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:
- Potential changes in milk protein composition which might favour allergic reactions.
- 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.
References
Baldwin R L. and Knapp J R (1993) Recombinant bovine somatotropin’s effects on patterns of nutrient utilization in lactating dairy cows. Am. J. Clin. Nutr,58 (Suppl. 1),282S-286S Bauman D E (1992) Bovine somatotropin: Review of an Emerging Animal Technology, J Dairy Sci.72, 3432-3451
Bauman D E and Vernon R G (1993) Effects of Exogenous Bovine somatotropin on Lactation. Ann. Rev. Nutr. 13, 437-461
Bauman D E et al (1994) Somatotropin (BST): International Dairy Federation Report, Bulletin of the International Dairy Federation, No.293
Bauman, D E, (1995) IGF-1 Fact Sheet, Cornell University, Department of Animal Science
Baumrucker C Ret al (1994) Effects of dietary insulin-like growth factor I on growth and insulin-like growth factors in neonatal calf intestine. J. Anim. Sci. 72, 428-433
Bohlke K et al (1998) Insulin like growth factor-I in relation to premenopausal ductal carcinoma in situ of the breast. Epidemiology 9, 570-573
Booth C et al (1995) Growth factor regulation of proliferation in primary cultures of small intestinal epithelium in vitro Cellular and Developmental Biology-Animal 31 (3), 234-243.
Burrin, D G et al (1996) Orally administered IGF-1 increases intestinal mucosal growth in formula-fed neonatal pigs. Am. J. Physiol. 270(5), R1085-R1091
Burrin D G (1997) Is milk-borne insulin-like growth factor-I essential for neonatal development. J. Nutr. 127, 975S-979s
Burrin D G et al (1997) Role of milk-borne vs. endogenous insulin-like growth factor I in neonatal growth. J. Anim. Sci. 75 ,2739-2743
Burton J L et al (1994) A Review of Bovine Growth Hormone Can. J. Anim. Sci.74, 167-201
Burvenich et al (1988) Bovine somatotropin and Acute Escherichia coli Mastitis. Ann. Med. Vet., 132, 601-606
Chan J M et al (1998) Plasma insulin-like growth factor-I and prostate cancer risk: a prospective study. Science 279, 563-566
Chen K R and Nezu R (1997) Beneficial effects of growth hormone combined with parenteral nutrition in the management of inflammatory bowel disease: an experimental study. Surgery 121, 212-218
CVM Update (May 1996). Two Year Report on BST. FDA, Center for Veterinary Medicine, Rockville, USA. Collier R J et al (1991) Factors affecting insulin-like growth factor-I concentration in bovine milk. J. Dairy Sci. 74, 2905–2911
Costigan D M et al (1988) Free Insulin-Like Growth Factor I (IGF-1) and IGF-1I in Human Saliva. J. Clin. Endocrinol. Metab., 66, 1014-1018
Daughaday W H and Barbano D M (1990) Bovine somatotropin Supplementation of Dairy Cows. Is The Milk Safe? J.A.M.A, 254, 1003-1005
Del Guidice M E et al (1998) Insulin and related factors in pre-menopausal breast cancer risk. Breast Cancer Res.Treat. 47, 111-112
Dewdney J M et al (1991) Risk Assessment of Antibiotic Residues of beta-Lactams and Macrolides in Food Products with Regard to their Immuno-Allergic Potential. Fd. Chem Toxic., 29, 477-483
Donovan S M and Odle J (1994) Growth factors in milk as mediators of infant development. Annual Rev. Nutr. 14, 147-167
Donovan S M et al (1997) Orally administered iodinated recombinant human insulin-like growth factor-I (IGF-1) is poorly absorbed by the neonatal piglet. J. Pediatr. Gastroenterol. Nutr. 24, 174-182
Dvorak B et al (1996) Insulin-like growth factor-I (IGF-1) mRNA in the small intestine of suckling and adult rats. FEBS Letters 388,155-160
Eppard P J et al (1994) Survey of milk insulin-like growth factor in retail milk samples. (Unpublished report cited in WHO: Food Additive Series 41,125-146, 1998).
Etherton, T D. and Bauman, D E. (1998) The biology of somatotropin in growth and lactation of domestic animals. Physiol. Rev. (In press).
FAO/WHO Joint Committee on Food Additives (1998) Summary and conclusions from Fiftieth Meeting, Rome 17-26 February 1998
Fholenhag K et al (1996) Effects of insulin-like growth-factor-1 (IGF-1) on the porto-arterial concentration differences of amino acids and glucose: a comparison between oral and intraperitoneal administration in the newborn piglet. Hormone and Metabolic Research 28, 582-587
Fholenhag K et al (1997) Effects of insulin-like growth factor I (IGF-1) on the small intestine: a comparison between oral and subcutaneous administration in the weaned rat. Growth Factors 14, 81-88
Food and Drug Administration (1988) Veterinary Note
Food and Drug Administration (1994) Statement of 16 March 1994.
