430 - Effects of Exogenous Glucocorticoid Administration on Feed Intake in Beef Cattle

Calves (n = 63) from Angus crossbred cows were weighed and randomly assigned to treatments within 4h of parturition (d0). Each calf was intravenously infused with either a low cortisol [LC; n = 22, 3.5 µg hydrocortisol sodium succinate/kg body weight (BW)], high cortisol (HC; n = 20, 7.0 µg/kg BW), or a sham infusion control (CON; n = 21, similar volume of saline). Each calf was administered a second infusion of its respective treatment 24h postpartum. Blood was collected via jugular venipuncture before infusion and daily from d0–17 of age and analyzed for leptin concentrations using a validated radioimmunoassay. Animal BW was collected every 14d from d0 until the end of the study. Heifers (n = 31; 367±4d of age) and steers (n = 32; 385±4d of age) entered a Growsafe system to measure feed intake (FI) and were allowed a 2wk adjustment period to a commercial ration (1.27 Mcal NE_m/kg and 15.8% CP and 0.45 Mcal NE_g/kg and 13.8% CP, respectively; DM basis). Heifer body condition score (BCS) was collected at the beginning and end of the trial. Heifers were fed for 70d and steers until they obtained a 12^th rib back fat (BF) thickness of 1.15cm. Data were analyzed via ANOVA or repeated measures using appropriate models of SAS. Serum leptin concentrations observed a treatment by day interaction (P = 0.0028), in which HC and LC were decreased compared to CON from d2-17 of age. Calf birth BW and adjusted 205d BW did not differ (P > 0.056) between treatments. Heifer BW gain, BCS change, and number of feed events were increased (P = 0.001) in LC compared to HC and CON. Steers did not differ between treatments (P > 0.080) in BW, BW gain, or BF thickness. However, LC steers observed greater daily FI (P = 0.047) and tended to have greater final BW (P = 0.080). In summary, exogenous cortisol administered to calves at parturition reduced leptin concentrations and improved FI of beef steers during a feeding trial.