directly contrary to FDA’s).

In the European Union, the re-examination of the issues during 1999 has arisen from the fact that the moratorium since 1990 on BST treatment (initially to give time to study the situation, and extended in December 1994 mainly on animal welfare and socio-economic grounds) is due to expire in December 1999.

The EU Scientific Committee on Veterinary Measures relating to Public Health (SCVMPH) was asked to examine the use of BST to dairy cows as a productivity aid to milk production. In particular the Committee was invited to assess the possible direct and indirect adverse effects on public health caused by the use of BST under normal conditions. The Committee did not reach a clear-cut judgement, but pointed to areas where it considered more research was needed, concluding:

  • “Direct risks associated with the use of rbST in dairy cows appear to be related to the possible increase of IGF-1 levels in milk. The diverse biological effects attributable to the intrinsic activity of IGF-1, exerting a broad variety of metabolic responses through endocrine, paracrine and autocrine mechanisms, make the definition of an in vivo quantitative dose-effect relationship virtually impossible.
  • Risk characterisation has pointed to an association between circulating IGF-1 levels and an increased relative risk of breast and prostate cancer. In addition, the possible contribution of life span exposure towards dietary IGF-1 and related proteins, present in milk from rbST treated cows, to gut pathophysiology particularly of infants, and to gut associated cancers need to be evaluated.
  • The available data basis for exposure assessment, i.e. the amount of IGF-1 and/or its truncated forms excreted in milk following the administration of rbST to dairy cows, is incomplete.
  • In addition secondary risks associated with the use of rbST in dairy cows are:
    1. Potential changes in milk protein composition which might favour allergic reactions.
    2. An increased use of antimicrobial substances in the treatment of rbST related mastitis which might lead to an increased risk of residue formation in milk and to the selection of resistant bacteria. “

    In a parallel exercise, the EU Scientific Committee on Animal Health and Animal Welfare (SCAHAW)was asked to report on the incidence of mastitis and other disorders in dairy cows and on other aspects of the welfare of dairy cows. The Committee stated

    “BST use substantially increases foot problems, mastitis and injection site reactions in dairy cows. These conditions are painful and debilitating, leading to significantly poorer welfare of the animals. BST also causes reproductive disorders. Therefore, from the point of view of animal welfare and health, this substance should not be used.”

    On the matter of animal health, the Canadian and EU assessments run directly contrary to those of the FDA and JECFA. Opponents of the use of BST argue that FDA is defending its past decision and the interests of a US company, and that JECFA was unduly influenced by the US position. Supporters of its use point out that FDA’s assessment was the only one based on actual experience and real data arising from the PAMP. The UK Veterinary Products Committee (VPC) has been asked by the UK Government to review the latest scientific information relating to the safety of BST. A VPC Working Group of experts in veterinary medicine, toxicology and effects of IGF-1 has been set up.and is expected to report to the VPC some time in Summer 1999, following which the VPC report to Ministers will be published. The science of the issues taken account of in the foregoing assessments is considered in more detail below.

    Human Health – General

    This may be considered in two categories, namely the possible effect of BST itself and the possible effect of IGF-1.

    The above-mentioned clinical studies on treatment of human dwarfism established that BST does not elicit any of its recognisable biological actions in humans even if injected. The reason for this is that, in consequence of its amino acid sequence, its three-dimensional shape differs by about 35% from that of HST. To have a biological effect, a protein hormone must first bind to a specific receptor on the cell surface. The amino acid sequence dependent shape determines whether the protein will be able to bind to a receptor. Receptor binding studies have shown that the affinity for BST of human receptors is very much less (10,000 to 100,000 times) than their affinity for human somatotropin and thus BST has negligible hormone activity in humans. (Moore et al, 1985; Hoquette et al, 1989; Souza et al. 1995). The trace level of BST in milk does not differ significantly regardless of whether or not the animal has received supplemental BST. Furthermore, heat treatment, such as occurs with pasteurisation, inactivates 90% of the BST in milk. BST which is present in consumed milk is not absorbed as such. It is digested like any other protein to single amino acids and oligopeptides by protease enzymes in the stomach and small intestines. Protein hormones such as BST have to be injected directly into the body to be biologically active (e.g. insulin injections taken by a diabetic). However, only HST is active in humans and BST has no biological effects even if injected directly into the body. It may therefore be concluded that BST itself in milk is not a matter of human health concern. However, BST, whether natural or injected into cows, causes increased milk production by promoting production of the hormone IGF-1, and IGF-1 is present in the milk. Three questions then arise, namely

  • Is there an increased IGF-1 level in the milk of cows supplemented with BST?
  • If there is an increased level, to what extent does it reflect itself in an increased level in the human body?
  • To what extent would any increase in IGF-1 in the human body be a health concern?
  • On the matter of comparative IGF-1 levels, various studies have reported inconsistent values, partly due to variations in analytical methods and partly due to the fact that natural IGF-1 content of milk varies widely depending on the stage of lactation, the age of the cow, and management of the herd. During a lactation period, a typical IGF-1 profile in cow’s milk varies from 150 ng/ml after parturition to 25 ng/ml at the end of the first 7 days of lactation, to 1 to 5 ng/ml at day 200 of lactation (Prosser, 1988; Xu, 1998). In colostrum of cows which had not been treated with somatotropins, IGF-1 exists in a truncated form. In this form three amino-acids (glycine, proline and glutamate), have been deleted from the N-terminal end. This truncated IGF-1, known as destripeptide IGF-1, has been estimated to be between 5 and 10 times more potent than IGF-1 (Shimanoto, 1992).

    IGF-1 concentrations in milk are much higher in the early phase of lactation, a period before BST supplements are used. Colostrum milk (produced at the onset of lactation) has especially high concentrations of IGF-1 (up to 500 times greater than normal milk). The first few days of lactation is also a period in which the newborn of many species can absorb whole proteins. However, in this situation the oral administration of IGF-1, even in pharmacological doses, does not affect circulating concentrations of IGF-1 in the neonate (Donovan and Odle, 1994; Odle et al., 1996; Burrin, 1997; Burrin et al, 1997). Direct measurements using radiolabelled IGF-1 demonstrate that intestinal absorption of IGF-1 is negligible (Donovan et al, 1997).

    A comparison of retail milk originating from ‘labelled’ milk (from non-treated cows) and ‘non-labelled’ milk (non-specified samples originating from treated and non-treated cows) demonstrated an insignificant increase of IGF-1 concentrations in the non-labelled milk samples (Eppard et al, 1994). However, in this study the actual number of animals treated with commercial rbST is not known. Prosser et al (1989) showed a 3.6-fold increase in the IGF-1 concentration over a 7-day period of treatment. In 1994, Burton et al highlighted several studies demonstrating a two to fivefold increase of IGF-1 as a consequence of rbST treatment (Van den Berg, 1989; Gluckman, 1990; Groenewegen et al, 1990; Juskevich and Guyer, 1990).

    Zhao et al (1994) reported on experimental daily injection and administration of a sustained release formulation of BST to 74 lactating cows. Treatments began in the fourth week of lactation and lasted 40 weeks. IGF-1 was monitored through early, mid- and late lactation. BST treatment resulted in a significant increase of plasma IGF-1 in all lactation periods for both treatment groups. A higher milk IGF-1 concentration, however, only occurred in mid- and late lactation periods for the daily injection (application of BST is normally restricted to the mid- and late lactation).

