The effect on interaction of systematic factors on milk performance of Simmental cows in complete lactation

Abstract

The effect of interaction between the farm and calving season, as well as the farm and group of lactations on milk performance traits (duration of lactation, milk yield, yield of milk fat, 4% fat corrected milk and milk fat content) was analyzed on sample of 2805 Simmental cows with total 9718 complete lactations, housed on dairy farm “Zlatiborski suvati” on Zlatibor (578 cows and 1968 lactations), dairy farm of the Agricultural holding Dobričevo in Ćuprija (964 cows and 3237 lactations) and dairy animals housed on family farms/households in the region of Kotraža (1263 cows and 4513 lactations). The significance of the effect of interaction between the farm and calving season, as well as interaction between the farm and group of lactations on all milk performance traits complete lactations was very high (P<0.001), which justified their inclusion into models for assessment of the breeding value of dairy cows. The share of variance of interactions in total variance of milk performance traits in complete lactations was low (below and around 3%), which clearly indicated even more systematic factors and their interactions which influence the total variability of observed traits of milk performance of cows in complete lactations.