GxE

Bayesian evaluation of genotype-by-nutrition interactions affecting reproductive success in grazing beef cows

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Abstract

Reproductive efficiency is a key determinant of productivity and sustainability in cow-calf systems. This study aimed to evaluate the effects of cow genotype and herbage allowance on reproductive success in grazing beef cows using Bayesian hierarchical models, to identify genotype-by-nutrition interactions influencing performance under extensive conditions. Data included 1,069 reproductive records from Hereford, Angus, and reciprocal crossbred cows managed between 2007 and 2022 on native grasslands in Uruguay. Cows were classified by genotype (purebred vs. crossbred) and herbage allowance (high vs. low), and reproductive success was analyzed across three biologically relevant periods: I) service to pregnancy diagnosis, II) pregnancy to calving, and III) calving to weaning. Each outcome was modeled as a binary trait (1 = success, 0 = failure) using Bayesian generalized linear mixed models implemented in the brms package (R 4.4.2) with Bernoulli likelihood, logit link, and random cow effects to account for repeated measures. Weakly informative priors (Normal 0, 5 and half-Cauchy 0, 2) were used, and posterior inference was based on 12,000 post-warm-up samples per parameter. Crossbred cows consistently exhibited higher posterior probabilities of reproductive success than purebreds across all stages. In Period I (service to diagnosis), pregnancy probability under low herbage allowance was 0.93 (95% HPDI 0.81-1.00) for crossbred and 0.80 (0.54-0.99) for purebred cows (Δ = 0.13; P(Δ > 0) = 0.999). In Period II (diagnosis to calving), probabilities were 0.93 (0.82-1.00) and 0.80 (0.56-0.99), respectively (Δ = 0.13; P(Δ > 0) = 0.999). In Period III (calving to weaning), success was 0.90 (0.77-0.99) for crossbreds and 0.67 (0.42-0.91) for purebreds under low herbage allowance (Δ = 0.22; P(Δ > 0) = 1.00). Under high herbage allowance, probabilities improved in both genotypes but differences persisted. The cumulative probability of weaning per cow served was approximately 0.43 for purebred-low, 0.63 for purebred-high, and 0.78 for crossbreds under both conditions, equivalent to 30-35 more calves weaned per 100 cows served when using crossbred females. Posterior predictive checks confirmed model convergence and robustness to prior assumptions. These results demonstrate that both crossbreeding and adequate herbage allowance enhance reproductive performance in grazing beef cows. The observed genotype à— nutrition interaction was moderate but biologically meaningful, with crossbred cows showing greater resilience to nutritional restriction and maintaining high reproductive success under low herbage conditions. This advantage likely reflects heterosis for reproductive and maternal traits, emphasizing crossbreeding as a robust, cost-effective strategy for improving fertility and sustainability in rangeland systems. Bayesian modeling proved valuable for quantifying uncertainty and detecting biologically relevant effects under complex field conditions.

Keywords: 2026

How to Cite:

Vivián, R., Pérez Clariget, R. & Espasandin, A., (2026) “Bayesian evaluation of genotype-by-nutrition interactions affecting reproductive success in grazing beef cows”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2284222. doi: https://doi.org/10.31274/wcgalp.23559

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