Embryonic mortality in different species of mammals is extremely high, reaching 10–40 % in cattle [1,2]. This loss is greater in embryos produced in vitro, reaching losses of 60–70 % from cleavage to blastocyst [3]. Many studies have investigated factors or culture systems that improve oocyte and embryo health [[4], [5], [6], [7]] or blastocyst rate [[8], [9], [10]] for in vitro embryo production. However, so far, it is not clear what specific factors may negatively regulate embryonic development.

A large portion of early embryonic mortality is caused by DNA repair failures [11]. DNA damage has been classified as lesions and strand breaks, the latter of which can be single-strand breaks or more severe double-strand breaks. Both single and double-strand breaks lead to cell mortality, and have different repair mechanisms [12,13]. Embryos with low developmental capacity have a higher percentage of nuclei positive for phosphorylated histone H2AFX (γH2AFX) and a high abundance of mRNA encoding 53BP1 and RAD52 [14]. Another important marker of DNA damage is the GADD45B gene, which has been linked to physiological or environmental stress [15]. Growth factors have been implicated in the activation or inhibition of DNA repair genes, including the fibroblast growth factor (FGF) family [16,17], and several have been demonstrated to play a part in the regulation of follicle function, such as FGF2 [18,19]. Of interest is the FGF8 subfamily of which FGF8, FGF18, and their receptors are expressed in the ovary and uterus [20,21]. FGF8 has a positive role in the follicle as it cooperates with oocyte-derived bone morphogenetic protein 15 (BMP15) to enhance cumulus metabolism in mice [22]. In contrast, FGF18 has a negative effect on follicle development, as it increases granulosa cell apoptosis [23,24]. In the mouse ovary, FGF18 is predominantly expressed in oocytes [25] whereas in cattle FGF18 is expressed mainly in the follicular theca layer under the control of bone morphogenetic proteins [26]. The uterus is also a potential source of FGF18 as FGF18 mRNA has been detected in the human uterus [27]. Therefore FGF18 of follicular and of uterine origin may impact the oocyte and early embryo, and may be a contributing factor to early embryonic loss. The aims of this study were therefore to determine the effects of FGF18 on cumulus cell expansion, oocyte maturation and embryo development from cleavage to blastocyst stage using a model of bovine embryo production in vitro. We also assessed the impact on markers of DNA damage and repair, 53BP1, RAD52 and GADD45B and on markers of oocyte developmental competence PTGS2 [[28], [29], [30]] and IFNT2 [31].