NOVEL NUTRITIONAL STRATEGIES TO AMELIORATE EFFECTS OF HEAT STRESS IN LACTATING DAIRY COWS

Effects of heat stress on dairy production have been a subject of investigation for decades and yet an economically feasible and sustainable solution to mitigate these effects remains elusive. The collective goal of this dissertation was to test novel dietary strategies to ameliorate the effects of heat stress on dairy production. To achieve this goal, two animal experiments with heat stressed-lactating dairy cows were conducted. Experiment 1 was designed to evaluate the effects of dietary supplementation with resveratrol (0.5 g/cow/d), on productivity and welfare of heat stressed lactating dairy cows. The study utilized 48 lactating Holstein cows in first, second and third or more lactations, under natural summer heat stress conditions. Results revealed that resveratrol reduced noon rectal temperature and increased respiratory rate in cows. Resveratrol supplementation improved milk yield by 0.7 kg, lactose yield by 60 g and protein yield by 40 g in heat stressed lactating cows. With a significant treatment × parity interaction, resveratrol improved body weight in first lactation cows. Analysis of antioxidant markers in circulation revealed that resveratrol improved total antioxidant capacity in heat stressed parity 2 cows. To conclude, resveratrol seems to be an effective compound in reducing heat induced productivity loss and welfare issues in dairy cows. Experiment 2 was designed to test the dietary modification of changing molasses inclusion (10.7% DM), on heat stress associated inflammation and productivity loss in dairy cows. Study utilized 24 multiparous Holstein cows in a 2×2 factorial arrangement of environment (thermoneutral (TN) or heat stress (HS)) and diet (corn grain or molasses). Study was conducted in three periods: P1: adaptation to diet for 15 d, P2: adaptation to facility for 6 d, P3: treatment period for 6 d (induced heat stress in climate controlled facility for HS cows and pair feeding for TN cows). Our results revealed that dietary modification with molasses did not mitigate production loss in heat stressed dairy cows. Molasses maintained lactose content and reduced somatic cell count in heat stressed cows. Heat stress reduced basophil and monocyte concentrations and increased eosinophil percentage in cows. Interestingly, molasses maintained hematological profile with no change in basophil and monocyte concentrations, eosinophil percentage. Taken together, supplementation of resveratrol and molasses are effective in reducing heat stress effects on lactating dairy cows.