Reproduction

Genetic variability in sperm quality traits for Norwegian Red bulls

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Abstract

Computer-assisted sperm analysis (CASA) provides objective measures of semen production and quality traits, offering new opportunities to define phenotypes related to sperm motility and morphology that could be used in genomic selection. This study aimed to estimate genetic parameters for an initial subset of semen quality measures for Norwegian Red bulls. The dataset included CASA-derived measurements from 8,615 ejaculates collected from 278 bulls. We used data from the routine production at the AI center and included all collected ejaculates from Norwegian Red AI bulls between November 2021 and September 2025. The number of records per bull varied from 1 to 361, with an average of 31. Aggregated CASA data were used, summarizing single-cell observations into one record per ejaculate. Four semen quality traits were analyzed: percent motile sperm, percent progressive motile sperm, proportion of sperm with defects, and proportion of sperm with cytoplasmic droplets. On average, 85 % of sperm exhibited motility (movement), 81 % showed progressive motility (moving actively forward), 3.2 % of the sperm had defects (head, tail, or midpiece abnormalities), and 6.7 % had droplets (proximal and distal). Variance components were estimated using DMU software, applying single-trait linear animal repeatability models. Fixed effects included bull age, days since the previous semen collection, and collection date. Bull age at the time of semen collection was categorized into 20 classes: ≤12 months were assigned to the first class, >30 months to the final class, and the remaining ages were grouped in one-month intervals. The interval since the previous semen collection was categorized into 10 classes: daily intervals from 1 to 7 days, followed by grouped intervals of 8-14 days, 15-21 days, and >21 days. Collection date was modeled with 801 classes and accounted for seasonal variation and effects of personnel involved in semen collection and laboratory analysis. Pedigree information of the bulls with data was traced back five generations and included a total of 4597 animals. Estimated heritabilities were 0.04 and 0.05 for the motility traits and 0.02 for defects, but with standard errors of 0.05 they were not significantly different from zero. The estimated heritability (s.e.) for the proportion of sperm with droplets was 0.27 (0.07). Droplets may indicate immature sperm with retained cytoplasmic droplets. Further research should investigate potential associations between this trait and field fertility outcomes, such as conception rate. The available data also allows for expanding the analysis to a broader set of motility and morphology traits. Semen production and quality traits are crucial traits for AI bulls. Genomic breeding values for traits related to sperm motility and morphology could be useful when recruiting bull calves to become future AI bulls and can also be used to monitor genetic trends in bull fertility.

Keywords: 2026

How to Cite:

Heringstad, B., Larsgard, A., Gjuvsland, A. & Andersen-Ranberg, I., (2026) “Genetic variability in sperm quality traits for Norwegian Red bulls”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2283834. doi: https://doi.org/10.31274/wcgalp.23519

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