Supplementation of rapeseed and linseed oils to sheep rations: effects on ruminal fermentation characteristics and protozoal populations

The study was performed on six sheep fitted with a cannula in the rumen and re-entrant cannula in the duodenum; divided into three groups, two sheep in each. The animals were fed meadow hay and the concentrate alone or the same diet supplemented with rapeseed or linseed oils at a dose of 5% of the basal diet. Ruminal degradation of protein and acid detergent fibre were lower when sheep were fed rapeseed compared to linseed oil (P < 0.05). The addition of oils to diets caused increased ruminal degradation of fat (P < 0.01). The density of protozoa in the rumen at 2 or 4 h after feeding was lower than before feeding in each experimental group. The inclusion of rapeseed oil in the diet decreased the total number of ciliates and Entodinium spp. compared with control and animals fed linseed oil (P < 0.01). Before feeding, the concentration of Diplodinium and Ophryoscolex spp. were lower in sheep fed rapeseed oil compared to control (P < 0.05), and the number of Dasytricha species decreased 2 h after feeding linseed oil compared to animals fed rapeseed oil (P < 0.05). Each of the oil supplements decreased the bacterial mass in the rumen compared with control (P < 0.01). The addition of rapeseed oil to the diet decreased total volatile fatty acid and acetate concentrations in the rumen in comparison to control and sheep receiving linseed oil (P < 0.01). In both diets, the estimated emission of methane and carbon dioxide (P < 0.01) increased 2 and 4 h after feeding compared to that at 0 h. The oleic acid more strongly reduced protozoa and digestive processes in the rumen than linolenic acid. Nevertheless, the quantity of oils added was still too low to induce detectable changes in methane formation in the rumen.