Date of Award

5-2018

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Frank Neal Schrick

Committee Members

J. Lannett Edwards, Ky G. Pohler, Lewrell G. Strickland

Abstract

To determine the occurrence of proximal droplets in performance-tested bulls, parameters related to breeding soundness examination (BSE) classification were evaluated. Bulls (542 Angus bulls) were classified as satisfactory (BSE guidelines; Society for Theriogenology) or deferred. On-test risk factors were identified, associated with increased probability for bulls to be deferred due to proximal droplets. On-test weight (P = 0.019), on-test scrotal circumference (P = 0.018) and the covariate of age (P = 0.007) were all associated with the probability for a bull to be deferred on test due to proximal droplets. Accounting for the covariate of age and the effect of on-test SC, bulls in weight category 5 (>500 kg on-test weight) had 12.5 times the odds of deferral due to proximal droplets compared to bulls in weight category 2 (350 – 400 kg) (OR: 12.5, 95% adj. CI: 1.47, 111.11; adj. P = 0.017). Accounting for the covariate of age and the effect of on-test weight, bulls that were categorized as SC on-test 1 (< 30 cm) had 7.9 times the odds for deferral due to proximal droplets compared to bulls categorized as SC 3 (33 – 36 cm; OR: 7.9, 95% CI: 1.4, 44.4; P = 0.012). Additionally, bulls that were categorized as SC 2 (30 – 33 cm) had 4.7 times the odds for deferral due to proximal droplets compared to bulls categorized 3 (33 – 36 cm; 95% CI: 1.1, 20.0; P = 0.03). After accounting for age and bull on-test weight, bulls that were categorized as SC growth 3 (> 6.2 cm growth) had 3.7 times the odds for deferral due to proximal droplets compared to bulls categorized 2 (3.4 to 6.2 cm growth; OR: 3.7, 95% CI: 1.69, 8.26; P = 0.001. In summary, bull on-test weight, on-test scrotal circumference, scrotal circumference growth and age are important factors associated with unsatisfactory classification due to proximal droplets. Occurrence of proximal droplets have been previously associated with bull maturity; however the cause of its relationship to on-test weight, on-test scrotal circumference and rapid scrotal circumference growth in performance-tested bulls remains unclear.

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