Effects of dietary sunflower seed oil on rumen protozoa population and tissue concentration of conjugated linoleic acid in sheep

Two experiments with sheep were performed to test the efficacy of a linoleic acid-rich sunflower seed oil as a supplement to barley silage-based diet (6% of the dietary dry matter) to suppress protozoal numbers in the rumen and measure effects of the oil on the growth performance and tissue content of conjugated linoleic acid (CLA). In the first experiment, rumen contents were sampled (2 h after feeding) from the two treatment groups of five rumen cannulated sheep on each day 0-14, and on days 16, 19, 21, 28, 35, 42 and 49. The pH and protozoal counts were determined in each sample, while volatile fatty acids (VFA) and ammonia nitrogen were determined in samples from days 7, 14, 21 and 49. In the second experiment, nine lambs were fed each of the two diets for 168 days. Thereafter, the lambs were harvested and samples of diaphragm muscle, leg muscle, rib muscle, heart, liver, kidney and subcutaneous fat were analyzed for lipid and fatty acid concentrations. Feeding the oil supplement decreased (P < 0.05) the total protozoal numbers in rumen fluid samples from approximately 1,000,000 to less than 200,000 ml(-1) within 6 days and maintained low numbers thereafter. This was associated with higher (P < 0.05) pH on days 9 to 12, 21, 35, 42 and 49 and lower (P < 0.05) concentrations of ammonia nitrogen and total VFA. However, average daily gain, daily dry matter intake, feed conversion ratio, carcass weight and clean fleece weight were not affected (P > 0.05) by feeding of oil. The CLA content was increased (P < 0.05) by dietary supplementation of the oil in tissue samples of diaphragm muscle (55%), leg muscle (37%), rib muscle (33%) and subcutaneous fat (33%). It was concluded that sunflower seed oil reduced rumen fauna and the C16:0 proportion of fat, while increasing C18:2 and CLA content in the muscle and fat tissues.