PSI-16 Effects of Melatonin on Physiological Parameters, Chute and Exit Scores in Beef Calves Exposed to Summer Heat Stress

Abstract

Abstract This study was designed to evaluate the effects of melatonin on rectal temperature (RT), respiratory rate (RR), heat shock protein 70 (HSP 70), growth hormone (GH), chute (CS) and exit scores (ES) in beef calves exposed to heat stress during the summer. A total of twenty (20) eight months old calves divided into 2 groups were used for the study: melatonin group (MEL, n = 10) received 24mg of melatonin, once every 28 days, and control group (CON, n = 10) did not receive any subcutaneous melatonin implant. The effect of melatonin on RT, RR, HSP 70, GH, chute (CS) and ES were evaluated biweekly (Day 0, 14, 28, 42, 56, 70). The mean ambient temperature (AT) 24.00 ± 0.21°C, relative humidity (RH) 81.60 ± 0.76 % and temperature-humidity index (THI) 89.97 ± 0.70 recorded during the study were above the normal range reported for calves. The biweekly fluctuation of weight gain (WG) in MEL were higher than the CON. The mean RT (39.40 ± 0.06°C), RR (62.57 ± 1.15 cpm), CS (1.13 ± 0.04) and ES (1.5 ± 0.09) in the MEL group were lower (P < 0.05) than the corresponding values of 40.10 ± 0.06°C, 71.53 ± 1.59 cpm, 1.40 ± 0.07 and 1.80 ± 0.10 in the CON group. The biweekly variations in RT, RR, CS, ES, HSP 70 were lower (P < 0.05) in the MEL than the CON. Growth hormone concentrations were higher at D56 and 70 in MEL compared to the CON. Our results demonstrated that MEL ameliorates heat stress during the summer by lowering RT, RR, CS, and ES of beef heifers during the study period. In addition, melatonin influenced the biweekly variation in WG, RT, RR, CS, ES, HSP 70 and GH of heifers during the study period.