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

## TL;DR

Holstein cows on high- or low-energy diets in late lactation showed different energy use patterns, affecting milk production and insulin levels based on body condition changes.

## Contribution

The study reveals how insulin resistance and milk production mediate body condition responses to diet in late-lactation cows.

## Key findings

- High-energy nonresponsive cows increased milk production and had lower dry-off insulin concentrations.
- Low-energy nonresponsive cows decreased milk production and had higher dry-off insulin concentrations.
- Circulating insulin concentrations converged near parturition across all groups.

## Abstract

Summary: Cows fed high- and low-energy diets differentially exhibited changes in body condition by altering milk production and circulating insulin concentrations. Cows fed a low-energy diet that did not alter their body condition during the late-lactation treatment period had decreased milk production and increased insulin concentrations compared with responsive cows. Cows fed a high-energy diet that did not increase their body condition during the late-lactation treatment period had increased milk production and reduced insulin concentrations compared with the responsive cows. Figure created in BioRender.

Summary: Cows fed high- and low-energy diets differentially exhibited changes in body condition by altering milk production and circulating insulin concentrations. Cows fed a low-energy diet that did not alter their body condition during the late-lactation treatment period had decreased milk production and increased insulin concentrations compared with responsive cows. Cows fed a high-energy diet that did not increase their body condition during the late-lactation treatment period had increased milk production and reduced insulin concentrations compared with the responsive cows. Figure created in BioRender.

•Insulin resistance mediates milk production to control body condition in late lactation.•High-energy-fed cows that did not gain body condition increased milk production.•Low-energy-fed cows that gained body condition decreased milk production.•High-energy responsive and low-energy nonresponsive cows had the highest insulin concentrations.

Insulin resistance mediates milk production to control body condition in late lactation.

High-energy-fed cows that did not gain body condition increased milk production.

Low-energy-fed cows that gained body condition decreased milk production.

High-energy responsive and low-energy nonresponsive cows had the highest insulin concentrations.

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.