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Animal Breeding and Genetics
Asian-Australasian Journal of Animal Sciences 1996;9(6): 685-694.
https://doi.org/10.5713/ajas.1996.685    Published online December 1, 1996.
The relationship between milk protein phenotypes and lactation traits in Ayrshires and Jerseys
S. Kim, K. F. Ng-Kwai-Hang, J. F. Hayes
A total of 3,610 Ayrshire and 1,711 Jersey cows were phenotyped for the genetic variants of 慣s1-casein, 棺-casein, x-casein, 棺-lactoglobulin and 慣-lactalbumin. Least squares analyses showed possible associations between milk protein phenotypes and lactational production traits. Depending on lactation number, 棺-casein phenotypes in Ayrshires were associated with milk production(A2A2>A1A2>A1A1), and with milk protein content. In the third lactation, Ayrshire cows with 棺-casein A1A1 produced milk with 3.43% fat compared to 3.37% fat for 棺-casein A2A2. In Ayrshire, x-casein phenotypes affected the protein content during the three lactations(BB>AB>AA) and 棺-lactoglobulin phenotypes significantly influenced the milk fat during the first lactation(4.06% for AA and 3.97% for BB). In Jerseys, protein content of milk was influenced by phenotypes of 慣s1-casein(3.98% for CC v/s 3.86% for BB in the first lactation). In the third lactation, x-casein AA of Jersey milk contained 5.35% fat compared to 4.82% for phenotype BB. The effects of 棺-lactoglobulin phenotypes on protein content were apparent in Jerseys during the second lactation with the A variant being superior to the B(4.00% for AA v/s 3.87% for BB).
Keywords: Ayrshire; Jersey; Genetic Variants; Milk; Fat; Protein

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