The objective of the current study was to evaluate the effects of dietary supplementation with chromium yeast (Cr-yeast) and dihydropyridine (DHP) on nutrient utilization, milk composition, and antioxidative status of prepartum dairy cows under heat stress. Twenty-four perinatal dairy cows (600 ± 14 kg; parity 2–3) were divided into three groups and fed the same basal diet with no supplement (control group), 8 g of Cr-yeast (Cr-yeast group), or 3 g of DHP (DHP group) per day. The experimental period consisted of a 7-d adaptation period and a 30-d data collection period from day 27 prepartum to day 3 postpartum. The temperature humidity index (THI) observed at daytime during the trial period exceeded 72, and the mean daily THI was 79.43. Norepinephrine in the Cr-yeast group decreased in prepartum cows. Serum cortisol in Cr-yeast or DHP group cows was lower in the postpartum period than in the control; however, serum cortisol levels decreased in the DHP group in the prepartum period. Dietary supplementation with Cr-yeast increased the digestibility of ether extract and the concentration of milk fat, while the solid non-fat (SNF) level was reduced. In the DHP group, the lactoprotein content was higher than the control. Total antioxidant capacity (T-AOC) was higher and the malondialdehyde (MDA) content tended to increase before calving in the Cr-yeast and DHP groups. Dietary supplementation with Cr-yeast or DHP can relieve the adverse impact caused by heat stress in prepartum dairy cows.
"Experientia docet" - Experience is the best teacher