Genetic and phenotypic association between birth weight, age at first calving and gestation length in dairy cattle herds of Isfahan province
Associations between birth weight, age at first calving and gestation length were studied using bivariate sire models. Records of 13617, 24966 and 24386 female calf from first-parity cows during years of 1998 to 2010 for birth weight, age at calving and gestation length were used, respectively. The fixed effects were as herd-year-season and twins. Estimates of the genetic correlation between birth weight and age at first calving, birth weight and gestation length and age at first calving and gestation length were 0.13±0.09, 0.25±0.09 and 0.22±0.06, respectively. All of the estimated genetic and non-genetic correlations between traits were significant (p<0.05); the only exception was for genetic correlation between birth weight and age at first calving. Based on current study direct selection for reducing age at first calving could reduce gestation length and also birth weight (indirectly).
Keywords: birth weight, age at first calving, gestation length, heritability, sire model, correlation and response to selection.