Effects of rumen-protected choline supplementation in Holstein dairy cows during electric heat blanket-induced heat stress

摘要

Dairy cows experiencing heat stress (HS) attempt tothermoregulate through multiple mechanisms, such asreducing feed intake and milk production and alteringblood flow to increase heat dissipation. Effects ofcholine on energy metabolism and immune functionmay yield it a viable nutritional intervention to mitigatenegative effects of HS. The primary objective ofthis experiment was to determine if supplementation ofrumen-protected choline during, or before and during,an increased heat load would ameliorate the negativeeffects of HS on production and immune status. Heatstress was induced via an electric heat blanket modelwith a 3-d baseline period and 7-d HS period for allcows. Multiparous mid-lactation (208 ± 31 days inmilk) Holstein cows were fed the same basal herd diet,blocked by pre-experiment milk yield, and randomlyassigned to receive one of the following: (1) no rumenprotected(RP) choline (n = 7); (2) RP choline (60g/d) via top-dress during the HS period (n = 8); or (3)RP choline (60 g/d) via top-dress during the baselineand HS periods (n = 8). Imposing HS via electric heatblanket raised respiration rate with all cows surpassingthe HS threshold of 60 breaths/min. The increase inrespiration rate tended to be ameliorated with eitherschedule of RP choline supplementation. Milk yieldtended to increase when RP choline was supplementedin both the baseline period and during HS. Supplementationof RP choline tended to reduce blood fattyacid and triglyceride and tended to increase the revisedquantitative insulin sensitivity check index. The role ofRP choline supplementation to partially ameliorate theeffects of HS should be further explored as a potentialnutritional strategy to mitigate the negative consequencesof HS on health and production.