Effect of long‐term overfeeding of a high‐energy diet on glucose tolerance in Shetland pony mares

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 highenergy 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

Overfeeding Extends the Period of Annual Cyclicity but Increases the Risk of Early Embryonic Death in Shetland Pony Mares

“…In cattle, exposing oocytes to insulin during in vitro maturation resulted in a decreased blastocyst formation rate and led to upregulation of genes involved in lipid metabolism in day 8 blastocysts, indicating that exposure of oocytes to insulin had an effect that lasted until at least the blastocyst stage [ 32 ]. Since the overfed mares in the present study were previously shown to exhibit hyperinsulinemia in response to an oral glucose challenge [ 16 ], it seems reasonable to propose that elevated plasma and FF insulin concentrations may have compromised oocyte and embryo developmental competence. However, follicular fluid insulin concentrations were not measured.…”

“…As reported in a previous article, the HE mares showed insulin dysregulation (ID) after 10–12 weeks of overfeeding in 2014, as determined by periodic oral glucose tolerance tests [ 16 ]. During the winter period when the HE diet was stopped, the ID was reversed.…”

“…The composition of the diet has been described previously [ 16 ]. In brief, the diet of both the control and HE groups consisted of a concentrate feed (36% sugar + starch, 13% fat), grass hay (9% sugar, 2% fat) and a feed supplement to ensure adequate provision of minerals, trace elements and vitamins (Pavo Vital Complete; Pavo, Boxmeer, the Netherlands).…”

Effect of Overfeeding Shetland Pony Mares on Embryonic Glucose and Lipid Accumulation, and Expression of Imprinted Genes

“…General health of all mares was assessed daily by monitoring heart rate, rectal temperature and gait. The ID status of the HE mares was examined via periodic oral glucose tolerance testing, which was performed 3 to 4 times per study year and reported in a previous study [ 24 ]. The experimental protocol was approved by the Committee on Animal Welfare of Utrecht University (DEC 2014.III.01.004).…”

“…The aim of this study was to determine the effect of maternal overfeeding on early epigenetic reprogramming and pathways for conceptus nutrient uptake. Mares were fed either a high-energy (HE) diet equating to 200% of net energy requirements, which resulted in gradual onset of obesity and ID [ 24 ], or a control maintenance diet. The effect of maternal overfeeding on pre-implantation conceptus development was investigated by transferring day-seven embryos (i.e., immediately after blastocyst formation) between HE and control mares and assessing the expression of genes coding for various imprinted genes and DNMTs, glucose and amino acid transporters in the conceptus membranes at day 28 of gestation (i.e., late in the pre-implantation period).…”