    The JECFA Report (1998) cites average control values for IGF-1 in milk of 3.7 ng/ml for untreated cows, and a significant increase to an average of 5.9 ng/ml as a consequence of BST-treatment (FAO FNP 41/5, 1993). Similarly, studies by different pharmaceutical companies report an increase of IGF-1 levels in milk between 25 and 70 percent in individual animals (Burton et al, 1994).

    Bovine IGF-1 and human IGF-1 are identical in structure. IGF-1 is a normal component in human gastrointestinal secretions; and concentrations in these secretions (e.g. saliva) are higher than in milk. In fact, the amount of IGF-1 contained in 1.5 litres of milk is less than 1% of the IGF-1 present in human daily gastrointestinal secretions (FAO/WHO, 1998). Moreover, IGF-1 is a normal component of blood and other body fluids; and the concentration in the blood of adults and children can be over 100 times greater than found in cows’ milk. The amount of IGF-1 in 1.5 litres of milk is less than 0.1% of the amount our body produces each day (Bauman, 1995; FAO/WHO, 1998). Thus, the amount of IGF-1 in milk is extremely small compared with our bodies’ daily production. it may be argued that any increase in IGF-1 as a result of BST treatment is negligible compared with either the amount of IGF-1 produced in our own daily gastrointestinal secretions or our own total production of IGF-1. IGF-1 is broken down in the human digestive system in the same way as other proteins including BST. Milk is but one of the many protein sources we consume in the diet and the IGF-1 in milk comprises one-tenth of one millionth of the total milk proteins (Bauman, 1995). However, it is not only a question of how much additional IGF-1 is in the milk, but what happens to it. Unlike BST, IGF-1 is not destroyed by normal milk pasteurisation conditions. Bovine IGF-1 is not denatured by normal pasteurisation (79° C for 45 seconds) but following processing of milk for infant formula (121° C for 5 minutes) IGF-1 is no longer detectable (Collier et al., 1991). In contrast an increase of measurable IGF-1 levels up to 70% following pasteurisation has been reported (Juskevich and Guyer, 1990) the different analytical methods applied allow no direct comparison of these different reports. Having regard to all the foregoing factors, consumption of milk from BST-treated cows can result in only a negligible increase of IGF-1 to be absorbed by the body or enter the blood. Despite this, there has been concern and speculation about what might be the effect of a lifetime’s exposure to even a very small increase in IG-1 in the body, and research has particularly centred on the possibility of cancer promotion.

    Human Health - IGF-1 and Cancer?

    Concern and media stories have been fuelled by statements from Dr Samuel Epstein of the University of Chicago (for many years an activist opponent of ‘chemicals in food’). In 1994, when the US Food and Drug Administration (FDA) was in the process of approving the use of BST, he made allegations that milk from cows supplemented with BST was a potential risk factor in breast and gastrointestinal cancers. This was strongly refuted by FDA in a statement of 16 March 1994:-

    “FDA has been receiving inquiries about whether insulin-like growth factor (IGF-1) associated with the use of recombinant bovine somatotropin (rbST) in dairy cows could have adverse effects on people who consume the milk from treated cows. Specifically, allegations have been made that dietary IGF-1 will cause breast cancer ……. FDA and other scientific and regulatory bodies have thoroughly examined the safety of milk produced by rbST-treated cows and have concluded that it is safe. The consumption of dietary IGF-1 plays no role in either inducing or promoting any human disease, nor does it cause malignant transformations of normal human breast cells ………the suggestion that IGF-1 in milk can induce or promote breast cancer in humans is scientifically unfounded and misguided. FDA has determined that milk from rbST-treated cows is safe for human consumption and has not been found to be different from milk from non-treated cows.”

    In January 1996, in an article in the International Journal of Health Services (which is not a research journal) Dr Epstein, who is on its editorial board, resurrected his allegations, and repeated them in a series of media interviews. Dr Epstein’s renewed allegations were rejected by the American Cancer Society which stated “there are no valid scientific findings to indicate a risk of carcinogenesis”. In 1998 Dr Epstein raised the cancer issue again in the same journal, this time in relation to prostate cancer. A prospective study was published by Hankinson et al (1998) in which the IGF-1 content of blood samples taken in 1989-90 from women within the Nurses Health Study cohort in USA were correlated with subsequent occurrence of breast cancer, and in which there was a positive relationship with circulating IGF-1 concentration among premenstrual but not postmenstrual women nor in the whole study population. It is notable that the study refers to a large amount of data collected about the subjects, but not their dietary information or habits. It is also notable that the blood samples were taken some 4-5 years before the start of treatment of cows with BST. The findings, which appear to run contrary to the concept of “a lifetimes exposure”, merit further investigation. Consideration by the EU SCVPH is best conveyed by the relevant extract from its March 1999 Report (see Appendix 1).

    Antibiotic Residues in Milk

    Discussion about mastitis (see Animal Health, below) has fuelled concerns of increased use of antibiotics and of increase in their residues in milk. The level of antibiotic residues in milk has been strictly controlled in the UK for many years. Such controls are also laid down in EC Directives on Milk (85/397/EEC and 92/46/EEC) and the EC Regulation on Maximum Residue Limits (EEC/2377/90). Both in the UK and USA, there are very tough financial penalties on producers exceeding the tight limits laid down. During May to November 1994, in New York State, 83 antibiotic violations were detected, seven fewer than occurred in the same (pre-BST) period in 1993.

    The risk of allergy due to antibiotics in milk has been assessed, and Dewdney et al (1991) have concluded that the currently established permitted levels of penicillin in milk and meat products are appropriate to safeguard human health. The allergenicities of both BST and IGF-1 (whether in milk from treated or untreated cows) are low and are comparable with those of other proteinaceous components of milk.

    Mastitis and Somatic Cell Count

    The EU Committee on Veterinary Medicinal Products (CVMP) considered that a sufficient number of animals had been treated in clinical trials to test the effect of somatotropin on the incidence of mastitis. They concluded that, using conventional statistical techniques, there was no evidence of a significant direct treatment-related effect on mastitis. The incidence of mastitis is linked to milk yield. BST treated cows have a higher incidence of mastitis and more somatic cells in milk than lower yielding controls, but the levels are comparable with untreated cows with a similar yield. Other means of increasing milk yield, such as selective breeding, have also been seen to increase the incidence of mastitis. There is evidence that BST may reduce the severity of mastitis in treated animals (Burvenich et al, 1988). In such circumstances, animals treated with BST would suffer less pain and for a shorter duration than untreated animals of similar yield. In fact, after over a year of use of BST in USA, during which, in the major dairy state of New York alone, BST treatment had been given to 335,000 cows (45% of the state total) the New York State Mastitis Control Program reported “There is no indication that BST has had any effect in increasing mastitis.”. Susceptibility to mastitis is related to many factors, especially environmental conditions and milking management practices. At the BST/Mastitis public hearing, FDA and the Expert Advisory Committee considered results from BST studies and concluded affects were of no biological significance because they were inconsequential relative to the major causes of mastitis. In the first instance, typically 30 to 50% of mastitis cases occur in the first 60 days postpartum - a period when BST is not even used. Secondly, they pointed out that the impact of BST was minor as a cause of mastitis - for example, the effect of season was 9.8-fold greater, the effect of parity was 6.5-fold greater, the effect of herd was 4.8-fold greater, and the effect of stage of lactation was 7.1-fold greater, to name just a few factors. Furthermore, BST does not alter typical relationships between herd factors and incidence of clinical mastitis. Once all the major factors causing mastitis were accounted for, there remained a small positive relationship between milk yield and the incidence of mastitis when expressed on a per cow basis, and BST treatment did not alter this relationship. However, from both a consumer and farmer perspective a more realistic evaluation of risk is to consider cases of mastitis per volume of milk produced. When expressed per unit of milk, mastitis incidence declined slightly as milk yield increased and this relationship was not altered by BST (e.g. White et al, 1994). Therefore, the higher producing BST-treated cow presents a lower risk per unit of milk than the same cow not administered BST. The higher somatic cell count in milk from high-yielding cows and BST treated cows is not a problem. Somatic cell count in milk is monitored, and milk for human consumption must have a mean somatic cell count below 400,000 per ml, in accordance with EU Directive 92/46/EEC.

