Genetic and phenotypic correlations among reproductive traits of dairy cows.
Keywords:Genetic relationships, days open, calving interval, Holstein Friesian, Brown Swiss.
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
DFS-CI, DFS-DO, DFS-NSC, CI-DO, CI-NSC, and DONSC
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
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