Genetic-quantitative analysis for reproductive traits in Nellor cattle selected for sexual precocity

Context. The selection of animals for sexual precocity and reproductive efficiency is a trend to reduce the production cycle, promote higher economic viability to the system, increase selection intensity and higher genetic gain, as well to promote the profitability of production systems. To include these traits as selection criterion in cattle breeding programs, estimating genetic parameters and studying the possibility of obtaining genetic gains is required. The hypothesis tested was that the indicators of sexual precocity traits present genetic variance and moderate heritability that allows these to be used as a criterion of selection to obtain improvement for sexual precocity, without negative implications for the reproductive efficiency in Nellore cattle. Aims. This study was carried out to estimate the genetic parameters for reproductive traits (scrotal circumference at 365 and 450 days of age, gestation length, days open, calving interval, real fertility, cumulative productivity, calf weight : cow weight ratio) and age at first conception and first calving in a Nellore cattle herd under selection for sexual precocity. Methods. Data of reproductive traits and indicators of sexual precocity traits from 4081 Nellore cattle born between 2009 and 2015 were used. The covariance components, heritabilities and correlations were estimated using the restricted maximum likelihood method, available in the BLUPF90 package, in single- and multiple-trait animal mixed models. Key results. Estimates of heritability and standard errors for scrotal circumference at 365 and 450 days of age, gestation length, days open, calving interval, real fertility, cumulative productivity, calf weight : cow weight ratio, age at first conception (AFCo) and age at first calving (AFCa) were 0.33 +/- 0.03, 0.33 +/- 0.01, 0.23 +/- 0.03, 0.34 +/- 0.11, 0.23 +/- 0.12, 0.21 +/- 0.16, 0.23 +/- 0.08, 0.25 +/- 0.10, 0.21 +/- 0.08 and 0.24 +/- 0.08 respectively. The genetic correlations estimated between AFCo and the other reproductive traits ranged from -0.61 to 0.14 (standard error 0.1-0.21), and between AFCa and the other reproductive traits ranged from -0.60 to 0.16 (standard error 0.1-0.19), all of them in a favourable direction. Conclusions. Selection for sexual precocity based on AFCo and AFCa may promote improvement in reproductive efficiency and fertility, except for the calf weight : cow weight ratio, whose correlation was close to zero.