Masters Theses

Date of Award

8-2025

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Saulo M. Zoca, Sarah E. Moorey

Committee Members

F. Neal Schrick

Abstract

Understanding the causes of bull subfertility and developing reliable diagnostic tools are critical to reducing economic losses caused by reproductive failure in beef cattle. Currently, the primary method to evaluate bull fertility is a breeding soundness exam, but this does not provide a detailed account of intracellular processes that may be dysfunctional in normal appearing sperm cells from subfertile males. Metabolomic analysis of sperm from bulls with diverging field fertility may provide insights of sperm metabolism that are associated with pregnancy outcomes. The objective of this study was to perform metabolomic analyses of sperm from bulls with differing field fertility and evaluate the difference of metabolome profiles. Angus bulls (n = 15) were classified based on a composite field fertility index. Frozen-thawed semen straws (n = 10 per bull) underwent a Percoll gradient sperm purification process. An aliquot of each sample containing 4 million sperm in 100 μl [microliter]. underwent five rounds of freezing/thawing in liquid nitrogen. Metabolomic analysis was performed through ultra- high performance liquid chromatography coupled high resolution mass spectrometry at the University of Tennessee Biological and Small Molecule Mass Spectrometry Core. The GLM procedure of SAS was used to evaluate linear and quadratic relationships between metabolites and CFI. After linear and quadratic analyses, the four highest and lowest fertility bulls were used to evaluate the relationship between fertility class and each metabolite. The MIXED procedure was used with the model including the dependent variable of metabolite, fixed effect of class, and a random statement of date of semen processing and technician. Significance was determined when P ≤ 0.05 and tendency was declared when P ≤ 0.10. A total of 75 metabolites were detected. Quadratic relationships with fertility were observed for kynurenine, xanthine, and ophthalmate (P < 0.05). Tricarballyic acid and creatinine showed a negative linear relationship with fertility (P ≤ 0.05). When differences in metabolite abundance were assessed between the four highest and lowest fertility bulls, N-acetylglutamate and N-acetylglutamine (P ≤ 0.05) had greater abundance in low fertility bulls. Using metabolites as a fertility marker to identify subfertile bulls from a breeding population has promising future implications.

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