At present, breeding programs aimed at raising milk yield of sheep in Slovakia, are based on phenotype values of dams. For more efficient selection, a multivariate genetic evaluation of milk sheep has been done. Predicting accurate breeding values needs all effects affecting the traits to be accounted for and the estimates of variance-covariance components to be known.  Genetic evaluation of milk yield can either be based on cumulative lactation or individual test day records. The latter have a number of advantages and are quickly becoming the basis for state of the art of genetic evaluation. One main advantage, apart from operational ease lies in a better possibility to account for sources of variation affecting each test day. The traditional approach of trivially aggregating test day into lactation records and then subjecting them to sophisticated statistical analyses accounting for an optimum differentiation of genetic and environmental effects (Swalve, 1998) does not make much sense. The objective of this study was to present the simultaneous estimates of genetic parameters and covariance components for milk production traits (daily milk yield, fat and protein percentages) of two most numerous sheep breeds in Slovakia - Improved Valachian (IV) and Tsigai (T) using a multiple trait animal model based on test day records. 

M. Oravcova, Eildert Groeneveld, M. Kovae, D. Peskovieova, M. Margetin

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 1, , 1.47, 2002
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