    Antibiotic Residues in Milk

    Discussion about mastitis has fuelled concerns of increased use of antibiotics and of increase in their residues in milk. The level of antibiotic residues in milk has been strictly controlled in the UK for many years. Such controls are also laid down in EC Directives on Milk (85/397/EEC and 92/46/EEC) and the EC Regulation on Maximum Residue Limits (EEC/2377/90). Both in the UK and USA, there are very tough financial penalties on producers exceeding the tight limits laid down. During May to November 1994, in New York State, 83 antibiotic violations were detected, seven fewer than occurred in the same (pre-BST) period in 1993.

    In 1998, FAO/WHO revisited BST in the light of the most up-to-date research evidence. The Joint FAO/WHO Expert Committee on Food Additives (JECFA), met at FAO in Rome from 17 to 26 February 1998 to evaluate certain residues of veterinary drugs in food. JECFA considered possible problems such as the likelihood of a possible increase in the udder disease mastitis in BST-treated cows which could lead to contamination of milk with antibiotics used to treat mastitis. The Committee concluded that the use of BST will not result in a higher risk to human health due to the use of antibiotics to treat mastitis and that the increased potential for drug residues in milk could be managed by practices currently in use by the dairy industry and by following label directions for use. JECFA’s further concusions are referred to below The risk of allergy due to antibiotics in milk has been assessed, and Dewdney et al (1991) have concluded that the currently established permitted levels of penicillin in milk and meat products are appropriate to safeguard human health. The allergenicities of both BST and IGF-1 (whether in milk from treated or untreated cows) are low and are comparable with those of other proteinaceous components of milk.

    Animal Health and Welfare – General

    Within the whole subject of BST treatment of cows, its effect on animal health and welfare, and in particular on the incidence of mastitis, has been, and remains, the area of greatest controversy. The Institute’s nine-point policy statement on “the public interest in respect of food” includes

    “Animal Welfare - that where animals are used in food production, responsible attention should be paid to their welfare”.

    In its 1999 Report, the EU Scientific Committee on Animal Health and Animal Welfare (SCAHAW) expressed the emphatic view that BST use substantially increases foot disorders, mastitis, reproductive disorders and other production related diseases, problems which, it stated, would not occur if BST were not used and which often result in unnecessary pain, suffering and distress. It added that if milk yields were achieved by other means which resulted in these health disorders and other welfare problems, those means would not by acceptable. The injection of BST and its repetition every 14 days was said also to cause localised swellings, likely to result in discomfort and hence poor welfare. However, at least with regard to mastitis, this view is contradicted by earlier EU findings based on clinical trials, experience in USA, and the results of some researchers.

    Animal Health - Mastitis

    The incidence of mastitis is linked to milk yield. BST-treated cows have a higher incidence of mastitis and more somatic cells in milk than lower yielding controls, but the levels are comparable with untreated cows with a similar yield. Other means of increasing milk yield, such as selective breeding, have also been seen to increase the incidence of mastitis.

    In 1993 the EU Committee on Veterinary Medicinal Products (CVMP) considered that a sufficient number of animals had been treated in clinical trials to test the effect of BST on the incidence of mastitis. They concluded that, using conventional statistical techniques, there was no evidence of a significant direct treatment-related effect on mastitis.

    treatment-related effect on mastitis. There is evidence that BST may reduce the severity of mastitis in treated animals (Burvenich et al, 1988). In such circumstances, animals treated with BST would suffer less pain and for a shorter duration than untreated animals of similar yield

    After over a year of use of BST in USA, during which, in the major dairy State of New York alone, BST treatment had been given to 335,000 cows (45% of the state total) the New York State Mastitis Control Program reported “There is no indication that BST has had any effect in increasing mastitis.”. Susceptibility to mastitis is related to many factors, especially environmental conditions and milking management practices. At the BST/Mastitis public hearing, FDA and the Expert Advisory Committee considered results from BST studies and concluded that effects were of no biological significance because they were inconsequential relative to the major causes of mastitis. In the first instance, typically 30 to 50% of mastitis cases occur in the first 60 days postpartum - a period when BST is not even used. Secondly, they pointed out that the impact of BST was minor as a cause of mastitis - for example, the effect of season was 9.8-fold greater; the effect of parity was 6.5-fold greater; the effect of herd was 4.8-fold greater; and the effect of stage of lactation was 7.1-fold greater.

    Furthermore, BST does not alter typical relationships between herd factors and incidence of clinical mastitis. Once all the major factors causing mastitis were accounted for, there remained a small positive relationship between milk yield and the incidence of mastitis when expressed on a per cow basis, and BST treatment did not alter this relationship. However, from both a consumer and farmer perspective a more realistic evaluation of risk is to consider cases of mastitis per volume of milk produced. When expressed per unit of milk, mastitis incidence declined slightly as milk yield increased and this relationship was not altered by BST (e.g. White et al, 1994). Therefore, it was argued, the higher producing BST-treated cow presents a lower risk per unit of milk than the same cow not administered BST.

    It has been claimed that US results illustrate that BST-supplemented cows are healthier because farmers have routinely gone to extended lactations. This change is possible because BST increases the persistency of lactation (Van Amburgh et al, 1997). That paper concluded

    “On a herd base, through two years of studies (with BST), extended calving interval resulted in fewer calvings, lower incidence of postpartum metabolic diseases, lower veterinary costs, less culling with fewer replacements needed, and an overall improvement in herd life, animal well-being and dairy profitability.”

    Socio-economic Concerns

    Before the introduction of BST treatment in USA in February 1994, there was much debate about such issues as the effect of permitting BST treatment on the overall volume of milk produced, on the economics of production and pricing, and on the effects on large and small producers. Discussion at length of socio-economic hypotheses is outside the scope of this paper. However it is worth observing that this is a technology involving no capital cost and therefore readily utilised equally by large and small farmers; and that, in a situation where supply outstrips demand, or is restricted (as in the EU) by quotas, farmers would be likely to use the technology to improve productivity rather than production volume, i.e. the same volume of milk production from fewer cows.

    In the event, in the ensuing five years of practical experience none of the forecast adverse effects has come to pass. The conditions of use of BST in the USA are similar to those that would apply in the UK and Europe (described above), one of the major differences being that sales are not subject to the need for a veterinary prescription. The arrangements for the product’s distribution ensure that veterinary expertise and advice is provided to farmers before the product is used.

    Monsanto’s BST product is licensed in the USA for administration to healthy dairy cows. It went on sale on 4 February 1994 under the trade name ‘POSILAC’. At January 1998, of nearly 9 million dairy cows in USA, around 25% are in treated herds, and 300 additional dairy farmers a month are reported to be taking up its use . The average dairy farmer using POSILAC is supplementing more than 50% of the herd at any one time, dependent on individual herd management practices and stage of the adoption. Overall usage showed an increase of 45% in 1996 over 1995; and a further increase of 30 per cent in 1997 over 1996.

