Genetic gain & Inbreeding

Within herd genetic relationships between bulls and active females in Canadian dairy breeds as a metric for controlling inbreeding

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Abstract

Inbreeding levels in dairy cattle continue to rise, primarily due to the high genetic relatedness between available bulls and active cow and heifer populations. This trend raises concerns about adverse effects on economically important traits. Identifying outcross sires at the herd level may help reduce genetic relatedness and slow the rate of inbreeding. The objective of this study was to estimate pedigree-based (R-values) and genomic-based (GR-values) relationship between bulls and active Canadian Ayrshire, Brown Swiss, and Jersey females within herds. Pedigree and genotype data were provided by Lactanet Canada (Guelph, ON). Bulls were selected based on Lifetime Performance Index (LPI) values and were required to have at least 20 active daughters within the population from the November 2025 official release comprising 501 Ayrshire, 250 Brown Swiss, and 500 Jersey. Active females included herdbook-registered cows and heifers participating in Dairy Herd Improvement (DHI) programs, defined as cows remaining in the herd with at least one test-day record in the previous 365 days. In addition, female calves and heifers currently in the herdbook without a herd left date were included as they could serve as replacement animals and used for mating. The dataset comprised of 11,107 Ayrshire, 2,066 Brown Swiss, and 31,704 Jersey cows and heifers from 126, 35, and 391 herds, respectively. Pedigrees included 46,352 Ayrshire, 18,188 Brown Swiss, and 104,808 Jersey animals, with genotypes available for 2,388 Ayrshire, 638 Brown Swiss, and 5,386 Jersey animals. Genetic relationships were computed using both pedigree and genomic information, representing expected and realized proportions of shared DNA with the active female population. Substantial variation in genetic relationships across herds was found. Average R-values between bulls and the active female population were 13.09% in Ayrshire, 15.89% in Brown Swiss, and 15.33% in Jersey, with corresponding GR-values of 16.91%, 20.03%, and 20.15%, respectively. Within herds, R-values between bulls and the active females ranged from 4.43 to 14.61% in Ayrshire, 10.63 to 18.25% in Brown Swiss, and 0.74 to 17.32% in Jersey, while GR-values ranged from 5.51 to 20.16% in Ayrshire, 12.25 to 24.13% in Brown Swiss, and 0.91 to 25.97% in Jersey. The findings from this study demonstrate that outcross bulls with low genetic relationships to active females can be identified for specific herds. Incorporating such bulls into mating programs could help manage inbreeding and maintain genetic diversity in Canadian dairy breeds.

Keywords: 2026

How to Cite:

Makanjuola, B., Miglior, F., Maltecca, C., Cole, J., Schenkel, F. & Baes, C., (2026) “Within herd genetic relationships between bulls and active females in Canadian dairy breeds as a metric for controlling inbreeding”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2295662. doi: https://doi.org/10.31274/wcgalp.24357

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