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    Genetic Parameters and Correlations for Lactation Milk Yields According to Lactation Numbers in Jersey Cows
    (KAFKAS UNIV, VETERINER FAKULTESI DERGISI, 2010) Unalan, Adnan; Cankaya, Soner
    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.
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    Selection of a mathematical model to describe the lactation curves of Jersey cattle
    (ARCHIV FUR TIERZUCHT, 2011) Cankaya, Soner; Unalan, Adnan; Soydan, Ercan
    The extent of the usefulness of a lactation model depends on how well it succeeds in imitating the biological lactation process and how well it adjust for environmental and other factors that could influence production. Therefore, the objective of this study was to compare five different lactation curve models (Wood, Cobby and Le Du, Wilmink, Exponential and Parabolic Exponential model), and to find the best model that provided a good description of the lactation curve of Jersey cattle herd. Data used in this study were the first to seventh lactation official milk yield records from monthly recording of 3 630 lactations between 1984 and 2008 in the farm. The results showed that Wood model which has minimum residual standard deviation (3.562), maximum adjusted R(2) value (91.6%) and maximum persistency value (93.3%) performed the best fit to the data and allowed a suitable description of the lactation curve. It was concluded that the Wood model provided accurate estimates of milk yield for all lactation numbers because this model was found to be more superior to the other models. Consequently, the usage of Wood model would provide some useful information on genetic improvement of the Jersey breed under pasture-based dry seasonal production systems.