    Despite hostile media coverage, the activities of anti-BST pressure groups and the initial reaction of several US supermarket chains to the effect that they would not purchase BST derived milk and milk products, milk consumption, far from falling, slightly increased.

    US Department of Agriculture data showed that In the first 10 months of 1994, liquid milk consumption increased by 1% over (pre-BST) 1993; milk prices received by farmers did not plummet but increased slightly; farmers using BST did increase their productivity; and, far from large farmers using the technique exclusively and driving small farmers out of business, the size of herds supplemented with BST closely resembled the distribution of herd sizes found in USA, and 55% of all sales of BST have been to farmers with 100 or fewer cows (Hartnell, 1995).

    Labeling Problems

    In the early days of the use of BST treatment in the USA, some suppliers of milk from sources where BST treatment had not been used, and of milk products made from such milk, sought to label them “BST free”. FDA would not permit this, on the grounds that no milk is BST free. However, US regulations do allow niche market labelling of food products as long as the label is truthful and accurate. Thus, FDA allows a label stating that BST treatment has not been used provided that the farmer signs an affidavit that he has not used the BST treatment in his herd. Currently in the USA a small percentage of the fluid milk sales represent milk labelled as coming from cows not treated with BST; for example in upstate New York this is less than 1% of total fluid sales. This is not easy to apply in distribution systems where milk from farms in a geographical are is bulked regardless, though in these days where segregation and traceability of raw materials have assumed a greater importance, that difficulty may be more easily overcome. It is easy to apply where the supply goes direct to the consumer or to the milk products manufacturer from a single farm or a group of farms none of which is using BSE treatment.

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    Editorial Footnotes

    Before issue, IFST draft Position Statements go through a vetting procedure by the Technical & Legislative Committee and the Public Affairs Committee, to ensure that the contents are scientifically valid, entirely objective and suitable to be issued in the name of the Institute. As this work is being done by volunteer members as a spare-time activity, there are obvious limitations on the frequency with which such procedure can be invoked.

    As an interim means of providing additional up-to-date information to visitors to our Web site, the device of “Editorial Footnotes” is adopted. These are written by the IFST Web Editor, in consultation with other members of the relevant Position Statement drafting team, and are provisional.

    Editorial Footnotes

    Editorial Footnote [1] dated 25 January 2000. Report of UK Veterinary Products Committee

    Editorial Footnote [2] dated 25 January 2000. Continued European Moratorium on Use of BST

    The Institute of Food Science & Technology (IFST) is the independent professional qualifying body for food scientists and technologists. It is totally independent of government, of industry, and of any lobbying groups or special interest groups. Its professional members are elected by virtue of their academic qualifications and their relevant experience, and their signed undertaking to comply with the Institute’s ethical Code of Professional Conduct. They are elected solely in their personal capacities and in no way representing organisations where they may be employed. They work in a variety of areas, including universities and other centres of higher education , research institutions, food and related industries, consultancy, food law enforcement authorities, and in government departments and agencies. The nature of the Institute and the mixture of these backgrounds on the working groups drafting IFST Position Statements, and on the two Committees responsible for finalising and approving them, ensure that the contents are entirely objective.

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    1. to serve the public interest by furthering the application of science and technology to all aspects of the supply of safe, wholesome, nutritious and attractive food, nationally and internationally;
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    IFST current hot topics are

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  • Foodborne Campylobacteriosis — and How to Safeguard Against It
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  • New Approach to Risk Assessment of Natural Toxicants in Foods?
  • Bovine somatotropin (BST)
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    Source: Institute Of Food Science & Technology

    J. Dairy Sci. 85:1218–1226

    American Dairy Science Association, 2002.
    Dairy Herd Management Practices that Impact
    Nitrogen Utilization Efficiency1
    J. S. Jonker,*,2 R. A. Kohn,* and J. High
    Department of Animal and Avian Sciences
    University of Maryland, College Park, 20742
    Lancaster Dairy Herd Improvement Association
    Manheim, Pennsylvania, PA 17545

    ABSTRACT

    Improving the efficiency of feed N utilization by dairy cattle is the most effective means to reduce nutrient losses from dairy farms. The objectives of this study were to quantify the impact of different management strategies on the efficiency of feedNutilization for dairy farms in the Chesapeake Bay Drainage Basin. A confi- dential mail survey was completed in December 1998 by 454 dairy farmers in PA, MD, VA, WV, and DE. Nitrogen intake, urinary and fecal N, and efficiency of feed N utilization was estimated from survey data and milk analysis for each herd. Average efficiency of feed Nutilization for milk production by lactating dairy cows (N in milk/N in feed ? 100) was 28.4% (SD = 3.9). On average, farmers fed 6.6% more N than recommended by the National Research Council, resulting in a 16% increase in urinary N and a 2.7% increase in fecal N. Use of monthly milk yield and component testing, administration of bovine somatotropin (bST), and extending photoperiod with artificial light each increased efficiency of feed N utilization by 4.2 to 6.9%, while use of a complete feed decreased efficiency by 5.6%. Increased frequency of ration balancing and more frequent forage nutrient testing were associated with higher milk production, but not increased N utilization efficiency. Feeding protein closer to recommendations and increasing production per cow both contributed to improving efficiency of feed N utilization. (Key words: nitrogen pollution, milk urea nitrogen, dairy cattle protein requirements) Abbreviation key: MUN = milk urea N, 3? milking = three-times daily milking.

    Introduction

    Nitrogen losses from agriculture to water resources present a major environmental challenge for the Chesapeake Bay Drainage Basin (Thomann et al., 1994). Dairy farming is a large agricultural enterprise in the region, making dairy farms a major contributor to the nonpoint N loading of the bay. Kohn et al. (1997) used a simple mathematical model to evaluate which management practices had the greatest impact on reducing N losses from the farm: dairy herd feeding and management, soil and crop management, or manure storage and handling. This model suggests that improving herd management is the most effective means to reduce nutrient losses to the environment. Improving herd nutrient utilization efficiency by 50% was calculated to reduce nitrogen losses to water by up to 40%, but improving manure utilization efficiency by 100% only reduced N losses to water by 10 to 14%. Other authors determined the effect of several management practices, such as animal grouping (St-Pierre and Thraen, 2001), use of bST, milking three times daily (3? milking) or artificial lighting (Dunlap et al., 2000), on nutrient utilization efficiency and nutrient excretion in research dairy herds. However, the variation in herd nutrient utilization efficiency on commercial dairy farms is not known. Jonker et al. (1998) developed and evaluated a model to estimate N excretion, N intake, and N utilization efficiency for lactating dairy cows. The model requires knowledge of milk production per cow, milk protein percentage, and milk urea N (MUN). The first objective of this study was to determine current N utilization efficiency of dairy herds in the Chesapeake Bay Drainage Basin. The second objective was to identify factors that contribute to variation from herd to herd in nitrogen utilization efficiency. With a better understanding of current management practices and their effect on potential N loading to the environment, opportunities to improve overall management may be identified.

    Materials and Methods

    A confidential mail survey was conducted in December 1998 with the Maryland and Virginia Milk Produc ers Cooperative (West Reston, VA). An introductory letter was mailed 1 wk prior to the survey, and a reminder letter was sent 1 wk after the survey. The cooperative had 1156 members located throughout most of the Chesapeake Bay Drainage Basin, including Delaware (n = 23), Maryland (n = 432), Pennsylvania (n = 519), Virginia (n = 172), and West Virginia (n = 18). Participants were offered monthly bulk tank milk analysis of MUN for 6 mo as an incentive to return the survey. The survey included information on dairy herd characteristics, milk production, crop production, feed inputs, management characteristics, and MUN knowledge and use. Herd characteristics included information regarding breed, number and distribution by parity of milking animals, and number and age distribution of replacement heifers. Milk production included volume and compositional data. Crop production and management included types and acreage of crops grown and use of a nutrient management plan (NMP). Feed inputs included types of feeds routinely fed and frequency of ration balancing and nutrient composition testing. Management characteristics indicated the use of various technologies (bST, increased milking frequency, etc.).

