Distinct proteomic profile of ovarian follicular fluid in ewes from small versus large developing follicles

•Fifty-five major proteins were identified in the 2 groups.•The gene ontology identified as the main molecular function - catalytic activity and binding, as the main biological processes - the cellular and metabolic processes, and as the main cellular component - the cell part.•Only 2 proteins were found in higher abundance in follicles < 4 mm.•In the group of follicles  ≥ 4 to 6 mm, 10 proteins were in higher abundance.