Genetic parameters of birth weight, age at first calving and gestation length in dairy cattle herds of Isfahan province
In order to estimate (co)variance components of birth weight, age at first calving and gestation length, records of 13617, 24966 and 24386 of first-parity cows in years of 1998 to 2010 were studied, respectively. Different statistical models were used in two steps accordance to the definition of traits as either cow or calf trait. Heritabilities for cow and calf traits were estimated using animal and sire models, respectively. Fixed effects were included in both models as: herd-year-season and twins. Least square means (±SE) of birth weight, age at calving and gestation length were 39.47±4.13 Kg, 775.29±77.2 d and 276.74±4.85 d, respectively. Estimates of heritability (±SE) for birth weight, age at calving and gestation length using animal model were 0.22±0.02, 0.26±0.02 and 0.32±0.02 and in sire model, 0.19±0.03, 0.77±0.05 and 0.35±0.03, respectively. The significant differences were not observed between the estimated heritabilities for birth weight and gestation length, when they considered as either cow or calf traits. However, the heritability coefficients for age at first calving as calf trait were significantly different. The results of this study showed significant genetic variances in the studied traits and it seems to be useful to include age at first calving as calf trait in future breeding schemes.