DIFFERENT AMOUNTS OF BETA-LACTOGLOBULIN-A AND BETA-LACTOGLOBULIN-B INMILK FROM HETEROZYGOUS AB COWS

The concentrations of total protein, casein and whey protein were dete rmined in milk samples derived from 1278 Ayrshire, 718 Jersey, 396 Bro wn Swiss and 271 Canadienne cows which were all heterozygous P-lactogl obulin AB The mean values for the respective components were: 3.40, 2. 69 and 0.70% for Ayrshire, 3.82, 3.08 and 0.74% for Jersey, 3.54, 2.80 and 0.74% for Brown Swiss and 3.60, 2.88 and 0.72% for Canadienne. Po lyacrylamide gel electrophoresis, followed by densitometric scanning, was used to quantify the relative proportions of beta-lactoglobulin A and beta-lactoglobulin B in the whey protein fraction. For the four br eeds studied, a higher proportion of beta-lactoglobulin was produced a s the A variant than as the B variant. In the heterozygous beta-lactog lobulin AB, the A form was present in higher amounts of 49, 41, 40 and 31% when compared to the B form of the protein in Jersey, Canadienne, Brown Swiss, and Ayrshire, respectively. These results support previo us observations that the concentrations of beta-lactoglobulin in milk are associated with the genetic variants of the protein and are in the following decreasing order of magnitude, according to phenotypes: AA > AB > BE. Copyright (C) 1996 Elsevier Science Limited