Allele frequencies of casein loci in "Pyrénées" goats : the particular case of the null allele for the β casein

Abstract

After 4 years of preliminary observations (1992-1995), the genetic polymorphisms of caseins of "Pyrénées" goats was analyzed in 1996, using blood and milk samples from 862 females and 63 males spread in 45 herds. Three of the 4 main caseins were studied:  αS1, αS2 and β. For the αS1 casein, the intermediate allele E is predominant, more frequent than the "strong" alleles (A, B3 and B4), the "weak" allele F and 2 null alleles. Within the null alleles, the O2 allele is rather frequent in the sampled males and females and its geographic origin may be located. The β casein has 2 alleles: the null allele was found in 82 % of herds at a 0.11 frequency. About 40 % of females have a mutant defective allele, either at the αS1 locus or at the β locus, with important consequences on milk quality for cheese production. For the null allele of the &beta casein, the population is at the equilibrium but different frequencies exist among groups. In perspective, the selection decision on mutant defective alleles depends on the orientation of the breeders: kid production for meat in the herds under genetic conservation policies or improvement of milk quality for cheese production in the traditional dairy herds.