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Intensive genetic selection for increased milk production, coupled with technological improvements in nutrition, has led to significant increases in milk yield in cows in recent decades. However, this increase in milk output per cow has been accompanied by a worldwide decline in cow fertility . The decline in pregnancy rate to a single artificial insemination has been reported to be approximately 0.45%–1% per annum ]. High-yielding dairy cows are typically in a state of negative energy balance postpartum because the amount of energy required for maintenance both of metabolic function and milk production exceeds the amount of energy cows consume. Insufficient energy supply results in poor reproductive performance, which includes a delay in the onset of estrous cycles postpartum [] and a reduction in oocyte quality , resulting in low conception rates and a high rate of early embryonic death

Embryo mortality during the preimplantation period is a key contributor to the reduced fertility in cattle, with up to 40% of total embryo loss occurring between Days 8–17 of pregnancy []. This stage of embryonic loss coincides with the inhibitory effects of interferon tau (IFNτ), produced by trophectoderm cells of embryos, on prostaglandin release from the uterus . This suggests that a proportion of embryos are unable to inhibit prostaglandin F2α(PGF2α) release leading to regression of the CL, reduction in progesterone production ], and termination of pregnancy []. Hence the quality of the preimplantation embryo, and its ability to communicate with the cells of the uterus, are critical for the establishment and continuation of pregnancy.

Short-term changes in plane of nutrition have been shown to have a direct effect on ovarian follicular dynamics in cattle, without any changes in circulating concentrations of gonadotropins []. It has been hypothesized that endocrine and metabolic signals that regulate follicular growth also influence oocyte development either through changes in hormone/growth factor concentrations in follicular fluid or via granulosa-oocyte interactions []. For example, as well as regulating follicular growth [], short-term changes in dietary energy intake influence both oocyte morphology and developmental potential]. The majority of these studies have been carried out in sheep, beef cows, or heifers; thus far, the effects of dietary fatty acids on oocyte quality in lactating dairy cows, which are under greater metabolic pressure, have not been investigated fully.

Fatty acids are rich sources of energy and have important roles in the structure and function of biological membranes ]. Dietary fats influence reproductive function, either by increasing energy balance [or by actions on reproductive processes that are not related to energy Supplementation of the diet with fat has been shown to increase the total number of follicles and to stimulate growth and size of the preovulatory follicle []. In addition, increased availability of fatty acid precursors is coupled with increased steroid and eicosanoid secretion, which can alter ovarian and uterine function and affect embryo implantation []. Maternal dietary fat also influences amniotic fluid and fetal intestinal membrane structural lipid in the rat []..