Altered embryotrophic capacities of the bovine oviduct under elevated free fatty acid conditions: an in vitro embryo--oviduct co-culture model.

Maternal metabolic stress conditions are of growing importance in both human and dairy cattle settings as they can have significant repercussions on fertility. Upregulated lipolysis is a common trait associated with metabolic disorders and results in systemically elevated concentrations of non-esterified fatty acids (NEFAs). The effects of high NEFA concentrations on the follicular environment, oocyte and embryo development is well documented. However, knowledge on the effects of NEFAs within the oviduct, representing the initial embryonic growth environment, is currently lacking. Therefore, the experiments outlined here were designed to obtain fundamental insights into both the direct and indirect interactions between NEFAs, bovine oviductal cells and developing zygotes. Hence, zygotes were co-cultured with NEFA-pre-exposed bovine oviductal cells or subjected to simultaneous NEFA exposure during the co-culture period. The outcome parameters assessed were embryo development with cleavage (48h post insemination (pi)), morula (120-126h pi) and blastocyst (192h pi) rates, as well as morula intracellular lipid content and blastocyst quality using Bodipy and differential staining respectively. Our data suggest a direct embryotoxicity of NEFAs as well as impaired embryo development through a reduced oviductal ability to support and protect early embryo development.