Effects of oral tilmicosin on health and performance in newly received beef heifers

ABSTRACT The objective of these studies was to determine the effects of feeding tilmicosin on health and performance of newly received beef cattle. Beef heifers (n = 480) were used in 2 studies to determine effects of oral tilmicosin on health and performance. In Exp. 1, 320 heifers (BW = 196 ± 3.3 kg) were administered antimicrobial metaphylaxis before shipment. At arrival they were monitored for signs of bovine respiratory disease. When 10% of the population was morbid, heifers were assigned to either a control receiving diet (CON) or a diet providing 12.5 mg of tilmicosin/kg of BW (TIL). Treatments were fed for 14 d, and morbid animals were treated with injectable antibiotics. Cattle were weighed individually on d 0, 28, and 56. Data were analyzed as a randomized complete block, and morbidity was analyzed as nonparametric data. Feeding TIL resulted in reduced BW at d 28 ( P = 0.03). Moreover, TIL decreases DMI during the first 14 d ( P = 0.0001) and decreased ADG ( P = 0.03) and G:F ( P = 0.05) from d 0 to 28. There were no differences in morbidity ( P = 0.20), and TIL increased total antibiotic cost ( P = 0.004). In Exp. 2, 160 beef heifers (BW = 227 ± 2.3 kg) received no metaphylaxis and were processed at arrival. Feeding TIL did not affect morbidity ( P = 0.44); however, TIL decreased the number of animals re-treated ( P = 0.03) and increased total antibiotic cost ( P = 0.04).