Short communication : The unusual genetic trend of αS1-casein in Alpine and Saanen breeds

Genetic variation at the αS1-casein locus (CSN1S1) is recognized as being crucial in the selection of dairy goats for cheese yield. At this locus, the existence of alleles that have strong, intermediate, weak, and null favorable effects on cheese yield and curd firmness is well known. Selection for alleles that have a strong favorable effect has been deliberately carried out, especially in France. In fact, the importance of αS1-casein in selection was recently confirmed in the selling policies of semen, where bucks are marketed according to their genotypes. We evaluated genotypes and alleles frequencies at the αS1-casein locus in 491 Italian Saanen and Alpine goats and compared them with previous data to investigate their evolution over the past decade. We also estimated soft cheese yield in a subset of the most represented genotypes to quantify the economic importance of considering the genetic trend of αS1-casein genotype frequencies. We found a significant increase in frequency of the allele with the strongest favorable effect, A (+12 and +13%), and of the intermediate allele E (+17 and +7%) in Saanen and Alpine goats, respectively. Surprisingly, the frequency of the strong allele B decreased strikingly over time (−12% in Saanen, −6% in Alpine from 2004 to 2012). This is consistent with the current marketing of semen, in that bucks that are homozygous for strong (AA and BB) and intermediate alleles (EE) and even heterozygous for these alleles (BE and AE) are considered equal. It is worth noting that this practice strongly penalizes the best breeders that have flocks composed almost entirely of goats that are homozygous for strong alleles. For heterozygous goats, we estimated an economic loss of €85 and €215 per goat per lactation, respectively, for AE and BE, compare with AA and BB genotypes. The marketing of buck semen should clearly differentiate these 2 alleles to ensure the best economic genetic progress at this locus.