Effect of Feeding Hazelnut Skin on Animal Performance, Milk Quality, and Rumen Fatty Acids in Lactating Ewes

Simple Summary The by-products originating from the agro-industry processes are often rich in bioactive compounds. This is the case of hazelnut skin, waste biomass of the pastry industry, rich in polyphenols and fatty acids that, if included in animal feeding, could contribute (i) to improve animal health and products' quality and (ii) to reduce the feed costs and feed-to-food competition in animal production. We tested this by-product as an ingredient of the diet for lactating ewes. Noteworthy, despite we observed a slight reduction of milk protein percentage, the dietary administration of hazelnut skin improved the composition of the milk lipid fraction by increasing the presence of health-promoting fatty acids and by reducing atherogenic fatty acids. Also, a healthier status of the udder could be hypothesized as a consequence of the inclusion of hazelnut skin in the diet of lactating ewes. Abstract The hazelnut skin is waste biomass rich in bioactive compounds that may affect lipid rumen metabolism, ruminant performance, and products' quality. Therefore, we investigated the effect of dietary hazelnut skin on milk production and composition and on rumen fatty acids in ewes. During 28 days, 20 Comisana lactating ewes received alfalfa hay ad libitum plus 800 g/head/day of pelleted concentrate containing 36% dried beet pulp (CTRL group; n = 10) or 36% hazelnut skin (HS group; n = 10). The protein percentage was lower in HS milk. Milk fatty acids (FA) partially reflected those of rumen content. Total saturated FA (SFA), odd and branched-chain FA, and n-3 polyunsaturated FA (PUFA) were greater in CTRL milk. Total monounsaturated FA (MUFA) and 18:1 trans were greater in HS milk; moreover, HS milk showed a double percentage of oleic acid than the CTRL group. Individual SFA were greater in CTRL milk except for 18:0. Differing from the rumen content, total PUFA, n-6 PUFA, and 18:2 n-6 were comparable between groups. Vaccenic and rumenic acid were greater in HS milk. To conclude, dietary HS slightly reduced milk protein percentage but improved atherogenic index and healthy FA in milk. The content of the somatic cells suggested a healthier udder in the HS group.