Milk protein polymorphism and genetic structure of Croatian Simmental cattle

Milk samples (621) were taken from the area of seven breeding units (Bjelovar, Koprivnica, Veliki Zdenci, Dur evac, Vrbovec, Cakovec and Dakovo) and were genotyped, using iso-electric focusing, for alphas1-, beta-, kappa-casein and beta-lactoglobulin. The genetic structure of population was modelled by Wright's "F-statistics" (FST, FIS and FIT coefficients) and was related only to milk protein polymorphism. Four models were built for that purpose: (a) a model that included Austrian, German, Hungarian, Swiss and Croatian Simmental as subpopulations, (b) a model that included Austrian, German, and Croatian Simmental as subpopulations, (c) a model that included breeding units as subpopulations, and (d) a model where hypothetical subpopulations were formed on the basis of the "blood" origin. Frequencies of milk protein alleles for Croatian Simmental breed were similar to other Simmental populations. Two alleles in alphas1-casein locus B (0.94) and C (0.06), four alleles in beta-casein locus A1 (0.19), A2 (0.63), B (0.15) and C (0.03) and three alleles in kappa-casein locus A (0.64), B (0.30) and C (0.06) were present with corresponding related frequencies marked in parentheses. Two alleles A and B with frequencies 0.52 and 0.48, respectively, were present in the beta-lactoglobulin locus. In spite of these similarities and constant immigration of genes from other Simmental populations, there was a significant genetic heterogeneity among Austrian, Croatian and German Simmental (FST = 0.0056), as well as among Austrian, Croatian, German, Hungarian and Swiss Simmental (F = 0.0083). Significant genetic heterogeneity was also observed among breeding units (FST = 0.0114). The genetic heterogeneity among breeding units is a consequence of the organization of Croatian Simmental cattle breeding and should be taken into account: (a) in the population and quantitative genetic research related to milk protein polymorphism, and (b) when milk protein polymorphisms are going to be implemented as additional information in breeding of Croatian Simmental cattle. Approximately equal frequencies of alleles A and B for beta-lactoglobulin locus in all Simmental breeds, as well as in breeding units of Croatian Simmental, in addition to negative values of FIS coefficients in all models, indicate a natural topic for further research.