Beef cattle

Genetic correlation estimates between pregnancy loss in early-challenged heifers and economically important traits in Nellore cattle

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Abstract

Reproductive efficiency is a major determinant of profitability in beef cattle systems, and pregnancy loss (PL) remains a critical limitation, particularly in Zebu breeds, where its genetic basis remains limited. This study aimed to estimate genetic parameters for PL in Nellore heifers, evaluate its genetic associations with reproductive, growth, feed efficiency, and carcass traits, and quantify direct and correlated genetic responses from selection aimed at reducing PL. The dataset comprised 23,507 Nellore heifers with pregnancy diagnosis records, of which 17,052 were genotyped from the breeding program of the National Association of Breeders and Researchers. Genetic parameters were estimated using two-trait threshold-threshold animal models for PL jointly with the probability of early calving at 30 months of age (PP30; N=127,420) and stayability (STAY; 25,837), and two-trait threshold-linear models for PL with age at first calving (AFC; N=148,770), scrotal circumference adjusted at 365 days (SC365, N=47,208), cumulative cow productivity (CCP; N=31,001), body weight adjusted at 240 (W240; N=111,727) and 455 days of age (W455, N=127,232), ribeye area (REA, N=144,458), rump fat thickness (RFT, N=143,868), marbling (MAR, N=44,391), residual feed intake (RFI, N=20,972), and dry matter intake (DMI, N=20,514). All analyses used the single-step GBLUP approach with Bayesian inference implemented in GIBBSF90+. Correlated genetic responses (CR) and relative selection efficiencies (RES) were calculated considering genetic correlations, prediction accuracies, selection intensity, and generation interval. RES was expressed as the ratio between direct and correlated genetic gains, indicating the efficiency of indirect versus direct selection. The estimated heritability (h²) for PL was low (0.033±0.01), indicating a strong environmental component. Genetic correlations (± standard deviations) between PL and reproductive traits (PP30, STAY, AFC, CCP, and SC365) were -0.81±0.06, 0.23±0.21, 0.93±0.03, -0.15±0.20, and -0.22±0.16, respectively. Correlations with W240, W455, REA, RFT, MAR, RFI, and DMI were 0.01±0.14, -0.16±0.15, -0.16±0.12, -0.09±0.10, -0.08±0.12, −0.44±0.23, and 0.07±0.17. The direct genetic gain for PL was of low magnitude. The relative efficiency of selection indicated that indirect selection was more effective than direct selection for reducing pregnancy loss. Reproductive precocity traits, particularly PP30 and AFC, showed the most favorable correlated responses, highlighting their potential as indicator traits for reducing PL. Growth and carcass traits showed little association with PL, suggesting limited correlated responses. In contrast, the unfavorable relationship observed with RFI indicates that selection for improved feed efficiency should be carefully balanced to avoid potential adverse effects on reproductive performance.

Keywords: 2026

How to Cite:

Bis, F., Silva Neto, J., Brunes, L., Espigolan, R., de Mattos Oliveira, E., Pereira, L., Ferraz, J., Baldi, F. & Amorim, S., (2026) “Genetic correlation estimates between pregnancy loss in early-challenged heifers and economically important traits in Nellore cattle”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2285658. doi: https://doi.org/10.31274/wcgalp.23770

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