Physiology and Endocrinology: Effects of nutrition and metabolism on ruminant reproduction

The adaptive response to a given metabolic load during energy deficiencies varies considerably among animals. The aim of this study was to investigate if individual cows respond in a repeated manner to a negative energy balance (NEB) in early and mid-lactation. Twenty-five multiparous Holstein dairy cows (3.0 ± 1.1 parities; mean ± SD) experienced a NEB during the first weeks of lactation, and after getting into a positive EB, cows were exposed to a 3-wk feed-restriction period providing 50% of estimated requirements starting at around 100 DIM. Dry matter intake and milk yield were recorded daily. Blood samples for analysis of plasma concentrations of glucose, NEFA, BHBA, cholesterol, and IGF-1 were obtained once weekly. Retrospectively, cows were ranked according to plasma NEFA concentration in early lactation. The cows with the 33% highest and 33% lowest NEFA concentrations (8 animals each) were selected and classified either a high response (HR) or a low response (LR) group, respectively. Data were analyzed using MIXED models in SAS including wk, group (HR or LR), parity, and the wk × group interaction as fixed effects and the individual cow as repeated subject. Differences between HR and LR over time were detected by the Bonferroni t-test. Significant effects were assumed at a level of P < 0.05. Before parturition, no differences were detected between LR and HR. After parturition, milk yield and ECM were higher for HR (milk yield: +7.4 kg/d, ECM: +4.9 kg/d from wk 2 to 14 pp) compared with LR (P < 0.05). Although plasma concentrations of glucose and cholesterol showed group differences in early lactation, but not during feed-restriction, concentrations of NEFA, BHBA, and IGF-1 showed a consistent similarly directed, but different response to a NEB at the 2 stages of lactation despite a similar EB. HR had higher NEFA (+0.8 mmol/L in wk 2 pp, +0.2 mmol/L in wk 2 of feed-restriction), BHBA (+1.3 mmol/L in wk 3 pp, +0.3 mmol/L in wk 1 of feed-restriction) and lower IGF-1 concentrations (−48.7 ng/mL in wk 2 pp, −54.9 ng/mL in wk 2 of feed-restriction) compared with LR at the 2 stages of lactation (P < 0.05). Cows responding to high milk production and negative energy balance with higher plasma NEFA and BHBA did again respond with higher NEFA and BHBA to a negative energy balance in later lactation as compared with cows with lower NEFA and BHBA concentrations with similar production levels.