Homogeneity and heterogeneity of variance components for milk and protein yield at different cluster sizes in Iranian Holsteins

Abstract This study was conducted to investigate the homogeneity and heterogeneity of variance components for milk yield (MY) and protein yield (PY) at different cluster sizes and to evaluate effect of different data transformation methods on the ranking of elite animals in Iranian Holsteins. Data included 305-day lactation records for MY and PY from the first three lactations that were collected in the period from 1983 to 2014 by the Animal Breeding Center and Promotion of Animal Products of Iran. The mean and standard deviation of 305-day MY and PY for each herd were obtained and used as the basis for clustering the herds. Four different data transformation methods including Logarithmic, Arc sin, Square root and Box-Cox were applied and the data were tested for heterogeneity of variance before and after transformation using Bartlett's test. Genetic parameters and heritability estimates as well as animals’ breeding values (BVs) were estimated by the VCE program, using animal model. The results indicated the heterogeneity of variance in all clusters (P