An overview on how cumulus cells interact with the oocyte in a condition with elevated NEFA levels in dairy cows

•Metabolic stress in human and animal is associated with impaired fertility.•Elevated levels of free fatty acids (NEFAs) in blood are a characteristic of metabolic stress.•Elevated NEFA levels in blood are reflected in follicular fluid.•Saturated NEFAs can have a detrimental impact on the competence of the oocyte to develop into an embryo.•Recent data shows that cumulus cells protect the oocyte against elevated levels of NEFAs. Metabolic stress in humans and animals is associated with impaired fertility. A major characteristic of metabolic stress is elevated levels of free fatty acids (NEFAs) in blood due to mobilization of body fat reserves. Dairy cows undergo a period of metabolic stress during the peri-calving period, the so-called negative energy balance (NEB) in the early weeks postpartum. At the time of NEB, both saturated and unsaturated NEFAs are mobilized to serve as an alternative energy supply for cells, however in particular saturated NEFAs can have a detrimental effect on somatic cells. Circulating NEFAs are also reflected in the follicular fluid of ovarian follicles and hence reach the cumulus-oocyte-complex (COC), which implies a potential risk for the developing oocyte. To this end, the current review focusses on the impact of NEFAs on the quality of the oocyte.