320 Carcass characteristics of Bos indicus-Bos taurus steers following BVDV type 1b challenge

Abstract

Abstract Bovine Viral Diarrhea virus (BVDV), is a component of bovine respiratory disease (BRD) worldwide. Documentation of animal genetic influences and performance variability specific to BVDV challenge is limited. This study evaluated individual animal effects in the 14 d following BVDV Type 1b intranasal challenge in yearling, Nellore-Angus (Bos indicus-Bos taurus) F2 and F3 crossbred steers (n = 363) on carcass traits 180 d post-challenge. Prior to challenge steers were confirmed to be free of BVDV infection with families balanced across non-vaccinated control, killed (KV), or modified-live (MLV) commercial BRD vaccines. Hot carcass weight (HCW), adjusted fat thickness (AFT), longissimus muscle area (REA) and marbling score (MARB) were analyzed through mixed models with sire and pen(year) as random effects; potential fixed effects of vaccine, type of cross, pyrexia status, clinical sign presentation, and levels of feed intake and ADG 14 d post-challenge were investigated. Vaccine influenced AFT (P = 0.016); MLV steers had 0.26 cm less AFT than KV steers. Marbling was affected by type of cross (P = 0.023) with up to 0.60 marbling scores higher (P < 0.05) in some parental combinations; an interaction between type of cross and pyrexia status also affected MARB (P = 0.017) with one parental combination having higher MARB associated with pyrexia. Hot carcass weight was not affected by pyrexia, but was affected by feed intake (P = 0.019), with steers in the highest vs. lowest category averaging 24.0 kg heavier. No animals presented morbidity signs severe enough for therapeutic treatment, yet presence of mild clinical symptoms affected REA (P = 0.012), resulting in 3.4 cm2 lower REA, however, this pattern was inconsistent among feed intake levels. This study affirms the complexity of health impacts on beef carcass traits and the need for improved study of subclinical illness in beef production systems.