    MUN Sampling and Analysis

    Bulk tank MUN analyses were performed monthly for 6mo for dairy farms from the Maryland and Virginia Milk Producers Cooperative (n = 1156) from December 1998 through May 1999. Only the December samples are used in the current paper because other results were affected by our correspondence with farmers. Milk samples were collected weekly from Environmental Systems Services (College Park, MD) after routine milk component analyses were performed for cooperative members. One sample for MUN analysis was analyzed per herd per month. The fresh milk samples were treated with an antimicrobial preservative (Broad Spectrum Microtabs II, D & F Control Systems, San Ramon, CA). The milk samples were then shipped to Lancaster DHIA (Manheim, PA) for MUN analysis using the Bently Chemspec autoanalyzer (Chaska, MN).

    Modeling and Data Analysis

    The mean and standard deviation in N feeding parameters were calculated based on model predictions (Table 1) from the survey data and December milk analysis. Nitrogen intake, urinary and fecal N, and N utilization efficiency were determined for each herd using the model of Jonker et al. (1998), except prediction of urinary N was equal to 0.0259 times body weight times MUN, as recommended by Kauffman and St-Pierre (2001). Average BW for the cows in each herd was predicted as the weighted mean for all cows, where each cow’s body weight was assigned according to breed as follows: Holstein and Brown Swiss, 600 kg; Ayrshire and Guernsey, 500 kg; and Jersey, Milking Shorthorn, and Dutch Belted, 400 kg. Estimates of body weights were made based on DHIA data summarized by Dunlap et al. (2000). Crossbred animals were assumed to weigh the average of the breeds crossed. Crude protein requirements were determined using the National Research Council (NRC, 1989) recommendations for dairy cattle, assuming a one-group TMR was fed (Jonker et al., 1999). The protein required was assumed to be that needed by the 83rd percentile cow with respect to protein requirements for the entire milking herd (Stallings and McGilliard, 1983). Excess N feeding was determined as the difference between observed N intake, estimated using the model described previously (Table 1), and that predicted to be required. Thus, negative values represented underfeeding and decreased the average estimate of overfeeding. The accuracy ofNfeeding was calculated by taking the absolute value of observed minus required N, so that the average represents both overfeeding and underfeeding. Statistical analyses were performed using the software package JMP (SAS, 1995). Herds were excluded from the analysis whenever incomplete survey answers resulted in missing data for a variable in the model to predict N intake or utilization efficiency. Treatment means for each observed or calculated value were compared using ANOVA for discrete variables or regression for continuous variables. Observations were excluded when either X or Y values were missing (i.e., missing data were not estimated by the model). When more than two discrete variables were compared (e.g., frequency of diet formulation), the Tukey-Kramer t-test was used to compare each pair. The environmental and economic impact of overfeeding dairy herds was estimated based on summarized results. Excess N fed in the watershed was calculated by multiplying the number of cows in the watershed during the study (n = 758,347 [United States Department of Agriculture, 1998]) by the fraction of farms overfeeding N and the average excess N per overfed cow. The N losses to water resources that result from overfeeding were calculated by accounting for losses from manure during storage and application. The total excess N fed was assumed to be excreted into manure. Assuming that 25% of manure N excreted eventually becomes available to crops, excess feed N was multiplied by 0.75 to estimate manure N losses (Kohn et al., 1997). There would be additional losses of N from the production of crops. However, imported soybean meal was assumed to provide the excess feed N, so the N losses would not have occurred in this watershed. The cost of feeding excess N was estimated assuming that soybean meal (44%) could be replaced by corn grain to decrease N content. The 5-yr average prices (1996 to 2000) for soybean meal ($0.210/kg) and corn grain ($0.097/kg) were used (Bridge Information Systems, Inc., 2000).

    JONKER ET AL.

    Table 1. Prediction equations.

    Variable Equation
    Urinary N (UN), g/d 0.0259 · milk urea N (mg/dl) · BW (kg)
    N Intake (NI), g/d (Predicted UN+ milk N+ 97)/0.83
    Fecal N, g/d Predicted NI+ predicted UN− milk N
    N utilization efficiency, % (Milk N · 100)/predicted NI
    DMI, kg/d (Predicted NI · 6.25)/dietary CP percentage

    RESULTS AND DISCUSSION

    A total of 472 dairy farmers responded to the survey, for a 40.8% rate of return. However, nine farms stopped shipping milk shortly after completing the survey and were therefore excluded, and 91 farms were excluded because of incomplete data (usually rolling herd average or milk protein percentage was missing). For the final data, the largest number of surveys were from Pennsylvania (n = 165), followed by Maryland (n = 139), Virginia (n = 56), West Virginia (n = 6), and Delaware (n = 6). A large range in farm size and production was represented in the survey (Table 2). Average FCM was 28.3 kg/d per cow (SD = 4.2) with 3.74% (SD = 0.24) fat and 3.25% (SD = 0.15) true protein. The average farm surveyed had 109 cows (93 milking and 16 dry cows)and 86 replacement heifers (Table 2). Several farms reported not raising any replacements. Nearly every farm (>98%) reported having Holstein cows. Jersey cattle were the second most predominant breed—reported on 11.7% of the farms—and made up 3.7% of all dairy cattle. Other breeds represented less than 1% of total dairy cattle.

    The farmers participating in the program generally appeared to represent the range of farmers in the Chesapeake Bay Drainage Basin. The average milk production reported by participants was 28.3 kg/d per cow, compared to the average of 29 kg/d per cow reported for Lancaster DHIA members between July 1996 and April 1998 (Dunlap et al., 2000). Herd distribution (Table 2) was also similar to results reported for those records. The mean MUN for participating farms was 12.8 mg/dl (Table 3), compared to 12.4 mg/dl for all farms in the cooperative (Jonker et al., 2002). Higher MUN may have resulted from a tendency of participants to have higher milk production or to feed higher CP diets than nonparticipants, but the error imposed by nonrandom participation of farmers compared to all cooperative members would be 3.2% of MUN.

    The model of Jonker et al. (1998) enables calculation of the variance in N utilization efficiency for a large number of herds in the field. The mean and standard deviation in N utilization parameters for lactating cows across all herds are given in Table 3. These calculations do not include dry cows or heifers, which would otherwise add to excreted N and decrease N utilization effi- ciency for the herd. Observed parameters differed significantly from recommended levels for all parameters. Observed MUN was 12.7 mg/dl, but feeding according to NRC (1989) and allowing for variation within the herd by feeding the 83rd percentile cow would have resulted in a MUN of 11.0 mg/dl.

    As with any measurement, the variance can be attributed to both errors in measurement and true variance within the population. The root mean square prediction error (RMSPE) for the model used in this analysis was 16.9% of mean urinary N prediction (Jonker et al., 1998). A similar prediction error for the current study would result in prediction error accounting for 40% (100 ? RMSPE2/SD2) of the total variance (SD2) among farms reported in Table 3. The RMSPE for prediction of N utilization efficiency was 11% of prediction (Jonker et al., 1998). A similar prediction error in the present study would explain 64% of total variance in utilization efficiency among farms. Most of the model prediction error used for these calculations was associated with lab and cow variation (Jonker et al., 1998), and these would be reduced by using a single lab that uses wet chemistry and bulk tank samples representing an average of 109 cows. Therefore, we do not have adequate data to accurately estimate model prediction error under the circumstances in which the model was used in the present study. Nonetheless, the model prediction errors reported previously provide an upper limit of model prediction error.

