Document Type : Research Paper

Authors

Abstract

The objective of this research was to study the heterogeneity of variance components for protein yield from the first three lactations of Iranian Holstein cows which collected from 1983 to 2014 by the Animal Breeding Center and Promotion of Animal Products of Iran. Data set were
141670, 115395 and 82529 records in the first, second and third lactations. Data were classified into three categories of Mediteranean, Dry desert and Humid using Domarten method. The heterogeneity of variances was studied using the Bartlett’s test. The results of Bartlett’s test before data transformation in the first three lactations were significant (P<0.0001) which indicated the heterogeneity of variance in all three climatical regions. In order to reduce or removing the heterogeneity of variances, transformation methods of Logarithmic, Square root and Box-Cox were used which the Square root transformation method caused homogenous variance for protein yield in the third lactation. Genetic parameters, heritability and variance components were estimated by VCE software. The model was included additive genetic effects of animal, herd-year-season and age at calving. Heritability estimates varied from 0.15 to 0.19 and 0.12-0.20 for untransformed and transformed data, respectively. Square root transformation method caused 6.88 and 42.66% of top sires and dams excluded from the usual list, respectively. The results of this study indicated that variance components of milk protein yield in Holstein cows are heterogeneous. Therefore, it is suggested effects of heterogeneity of variance should be considered during genetic evaluation and selection of superior sires and dams.

Keywords

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