EFFECT OF DIFFERENT MILK PRODUCTION LEVELS ON VARIANCE IN IRANIAN DAIRY CATTLE
Abstract
Author(s): Sheida Varkoohi
In this research, effect of different milk production levels in Holstein dairy cattle in Iran was studied by using collected data from 1991 to 2010. The data set included the following: 161328 record s of first, 123369 records of second and 81013 records of third lactations. Records were divided in three categories based on mean herd- year production of low (less than 0.5 SD to mean), medium (between less than 0.5 SD to mean and more than 0.5 SD to mean) and high (more than 0.5 to mean). Bartlett test for heterogeneity of variance components was significant among all subgroups. Genetic parameters and heritabilities were estimated for all production levels in the first three lactations. Additive variance was the highest in high milk yield and residual variance was the highest in high milk yield, but in the high milk yield within the second and third lactations, all variance components were the highest amount. Estimated heritability and variance components for production levels were similar in univariate and multivariate animal model analyses. Key words: Production level, variance, dairy cattle