    Table 2. Milk production and distribution of cows from surveyed

    farms.


    Range1


    Mean SD 10th percentile 90th percentile

    Production
    FCM, kg cow-1d-1 28.3 4.2 22.4 33.6
    Fat, % 3.74 0.24 3.50 4.00
    Protein, % 3.25 0.15 3.10 3.40
    Cows
    Total 109 103 40 200
    Milking 93 88 34 173
    Dry 16 16 4 30
    1st lactation 35 35 9 70
    2nd lactation 31 29 7 56
    Mature 42 46 14 76
    Heifers
    Total 86 80 23 173
    <1 yr 42 41 11 85
    >1 yr 44 41 11 90

    1Reported range of surveyed dairy farms (n = 372).

    Source: Feedstuffs Magazine
    Author: Michael Howie

    Managing Nutrients Across Regions of US

    Posted by admin on May 25th, 1999
    1999
    May 25
    Title : Managing Nutrients Across Regions of US
    Source : Monsanto Dairy Group
    Author : CJ Nelson
    Date : 1999
    Content : Report

    Managing Nutrients Across Regions of the United States

    ABSTRACT

    Nutrient balance in the ecosystem involves profitability of the agricultural enterprise and commitments to resource management to maintain quality of air, water, and land resources. Phosphorus and N are the two nutrients of major concern, and they behave differently in soils. Most P adheres strongly to soil particles and moves laterally with the soil during erosion processes, but with high concentrations more P remains in soluble forms and moves in the water fraction. Most N is soluble and moves laterally or downward with soil water. Soil scientists and agronomists have researched soil processes, plant nutrition, cropping systems, and water quality issues mainly on a field and farm level, but now the movement is to management and regulation of nonpoint problems on a watershed basis as proposed in the Clean Water Action Plan. The plan recognizes the vast diversity of soil parent materials and climates among geographic areas, even among and within watersheds, that determine crop adaptation and cropping systems, the role of states in regulatory processes, and the need for local citizens to have operational involvement. This process insures that nutrient management guidelines will be more sitespecific and solutions can be focused on the direct problem. Directed efforts will be needed to educate local citizens, landowners, and caretakers of agricultural enterprises, and regulatory agencies. Several factors, including economic and social incentives for implementation must be considered along with the technologies available. The solutions are multidisciplinary, will require long-term research to accommodate climate variation, and should be associated with a strong commitment to education. Public funding will be needed to support the effort.

    (Key words: nutrients, land-use, watershed, soil management)

    Abbreviation key: MLRA = major land resource area, AFO = animal feeding operation, CAFO = concentrated animal feeding operation.

    INTRODUCTION

    The role of nutrient management in livestock systems takes on new meaning as producers and the public together consider economic and noneconomic issues. Until recently, landowners and land managers had relative freedom for application and redistribution of mineral elements. Similarly, the producer, who often was the landowner, had near total responsibility for proper land stewardship to minimize detrimental effects on soil and water resources. But as technologies improved and populations grew, fewer people were involved directly with agrarian society, pesticides and chemical fertilizers increased in use, and the public became more aware of the need to insure a quality environment. Today, there is increased accountability for stewardship of natural resources, i.e., sound land management, clean air, and high quality water.

    For several years, point-source problems were the major concern, and effective policies and practices have been developed. But with advances in assessment technologies, increased concentrating of livestock, and increased public concern about safety in the food production process, nonpoint-source problems are also being addressed. As judicious users and vested guardians of much of the nation’s public resources, the agriculturalist is accountable. Water and air quality are affected by agriculture and both require new technologies and the expertise to apply them. Thus, this symposium on nutrient management is well founded and timely. My goal is to review effects of geographic, climatic, and agronomic factors on nutrient balance. Within these constraints local approaches to solutions will need to be fitted. The solutions will differ, however, depending on the location of the watershed, nature of the individual agricultural enterprise, management alternatives available, and social and economic variables that affect local decision-making.

    EVOLUTION OF THE PROBLEM

    Geologic processes, climatic variables, and thedegree of human intervention have led to differentsoils and landscapes that are occupied by natural and agricultural ecosystems, each with its own distinction.In addition, each mineral element has a uniquechemistry in the soil and availability to plants, i.e., itsown niche in the ecosystem. Although there can besome grouping for principles, the two nutrients ofmost concern are P, a major cause of eutrophication,and excess N, a major risk to human health. Thesetwo differ markedly in origin, use, and behavior in theenvironment. Many other minerals in the ecosystem,in addition to those required by plants and animals,can accumulate, cycle, and be transported in agriculturalsystems (32).

    Figure 1 summarizes factors influencing nutrient balance. Agricultural practices have a large effect on nutrient balance in both positive and negative ways. For sustainability, nutrient losses to the environment and removal of crop and livestock products need to be offset by release of new soil minerals (inorganic) from the parent material, additions of nutrients through fertilizers and wastes, and retention or improvement of the organic matter content. Maintaining or improving the soil and minimizing losses to the environment are major goals. Agricultural and land use practices alter the routes and rates that nutrients pass through or are recycled in the system. Fertilizers and manures can be applied to supplement the balance, especially in managed ecosystems. Human and industrial waste also need to be considered in the total balance.

    Over 30 years ago Cooke ( 6 ) reviewed nutrient balance on a country level and indicated a growing awareness of P accumulation in developed countries. More than a century ago, Johnston and Cameron (13) indicated P reserves were building up in the United Kingdom because P removal through cropping and pastures was only 85% of that added. Animal manures, but not recycling of human or industrial products, were included in the balance. In 1956 (again not considering recovery of human or industrial waste by crops and livestock) the United Kingdom showed an even greater annual rate of P buildup in the system, mainly in the soil (5) . Nitrogen was also in a positive balance and was assumed to be accumulating as a major component of soil organic matter or lost to air and water. Potassium was not yet in a positive balance. Clearly, P was accumulating as a reserve.

    In the United States, a much larger and more diverse country, Lipman and Conybeare (19) in 1936 added erosion and leaching losses to the crop and livestock removal and concluded nutrients returned annually to the soil replaced about 67% of the N and

    only 33% of the P that was removed or lost. By 1963, largely because of the rapid increase in fertilizer use, 70% of the N and 54% of the K loss and removal was supplied by fertilizer. Additions of P were 18% greater than loss and removal, indicating soil-P reserves were increasing. In the early 1960s Donald ( 9 ) recognized that P was accumulating in Australia’s soils, even when losses caused by erosion and leaching were considered.

    During the past few decades the agricultural communityand general public have became more awareof eutrophication, or overenrichment of nutrients,caused largely by P accumulation in lakes, reservoirs,and slower moving streams (18). Nitrogen enrichmentcontributes to eutrophication in saline waters ofestuaries and bays and to other water qualityproblems resulting from leached N, largely as NO3–(11). Many industrialized nations have becomeacutely aware of the need to consider land, includingcropland, as a disposal site for human and manufacturingwaste. For example, Korea and Japan haveimported vast quantities of N, P, K, and othermineral elements in food and feedstuffs, to the pointthat reserves of soil P from recycling waste materialsin many agricultural soils are well beyond those needingsupplemental fertilizers for crop production(Kwang Yong Jung, 1998, personal communication,Rural Development Administration, Suweon, Korea).In contrast, soil P levels are still deficient for cropproduction in many tropical soils (26).

