Masters Theses
Date of Award
8-2025
Degree Type
Thesis
Degree Name
Master of Science
Major
Animal Science
Major Professor
Saulo M. Zoca
Committee Members
J. Lannett Edwards, Lew G. Strickland, Charley C. Martinez
Abstract
Bull selection in the beef industry is commonly based on a combination of visual appraisal and genetic merit, often expressed through Expected Progeny Differences (EPDs). While EPDs are valuable tools for selecting growth, carcass, and maternal traits, no current EPD directly evaluates semen quality or the likelihood of passing a breeding soundness exam (BSE), key indicators of bull fertility. To better understand the relationship between genetic potential and actual reproductive performance, two studies investigated associations between Angus bull EPDs and fertility outcomes using two datasets. The first study analyzed 167 Angus bulls undergoing BSEs, evaluating semen quality, scrotal circumference, and pass/fail classification according to Society for Theriogenology guidelines. The second study evaluated 13 Angus bulls used in fixed-time artificial insemination (FTAI) programs, where fertility was measured based on actual pregnancy rates in the field. EPDs for multiple traits, including docility (DOC), were included in both analyses. Across both studies, the docility EPD (DOC) consistently showed significant associations with fertility outcomes. In Study 1, bulls with higher DOC scores were less likely to pass a BSE and more likely to exhibit abnormal sperm morphology, including head, midpiece, and tail defects. Similarly, in Study 2, bulls in the High Fertility group had significantly lower DOC values compared to their lower-performing counterparts. These results suggest that while EPDs are not direct fertility measures, certain traits, such as DOC, may offer predictive value for reproductive performance. Incorporating such indicators may enhance bull selection strategies for improved herd fertility.
Recommended Citation
Lonas, Adella B., "RELATIONSHIP OF EXPECTED PROGENY DIFFERENCES (EPDS) AND BULL REPRODUCTIVE EFFICIENCY. " Master's Thesis, University of Tennessee, 2025.
https://trace.tennessee.edu/utk_gradthes/14546