The effect of olive, sunflower or linseed oils on the fermentation pattern and methane production in the rumen simulating technique

The objective of this study was to investigate the effects of the addition of different vegetable oils to the diet on the fermentation pattern and methane production in Rusitec fermenters. For this purpose four treatments were randomly allocated to sixteen fermenters in a completely random design. Inoculum was obtained from four ruminally fistulated Merino sheep fed lucerne hay and concentrate. Treatments were defined by the diet supplied to the fermenters, so that the control treatment (C) diet was a total mixed ration for ewes on lactation. In the other experimental treatments the control diet was supplemented with olive oil (OO), sunflower oil (SO) or linseed oil (LO) to reach a final concentration of 50 g oil/kg diet. After 7 days of adaptation, samples of effluent, fermenters’ fluid content and digesta of each fermenter were collected during 10 days. There were no significant differences (P>0.05) between treatments in pH values in the fermenters’ fluid content. The LO diet showed (P<0.05) the highest dry matter, organic matter and NDF disappearance. The lowest values were observed with the SO diet (P<0.05). However, there were no differences for ADF disappearance (P>0.05). All three oils reduced methane production compared with control cultures (P<0.05), but there were no differences in the daily gas production. There were no differences in acetate production. The LO diet gave rise to the highest and the control diet the lowest propionate production (P<0.05), whereas butyrate production decreased as a result of any oil addition. The acetate to propionate ratio was also decreased by any oil addition. There were no significant effects (P>0.05) of oil supplementation on Llactate concentration. Ammonia N concentration was higher (P<0.05) in the control treatment, but there were no significant differences between treatments in microbial protein output. In conclusion, these results indicate that fermentation pattern is affected by oil supplementation mainly by decreasing the acetate to propionate ratio, as well as methane production.