Pros and cons of the supplementation with oilseed enriched concentrates on milk fatty acid profile of dairy sheep grazing Mediterranean pastures

•This is the first paper on the effect of oilseed supplementation in grazing dairy sheep.•Oilseed enriched concentrate increased milk total trans C18:1 compared to grazing dairy sheep.•The level of PUFA in milk was increased by 45% in the enriched oilseed concentrate group.•Supplemented groups decrease n-3/n-6 ratio in milk compared to sheep fed pasture only.