Genetic Parameters and Correlations for Lactation Milk Yields According to Lactation Numbers in Jersey Cows

In this study, heritabilities, genetic and phenotypic correlations for lactation milk yields were estimated using 3630 305-day lactation milk yield records obtained from cows calved from 1984 to 2007 years in Jersey cattle herd of Karakoy Agricultural State Farm in Samsun. Calving year. calving month and lactation number were assumed as fixed effect factors in statistical analysis of data. Heritabilities, genetic and phenotypic correlations were estimated by derivative-free REML with the animal model. Analysis showed that the overall means of 305-day milk yield, lactation length, dry off period and calving interval were 3467 kg, 297 days, 70 days and 367 days, respectively. Variance analysis results showed that all of the fixed effect factors were statistically significant on lactation milk yields (P<0.001). REML estimates of heritability were 0.289, 0.319, 0.324, 0.331, 0.339, 0.357 and 0.379 for lactation milk yields (from the first to seventh lactation numbers, respectively). Genetic correlations among the first and sub-sequent lactation milk yields were 0.687, 0.676, 0.631. 0.601, 0.590 and 0.551, respectively. All genetic correlations were high and statistically significant (P<0.01). High genetic correlations among lactation numbers reflected that the first lactation milk yield of cows would be useful indicator for the sub-sequent lactations and selection of breeding stock.