Effects of short-term exposure of feeder cattle to calves persistently infected with bovine viral diarrhea virus

Abstract

Research using 2,954 auction-derived feeder steers and heifers was conducted at a single commercial feedlot in Kansas to determine the effects of testing for cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV) at 10-14 days-on-feed (DOF), and removing them at 13-18 DOF. After removal of test-positive animals, the effect of the short-term exposure (STE) to PI cattle on health, performance and carcass characteristics was determined. The percentage of calves exhibiting signs of illness was increased (P<0.01) in cattle with STE to PI-BVDV. Cattle with no exposure (NE) to PI-BVDV calves had a morbidity rate of 18.8%, while a 29.6% morbidity rate was observed in pens of calves with STE to a PI-BVDV calf. Characterization of the temporal pen morbidity rate of STE and NE calves revealed that 31.7% of all STE and 15.3% of NE illness occurred in the first seven DOF. Additionally, the incidence of cattle treated for bovine respiratory disease in STE calves was 2.17 (95% CI 1.73 to 2.72) initial treatments per 1,000 head-days at risk, whereas the incidence of treatment of calves in NE pens was 1.28 (95% CI 0.98 to 1.68) initial treatments per 1,000 head-days at risk. Short-term exposure to PI-BVDV calves had no effect on retreatment rate, death loss, or performance. There was no evidence of a BVD-PI exposure X sex interaction (P=0.62) for carcasses that graded USDA Choice or better, but there was a main effect of sex (P<0.01). There was evidence of a BVD-PI exposure X sex interaction for Yield Grade 2 or greater carcasses (P=0.03). In this study, testing at 10-14 DOF was too late in the feeding period to eliminate the initial morbidity spike that occurred during 0-7 DOF, and the subsequent morbidity differences between calves with STE or NE to PI calves.