Utilization of grape seeds in ruminant nutrition: effects of this by-product on health conditions, milk production and quality, and ruminal metabolism in Sarda dairy sheep

Grape seed is a by-product derived from winery and distillery industries, containing relevant concentrations of polyphenolic compounds. The use of this by-product in ruminant nutrition had not been evaluated yet. The present work studied the effects of dietary inclusion of grape seed, alone or in combination with linseed, as source of PUFA, on immune response, liver and kidney metabolic activity, ruminal metabolism, and milk yield, composition, fatty acid profile and oxidation stability in Sarda dairy sheep. It was demonstrated that grape seed and linseed can be included, alone or in combination, in dairy ewes diet without adverse effects on milk production traits and health status; in addition, an immunomodulatory effect of this residue was evidenced. Grape seed was not effective in reducing PUFA ruminal biohydrogenation; however, it increased the ruminal accumulation of CLAcis-9,trans-11 when used alone, and of vaccenic acid when combined with linseed, manly due to its high content in linoleic acid. Milk quality was improved, in term of FA composition, by the inclusion of grape seed and linseed, especially when used in combination. Moreover, dietary grape seed improved oxidative stability of milk, by reducing the accumulation and formation of lipid hydroperoxides and volatile secondary lipid oxidation products, i.e., hexanal and benzaldehyde, after light exposure. In conclusion, the inclusion of grape seeds in the diet of dairy ewes is an alternative use of this by-product.