Abstract
Crossbred beef steers (n = 8160; 294 + 10.4 kg) were used in a randomized complete block designed study to determine the effects of post-metaphylactic interval (PMI) on health, live and carcass performance. Steers were administered tildipirosin for the control of bovine respiratory disease (BRD) before being randomly allocated to PMI treatments (4-, 7-, 10-, or 13-day PMI). Treatments were replicated in forty - 204 head pens with each treatment represented within 10 arrival blocks. Blocks ranged from 4 to 15 unique sources of cattle representing five states (AR, FL, GA, LA, TX). Steers were observed daily (217 + 14 d) by trained pen riders with steers suffering from BRD receiving a common antibiotic therapy across PMI treatment. Data were evaluated using linear, quadratic and cubic contrasts. First pull BRD morbidity decreased linearly (P < 0.01) and tended to decrease quadratically (P = 0.08) as PMI increased with the greatest BRD morbidity at 7 days (12.9%) and the least at 13 days (9.5%). First pull BRD relapses tended to decrease linearly (P = 0.10) with increasing PMI. Total first pull morbidity, for all causes, decreased quadratically (P = 0.02) as PMI increased with the greatest morbidly occurring with a 7-day PMI (15.8%) and the least with a 13-day PMI (11.5%). Mortality caused by BRD (0.73%; P > 0.70) and all causes (1.41%; P > 0.20) or chronicity (1.60%; P > 0.15), resulting from failure to respond to therapy, were not affected by PMI. Final body weight, ADG, DMI, Gain:Feed, and HCW were not affected (P > 0.20) by PMI. Total and BRD morbidity can be reduced by increasing PMI up to 13 days in cattle at moderate risk of developing BRD (15% morbidity, 1% mortality, 1% chronicity) without adversely affecting mortality, chronicity or live and carcass performance.
Net return distributions when metaphylaxis is used to control bovine respiratory disease in high health-risk cattle
