Effect of dietary fat quality on C18:1 fatty acids and conjugated linoleic acid production. An in vitro rumen fermentation study.

Samples of three diets, previously tested with lactating dairy cows, were incubated in vitro with rumen fluid with the aim of monitoring the concentration of cis and trans C-18:1 fatty acids and of the isomers of conjugated linoleic acid with fermentation time. The three diets had a common forage basis (lucerne hay and maize silage), but different fat sources in the concentrate (basically made up of maize meal and soybean meal). The control diet (diet C) had no fat added and the other two diets were supplemented either with a calcium salt of olive oil (diet O) or with extruded full fat soybean (diet S). The fatty acid pattern in the fermentation vessels was affected by the kind of dietary fat in the samples, both in terms of concentration and of fermentation times (12, 24, 36, 48 h). Oleic acid (OA), elaidic acid and conjugated linoleic acid (CLA) isomers were particularly looked at. OA was not completely saturated to stearic acid, but isomerized to other acids of the C-18:1 family as well. Vaccenic acid was increased with all the three diets, especially with diet O after 36 h.CLA resulted increased with diet S only (P < 0.05), with significant differences between isomers. The saponification of olive oil appeared to be a partial protection against rumen biohydrogenation. The possibility of affecting the concentration of intermediate acids of the biohydrogenation pathways by dietary means was confirmed. (c) 2005 Elsevier B.V. All rights reserved