Editor’s note: The following answer is excerpted from a presentation made by Ron Butler, dairy scientist at Cornell University, at the recent Cornell Nutrition Conference.
Q: What are some of the nutritional and management strategies during the dry period to reduce negative energy balance and improve fertility in the next lactation?
A: During late pregnancy, insulin resistance in adipose tissue contributes to increasing plasma non-esterified fatty acid (NEFA) concentrations. And subsequent oxidation of NEFA by the liver is the cause of decreasing dry matter intake as cows approach calving.
Studies over the past few years suggest that energy nutrition during the dry period interacts with insulin resistance during the late prepartum period. Excess energy intake not only during the close-up period, but also during the far-off dry period, exacerbates insulin resistance.
Collectively, these reports indicate that overfeeding energy to dry cows results in changes in metabolism that, in turn, likely predispose cows to decreased dry matter intake and higher NEFA in the peripartal period. Cows with high body condition scores are particularly at risk.
Recommendations for energy nutrition of dairy cows during both the far-off and close-up periods have evolved over the past several years toward the goal of meeting, but not markedly exceeding energy requirements ie. no more than 110 to 120 percent. Controlling energy intake via high-bulk diets (containing straw) or moderately restricted feeding prepartum result in similar metabolic profiles, but limit feeding is difficult to manage successfully, especially when cows and heifers are co-mingled in pens with the associated social and behavioral interactions.
Currently, there is global interest and widespread research activity toward identifying genetic mechanisms regulating feed intake, feed efficiency, early ovulation and IGF-I production. Such studies seek to relate these characteristics to single nucleotide polymorphisms utilizing the tools of genomic analysis, data records on performance, and genetic selection. As an early example, Fert (+) cows express higher milk yield and higher conception rates to AI, but no difference in feed intake or energy balance. Future benefits and opportunities from this type of research will have major impacts.
Summary
Negative energy balance (NEBAL) may begin prepartum in association with declining feed intake. Excess body condition is one factor related to decreased feed intake. During the first three weeks of lactation, NEBAL delays early ovulation and recovery of postpartum reproductive function and provides the major nutritional link to low fertility in lactating dairy cows. NEBAL may detrimentally impact the oocyte that is released after ovulation and exert other carryover effects on uterine conditions, resulting in reduced conception rate to insemination. Reducing NEBAL is beneficial, but very difficult to achieve in cows being managed for high milk yield. Maintaining intakes through the prepartum period to calving and increasing intake rapidly thereafter reduces NEBAL and the detrimental effects on coordinated ovarian and liver function.
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