Effect of age at first conception as selection criteria on growth and carcass traits in Nellore cattle

Abstract Despite the economic importance of sexual precocity for beef cattle production systems, in heifers, this indicator is commonly assessed indirectly using the scrotal circumference or with age at first calving (AFCa), which can delay the identification of precocious females. The study aimed to investigate the genetic parameters for age at first conception (AFCo), AFCa, and their relationship with growth and carcass traits, to verify the possibility of using AFCo as selection criteria for the genetic improvement of sexual precocity. The AFCo was considered the age at which the female presented the first positive diagnosis for pregnancy. The estimation of (co)variance components and genetic parameters was performed using a linear animal model in two-trait analyzes. The heritability estimates were moderate. The highest genetic and phenotypic correlation were obtained between AFCo and AFCa (0.88 ± 0.13 and 0.96 ± 0.13, respectively). In general, genetic correlations estimates between sexual precocity-indicator and growth and carcass traits were moderate and negative. The results of this study encourage the use of AFCo in Nellore cattle since this trait displayed enough genetic variability in Nelore cattle, can be used as selection criteria to improve sexual precocity, and would not display an unfavorable effect on other profitability traits. Selection for animals with early ages at first conception and calving would increase the carcass yield, fat deposition and growth performance. When the selection objective is to increase the heifer sexual precocity, we could use the first trait as criterion, as the measurement of this trait occurs at a lower age at first calving.