Dietary lipid supplementation on cow reproductive performance and oocyte and embryo viability: a real benefit?

The practice of “fat feeding” has become common in the dairy industry in a number of countries. There are several ideas as to how dietary lipids could influence reproductive performance. Highly saturated triacylglycerols (TAG), like palm oil, can increase milk yield but may aggravate negative energy balance and consequently impair fertility when fed during the first weeks postpartum. However, priming the lipid oxidation in the liver by feeding saturated lipid sources during the dry period has recently been shown to be a potentially promising strategy to mitigate fat mobilization and liver accumulation postpartum. Furthermore, polyunsaturated free fatty acids (FFA), such as omega-3 fatty acids and conjugated linoleic acids are fed to reduce the ‘de novo’ fatty acid synthesis in the udder and thus the milk TAG content, which may be of modest benefit for overall energy balance. Furthermore, omega-6 and -3 poly unsaturated FFA are reported to alter follicular growth, steroid synthesis and prostaglandin metabolism in the ovary and endometrium, respectively. Omega-6 FFA are believed to have proinflammatory and thus PGF2αstimulating properties rendering them extra value as “neutraceutical” early postpartum, while omega-3 FFA can weaken this inflammatory potency, leading to a higher chance of survival of the embryo when supplemented during the periconceptual period. Unfortunately, research results rarely provide a consensus in this perspective. The consequences of these fat feeding strategies on oocyte and embryo quality remain an intriguing issue for debate. Dietary lipid supplementation may alter the microenvironment of the growing and maturing oocyte, of the early and older embryo and thus may affect reproductive outcome. We recently reported that dietary induced hyperlipidemic conditions can be harmful for embryo development and metabolism. However, to date, research results remain somewhat conflicting most probably due to differences in fat sources used in diet, and duration of supplementation and in experimental set up.