Effect of fixed and continuous non-genetic factors on calf birth weight.

Abstract

Cattle reproduction is a highly important field and complex stage of production with large reserves of milk, meat, breeding cattle and by-products. In scientific literature, fertility is generally assessed through age at first conception, gestation length, length of service period, calving interval, and birth weight. Calf weight is governed by both genetic and non-genetic factors. Among non-genetic factors, the fixed effects commonly evaluated are effects of breeding region, season of birth, calving season, year of birth, calf sex and their interactions; and continuous or regression effects include age at first conception or calving. The effect of fixed and continuous non-genetic factors on calf birth weight was analysed in 1151 Simmental calves in three breeding regions, with the effect of breeding region, parity group, calf sex, and breeding region x calving season interaction being statistically very significant (P < 0.01). Birth weight was significantly (P < 0.05) affected by year of birth and calving season, whereas the fixed effect of birth season and the continuous effect of age at first conception were non-significant (P > 0.05). The coefficient of determination (R2) showing the level of variation in calf birth weight as explained by the effect of fixed and continuous non-genetic factors fitted in the model was 0.325.