Chromium yeast alleviates heat stress by improving antioxidant and immune function in Holstein mid-lactation dairy cows

Abstract

This study aimed to evaluate the effects of chromium yeast (CY) on lactation performance, antioxidant status and immune function, and chromium concentrations in the plasma of mid-lactation dairy cows under heat stress. Twenty-four healthy Chinese Holstein mid-lactation dairy cows with similar milk yield (27.0 ± 1.9 kg/day), parity (2 or 3), and days in milk (DIM, 105 ± 15 d) received the same basal diet containing 0.11 mg Cr/kg of DM. All the animals were divided into 2 blocks according to milk yield (block 1 and block 2 for low- and high-producing cows). Cows of block 1 or block 2 each were randomly allocated to four treatments: a negative control group (without CY supplementation, CON), and groups that received CY at 0.18, 0.36, and 0.54 mg Cr/kg DM, respectively. The experiment lasted 10 wk over a hot summer, including a pre-feeding period of 2 wk. Cows were experiencing heat stress as the average temperature-humidity index (THI) is greater than 72. The averagerespiration rates (RR) and rectal temperature (RT) of the cows in CON group were 81.11 ± 1.42 breath/min and 39.66 ± 0.05 ℃, respectively. The results showed that supplementation with CY reduced the RR and RT of dairy cows under heat stress in both a linear and quadratic manner; the lowest was 75.33 ± 0.76 breath/min and 39.40 ± 0.09 ℃ for the CY-0.36 group (P < 0.05). CY supplementation did not affect milk yield or milk composition, but linearly increased dry matter intake and milk lactose content (P < 0.05). Furthermore, increasing amounts of CY increased the activity of glutathione peroxidase, superoxide dismutase and total antioxidant capacity in serum, but decreased the concentration of malondialdehyde (P < 0.05). Although no differences were observed in the concentrations of IL-6, IL-10, IgA, and IgM, supplementation with CY decreased the concentrations of IL-2, IL-4, and IL-1β, but increased that of IgG (P < 0.05). The plasma Cr concentration increased as the dose of supplemented Cr increased (P < 0.05). In summary, CY supplementation improved the welfare of mid-lactation dairy cows by reducing RT and RR, and increased dry matter intake and milk lactose content. Supplementation with CY improved the antioxidant and immune function in mid-lactation dairy cows. The appropriate dose of CY at 0.36 mg Cr/kg DM is recommended for lactating dairy cows experiencing heat stress during hot summers.