Reproductive performance of Nelore cows in the North and Northeast regions of Brazil

The objective of this study was to estimate genetic and phenotypic parameters for reproductive traits of Nelore cows raised in the North and Northeast regions of Brazil. The traits studied were age at first calving (AFC), calving interval (CI), post-partum interval (PPI), number of services per conception (NSC) and gestation length (GL). The statistical analyses were done using the SAS program (Statistical Analysis System) and variance components were estimated by Restricted Maximum Likelihood method using the MTDFREML software. Means and heritability estimates for AFC, CI, PPI, NSC and GL were 45.14 +/- 10.93 months; 465.55 +/- 128.49 days; 165.76 +/- 110.29 days; 1.34 +/- 0.67 services and 295.03 +/- 5.85 days and 0.21 +/- 0:05; 0.05 +/- 0.02; 0.32 +/- 0.11; 0.05 +/- 0.04 e 0.12 +/- 0.04, respectively. The repeatability for CI, PPI, NSC and GL were, respectively, 0.05; 0.63; 0.09 and 0.22. The results suggest that despite the small genetic variability for the reproductive traits, AFC and GL must be included in selection programs. The high heritability estimate for PPI is probably associated to the structure of the data, in its majority coming from the same herd. The repeatability estimate for CI suggests that female culling based on first calving interval is not accurate and there is a risk of culling animals with probable good reproductive efficiency.