Effect of Oak Leaf Extract on Performance, Antioxidant Status and Omental Fat Composition in Finishing Lambs

 Most dietary recommendations have advocated for limitation of saturated fatty acids (SFAs) in food for the optimal management of cardiovascular diseases and cancer. Many evidences exist on the effects of saturated FA consumption on vascular function, insulin resistance, diabetes, stroke and cancer. Therefore, improvement of saturated fatty acids to polyunsaturated fatty acids (PUFAs) during meat production is required. Nutritionists have focused on the change of type of FA by feeding ruminants with the plant oils, which are rich in PUFAs. Plant oils in the form of whole seeds might have less adverse effects on rumen fermentation than in the form of free oils. Among all oil seeds, canola has a unique FA profile. The PUFAs are excellent targets for free radical attacks beginning peroxidation. The direct antioxidant activity of a dietary compound would assume its absorption along the gastrointestinal tract and its deposition in the tissues. Several natural compounds have been demonstrated to have clear antioxidant effects in vitro experiments and animal tissues. Among these, natural polyphenol compounds have largely been studied for their strong antioxidant capacities. Because of these antioxidant properties they inhibit lipid peroxidation and peroxygenases. Monomeric phenolic can be absorbed through the intestine and found in plasma. Tannins (hydrolysable and condensed tannin) are water soluble polyphenolic polymers that are found in a wide range of plant species commonly consumed by ruminants. Oak leaves are widely used as source of fodder for goats and sheep. Oak leaves have been reported to contain high levels of tannins in both hydrolysable and condensed forms. The objectives of the present study were to determine the influence of addition of oak leaf extract to a diet containing canola seed on performance, blood parameters, antioxidant status and fatty acid composition of omental fat.  Twelve lambs were randomly divided into two groups and kept individually for 105 days. Lambs were fed diet either with or without oak leaf extract. Diet contained 70% concentrate and 30% alfalfa hay. Ruminal fluid was at collected 4h after feeding in the final week of the experiment. Lambs were slaughtered after 105 days of finishing period. Following chilling the carcass, carcass components were determined and a sample of omental fat was taken from the pelvic area for fatty acid analysis. The fatty acids were determined using a direct method for fatty acid methyl ester synthesis using a gas chromatograph. The plasma overall antioxidant status, malondialdehyde concentration and other blood parameters were measured. Data were analyzed as a completely randomized design using the General Linear Model procedure of SAS.  The results of this study showed that addition of oak leaf extract had no significant effects on animal performance, dry matter intake, blood biochemical profile and ruminal parameters. Fat tail and omental fat as a proportion of cold carcass weight were decreased while empty intestine weight increased when oak leaf extract was fed. Addition of oak leaf extract significantly (P< 0.05) decreased plasma malondialdehyde although total antioxidant capacity was unaffected by diet. Supplementations of oak leaf extract increased mono and polyunsaturated fatty acids and decreased saturated fatty acids of omental fat. Oak leaf extract might inhibit lipid peroxidation and increase antioxidant enzymes activities and decrease malondialdehyde in plasma. Diets enriched with natural antioxidants protect cells and tissues from lipoperoxidative damage. Oak leaf extract may have modulated biohydrogenation of rumen fermentation hence fatty acid profile of omental fat. The plant extract containing polyphenols influence rumen biohydrogeation by altering rumen microorganisms. Changes in ruminal microbial community, indeed direct interaction of tannins with the enzymes responsible for biohydrogenation, affects the last step of the biohydrogenation process and changes the intermediate products resulting in increasing the production of C18: t11 and CLA in rumen and finally increasing PUFA in tissues. Reduction of lipid levels in carcass of lambs received the extract might be due to the anti-lipogenic effect of tannic acid in oak leaf extract. Addition of oak leaf extract to the diet containing canola seed decreased fat tail and abdominal fat in carcass and improved antioxidant status of animals. The results confirm the influence of the tannins on lambs’ carcass composition. Further research is needed to examine the effect of different doses of oak leaf extract on rumen microbial population particularly those involved in biohydrogenation process of fatty acids in the rumen.