Genetic correlations between male scrotal circumference and female productive and reproductive traits in Nellore cattle

Genetic parameters for scrotal circumference at 12 (SC12) and at 18 months of age (SC18) of males, and yearling weight (W365), weight at first calving (WFC), age at first calving (AFC), days to first calving (DC) and length of first gestation (GL) of females were estimated using records from 9,932 females and 14,521 males from 28 Nellore herds, located in the South and Southeast regions of Brazil. Covariance components were estimated by REML, fitting bivariate animal models. Heritability estimates were high for SC12 (0.25 to 0.26), SC18 (0.35 to 0.37), W365 (0.35 and 0.38), WFC (0.40 and 0.41) and GL (0.19 and 0.20), but low for AFC (0.14 and 0.15) and DC (0.05 and 0.06). Genetic correlation estimates between SC12 and W365, WFC, AFC, DC and GL were 0.28, 0.30, -0.15, -0.04 and 0.10, respectively. In the same order, the respective genetic correlation estimates between SC18 and female traits were 0.29. 0.32, -0.21, -0.08 and 0.14. These results Suggest that selection to improve female fertility efficiency based on SC18 would be more effective than by using SC12.