Correlation of the α-Lactalbumin (+15) Polymorphism to Milk Production and Milk Composition of Holsteins

Abstract

The α-lactalbumin (+15) polymorphism (a single base variation 15 basepairs 3′ of the α-lactalbumin transcription start point) was examined for its usefulness as a genetic marker for Holsteins. The +15 polymorphism is located in a region of the gene that is potentially involved in the regulation of α-lactalbumin gene expression. Animals from two dairy herds and young sires from progeny-testing programs of four AI organizations were used in the analysis. A group of sons from a heterozygous sire were also evaluated. Each individual animal was genotyped at the α-lactalbumin (+15) locus, and differences of genotypes were investigated. Estimated differences among alleles were calculated for PTA for milk, kilograms of protein, protein percentage, protein dollars, kilograms of fat, fat percentage, and fat dollars. Animals having the α-lactalbumin (+15) AA (an adenine on both alleles at position +15) genotype had statistically higher PTA for milk, kilograms of protein, protein dollars, kilograms of fat, and fat dollars than did the α-lactalbumin (+15) BB (a cytosine, guanine, or thymine on both alleles at position +15) animals. The α-lactalbumin (+15) BB animals had higher protein and fat percentages than the α-lactalbumin (+15) AA animals. Animals that were heterozygous at this locus, α-lactalbumin (+15) AB, had intermediate values for all traits analyzed. These results indicate a potential marker or actual locus effect of the α-lactalbumin (+15) polymorphism in Holstein cattle. © 1993, American Dairy Science Association. All rights reserved.