Effects of milk protein loci on content of their proteins

Abstract. Allele specific milk proteins were measured in 4544 samples from 2054 Fleckvieh (FV) cows in two succeeding years and in one year from 1809 Braunvieh (BV) cows partly crossbreds with Brown Swiss. The cows were from 454 and 403 sires, and in 316 and 46 farms, respectively. The allele specific milk proteins were measured photometrically.

Gene action was mainly additive, but the aS1-CN BC was 2 to 4 % above the mean of the homozygotes and the heterozygotes at the CSN2 locus deviated from –2 to + 8 % from the means of the respective homozygotes. The extent of expression of the alleles varied. At CSN1S1 higher expression was shown by the B alleles in heterozygotes, and by the C alleles in homozygotes. At the CSN2 locus the statistically highly significant order of degree of expression was C>B>A.

At the LGB locus allele both breeds showed higher expression than allele B and the difference between the expression of the two alleles in heterozygotes is twice of that observed in homozygotes.

The CSN1S1 and CSN2 loci affected the synthesis of all caseins. The CSN3 locus shows statistically significant influence on κ-CN in FV. κ-CN appears to be influenced in particular by C2N2 alleles. The LGB locus shows much influence on the ß-LG content but little on caseins. The effects of CSN1S1 and CSN2 loci on the contents of αS2-CN and k-CN indicate epistasis.

Polygenic influence accounted for one third to one half of the overall genetic variance of contents of Ca-sensitive caseins. k-CN shows much greater polygenic influence (two thirds to four fifth of the genetic variance) and ß-LG less (1/6 and less). The action of LGB was specific with none or very little influence on the caseins. Moreover, ß-LG was also unaffected by the casein loci. The effects of the alleles on the contents were similar in the two breeds. Repeatabilities were 2/5 to almost 3/5, heritabilities 1/4 to 1/3 with the exception of αS2-CN and k-CN where it was lower.