Beef cattle

Disentangling the effects of heterosis on cow fertility traits in American Beefmaster cattle

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Abstract

Female reproduction plays a key role in the production efficiency of livestock species and the economic success for cow-calf operations. However, these fitness-related phenotypes tend to be lowly heritable, expressed only in females, and have delayed expression, hindering phenotypic selection from generating genetic gain. Genetic progress for these traits can be accelerated by using estimated breeding values in selection programs. Additionally, these lowly heritable traits respond favorably to heterosis. We used Beefmaster Breeder's United (BBU) performance and Whole Herd Reporting data, consisting of 75,847 calving records and 25,823 females (11,078 heifers and 14,745 cows), with 5,776 animals that were genotyped, to explore six novel measures of cow fertility. We used these records to calculate six reproduction-related phenotypes: calving date (date of calving relative to her contemporaries), calving interval (days between calves), first calving interval (calving interval between first and second calving record), heifer pregnancy (did animal calve as a 2-year-old), heifer calving date (day heifer calved relative to her contemporaries), and discrete early calving (did female calve within the first 30 days of the season) as distinct, but correlated measures of fertility. We used pedigree and genomic REML to estimate these six phenotypes' genetic, permanent, and temporary environment variance components using GibbsF90+ from the BLUPF90 family of Programs. Our model effects included fixed contemporary group effects, random animal effects, and a permanent environment effect for mature cow phenotypes. Single-step estimated heritability estimates were 0.13 ±0.013 for calving date, 0.03 ±0.013 for calving interval, 0.30 ±0.217 for first calving interval, 0.27 ±0.066 for heifer pregnancy, 0.12 ±0.043 for heifer calving date, and 0.10 ±0.031 for discrete early calving. The inclusion of genomics for this analysis decreased all estimates by varying amounts. We observed a wide range of genetic correlations between these phenotypes (rG = -0.16-0.8). Genetic correlations between heifer pregnancy and our long-term indicators of cow fertility, like calving interval, were effectively zero (rG = 0.06), indicating that selecting for heifer fertility may not capture all measures of downstream reproductive efficiency. To further explore the impacts of heterosis on these traits, we estimated dominance variance (vd) components using a D-REML in GCTA and found that it explained around the same amount of variance as additivity (vd = 0.04-0.21). Dominance plays a larger role in controlling calving date than additive genetics alone (0.07 ±0.031), indicating that crossbreeding can improve this trait. We utilized ADMIXTURE to determine breed proportions for each genotyped animal and used this information to calculate two measures of retained heterosis: average genome-wide heterozygosity (H) and retained heterozygosity (rHetg). We found significant associations between both indicators and reproductive outcomes. Ongoing work involves using these two measures in genomic predictions and mapping additive and non-additive QTL for this suite of traits.

Keywords: 2026

How to Cite:

Catrett, C., Bauer, L. & Rowan, T., (2026) “Disentangling the effects of heterosis on cow fertility traits in American Beefmaster cattle”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286665. doi: https://doi.org/10.31274/wcgalp.24086

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