Abstract :
In this study, the influence of the -lactoglobulin, prolactin and S1-casein variants on milk
production traits of three Portuguese sheep breeds, including Serra da Estrela, White Merino
and Black Merino, was analyzed. The genetic variants of each marker were identified using
PCR-RFLP. -Lactoglobulin genotype AA was associated with lower milk yield in Serra da
Estrela and Merino ewes. This marker also affected milk fat content in Serra da Estrela
and protein content in Merino. First results regarding the influence of the sheep prolactin
gene on milk production traits are reported. In the Serra da Estrela breed, ewes carrying
prolactin genotypeAAwere significantly associated with lower milk yield, but this influence
of prolactin genotypes on milk yield was not detected in Merino. Prolactin genotypes were
also significantly associated with milk fat and protein contents in the Serra da Estrela breed.
A suggestive effect of the S1-casein locus on milk yieldwas detected in Serra da Estrela, but
no associations were found between the variants of this marker with milk fat and protein
content.
