The impact of overfeeding on equine metabolic health and reproductive function: How overfeeding affects body condition, glucose metabolism, cardiovascular function, locomotion, fertility and early embryo development in Shetland pony mares

Abstract

This thesis investigates the impact of overfeeding on the metabolic health and reproductive function of the horse. The study examined whether exposure to environmental factors during early life —specifically, overfeeding of the mare—affect early embryonic development in ways that may result in long-term consequences for the offspring's health. In addition, the development of various components of the equine metabolic syndrome (EMS) during prolonged excessive dietary intake was studied. Shetland pony mares, known for their increased susceptibility to EMS, were overfed (200% of daily energy requirements) and closely monitored over a three-year period. Overfeeding led to obesity and metabolic alterations that did not fully resolve after returning the mares to a maintenance diet, indicating the presence of deeply integrated physiological adaptations. Subtle changes in gait and blood pressure were also observed, suggesting early signs of laminitis, and cardiovascular adaptations. The effects of overfeeding on reproductive function were also examined. Embryos originating from overfed mares showed an increased risk of early embryonic death. Furthermore, embryo transfer between mares with differing metabolic statuses led to changes in gene expression in both the embryo and endometrial tissue, presumably indicating a need to better align maternal environment to embryonic needs. These findings highlight the importance of an appropriate diet for the mare—not only for her own health but also for the health and developmental prospects of the future foal.