Feedlot Heart Disease: Understanding Heart Score and Its Relationships to Economically Relevant Traits

• Main Author: Kukor, Isabella
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01.01.2022
• Subjects: Agriculture; Genetics
• ISBN: 9798368428291

The increasing occurrence of feedlot heart disease caused by pulmonary hypertension has precipitated a growing concern from producers and geneticists alike. Utilization of genetic technology for selection and breeding decisions has made a substantial amount of progress in past decades within economically relevant traits, but the focus on high performing cattle may have had adverse consequences on cardiovascular fitness. Pulmonary hypertension has become a more frequent occurrence in low to moderate elevation feedlots, causing feedlot death and the potential to predispose cattle to co-morbidities. Previously, once considered only a high-altitude issue, pulmonary hypertension appears prevalent in high genetic merit cattle within moderate elevation, high plains feedlots. With no options for treatment, management, and prevention in feedlot cattle may be the only strategy for producers struggling with the balance of desirable, fattening cattle and pulmonary hypertension risk. The objective of this study was to establish the foundation for a new heart grading system known as heart score and discover its genetic and phenotypic relationships with economically relevant traits and differentiate phenotypic differences between healthy and unhealthy scored Angus-influenced cattle. The third chapter of this thesis included phenotypic differences between cattle with healthy and unhealthy heart scores (n = 1,422). Data were obtained from Cactus Feed Yard LLC in Canyon, Texas over a two-year period (2020–2022). Means were compared between heart score groups (1, 2 & 3+) to test for significant differences between the two groups. Linear models and the ANOVA table displayed significant fixed effects to each model. Systolic, diastolic, PAP, and marbling scores differed among groups (P < 0.05), while hot carcass weight displayed a tendency (P < 0.10). Unhealthy heart scored cattle tended to be heavier carcasses associating heavier cattle with pulmonary hypertension. Healthy heart scored animals had overall lower (P < 0.05 ) PAP, systolic, and diastolic measurements. The fourth chapter of this thesis highlighted the differences between repeated PAP measurements at 9 and 14 months of age. The cohort of Angus influenced cattle were housed at a feedlot in Canyon, TX and was a moderate altitude (1,080 m). Repeated PAP measurements exhibited an increase in PAP measurements between 9 months and 14 months of age, which were later grouped by their heart scores. No differences were observed among heart scored cattle at 9 months (mean minimum: 39.61 ± 2.47; mean maximum: 40.36 ± 3.47) but distinct differences were observed among cattle grouped in their 14-month PAP (mean minimum: 45.27 ± 5.69; mean maximum: 79.20 ± 21.09). High heart scores were associated with higher PAP measurements. There was a correlation of 0.20 between the measurements showcasing a positive trend between measurements, but also the inability of PAP measurements taken at 9 months may not be predictive of cattle’s scores at 14-month-old. Furthermore, there were no differences between phenotypic traits of the cattle who had greater PAP differences between their measurements. The third study estimated the heritability of heart score and the phenotypic relationships with economically relevant traits (n = 1,507) in progeny of 88 sires. Phenotypes included heart scores, PAP (14 months), hot carcass weight, marbling, ribeye area, and backfat. Heart score was found to have a moderate heritability estimate 0.28 ± 0.10. Heart score had a very strong genetic correlation with PAP, and strong correlation with hot carcass weight. Positive genetic correlations were found between heart scores and carcass traits with genetic correlations between 0.07 to 0.63. Overall, these results suggest heart scores to be useful in genetic selection for a healthier cardiopulmonary system. while not drastically influencing carcass traits.