Goat's alpha-s1 casein genotype influences its milk fatty acid composition and delta-9 desaturation ratios

A large number of studies about impacts of alpha-s1 (alpha s 1) casein (CSN1S1) gene polymorphism on goat milk composition, including its milk fat concentration, secretion in mammary cells and transcriptome analysis, have been reported. Despite this knowledge, very little data is available on the fatty acid (FA) composition of goat milk according to the CSN1S1 genotype. The study reported here compares two groups of 33 and 38 goats with different CSN1S1 genotypes, associated respectively with low or high milk protein and fat concentrations, matched for lactation stage and diets. Results confirm the lower milk protein (-5.0 g/kg) and fat (-6.8 g/kg) concentrations in the Low genotype group, whereas milk yield and its lactose concentration were not changed. There were between-group differences in proportions in milk fat of at least 17 FA, particularly the C8-C12 saturated FA and palmitic, stearic, oleic, linoleic and rumenic acids. In addition, delta-9 desaturation ratios were higher in the Low CSNIS1 group for C10:0, C14:0, C17:0, C18:0, trans11-C 18:1 and trans13-C18:1, which strongly suggests an effect on mammary desaturase activity, especially for C 18:0 and trans11-C18:1. It is likely that higher delta-9 desaturation ratios for C10:0 to transC18:1 isomers in the Low genotype could compensate for the lower secretion of medium-chain FA (C8:0 to C12:0), thus contributing to maintenance of the melting point of milk fat in this genotype. The polymorphism in the CSN1S1 genotype has important impacts on goat milk fat, and its FA composition, possibly making the goat model of interest in the search for a better understanding of regulation of mammary function, in particular FA synthesis, desaturation and secretion, and how it could be related to protein synthesis and secretion. (c) 2006 Elsevier B.V. All rights reserved.