Effect of fixed and continuous environmental factors on milk production in the first three standard lactations in Simmental cows

Abstract

The effect of non-genetic factors on milk and milk fat production in first three standard lactations was examined in 241 Simmental cows. Milk performance traits in standard lactations (milk and milk fat production and milk fat content) were evaluated in terms of the effect of farm, lactation number, season of birth, season of calving, their interactions and age at first fertilisation. The mathematical and statistical analysis of data, involving calculation of least squares means, standard errors, analysis of variance and coefficients of determination, was performed according to the general linear model procedure. The effect of farm, lactation group and year of birth on milk and milk fat production was very highly significant (p<0.001). The interaction between year of birth and season of birth and the interaction among year of birth, season of birth and season of calving had a significant effect on the variability of milk and milk fat production, whereas season of birth, season of calving and age at first fertilisation did not significantly affect (P>0.05) milk and milk fat production. Milk fat content in standard lactations was very highly significantly affected (P<0.001) by breeding area and the interaction among year of birth, season of birth and season of calving; significantly affected by year of birth, season of birth and age at first fertilisation; and non-significantly affected by lactation number and season of calving. The coefficient of determination (R2) was very highly significant (p<0.001), ranging from 0.419 for milk fat content to 0.659 and 0.641 for the production of milk and milk fat, respectively, in standard lactations.