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 = Energy_consumed- Energy_required

Energy_required=Energy_maintenance+Energy_growth+ Energy_pregnancy+ Energy_production

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