Association of κ-Casein Glycosylation with Milk Production and Composition in Holsteins

Abstract

A total of 545 milk samples were collected from 53 Holstein cows for 1 yr. On test day, morning milk yields were recorded; milk samples were analyzed for N-acetylneuraminic acid, protein, fat, casein, κ-casein, and SCC. The relationship between the degree of glycosylation of κ-casein and morning milk yield and composition was investigated. Data were analyzed using least squares procedures with a model that included test day, parity, stage of lactation, SCC, and phenotype for κ-casein as fixed effects and N-acetylneuraminic acid content of κ-casein as covariate. After adjustments were made for effects of environmental and genetic factors, the degree of glycosylation of κ-casein was associated with morning milk yield, protein, and casein content. Milk yield increased linearly with an increase of N-acetylneuraminic content up to approximately 70μg/mg of κ-casein.