Application of a linear regression model to study the origin of C17 branched-chain fatty acids in caprine milk fat.

ABSTRACT

This research communications addresses the hypothesis that a part of iso 170 and anteiso 170 in milk fat could come from endogenous extraruminal tissue synthesis. In order to confirm this a linear regression model was applied to calculate the proportions of iso 170 and anteiso 170 in milk fat that could come from elongation of their putative precursors iso 150 and anteiso 150, respectively. Sixteen dairy goats were allocated to two simultaneous experiments, in a crossover design with four animals per treatment and two experimental periods of 25 d. In both experiments, alfalfa hay was the sole forage and the forage to concentrate ratio (33 67) remained constant. Experimental diets differed on the concentrate composition, either rich in starch or neutral detergent fibre, and they were administered alone or in combination with 30 g/d of linseed oil. Iso 150, anteiso 150, iso 170 and anteiso 170, the most abundant branched-chain fatty acids in milk fat, were determined by gas chromatography using two different capillary columns. The regression model resolved that 49% of iso 170 and 60% of anteiso 170 in milk fat was formed extraruminally from iso 150 and anteiso 150 elongation.