PSI-10 - Effect of Chronic Melatonin Supplementation During Mid to Late Gestation on Performance and Behavioral Responses of Cows Exposed to Summer Heat Stress

Abstract: Summer heat stress negatively impacts the health and welfare of animals. Melatonin is a highly potent antioxidant and free radical scavenger with immune modulation and anti-inflammatory effects in domestic animals. This study examined the effect of supplemental melatonin during mid to late gestation on serum cortisol, heat shock protein 90 (HS90) and glucose concentrations, performance, behavior and hemogram of pregnant cows and their offspring. Multiparous pregnant beef cows were randomly assigned to 1 of 2 groups and supplemented with Melatonin® implants 24 mg (MEL, n=13) or without (CON, n=12) at day 190, 218, and 246 of gestation. Also, offspring performance (n = 24) was evaluated. Body weight, rectal temperature, hemogram, behavioral responses of cows (chute score, vocalization and exit score) were scored biweekly for 16 weeks. The average daily gain (ADG), rectal temperature, glucose concentration and hemogram of cows and calves showed no significant difference (P>0.05) between treatments except in calves were platelet were higher in MEL treated calves than control. Cortisol levels were significantly lower (P< 0.05) in MEL cows compare to CON from day 14 (1437 ± 2.54 and 2028 ± 3.23 pg/ml respectively) to the end of the experiment. Also, serum HSP90 concentrations were significantly lower (P< 0.05) from day 14 to the end of the study period (0 ng/ml and 0.73 ng/ml respectively). Chute and exit score did not differ significant between groups. Our results revealed that chronic melatonin supplementation during mid to late gestation reduced serum cortisol and HSP90 in cows exposed to summer heat stress.