Beef cattle

Genetic parameters for reconception rate of early sexual precocious Nellore heifers

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Abstract

The reconception rate of Nellore heifers challenged at yearling age is a crucial determinant of reproductive efficiency and profitability in beef cattle breeding systems. These females, inseminated or exposed to a bull between 14 and 16 months of age, face the physiological challenge of balancing continued growth with the demands of gestation and lactation. Genetic selection for female sexual precocity has been an effective strategy to improve fertility and conception rates at first and second mating. However, the genetic contribution and selection potential for the reconception rate in early-challenged females remain unclear. This study aimed to estimate variance components for the reconception rate of early sexually precocious Nellore heifers. A total of 5,727 reconception records from primiparous cows that calved before 30 months of age were analyzed. The data, provided by the CFM (Cia. de Fomento Mercantil.) breeding program, included pedigree and phenotypic information. Animals were raised under grazing conditions with free access to mineral salt and strategic supplementation during the dry season. The average reconception rate among first-calving cows was 62%. A threshold animal model was used to analyze reconception rate (1 = failed; 2 = success). Different models were tested, including the fixed effects of dam age at first calving and Julian date of birth as covariates; sex, birth contemporary group, and weaning contemporary group of the first calf, contemporary group for probability of heifer pregnancy at 14 months, type of mating (artificial insemination or natural), and birth weight of the first calf as fixed effects. Random additive genetic and residual effects were also included. Analyses were performed using Bayesian inference via the Gibbs sampling algorithm implemented in the Gibbsf90+ software. The sampling chain consisted of 1,000,000 iterations, with a burn-in period of 200,000 and samples stored every ten cycles. Posterior means for variance components were calculated using 80,000 samples. Convergence was assessed by visual inspection and the Geweke test, using the Bayesian Output Analysis (BOA) R package. Model fit was evaluated using the Deviance Information Criterion (DIC). Heritability estimates for the reconception rate ranged from 0.14 to 0.17 across the models. According to the DIC, the best and most parsimonious model included the fixed effects of dam age at first calving, weaning contemporary group of the first calf, and contemporary group for the probability of heifer pregnancy at 14 months. The estimated heritability suggests that selection for reconception rate in early sexually precocious Nellore heifers is feasible and can promote genetic gains in reproductive efficiency, supporting its inclusion as a criterion in selection programs targeting improved fertility and sustainability in beef cattle systems.

Keywords: 2026

How to Cite:

Baldi, F., Bordin Temp, L., Espigolan, R., Ferraz, J., Oliveira, E., Pereira, L. & Pereira, A., (2026) “Genetic parameters for reconception rate of early sexual precocious Nellore heifers”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286540. doi: https://doi.org/10.31274/wcgalp.24043

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