The objective of this

work was to estimate the genetic and phenotypic correlations

among fertility traits of 317 Holstein Friesian and Brown

Swiss cows. Cows were born and reared under subtropical

conditions, during a 20-year period (1986 to 2006), and were

daughters of 116 sires and 199 dams. The study was carried

out in Las Margaritas research station, in Hueytamalco,

Puebla, México, which belongs to the Instituto Nacional de

Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP).

Fertility traits studied were: days to first service after calving

(DFS), calving interval (CI), days open (DO), number of

services per conception (NSC) and conception rate at first

service (CR). Genetic correlations were estimated with a

two-trait animal model (bivariate analysis), which included

individual additive genetic effect as a sole random effect.

Main fixed effects were: calving year, calving season and

breed of cow. Analyses were carried out with restricted

maximum likelihood, using an algorithm free of derivatives.

In general, fertility traits were favorably and strongly

correlated genetically. Estimates of genetic correlations for


were positive (0,89, 0,89, 0,25, 0,90, 0,59 and 0,97,

respectively), while all estimates of genetic correlations that

included conception rate to first service (DFS-CR, CI-CR,

DO-CR, NSC-CR) were negative (-0,45, -0,62, -0,72, -0,85).

The high estimates of genetic correlations between CI and

DFS or DO indicate that selection for less DFS or DO would

reduce CI.

Keywords: Genetic relationships, days open, calving interval, Holstein Friesian, Brown Swiss.