Comparison between different selection criteria in the genetic evaluation of Valle del Belice sheep

Lactation length in dairy sheep affects milk yield like other genetic and environmental factors. The length of the production period is affected by management decisions such as culling, mating and particularly ranking of animals with different parity and lambing in different months or seasons. Moreover the low heritability of lactation length (Barillet and Boichard, 1987; Dahlin et al., 1998) does not allow its use as a selection criterion. For this reason to achieve a good reliability in phenotypic and genetic evaluation of dairy species, production variability caused by systematic environmental effects must be removed. This is of particular interest for dairy sheep and goats reared in Sicily, where the typical production system is based on pasture, and related food availability is strongly affected by seasonal and annual climatic variations, which results in considerable variations in daily yields........