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1 Nutritional Physiology and Animal Breeding and Genetics Groups, Department of Animal Science, Iowa State University, Ames 50011-3150
The effects of
-casein (CN) and ß-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
-CN A allele additively increased the proportion of
-CN, and substitution of the ß-LG B allele additively increased the proportion of ß-LG in total milk protein. In response, proportions of the other milk proteins, mainly
S1-CN, were decreased. For proportions of
S1-CN,
-CN, and ß-LG in total milk protein,
-CN and ß-LG genotypes explain more than 50 and 25% of the heritability and repeatability estimates, respectively. We concluded that
-CN and ß-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
-CN B and ß-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
S1-CN.
Key Words: milk protein composition milk protein genotypes genetic parameter estimates
Submitted on January 25, 1999
Accepted on August 18, 1999
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