Study on the 305- day Milk Yield of Jersey Cows under Small Scale Family Conditions Raised in Albania. II. Adjustment Factors for 305- day Milk Yield

Data of 935 first lactations, 607 second lactations and 432 third lactations obtained by 1476 Jersey cows that are managed in small scale family farms, under conditions of low input production system, were analyzed in order to study effects of factors: calving age and season on variance of 305-day milk yield and their effect adjustment. ML (Maximum Likelihood) Method was used to obtain unbiased prediction for adjustment factors, as it is able to take into account and estimate not only differences “between cows ” but also “within cow”. Analysis of variance carried out according to mixed linear regression model indicates that all factors included in this model show statistically significant effects (P<0,001) on the variance of 305 day milk yield. Mixed linear model with “age of calving x month of calving ” increased significance (P<0.05) of this model in explanation of total phenotypic variance of milk yield for first three lactations only by 0,72 %. This situation doesn‟t justify the use of joint multiplicative factors for calving age and month