Olive mill wastewater as a sustainable feed supplement in dairy cows: effects on milk composition and the occurrence of bioactive compounds.

The use of agro-industrial by-products as feed supplements represents a promising approach to improve sustainability in dairy production systems. Olive mill wastewater (OMWW), a by-product of olive oil processing, is rich in phenolic compounds and natural antioxidants, which may contribute to an amelioration of the nutritional quality of animal-derived products. This study aimed to evaluate the feasibility of incorporating OMWW into dairy cow diets and to assess its effects on milk production performance, chemical composition, and the presence of bioactive compounds. Twelve multiparous Holstein dairy cows were assigned to two groups and fed either a control diet or a diet supplemented with OMWW. Milk samples were analyzed for chemical composition and bioactive compounds, including polyphenols, carotenoids, and fat-soluble vitamins, using high-performance liquid chromatography (HPLC). Dietary supplementation with OMWW had no adverse effects on feed intake, milk yield, or major milk components. Although no significant differences were observed between dietary groups, milk from OMWW-supplemented cows exhibited a slight increase in fat-soluble vitamins A and E over the experimental period. In addition, carotenoid compounds were detected and quantified in milk from both dietary groups, indicating that OMWW supplementation did not alter the natural bioactive profile of milk. Overall, these findings demonstrate the feasibility of using OMWW as a dietary supplement in dairy cows without compromising production performance or the natural bioactive profile of milk, thereby contributing to the sustainable valorization of olive oil by-products.