PSXIII-6 - Effects of Melatonin on Physiologic Responses and Behavior in Dairy Steers Following Lps-induced Inflammation

Abstract: Mitigation of stress is critical in the livestock industry, especially in feedlot cattle where stress yields lesser productivity due to behavioral and physiological changes. In this experiment, dairy steers were allocated to one of two treatment groups that either received a single intravenous bolus of saline, control (CON; n = 4) or saline with melatonin (MEL; n = 4) at a rate of 100 µg/kg of body weight, 30 min (-0.5 h) prior to each lipopolysaccharide (LPS) challenge. For each LPS challenge, all steers were administered LPS from E. coli O111:B4 at 0.5 µg/kg of body weight intravenously 30 min following treatment, labeled as 0 h. Blood samples were collected at -0.5, 0, 0.5, 1, 2, 4, 6, and 24 h relative to each LPS challenge for serum cortisol analysis. Steers underwent a two-week washout period following the first LPS challenge, switched treatments, and underwent a second LPS challenge with their new treatment. Data were analyzed using a mixed model ANOVA in SAS 9.4. Main effects included treatment and hour on sickness score (SS; numerical scoring system based on outward signs of illness), rectal temperature (RT), respiration rate (RR), and cortisol concentrations (CORT), with period as a random effect. Statistical significance was set at P ≤ 0.05 and tendencies at 0.06 ≤ P ≤ 0.10. Cattle that received MEL tended to exhibit a lesser SS (P = 0.06) compared with CON cattle (1.94 vs. 2.13 ± 0.087, respectively). Treatment did not influence RT, RR, or CORT. The time effect followed the trend that -0.5 h, 0 h, and 24 h post-LPS challenge were similar, while elevated levels were observed for hours 0.5, 1, 2, 4 and 6. No interactions were encountered, indicating further research is needed to determine the best dosage of melatonin in calves to decrease response to stress.