Implications of Feed Additives in the Mitigation of Heat Stress in Cattle

Nutritional supplements have been used to mitigate heat stress in cattle. A series of experiments were conducted under controlled environment conditions in the Animal Research Complex (ARC) to evaluate the value of nutritional intervention on mitigation of heat stress (HS) in cattle. Previous research and literature have shown mixed results in terms of performance benefits. In the first study, we evaluated the use of a proprietary yeast cell extract to help mitigate the effects of hyperthermia on growth development by improving metabolic and immune functions. Twelve crossbred Hereford steers (250 ± 100 kg) were randomly assigned to one of two dietary groups: control group (CON) received 56.7 g of placebo/hd/day; the feed additive group (BA) received 56.7 g of BA/hd/day. Steers were randomly assigned to one of two tie stall rooms with 6 steers per room and 3 steers per treatment/room. Rooms were exposed to cyclical daily temperature humidity index (THI) of 70 - 81 and 27 – 39 for HS and the thermoneutral (TN) rooms respectively for a total of 15 days. Average daily water consumption and average daily gain were calculated at the end of the experimental period. Heat stress increased water consumption (P<0.001), respiration rate (P<0.001), and skin temperature (P<0.001) and tended to increase rectal temperature (P<0.06). Supplementation with BA tended to reduce rectal temperatures (P<0.06) in heat stressed cattle. Exposure to heat stress lowered serum glucose (P<0.01) and insulin (P<0.01) while increasing NEFAS (P<0.01) and TAG (P<0.01). Supplementation with BA lowered TAG (P<0.05) and glucose (P<0.05). HS and BA supplementation had no effect on serum cortisol levels. Results of this study suggest that HS exposure for 15 days had performance and metabolic impacts in crossbred Hereford steers. Supplementation with the dietary BA alleviated some of the daily metabolic effects associated with heat exposure. The objective of the second study was to evaluate the effect of feeding a dietary supplement (PMI Nutritional Additives, Arden Hills, MN) on the HS response in multi-parturient dairy cows in mid lactation. Two pens of cows at a commercial dairy were fed either control (CON) or additive (YB) at 113 g/cow per d for two weeks prior to arrival. Study cows (n=12) were balanced in days in milk (DIM), milk production, and parity (111.91±4.85 d, 33.67±0.96 kg/d, and 2.25±0.18). Cows were randomly selected from both groups (6 TRT and 6 CON) and housed in environmentally controlled chambers for 18 d and fed appropriate diet. Cows were subjected to 7 d of TN conditions, 7 d of HS, and 4 d of recovery (REC) under TN conditions. HS increased RT (P<0.0001), RR (P<0.0001), BUN (P