Circular Economy on a Small Scale: The Sustainable Use of Olive Tree Biomass Residues as Feed for Lactating Cows in the Sorrento Peninsula

To enhance the sustainability of marginal olive and dairy farms in the Sorrento peninsula, two separate crossover trials were conducted on two farms in the area to evaluate olive pruning residue (OlPr) and olive mill leaves (OlLes) as forage sources for lactating cows. Each trial lasted six weeks and consisted of two treatment periods, each including a 15-day adaptation phase followed by a 6-day measurement phase. During the measurement phase, milk production, feed intake, and olive residue consumption were assessed for two homogeneous cow groups: one receiving a ration supplemented with olive by-products and the other receiving a control diet. The olive-supplemented groups exhibited higher dry matter intake and roughage consumption (hay + olive residue) compared to the control groups. The intake of OlLes was about 30% higher than that of OlPr. Compared to the respective control, milk from OlLe-fed cows a had higher fat content and a higher fat-to-protein ratio, a more favorable fatty acid composition in terms of higher monounsaturated and polyunsaturated fatty acids and conjugated linoleic acid contents, a reduced atherogenic index, and a saturated-to-unsaturated ratio. Likely due to the lower level of olive by-product ingestion, only marginal differences were observed in milk fatty acid composition of cows fed OlPr compared to the control. We conclude that the use of OlLes in dairy cow diets may represent a promising strategy for improving milk quality, promoting a more circular agricultural system, reducing reliance on external feed inputs, and mitigating the environmental impact of both olive and milk production.