Symposium review: Lipids as regulators of conceptus development: Implications for metabolic regulation of reproduction in dairy cattle1

Pregnancy losses are substantial in dairy cattle and threaten reproductive efficiency. A substantial proportion of these losses occur during early stages of conceptus development, including the elongation phase. Elongation of the preimplantation conceptus is a prerequisite for maternal recognition, implantation, and survival of pregnancy. The onset of elongation occurs when concentrations of lipids in endometrial epithelial cells are increased, and it requires substantial coordination of lipid metabolism by conceptus cells. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) seems to have a central role in coordinating gene expression in trophectoderm cells at the onset of elongation, particularly of genes involved in lipid metabolism. Numerous fatty acids are natural ligands of PPARγ and their concentrations in the histotroph are likely important to PPARγ activity and its downstream effects on conceptus biology. Changes in concentration or composition of fatty acids in the histotroph could alter conceptus development. Inflammatory diseases and excessive loss of body reserves are prevalent problems in postpartum dairy cows and represent important risk factors for early pregnancy loss in the subsequent breeding period. Although cows affected by these conditions likely have reduced developmental capacity of oocytes, embryo transfer studies indicate that impaired uterine environment also contributes to their subfertility. Long-lasting effects of these conditions on energy and lipid homeostasis might alter composition of the histotroph and could help explain developmental failures occurring during conceptus formation attributable to impaired uterine environment. Targeting of uterine lipid metabolism and PPARγ activity during preimplantation conceptus development through prevention of disease and optimized feed intake postpartum and through nutraceutical diets at the time of breeding are potential strategies to improve pregnancy survival and consequently reproductive efficiency in dairy cows.