Differential energy partitioning occurs in response to high- and low-energy diets in Holstein cows during late lactation

This study evaluated the impact of high-energy (HE) or low-energy (LE) diets during late lactation and the responsiveness of body condition changes to diet during the dietary treatment period. Sixty-six multiparous Holstein cows were blocked by parity and expected date of parturition and randomly assigned to HE (1.74 Mcal/kg DM) or LE (1.50 Mcal/kg DM) diets at 150 d of gestation to achieve high or average BCS by dry-off (233 d of gestation). Surprisingly, not all cows within dietary treatment groups were responsive to the diet based on BCS at dry-off. To determine the underlying physiology responsible for this observation, we classified cows as responsive (R) or nonresponsive to diet (NR) within each dietary treatment: HE (HE-R, >0.25 increase in BCS [28/35]; HE-NR, ≤0.25 BCS [7/35]) or LE (LE-R ≤0.25 increase in BCS [27/31]; LE-NR >0.25 BCS increase [4/31]). Feed intake did not differ within the HE-R and HE-NR subgroups or between the LE-R and LE-NR subgroups. During the dietary treatment period, cumulative ECM was greater in HE-NR than HE-R cows (3,304 vs. 2,236 ± 151 kg). In contrast, LE-NR produced less ECM than LE-R cows (1,622 ± 229 vs. 2,068 ± 77 kg) during the dietary treatment period. Circulating insulin concentrations were similar among subgroups at study enrollment (9.2 ± 1.1 mU/mL); however, dry-off insulin concentrations differed among subgroups (HE-R 17 ± 3.0; HE-NR 5.4 ± 2.0 mU/mL; LE-R 10.2 ± 2.0; LE-NR 23.6 ± 4.0 mU/mL). One week before parturition, circulating insulin concentrations converged and were no longer different among subgroups, averaging 12.5 ± 2 mU/mL. Our data suggest that circulating insulin concentration is involved in regulating the response to dietary treatment during late lactation.