Structure and the non-genetic and genetic effects on milk traits in Polish dairy goat population.

The aims of this study were to analyse the structure of Polish dairy goat population and to estimate the non-genetic and genetic sources of variation in five milk traits. The data set comprised 18,563 lactation records of 8,938 dairy goats, while the pedigree file covered information on 13,159 animals 6 generations deep. To estimate the environmental effects the GLM procedure, using a model with the random effect on the herd-sire interaction, the fixed effects of herd-year-season of kidding interaction, breed, litter size, parity, year of birth and regression on day-in-milk. To estimate the co(variance) of the components of milk, fat, and protein yields, as well as fat and protein contents the REML method based on the repeatability animal model was applied. The average inbreeding coefficient was 0.61% (sd=3.12%). Milk, fat and protein yields were affected by all the factors except for breed. The nanny goats with more than two kids had higher milk, fat and protein yields, but they had a lower percentage of milk components than those with one kid or twins. The goats in their first lactation had the lowest milk, fat and protein yields, but the highest fat content. The heritability estimates were moderate (0.21, 0.18, 0.19 for milk, fat and protein yields, respectively). Repeatability estimates ranged from 0.30 for milk, 0.28 for fat, and 0.27 for protein yields, and 0.25 and 0.28 for fat and protein contents. Genetic correlations between milk yield and fat and protein contents were negative and moderate (-0.27 and -0.30), between fat and protein contents (0.58) while those between yields were ranged from 0.71 to 0.86. In turn, correlations between fat yield and its content, and protein yield and its content were positive and moderate (0.35, 0.23).