جستجوی مقالات مرتبط با کلیدواژه « Combined traits » در نشریات گروه « علوم دام »

In this study, in order to multivariate analysis of genetic and phenotypic correlations of productive and reproductive traits in Iranian Holstein dairy cows, records of 64220 first lactation dairy cows were used. Data were collected from 749 herds during 1996 to 2009 by the Animal Breeding Center of Iran. The studied traits were productive (305 days milk yield, 305 days fat percentage, 305 days protein percentage and lactation length) and reproductive (dry days, age at first calving, calving interval and open days). Animals breeding values were predicted using a single trait animal model. A canonical correlation analysis using CANCORR procedure of SAS software was carried out to examine the relation between sets of productive and reproductive traits. Analysis indicated that first canonical correlation between first canonical variate pair for phenotypic and breeding values were 0.999 and 0.996, respectively (P<0.0001). Considering high and undesirable genetic correlation between sets of productive and reproductive traits, for long term profitability, designing selection programs based on a combination of these traits is recommendable.

In dairy cattle breeding, in addition to milk yield, consideration of other productive and reproductive traits is necessary. In order to determine optimum Holstein inheritance in Iranian crossbred dairy cattle, first lactation records of 4917 crossbred dairy cattle collected by Animal Breeding Center between 1991 to 2007 were utilized. Crossbred cows were consisted of different Holstein inheritance including 12.5, 25, 37.5, 50, 62.5, 75 and 87.5 percent. Phenotypic and genetic (co) variance components for milk yield, fat yield, lactation length and age at first calving were estimated by restricted maximum likelihood using single and multiple traits animal models. Then, a selection index was constructed to combine these traits. Optimum Holstein inheritance based on this index was determined by least squares mean comparisons of the index for different Holstein inheritance and simple linear regression. Results indicated that 87.5 percent Holstein inheritance was the optimum level.