Evaluation of Performance in Yearling Crossbred Steers following Bovine Viral Diarrhea Virus Challenge

This study investigated the effects of vaccine type, sire, day, threshold rectal temperature status, and their potential interactions on growth, daily feed intake and daily feed bunk frequency in response to a standardized Bovine Viral Diarrhea Virus (BVDV) challenge. Yearling, F2 and F3 Nellore-Angus steers (n = 380) from the Texas A&M McGregor Genomics herd were utilized over 4 years, and were stratified by sire over three vaccine groups of modified-live (MLV), killed (KV), and non-vaccinated (NON). Vaccines were used in accordance to label directions, and MLV steers were separated from KV and NON steers for 7 to 10 days to prevent transmission of viral particles. All steers were intranasally challenged with BVDV type 1b strain CA0401186A on day 0 of each year. Clinical signs of illness and feeding behavior data were collected daily, while rectal temperature and weight records were collected at days 0, 3, 7, 10, 14, 28, and 42 post-vaccination.

The influence of sire was a significant source of variation as both a main effect or as an interaction term for all response variables analyzed. Vaccine type was a significant source of variation as components of interaction terms; lower (P < 0.05) mean rectal temperature was seen in MLV as compared to KV and NON steers. Variation from sire and vaccine type interaction suggests the potential of matching genetic profiles and vaccine protocols to achieve optimum levels of production measures.

Daily feed intake and daily bunk visit frequency tended to decrease through day 7, but these traits should be interpreted separately due to the effects of sire and sire by vaccine type interactions. Higher number of bunk visits did not explain levels of intake within some sire groups and vaccine groups. Lung tissue disruption based on color scores of 3 or 4, on 5-point scale was present in more than 65% of cattle that did not have elevated rectal temperature above 40oC, the threshold basis for provision of antibiotic treatment. Interactions involving sire, vaccine type or rectal temperature status with other factors in this trial illustrates complexity regarding interpretation of cattle health impacts on production traits.