Reproduction

Genetic parameter estimation for bull fertility traits by combining stud collection and breeding soundness exam records

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Abstract

Fertility traits such as scrotal circumference (SC), sperm motility percentage (%MOT), motility score (MOTSC), primary sperm abnormalities (%PRIM), secondary sperm abnormalities (%SEC), and normal sperm morphology (%NORM) are widely used to assess a bull's reproductive ability. These measurements primarily come from breeding soundness examinations (BSE) and semen collection records for artificial insemination (AI) at bull studs. The objective of this study was to evaluate the potential of combining BSE and AI semen collection records into one dataset to estimate variance components, heritabilities, repeatabilities, and genetic correlations for bull reproductive traits. Data comprised 5,877 BSE records from 4,996 Angus bulls from 11 producers, and 64,869 semen collection records from 1,862 Angus bulls collected at two bull studs. Only 14 bulls had records in both datasets. Genetic relationships among animals were established using pedigree and genomic information. A univariate repeated records model was fitted for all traits to estimate variance components, heritabilities, and repeatabilities. Each model included fixed effects for age group and the concatenation of location and date of collection. Bull age was categorized into six groups (36 months). To determine whether BSE and stud data could be analyzed jointly, one set of bivariate models were applied to each trait, treating measurements from BSE and stud collections as separate but correlated traits (e.g., SCBSE vs. SCSTUD). The SC (0.45 ± 0.08), %MOT (0.58 ± 0.21), and %SEC (0.66 ± 0.30) models yielded moderate genetic correlations. Estimates for %PRIM (-0.11 ± 0.59) and %NORM (0.33 ± 0.46) were not significantly different from zero. The MOTSC model failed to converge. Despite these varied results, the BSE and bull stud data were merged into a single dataset, resulting in 70,746 fertility records from 6,845 bulls. Heritabilities from the combined data were: SC (0.40 ± 0.05), %MOT (0.10 ± 0.01), MOTSC (0.11 ± 0.07), %PRIM (0.06 ± 0.01), %SEC (0.07 ± 0.01), and %NORM (0.11 ± 0.05). Repeatability estimates were 0.82, 0.50, 0.35, 0.82, 0.53, and 0.81 for SC, %MOT, MOTSC, %PRIM, %SEC, and %NORM, respectively. Lastly, genetic correlations were estimated between different traits with the combined dataset. Correlations between SC and semen quality traits were unfavorable and ranged from weak to moderate (0.18 ± 0.14 to -0.46 ± 0.07). Strong and favorable correlations were estimated between semen quality traits (-0.94 ± 0.06 to 0.90 ± 0.05), except for a moderate correlation between %PRIM and %SEC. These findings suggest the feasibility of integrating fertility measurements from both BSE and stud collections into a single dataset for some traits but highlight the need for further research to clarify relationships among fertility traits.

Keywords: 2026

How to Cite:

Bormann, J., Ellinghuysen, D., Grieger, D., Hartman, A., Rolf, M., Semler, M., Tarochione, A. & Weaber, R., (2026) “Genetic parameter estimation for bull fertility traits by combining stud collection and breeding soundness exam records”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2295485. doi: https://doi.org/10.31274/wcgalp.24341

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