Circular feeding strategies in pasture-based dairy sheep systems: effects of stabilised olive cake supplementation on rumen microbiota and productive performance

This study evaluated the effects of dietary inclusion of stabilised partially destoned olive cake (PDOC) in the concentrate on productive performance, ruminal fermentation and microbial ecology of grazing dairy ewes. A total of 124 Valle del Belice ewes were assigned to two groups balanced for parity, days in milk, and milk yield. The control group (CTR) received pasture plus 0.5 kg/head per day of a concentrate without PDOC, whereas the experimental group (EXP) received an isoenergetic concentrate containing 17% PDOC (as-fed basis). Milk yield and composition were recorded in all ewes, while rumen fluid from five randomly selected animals per group was analysed for fermentative and metagenomic traits. PDOC did not affect milk yield and composition, although SCC increased (p < 0.05). In vitro fermentation showed lower OM degradability (p < 0.01), NDF degradability (p < 0.05), and total gas production (p < 0.01). Ruminal pH, methane production, VFAs, protozoal counts, ammonia concentration, and FA profile were unchanged. Metagenomic analysis showed modest compositional shifts, with numerically greater abundance of Bacteroidetes and lower abundances of Proteobacteria and Fibrobacteres in EXP, although no taxon remained significant after FDR correction. Alpha diversity was not significant after correction, and beta diversity was unchanged. Functional profiling revealed enrichment of the protocatechuate degradation pathway (q = 0.003), 2–methylisocitrate lyase (q = 0.019), and several racemase reactions (q = 0.049). Overall, inclusion of PDOC did not impair milk production or major ruminal fermentation traits while inducing limited microbial compositional and functional changes.