    SOIL PROPERTIES AND NUTRIENT MANAGEMENT

    Soil Water Management

    Soil hydrology is a major factor affecting nutrient management, especially relative to water quality issues (25). The two major processes of dispensing with incident precipitation are percolation, or flowthrough, and surface runoff (Figure 2). The proportional distribution of water movement depends on the slope of the land, rate of percolation in the soil, and the intensity and duration of the rainfall event. Percolation rate depends on physical properties of the soil, mainly texture and structure. In general, soils with high sand content have higher rates of percolation than do those with high clay content. Organic matter and the associated microflora contribute positively to development and maintenance of good soil structure that aids air and water movement within the soil.

    Soils with an open, porous structure percolate faster. Earthworms and decaying roots form macropores or channels to facilitate water movement. Animal and vehicular traffic cause compaction in the upper soil layers to reduce porosity and reduce percolation rates. Some soils are characterized by hardpans or claypans below the tilled horizons, which severely restrict continued downward movement of water and growth of roots to lower levels of the profile. Water that percolates to an impervious layer can move laterally in the soil and can exit again downslope as subsurface runoff. Surface runoff carries soluble nutrients such as N, K, and some forms of P to streams and impoundments.

    The slope of the soil and the nature and amount of vegetation cover determine the rate of lateral movement across the soil surface and, therefore, the energy for suspending and moving sediment, and the timespan a given unit of surface water has to percolate into the soil. Vegetation on and above the soil surface intercepts raindrops, reducing their force of impact, which helps retain soil structure and its ability to absorb water, and increases percolation by physically slowing lateral flow of surface water. Buffer strips and riparian areas are examples of methods used to decrease lateral flow before the water leaves a field or enters a stream.

    Soil Fertility and Crop Production

    Soil productivity refers to the capability of a soil to produce a crop and incorporates soil physical factors, the prevailing climate, natural fertility plus additional elements from manures or fertilizers, and management variables such as tillage and the cropping system (31). Nutrient management alters one component of the productivity index, the soil fertility status. Nitrogen is generally the yield-limiting nutrient in grasslands and extensively managed agricultural cropping systems and, when limiting, is efficiently recycled within the ecosystem and losses are minimal (11). Fertilizer or biological N is added to intensively managed systems. Once the N requirement is met, P is generally the limiting nutrient in more intensive cropping systems. The amount of soluble P in soils is generally small and losses are minimal unless erosion occurs. In natural systems, therefore, nature has built in checks and balances for regulating the loss of these two nutrients from the local system, either by efficient recycling among plants (N) or by having sufficient storage capacity in the soil (P).

    Fertilizer requirement is the amount of a nutrient or nutrients that needs to be added to achieve the desired, but not necessarily maximum yield level (31). Manures have long been recognized as good sources of nutrients. Although concentrations of P and N often limit productivity, the need for repositories of vast quantities of manures and waste materials has expanded thinking about requirements. No longer is the question focused only on crop response. Now manure or nutrient management includes the times and processes to minimize early nutrient loss after application to the soil and to enhance the ability of the soil and cropping system to sequester the nutrient for a long time in an environmentally friendly way. Social factors such as sight and odor of manures now also need to be considered. Agricultural engineers and agronomists are developing new methods to meet nutritional needs for plant growth in environmentally benign ways.

    Soil Fertility and the Environment

    It is beyond the scope of this assessment to review details about N and P cycles except for a few general principles. The main natural sources of N input include fixation by Rhizobia and other symbiotic bacteria, fixation by free-living soil bacteria, and some fixation by electrical discharge in the atmosphere (31). Other sources are industrial waste and recapture of N that is emitted from the soil in gaseous forms. When large amounts of carbonaceous material are available in the soil, the mineral N is incorporated into organic matter and is lessened as an environmental threat (12). The method for estimating N in the soil available for crop growth is generally based on its relationship with organic matter and the expected rate of organic matter decomposition by which N is changed to available forms (31).

    The abilities to measure soils for potential environmental problems began as a natural extension of methods for measuring the N or P that is available to support plant growth. This amount is less than the total and is dependent on the chemical nature of the element in the soil that allows it to be available to plants. Nitrogen applied to soils, regardless of the form, is usually rapidly changed to NO3 –, a form that is readily taken up by plants, but is very soluble and moves vertically and laterally in the water fraction. The NO3 – in the soil can be sampled at various depths, and the amount can be measured. But if it moves below the rooting zone, NO3 – can easily escape into the groundwater (Figure 2). When N is applied on the surface it can also dissolve and be moved laterally into the surface water.

    Because of its behavior in the soil, there is little storage capacity for N aside from accumulated organic matter in the soil (Figure 3). Thus, it is most desirable to apply N during or just prior to active uptake stages of the crop, and inject manure slurries below the soil surface or incorporate them into the soil to minimize lateral movement with surface water and loss of NH3 by volatilization.

    The situation is more complicated for P becausesoils can differ markedly among regions because ofparent material, and plant-available P varies withsoil properties, especially pH. Further, at low to

    moderate concentrations P binds tightly to clay particlessuch that it moves very little in the water phasefor leaching or runoff. At high P concentrations,however, the soil approaches saturation and more Premains in soluble forms, which move with water.The P soil test value for environmental purposes isgenerally much higher than for yield responses andagricultural applications because there is a largestorage capacity (Figure 4). Determining the safelimit of storage capacity has been difficult becauseerosion potential and management effects add complexityin determining tolerable losses of soil P.Nevertheless, regulatory agencies in many stateshave already established the upper limit for soil testP, usually with little research data, and often atlevels only marginally above the crop response.Generally, when the soil already tests at or above theacceptable maximum for P, annual application islimited to that equal to crop removal.

    The norm for testing soil for agricultural use is toextract plant-available P, but the P test for environmentalpurposes should extract all or a high proportionof the soil-P fraction that is susceptible to directsurface runoff, leaching, or dissolution from erodedsediments (21). This limitation suggests soil testingfor environmental purposes requires new methodologiesand interpretations (28). For example, the depthof soil sampling for environmental tests will vary(Figure 2); it will be shallower than for the agriculturaltest when surface runoff is the major problem

    and deeper when leaching losses of soluble forms are the major problem (21).

    Sims (27) proposed the Phosphorus Index, a system to guide P applications based on a weighting of eight soil and soil management characters. The potential for soil erosion, current soil-P test (upper 15 cm), and application rates of organic sources of P contribute most strongly to the index. The index uses coefficients that are based largely on the experience of scientists and not on multicomponent scientific data. But the index is relatively easy to learn, is relevant, and can be applied over a range of soil conditions. Scientific data support coefficients showing more P loss from surface runoff from soils that test high in P, especially in the upper 5 cm, than those testing low in P, and P loss from bare soil is greater than from the same soil covered by vegetation (1). With a high water table and very high concentrations of P in the soil, leaching and lateral subsurface flow can contribute dissolved P to surface waters.

    Soil Characterization and Mapping

    In an effort to bring organization to the natural diversity, early soil scientists developed maps delineating soil types based largely on the parent material, organic matter, and physical features of the soil and landscape. This classification system has proved to be very helpful for soil management and formed the national basis for decisions on crops and animal agriculture (14). With advances in technology,technology, especially geographic information systems and global positioning systems, today’s soil scientists have redirected the mapping process to be more detailed and to include multiple-use characteristics beyond agricultural production (2).

