Seminal plasma protein concentrations vary with feed efficiency and fertility-related measures in young beef bulls.

Fertility-associated proteins (FAP) found in seminal plasma indicate sexual maturity, which appears to be influenced by feed efficiency in cattle. This study characterized FAP via proteomics and verified associations of these proteins with feed efficiency, body composition and fertility-related measures in yearling beef bulls. Assessments including testicular ultrasonography, infrared thermography, seminal quality, seminal plasma proteomics, carcass composition, and reproductive organ biometry were obtained. From a population of 31 bulls, the seven most and least feed efficient (efficient, inefficient) bulls were used for categorical comparisons. Correlations between FAP, productive performance and fertility-related measures were determined. These traits were also correlated with orthogonal factors summarized from the FAP. Efficient bulls had increased epididymal sperm-binding protein-1 and decreased concentration of protein-C inhibitor compared to inefficient bulls. Correlations between FAP with age, body size, body composition, reproductive organ biometry, scrotal temperature, and seminiferous tubule maturity are reported. Acrosin and cathepsin D increased with development of the testes and osteopontin increased with greater numbers of mature seminiferous tubules. Phosphoglycerate kinase-2 was higher in animals with a higher scrotum temperature and a higher prevalence of sperm morphology defects. The principal factor indicated that FAP variability concentrations were positively correlated with age, reproductive organ biometry, body size and composition. Our results indicate that FAP changes with body size and sexual development, and demonstrates differences in the proteomics of bulls with diverging feed efficiency. This is related to the delay in the sexual maturity of efficient young bulls.