The use of nucleus breeding units (NBU) to accelerate the annual genetic gain in dairy sheep selection programs relies on the hypothesis that traits have the same phenotypic expression of genetic merit both in NBU and in multiplier and commercial flocks. Sarda dairy sheep is bred in Sardinia and continental Italy over a wide variety of climatic conditions and production systems, mainly based on available natural pastures. Thus milking yields of Sarda ewes are heavily affected by various feeding practices and seasonal weather pattern. To investigate the effect of a relative change in milk yield phenotypic expression of Sarda genotypes, raised in different environments, the estimated breeding values (EBV) of 25 widely used AI rams, obtained from daughters performances in 2 large flocks (the NBU) and in the whole Sarda Flock-Book, were compared. Pearson’s product moment and Spearman’s rank correlation coefficients between nucleus and on-farm EBV were respectively 0.86 and 0.75. Genetic superiority of rams chosen on the nucleus EBV was 17% (in terms of EBV standard deviation) lower than that achievable using on-farm EBV. This fact could be due to different accuracies resulting from the two genetic evaluations and to some differences in Sarda production systems related to availability of feeding resources and machine milking equipment and to economic constraints and management decisions. Such a result decreases the role of a nucleus-flock in the Sarda breeding scheme and supports the choice of an on- farm recording scheme that could ensure a good adaptation of selected animals to Sardinian dairy sheep production environments. 

S. R Sanna, A. Carta, S. Casu

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 24: Sheep and goats (fibre); sheep and goats (meat and milk); poultry; horses; buffaloes., , 141–144, 1998
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