Resveratrol supplementation improved antioxidant capacity and mitigated the impact of heat stress in lactating dairy cows

The relationship between oxidative stress, inflammation and productivity loss associated with heat stress has been documented in dairy cattle. Resveratrol, a naturally occurring plant-based polyphenolic compound possesses antioxidant properties due to its chemical structure. We hypothesize that supplementing resveratrol would improve the antioxidant capacity and reduce heat stress-induced oxidative stress in lactating dairy cows. The objective of the study was to determine the effects of resveratrol supplementation on plasma markers of oxidative stress and their relation with productivity, respiratory rate (RR), and rectal temperature (RT) in heat-stressed dairy cows. The study was conducted during summer using 30 Holstein cows averaging (±SD) 127 ± 33 d in milk (DIM), 48.9 ± 8.9 kg/d milk yield, and 2.1 ± 1.0 parity housed in a sand-bedded free stall barn at the University of Tennessee dairy farm. Following a one-week baseline period, cows were allocated to one of 2 treatment groups, control (CON; n=15, TMR with no resveratrol) or resveratrol (RES; n=15, TMR with 0.5 g resveratrol per cow/d) for 2 weeks of adaptation period. During baseline and adaptation periods, fans and soakers enhanced cows' evaporative cooling. Following the adaptation period, fans and soakers were disabled, cows experienced natural summer heat stress, and treatments were imposed for 3 weeks. Temperature and humidity loggers recorded weather variables in the barn. Rectal temperature and RR were recorded 3 times daily. Blood samples were collected once a week, and plasma was isolated to measure markers of oxidative stress. Data were analyzed using the MIXED procedure with repeated measurements in SAS. The effects of treatment, week, parity, and their interactions were considered fixed, and animal was considered a random effect. Baseline measurements were included in the statistical analysis as covariate if significant. A suitable covariance structure was used based on the lowest Akaike and Bayesian information criteria. Regression analysis determined the relations between milk yield and plasma total antioxidant capacity, and RT or RR with plasma total antioxidant capacity. Results showed that the ambient temperature and relative humidity ranged between 20 and 30°C and 49–84% during the treatment period. Compared with CON, the RES treatment increased plasma total antioxidant capacity up to 12% in parity 2 cows. The RES treatment did not affect plasma concentrations of superoxide dismutase (SOD) and malondialdehyde (MDA) but tended to reduce plasma pro-oxidant antioxidant balance in wk 2 and 3. Regression analysis indicated that plasma total antioxidant capacity had a positive relationship with in milk yield in RES (R 2 = 0.13) and CON cows (R 2 = 0.02) and the increase of 1 mM of plasma total antioxidant capacity in RES cows was associated with 8.5 kg of milk more than in CON cows. Regression analysis indicated that RR was explained weakly by plasma total antioxidant capacity in CON cows only (R 2 = 0.01). In conclusion, RES increased plasma total antioxidant capacity, mitigated oxidative stress and production loss in heat-stressed dairy cows. Resveratrol could be used as a feed additive to reduce the impact of heat stress on commercial dairy farms.