Economic Benefits of Using Genetic Selection to Reduce the Prevalence of Bovine Respiratory Disease Complex in Beef Feedlot Cattle

The prevalence of bovine respiratory disease complex (BRDC) has remained unchanged for decades despite efforts to suppress the disease through prevention programs aimed at vaccination and metaphylaxis. An additional approach that focuses on host response to infection by the pathogens responsible for BRDC, through the selection of animals that are less susceptible to the disease, has been undertaken as part of the USDA funded “Integrated Program for Reducing BRDC in Beef and Dairy Cattle” with Dr. James Womack at Texas A&M University as the Project Director. This study, now beginning its fourth year, has found that estimates of heritability for susceptibility to BRDC were greater than 17% for a binary case-control definition of BRDC and greater than 29% for a semi-quantitative (clinical score) definition of BRDC in a commercial feedlot in Colorado. The higher heritability estimate for the more precise definition of BRDC was anticipated as heritability improves as accuracy of a measured phenotype (in this case the BRDC phenotype) improves. The estimated annual rate of genetic gain due to selection on these phenotypes was estimated at 1.26% (case-control) and 2.08% (clinical scores). The economic cost of $253.97per BRDC feedlot steer was determined through the loss of carcass quality, death and treatment costs. When this value was combined with the 16.2% national prevalence of BRDC in the feedlot and the estimated reduced prevalence of BRDC (rate of genetic gain made by selecting to increase the proportion of cattle that are more resistant to disease), the feedlot industry could gain between $13 and $21.5 million per year Introduction Bovine respiratory disease complex is the result of of viral and bacterial pathogens and is the leading cause of illness and death in feedlot cattle (USDA 2001, Gagea et al. 2006, Snowder et al 2006). The prevalence of bovine respiratory disease complex (BRDC) detected in feedlot cattle varies by year with a 15 year range of from 5% to 44%, and also by season, with higher prevalence rates in the fall and winter (Snowder et al 2005, Miles 2009). The average prevalence rate of BRDC was 16.2%, with virtually all feedlots (96.9%) reporting one or more cases between July 1, 2010 and June 30, 2011 (USDA 2011). Recent reports have indicated that greater than 60% of all cattle in the feedlot have lung lesions resulting from BRDC and many of these animals were undetected as suffering from an illness (Schneider et al. 2009). Of animals that showed noticeable signs of illness, BRDC was the most common cause (67% to 82%) of illness detected in feedlot cattle (Edwards 1996, USDA 2011). An estimated 1.4% of all feedlot cattle die from BRDC prior to harvest. The high prevalence of BRDC in feedlot cattle has not fallen in spite of best management practices and vaccination programs (Gagea et al. 2006, Miles 2009). According to the USDA (2011), the majority of feedlots over 1,000 head used one respiratory vaccine to combat disease. Unfortunately, only about 25% of cattle were vaccinated for both the viral and bacterial pathogens associated with BRDC. Specifically, 96.6% of feedlots vaccinated for bovine viral diarrhea virus (BVDV), 93.7% vaccinated for infectious bovine rhinotracheitis virus (IBR), 85.1% vaccinated for parainfluenza 3 virus (PI3) and 89.5% of feedlots vaccinated for bovine respiratory syncytial virus (BRSV) (USDA 2011). Approximately 66% of feedlots used vaccines that incorporated BRDC bacterial pathogens Hemophilus somnus and Mannheimia haemolyti-ca (previously named Pasteurella haemolytica) and 21.8% vaccinated against Mycoplasma bovis. One strategy used to prevent or minimize an outbreak of BRDC is to treat cattle with an injectable antibiotic (metaphylaxis) for BRDC pathogens. Factors that heightened concerns of BRDC and caused feedlots to consider metaphylaxis included: cattle through the implementation of selection for cattle that are less susceptible to BRDC.