    The USDA (33) embraced the changing paradigm and developed a more forward-looking soil classification system, which is based on 204 major land resource areas (MLRAs) in the United States. These areas are geographically associated land units of several thousand hectares and include a particular pattern of elevation and topography, soils, climate, water resources, and land uses. The large MLRAs are independent of state boundaries but are important for statewide planning efforts on usefulness for productivity, operation of resource conservation programs, and they have value for interstate, regional, and national planning efforts.

    THE CLEAN WATER ACTION PLAN

    The MLRAs developed by the Natural Resources Conservation Service and the environmental initiatives promoted by EPA were brought together with the joint USDA/EPA release of the Clean Water Action Plan (35). This landmark effort between two large federal agencies provides the opportunity to apply new technologies into a plan that targets polluted runoff, habitat degradation, and safety of water supplies. It uniquely brings together a partnership of federal, state, tribal, and local agencies to work with nonprofit organizations and private groups (20).

    Operation of the Plan

    The plan is based on two fundamentals; 1) that problem solving is a bottom-up process that needs to be watershed based and requires site-specific solutions, and 2) that state agencies need to be involved because they administer many of the environmental laws enacted by the federal government. Many states have already adopted the watershed basis because it is difficult to develop a comprehensive program for nonpoint-source problems based on regulatory standards formulated for point-source problems.

    The state-federal partnership allows further state relations with local groups within a watershed to finetune, monitor, and administer the programs locally. This model places the oversight and procedural details at the local level, with the people within the watershed who are most fully aware of the potential for problems and the feasibility of solutions. The local effort also insures a broad base of public participa tion, which is critical because the problems and solutions are site specific. For example, in general, the combination of soil types and high precipitation in the southeastern United States leads to more challenges with surface runoff and associated P loss compared with much of the arid west and flatter Great Plains, where N may be a greater problem (29). Yet among watersheds within several of the geographic areas, the range among site-specific situations is nearly as diverse.

    Concentrations of Animals

    The action plan was accompanied by collective actionby USDA and EPA to have a more unified nationalstrategy (16) for an animal feeding operation( AFO) and a concentrated animal feeding operation( CAFO) . An AFO is a facility in which animals arestabled or confined for a total of 45 or more daysduring a 12-mo period, such that normal vegetation orforage growth is not sustained in a normal growingseason. These AFOs range from small facilities with afew animals to large facilities and land areas capableof dispersing several hundred animals that generatelarge amounts of waste. Most AFO issues are beingaddressed voluntarily by individual states, but thescope and nature of programs differ from state tostate. The programs offer technical assistance, costsharefinancial assistance, or other incentives.

    In contrast with an AFO, a CAFO is categorized asa point source and must have a pollutant dischargepermit for liquid and solid components of manure. ACAFO is defined as a facility with more than 1000animal units, or one with 301 to 1000 animal unitsthat discharges pollutants into waters governed bythe United States. Containment is a major issue thatrequires managed lagoons, perimeter barriers, andstrict record keeping (15). Operation of either anAFO or CAFO may be amenable to management as a‘closed system’ of nutrient balance (17), which usesdetailed accounting of all nutrient inputs and outputsin the farm system (Figure 5). Specific efforts aremade to reduce runoff and volatilization from manures,recycle nutrients in cropping systems, and trapNH3 release from structures and manure pits.

    Closed systems have been considered in some areasin the United States and may serve societal needs iflateral movement of surface water can be controlledand losses through percolation and subsurface lateralmovement of water are minimal. These systems mayalso be very useful for specific areas within awatershed. Some CAFOs may be amenable to use ofconstructed wetlands to process toxic and nontoxic

    contaminants before releasing the water into sensitive aquatic environments (22). Dealing with AFOs and CAFOs will be a major responsibility in planning and operation of the watershed.

    Implementing the Plan

    As part of the Action Plan, the contiguous United States has been divided into 2111 watersheds, each consisting of several thousand hectares (Figure 6). Alaska and Hawaii are to be considered later. Further, each watershed has been classified, using 15 water resource indicators, into one of six categories according as to its current condition of water quality (better, less serious, and more serious) and as to its vulnerability (low or high) to a decrease in quality (34). There are still many watersheds with insufficient data to classify.

    An upcoming step in the implementation of theClean Water Plan is the development of nutrientbudgets on a watershed basis that reflect relativecontributions of nutrients from all sources in the outflowof water from the watershed. First, USDA willidentify counties with excess nutrient losses from manure.Then EPA and USDA will combine data basedon fertilizer sales, the Agricultural Census, and permitlimits to establish a baseline of nutrient loads forthe sensitive watersheds. Funding for education andoutreach programs will likely be focused on problemwatersheds, especially those with high risks fromAFOs. The mechanisms for acquisition and scientificassessment of research data are less clear.

    The implementation and decision making of theAction Plan brings together several operating principlesand the underlying science of a watershed. It has

    been widely acknowledged that rates of runoff and sediment loss from a field plot or an entire field cannot be equated directly to a reduction in quality of water leaving a watershed, although it clearly contributes to the potential (8) . Similarly, rates of percolation and leaching of nutrients from a plot or field nearly always overestimate the amount that will eventually reach the groundwater or receiving streams (7).

    Implications of a Watershed Plan

    The quality of water as precipitation and the deposition of particulate matter that contains nutrients will differ from watershed to watershed. Overall, each field, pasture, AFO, CAFO, woodland, road and rightof- way, fenceline, farmstead, riparian strip, golf course, town, and any other land surface within the watershed contributes to the nutrient balance of the watershed in its own way. The proximity of the erosion event to the receiving stream is critical. Further, the geographic distribution of specific agricultural or nonagricultural activities within the watershed will alter their effect. This again points out the need for a good database and sound scientific assessment of the watershed.

    Most watersheds consist of a network of several third- and even fourth-order streams that collect the runoff and seepage from the landscape. This network allows for some pollutant disposition within the watershed itself, both in time and space (4) . Contaminants such as fecal coliform bacteria have a natural attrition that is time dependent as the water flows from the loading area into the tributaries and eventually the main receiving stream. Thus, contaminant entry near the mouth contributes disproportionately higher amounts of these organisms to watershed outflow than do similar loading areas further upstream. Generally, there is also some reduction of nutrient load as it moves in the water, but the exact dynamics and long-term effects in the ecosystem food chain need further research.

    The emphasis for each watershed should consider both the spatial distribution of the agricultural enterprises within the watershed and the practices used within each enterprise. For example, with similar managements, an AFO or CAFO at a less critical position or farther from the main receiving stream, in general, is less likely to be a major problem. Adding management practices to minimize soil erosion and nutrient losses due to runoff in cropping systems are also critical. Locating more intensive pasture management systems, where more fertilizer inputs are used, further from the receiving stream, and locating more extensive management systems nearer the receiving streams can improve water quality (7) . Use of riparian zones with proper vegetation and excluding livestock from sensitive areas of receiving streams are also very effective for nutrient management in a watershed (10).

    Grazing systems influence the distribution of nutrients in manure and urine because animals generally excrete nutrients at sites away from where they were ingested. Distribution patterns and high rates of urine and feces deposition in pastures and rangelands are often associated with spatial locations of water, shade, mineral supplements, and topographical features such as ridges and draws, areas where animals congregate and rest (23). Uniformity of manure deposition in the grazed areas is better when high stocking rates are used in rotational stocking systems compared with continuous stocking. Distance from potential grazing areas to water and the geometric shape of the allocated grazing area are also factors (24).

    SCALING FROM FIELDS TO WATERSHEDS

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