Quantitative analysis of β-lactoglobulin A and B genetic variants in milk of cows β-lactoglobulin AB throughout lactation

摘要

A number of reports show that β-lactoglobulin (β-lg) polymorphism markedly affects production traits. For instance, cows genotyped β-lg BB produced milk containing more casein, which is more suitable for milk processing (see Hill et al. 1997). As a primary effect, β-lg polymorphism induces a differential allele-specific expression of the β-lg gene, so that there is about 1.5-times more β-lg A variant protein than B variant protein in the milk of heterozygous β-lg AB cows (Graml et al. 1989; Wilkins et al. 1995). It has been suggested that mutations in the non-coding region of the β-lg gene affect the transcriptional activity so that the allele A-specific β-lg gene is expressed with higher efficiency (Lum et al. 1997; Folch et al. 1999; Prosser et al. 2000). In studies that examined the effects of β-lg polymorphism on milk composition during lactation (Graml et al. 1989; Mackle et al. 1999; Prosser et al. 1999) or in relation to nutritional status (Auldist et al. 2000), effects of β-lg polymorphism on milk composition tended to be less pronounced at the onset of lactation, in late lactation, and when dietary intake failed to compensate for energy demands. The objective of this work was to verify the possible interaction between these effects of β-lg gene polymorphism and stage of lactation on the expression of A and B variant proteins in milk samples collected, at different times during lactation, from cows β-lg AB.