Gluckman, P D (1990) The effects of growth hormone on lactation and performance in ruminants and humans: mechanisms of action and effects on milk hormone composition. In: NIH Technology Assessment Conference Abstracts. National Institutes of Health, Bethesda, Maryland, pp 41.
Groenewegen, P P et al (1990) Bioactivity of milk from BST-treated cows. J. Nutrition 120, 514-520
Hammond B G et al (1990) Food safety and pharmacokinetic studies which support a zero (0) meat and milk withdrawal time for use of sometribove in dairy cows. Ann. Rech. Vet.,21 (suppl. 1), 107-120
Hankinson S E et al (1998) Circulating concentrations of insulin-like growth factor 1 and risk of breast cancer. The Lancet, 351 (9113), 9 May 1998, 1393-96
Hartnell G F (1995) Bovine somatotropin: Production, Management, and United States Experience. I n Animal Science Research and Development; Moving Towards a New Century. Ed Ivan, M. Centre for Food and Animal Research, Agriculture and Agri-Food Canada. Ottawa ON K1A 0C6, Canada.
Hocquette J F et al (1989) The human liver growth hormone receptor. Endocrinol., 125, 2167-2174
Honegger A and Humbel R E (1986) Insulin-like growth factors I and II in fetal and adult bovine serum. Purification, primary structures and immunological cross-reactivities. J. Biol. Chem. 261, 569-575
Humbrel R E (1990) Insulin-like growth factors I and II. Eur. J. Biochem., 190, 445-462
Johnson D E et al (1992) The environmental impact of bovine somatotropin use in dairy cattle. J. Environ. Qual. 21, 157-162
Judge L J et al (1997) Recombinant bovine somatotropin and clinical mastitis: incidence, discarded milk following therapy, and culling. J. Dairy Sci. 80, 3212-3218
Juskevich J C and Guyer C G (1990) Bovine Growth Hormone - Human Food Safety Evaluation. Science, 249, 875-884
Katzenstein L (1995) Drugged-Cow Warnings are all Udder Nonsense, Philadelphia Enquirer, 21 April 1994
Lahm H (1992) Growth regulation and co-stimulation of human colorectal cancer cell lines by insulin-like growth factor I, II and transforming growth factor alpha. Br. J. Cancer 65, 341-346
Macaulay V M (1992) Insulin-like growth factors and cancer. Br. J. Cancer 65, 311-320
MAFF Consumer Panel (1994) Bovine somatotropin. CP(94), 18/5-6
MAFF Consumer Panel (1996) Minutes of 25th Meeting, 24 January 1996, 7-8.
McBride B W et al (1988) The Influence of Bovine Growth Hormone (Somatotropin) on Animals and their Products. Res. Dev. Agric., 5, 1
McClary D B et al (1994) The effect of Sustained-Release Recombinant Bovine somatotropin (Somidobove) on Udder Health for a Full Lactation,. J. Dairy Sci. 77, 2261-2271
McGuffey RK and Wilkinson J I D (1991) Nutritional Implications of Bovine somatotropin for the Lactating Cow. J. Dairy. Sci., 74 (suppl. 2), 63-71.
McGuire, M.A. and D.E. Bauman. (1997) Regulation of nutrient use by bovine somatotropin: The key to animal performance and well-being. IXth Int. Conf. Production Diseases in Farm Animals (H. Martens, ed) Free University of Berlin, 125-137
Michell N P et al (1997a) Insulin-like growth factor binding proteins as mediator of IGF-1 effects on colon cancer cell proliferation. Growth Factors 14, 269-277
Michell N P et al (1997b) Insulin-like growth factors and their binding proteins in human colonocytes: preferential degradation of IGFBP-2 in colonic cancers. Br. J. Cancer 76, 60-66
Moore W V et al (1985) Species variation in the binding of hGH of hepatic membranes. Horm. Res., 21, 33-45
National Research Council (1994) Metabolic Modifiers - Effects on the Nutrient Requirements of Food-Producing Animals. National Academy Press, Washington DC
Odle J et al (1996) Intestinal effects of milk borne growth factors in neonates of agricultural importance. J. Anim. Sci. 74, 2509-2522.
Oguchi S et al (1997) Growth factors in breast milk and their effect on gastrointestinal development. Chung Hua Min Kuo Hsiao Erh Ko I Hsueh Hui Tsa Chih 38 (5), 332-337
Peterson C A et al (1997) GH elevates serum IGF-1 levels but does not alter mucosal atrophy in parenterally fed rats. Am. J. Physiology - Gastrointestinal and Liver 35, G1100-G1108
Peyrat J P et al (1993) Plasma insulin-like growth factor-I (IGF-1) concentrations in human breast cancer. Eur. J. Cancer 29A, 492-497
Philipps A F et al (1997) Growth of artificially fed infant rats: effect of supplementation with insulin-like growth factor I. Am. J. Physiol. - Regulatory Integrative and Physiology 41, R1532-R1539
Phil
