Genetic Associations of Functional Longevity With Sexual Precocity and Growth Traits in Nellore Beef Cattle

Functional longevity (FL) is a complex trait that integrates many attributes directly contributing to the successful retention and productivity of a cow within the herd. Consequently, improving FL in beef cattle increases herd profitability. This study aimed to estimate the genetic associations between two alternative FL definitions and traits related to sexual precocity and growth in Nellore cattle from data comprising 2,607,400 calving records. Two FL traits, evaluated from 27 to 135 months of age, were analysed using random regression animal models: the ability to remain in the herd, evaluated as a binary trait (FLSTAY), and the cumulative number of calvings up to the predefined standard ages (FLNC). Approximate genetic correlations among FL measures, age at first calving (AFC), weaning weight (WW), and yearling weight (YW) were estimated using Calo's method based on the estimated breeding values (EBVs) of individuals with an accuracy of at least 0.60 for both traits. Heritability estimates for FLNC ranged from 0.020 (95% highest posterior density [HPD]: 0.018 to 0.022) to 0.075 (95% HPD: 0.067 to 0.084) and were consistently higher than those for FLSTAY, which ranged from 0.004 (95% HPD: 0.004 to 0.005) to 0.045 (95% HPD: 0.039 to 0.051) across all evaluated ages. The approximate genetic correlations between FLSTAY and FLNC were positive and high (≈0.90) throughout the productive lifespan. Approximate genetic correlations between AFC and both FL measures were favourable, exhibiting a high magnitude at 27 months of age (≈-0.75) and gradually decreasing to values around -0.25. Approximate genetic correlations between WW (direct effect) and FL traits were favourable, starting high at 27 months (≈0.58) and gradually decreasing to 0.06 for FLNC and 0.15 for FLSTAY at older ages. Approximate genetic correlation estimates between WW (maternal effect) and both FLSTAY and FLNC were also favourable (≈0.20) across ages. YW followed a similar trend, showing favourable genetic correlations of ≈0.28 at 27 months that decreased to ≈0.10 near 75 months. Both FL traits exhibit sufficient genetic variability for long-term selection. However, FLNC is recommended over FLSTAY as a selection criterion due to its consistently higher heritability. The favourable genetic associations demonstrate no antagonism between functional longevity and standard growth or sexual precocity traits, supporting the implementation of FLNC as a feasible alternative to traditional single-measure stayability in Nellore breeding programs.