Carcass Traits of Crossbred Steers After Vaccination and Bovine Viral Diarrhea Virus Challenge as Yearlings

Bovine Viral Diarrhea Virus (BVDV) is a component of bovine respiratory disease complex, which has been reported to cause the largest loss in productivity in feedlot cattle in the U.S., with annual economic losses in excess of $1.5 billion USD. The genetic influences and losses associated with BVDV challenge on carcass traits in controlled herds are not documented. This study evaluated individual animal effects in the first 14 days following challenge with BVDV Type 1b for carcass trait differences. Nellore-Angus (Bos indicus-Bos taurus) F2 and F3 crossbred steers (n = 363) were evaluated for clinical symptoms, body weights, and rectal temperatures immediately following challenge. Crosses and sire lines were balanced across the vaccine treatment groups of nonvaccinated control (NON), killed virus vaccinated (KV), or modified-live virus vaccinated (MLV). 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; fixed effects of vaccine, type of cross, pyrexia status (rectal temperature >40 C at least once), clinical symptom presentation, and levels of feed intake and ADG 14 d post-challenge were investigated. Vaccine influenced AFT (P = 0.016), where MLV steers had 0.26 cm less fat 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. HCW 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 symptoms severe enough to warrant potential therapeutic treatment, animals with mild clinical symptoms in the 14 d window post BVDV challenge had 4.98 cm^2 lower REA (P = 0.012). This study affirms the complexity of health impacts on beef carcass traits and the need for study of subclinical illness in beef production systems, particularly regarding BVDV