Bovine respiratory disease (BRD) is the most costly beef cattle disease in the U.S. Scientists at the U.S. Meat Animal Research Center analyzed 20 years of preweaning progeny records from nine purebred breeds, three composite breeds, and a variety of F1 and three-way crosses to characterize the genetic and environmental factors influencing BRD. Respiratory disease in the MARC herd followed a standard pattern of initial introduction, reaching epidemic stages at 70 to 170 days of age, followed by a rapid decline to weaning time.

Estimates of heritability of BRD were relatively low, with overall estimates of 0.07 and 0.19 depending on the dataset used. As the annual incidence of BRD increased, there was an associated increase in heritability. Consequently, the estimated heritability based on an underlying continuous scale was high (0.48), suggesting that response to selection for BRD resistance could be large if the phenotype of resistant animals could be identified.

Overall incidence of BRD was 10.5%, ranging from a high of 18.8% in the Braunvieh breed to a low of 7.0% in Limousin. The genetic correlation between direct (calf) and maternal (dam) genetic effects was large and negative, suggesting that dams genetically superior for resisting BRD raise calves that are more susceptible. The authors speculated that genetically superior dams provide passive immunity to their calves, which delays development of the calves’ immune systems, making them more susceptible to BRD during preweaning. Heterosis of crossbred calves resulted in a lower incidence of BRD than in purebred calves. Calves that were Continental x British or tropically adapted x British breeds had a lower incidence than did calves of British x British breeds (Snowder et al. 2005. J. Anim. Sci. 83: 1247).