Monensin effects on early weaned beef calves grazing annual ryegrass pastures

Abstract Text: The objective of this study was to evaluate the effects of monensin on performance of early weaned beef calves grazing annual ryegrass (Lolium multiflorium). The experiment was conducted at the UF/IFAS Range Cattle Research and Education Center, Ona, FL from January 12 to April 14 2015. Treatments were calves receiving monensin (20 mg/kg of estimated total DMI) or control (no monensin) distributed in a randomized complete block design with four replicates. Calves were weaned with 81±6 kg BW at 84±20 d of age. Calves were supplemented with 1% BW concentrate (CP = 18% and TDN = 78%) daily. Four calves were allocated to each pastures (0.3 ha, experimental unit) in a continuous and fixed stocking rate. Herbage mass and nutritive value were evaluated every 14 d and calf’ BW recorded every 28 d. Blood samples were collected at the termination of the study. Data were analyzed using the Proc Mixed of SAS with treatment as fixed effect and block as random effect. There was no difference (P ≥ 0.05) in herbage mass (mean = 1,450 kg/ha), CP (mean = 22.2%), and in vitro digestible organic matter (mean = 78.7%) between treatments. Calves receiving monensin had greater ADG (0.71 vs. 0.57 kg/d, P = 0.003) and tended to have greater IGF-1 (89.5 vs. 67.9 ng/mL, P = 0.09) but there was no difference (P ≥ 0.05) in BUN (mean = 26.7 mg/dL), glucose (mean = 86.3 mg/dL), and insulin (mean = 2.31 uIU/mL). The incidence of coccidiosis was lesser (0.49 vs. 1.35 log count) for calves receiving monensin. Adding monensin to the concentrate supplement is a feasible management practice to improve performance of early weaned calves grazing annual ryegrass pastures.

Keywords: supplementation, beef cattle, monensin