345 Breed differences within heart scores of fattening feedlot cattle

Abstract Feedlot heart disease (FHD) is a condition in fattening beef cattle that arises from right-side heart remodeling resulting from alveolar hypoxia. This hypoxic environment is hypothesized to result from the large body mass of fattened cattle. Sensitive cattle have increased incidence of pulmonary hypertension resulting from compensation mechanisms of the individual. The severity of this remodeling is quantified at harvest by gross examination of the heart utilizing a visual grading system of 1-5, where a score of 1 is a normal heart and a score of 5 is a severely remodeled heart. Previously, heart score was found to contain sire differences and to be moderately heritable. This led to more questions regarding other potential factors influencing heart scores, one of which was breed differences. Therefore, the objective of this study was to examine the prevalence of heart remodeling in beef and dairy cattle breeds and to investigate whether some breeds had a greater prevalence of heart remodeling. Heart scores were collected on Angus-influenced animals raised in the panhandle of Texas (1,103 m) and a Beef x Dairy group raised in western Kansas (846 m). The total number of animal observations was 2,069. Twenty-four percent of the individuals exhibited moderate to severe remodeling (score 3 and greater). Of this cohort, 1,307 animals had breed composition data (i.e., Angus, Simmental, Jersey, and Holstein) suitable for use in the analysis. Breed proportions ranged from 0% to 100% for Angus, 0 to 93.25% for Simmental, 0% to 69.22% for Jersey, and 0% to 78.06% for Holstein. Utilizing a linear regression model with heart score as the response and breed percentages and heart scorers as fixed effects, the importance of breed composition (covariate) was determined. The percentages of Angus influence tended to be associated with heart score (P = 0.0506), with a regression coefficient of -0.005. The percentage of Simmental had an association with the variation in heart score (P < 0.05) and had a regression coefficient of -0.008. Additionally, the percentages of Jersey and Holstein were found to reduce the incidence of heart score by a factor of -0.014 and -0.018 (P < 0.05), respectively. In summary, an increased percentage of either Jersey or Holstein breed resulted in reduced heart scores, while the incidence of beef breeds was found to be associated with some to little difference in the improvement of heart scores, alluding to potential breed advantages in mitigating right sided heart remodeling.