Effect of supplementation of dairy ewes diet with olive oil on milk fatty acid profile, animal performance and in vitro rumen fermentation

Contributed to: 5th Euro Fed Lipid congress and 24th Symposium of the Nordic Lipidforum, Oils, Fats and Lipids: from Science to Applications - Innovations for a better World (Gotherburg, Suecia, Sep 16-19, 2007).Effects of ruminant diet supplementation with linoleic or different polyunsaturated fatty acids (FA) have been well described. Less abundant information however, is found about the effects of incorporation of high amounts of monounsaturated FA such as oleic acid on the lipid metabolism or the animal performance. The purpose of this work was to evaluate the effects of feeding dairy ewes with a diet supplemented with high levels of olive oil (OO) on milk production, composition, with special emphasis on the FA profile, and in vitro ruminal fermentation. Twenty four Assaf ewes were fed ad libitum two diets (20/80 forage/concentrate ratio): control or supplemented with 6% OO (two lots of 6 animals per diet) for 4 weeks. Intake and milk yield and composition were recorded weekly. FA composition of milk fat was determined by GC and conjugated linoleic acid (CLA) profile by Ag+-HPLC. Differences between diets in ruminal fermentation were studied using the in vitro gas production technique. Ruminal inocula were collected from 4 cannulated sheep fed the control diet. In vivo data were analyzed by repeated measures analysis, with measurements at 0-week as covariate and in vitro data as a one-way analysis of variance. Milk production increased in ewes receiving OO (P<0.05), without differences in dry matter intake. The OO diet decreased milk protein percentage (P<0.01) but increased milk fat and protein (P<0.10), and total solids yield (P<0.05). Medium chain saturated fatty acids (C10-C16) contents were significantly reduced (P<0.05) with OO supplementation whereas C18 and cis-9 C18:1 amounts grew up (P<0.01). Leaving aside trans-11, most trans-C18:1 raised in supplemented ewes, mainly trans-10. The main CLA isomer (cis-9 trans-11 C18:2) slightly decreased (P<0.05) with OO supplementation, whilst 7-9 cis/trans and trans-9 cis-11 C18:2 showed a remarkable increment (P