Evaluating Heat Stress Response In Lactating Holstein Cows With Supplementation Of A Feed Additive During Mid Lactation

Abstract

In the dairy industry, the detrimental effects of heat stress on lactating cattle are a serious issue facing many producers. Feed additives have been shown to mitigate the effects of heat stress by improving metabolic and immune function, and this study served to evaluate the effects of feeding a specific dietary supplement on the heat stress response in multi-parturient dairy cows in mid lactation. Cows were randomly selected and housed in environmentally controlled chambers, subjected to seven days of thermoneutral conditions, seven days of heat stress, and four days of recovery under thermoneutral conditions. Dry matter intake, milk production, milk composition, rectal temperature, respiration rate, and blood samples were measured daily. Heat stress increased RT (P<0.0001), RR (P<0.0001), BUN (P<0.0001), insulin (P=0.04), neutrophil (P=0.009), and water intake (P=0.0005). Heat stress decreased lymphocyte (P=0.0008), dry matter intake (P=0.0007), energy corrected milk (ECM, P=0.01), and 4% fat corrected milk (FCM, P=0.02). The feed additive decreased the feed efficiency ratio (P=0.03) correlating higher milk production with decreased feed intake. Results of this study suggest that heat stress exposure had performance and metabolic impacts in mid lactation cows, and supplementation with the feed additive alleviated some of the negative effects associated with heat stress.