ABSTRACT
Maternal overfeeding is associated with disturbances in early embryonic epigenetic reprogramming, leading to altered expression of imprinted genes and nutrient transporters, which can affect both fetal and placental development and have lasting effects on the health of resulting offspring. To examine how maternal overfeeding affects the equine embryo, Shetland pony mares were fed either a high-energy (HE: 200% of net energy requirements) or maintenance (control) diet. Mares from both groups were inseminated, and day-seven embryos were recovered and transferred to recipients from the same or the alternate group. The expression of a panel of imprinted genes, glucose and amino acid transporters, and DNA methyltransferases (DNMTs) were determined in conceptus membranes after recovery on day 28 of gestation (late pre-implantation phase). The expression of nutrient transporters was also assessed in endometrium recovered from recipient mares immediately after conceptus removal. In addition, glucose uptake by day-28 extra-embryonic membranes, and lipid droplet accumulation in day-seven blastocysts were assessed. Maternal overfeeding resulted in elevated expression of imprinted genes (IGF2, IGF2R, H19, GRB10, PEG10 and SNRPN), DNMTs (DNMT1 and DNMT3B), glucose (SLC2A1), fructose (SLC2A5) and amino acid (SLC7A2) transporters following ET from an HE to a control mare. Expression of amino acid transporters (SLC1A5 and SLC7A1) was also elevated in the endometrium after ET from HE to control. Maternal overfeeding did not affect lipid droplet accumulation in blastocysts, or glucose uptake by day-28 membranes. It remains to be seen whether the alterations in gene expression are maintained throughout gestation and into postnatal life.
ABSTRACT
Obesity has been associated with altered reproductive activity in mares, and may negatively affect fertility. To examine the influence of long-term high-energy (HE) feeding on fertility, Shetland pony mares were fed a diet containing 200% of net energy (NE) requirements during a three-year study. The incidence of hemorrhagic anovulatory follicles (HAF) and annual duration of cyclicity were compared to those in control mares receiving a maintenance diet. Day-7 embryos were flushed and transferred between donor and recipient mares from both groups; the resulting conceptuses were collected 21 days after transfer to assess conceptus development. HE mares became obese, and embryos recovered from HE mares were more likely to succumb to early embryonic death. The period of annual cyclicity was extended in HE compared to control mares in all years. The incidence of HAFs did not consistently differ between HE and control mares. No differences in embryo morphometric parameters were apparent. In conclusion, consuming a HE diet extended the duration of cyclicity, and appeared to increase the likelihood of embryos undergoing early embryonic death following embryo transfer.
ABSTRACT
BACKGROUND: Overfeeding is associated with obesity and insulin dysregulation (ID), which are both risk factors for equine metabolic syndrome. How chronic overfeeding affects development of these factors is poorly understood. OBJECTIVES: To examine the influence of long-term high-energy diet provision on body condition and ID. ANIMALS: Eleven Shetland pony mares. METHODS: In a 3-phase study, the high-energy group (n = 7) was fed 200% of net energy (NE) requirements (hay; concentrate: 36% sugar and starch, 13% fat) for 24 weeks, followed by 17 weeks hay-only feeding before resuming the high-energy diet (n = 4) for an additional 29 weeks. Mares were weighed weekly. Oral glucose tolerance tests were performed 3 to 4 times per dietary period. Results were compared with those of a control group (phase 1, n = 4; phases 2 and 3, n = 6) that received 100% NE requirements, using a general linear mixed model with post hoc Bonferroni testing. RESULTS: The mean body weight of the high-energy group increased by 27% per high-energy feeding period. During both feeding periods, area under the curve (AUC) for plasma glucose concentration decreased (P < .01), whereas AUC for plasma insulin concentration increased. Mean basal plasma glucose concentration and peak plasma insulin concentrations were higher (P < .05) in the high-energy group than in the control group. CONCLUSION AND CLINICAL IMPORTANCE: Feeding a high-energy diet to healthy nonobese Shetland pony mares led to more efficient glucose metabolism within 5 weeks, followed by significant hyperinsulinemia and obesity. Hyperinsulinemic status was reversed during 17 weeks of hay-only feeding, regardless of body condition, but returned rapidly after restarting the high-energy diet.
