A randomized field study comparing differences in core body temperature, health, and performance in crossbred beef heifers administered 2 antimicrobial products given upon arrival at a stocker facility1

Antimicrobial metaphylaxis is an important tool used for the prevention of bovine respiratory disease complex, an economically important disease that typically affects newly weaned beef calves that are marketed and transported a distance from their origin. An experiment was conducted to determine the effects of administering 2 different metaphylactic products [tulathromycin (TULA) and gamithromycin (GAMI)] on differences on core body temperature, health, and performance on 284 highly stressed stocker calves. Calves were procured and delivered (transient time = 13.5 h average) from a southeastern United States order buyer in 3 truckload lots during a 6-d period in October 2011. The core body temperatures in nonmorbid calves in the TULA calves were greater compared with the GAMI calves the first 2 h after administration and at multiple time points on d 4 through 6 of the experiment (P < 0.05). Calves receiving TULA experienced less morbidity (P < 0.01) and less chronicity (P < 0.05) when compared with GAMI calves. Calves in the TULA group had greater ADG (P < 0.001) from arrival to d 45 compared with calves injected with GAMI. This experiment indicated that metaphylactic products may affect core body temperature differently, which may be an important consideration when managing the health of high-risk calves. Moreover, both health and performance differences may exist among calves administered different metaphylactic products. Therefore, product selection is an important decision when managing high-risk calves.