title: Effect of milk protein genotypes on milk protein composition and its genetic parameter estimates.
abstract: The effects of kappa-casein (CN) and beta-lactoglobulin (LG) genotypes on milk protein concentration and composition were estimated for the US Holstein-Friesian population using a single-trait, mixed, linear animal model on 592 individual milk samples from 233 cows. Both milk protein genotypes had no statistically significant effect on the total milk protein concentration; however, substitution of the kappa-CN A allele additively increased the proportion of kappa-CN, and substitution of the beta-LG B allele additively increased the proportion of beta-LG in total milk protein. In response, proportions of the other milk proteins, mainly alpha S1-CN, were decreased. For proportions of alpha S1-CN, kappa-CN, and beta-LG in total milk protein, kappa-CN and beta-LG genotypes explain more than 50 and 25% of the heritability and repeatability estimates, respectively. We concluded that kappa-CN and beta-LG genotypes affect the phenotypic and genetic variation of milk protein composition but do not significantly affect milk protein concentration. A possible explanation for our conclusion is that altered gene sequences in the promoter region of kappa-CN B and beta-LG A, linked closely to the respective genotypes, favor the transcription or translation of their own protein at the expense of the synthesis of other milk proteins, in particular of alpha S1-CN.
authors.affiliation: Department of Animal Science, Iowa State University, Ames 50011-3150, USA.
authors.forename: G
authors.initials: G
authors.lastname: Bobe
authors.forename: D C
authors.initials: DC
authors.lastname: Beitz
authors.forename: A E
authors.initials: AE
authors.lastname: Freeman
authors.forename: G L
authors.initials: GL
authors.lastname: Lindberg
mesh_terms: D000483:Alleles; D000818:Animals; D002364:Caseins / Q000235:genetics; D002417:Cattle / Q000235:genetics*; D005260:Female; D005838:Genotype; D007782:Lactoglobulins / Q000235:genetics; D016014:Linear Models; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000235:genetics*; D010641:Phenotype
chemical_list: D002364:Caseins; D007782:Lactoglobulins; D008894:Milk Proteins