Effects of dietary supplementation with yeast chromium or dihydropyridine on milk composition and serum biochemical indices of periparturient dairy cows under heat stress

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.