How metabolic disease affects reproduction

Experience suggests that mares with clinical signs of pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS) can be difficult to get in foal. Many stud vets will also have managed broodmares that are prone to developing laminitis during pregnancy. Insulin resistance, which is associated with laminitis [1] is a normal physiological adaptation in both human and equine pregnancy [2], but also occurs in disease states including PPID and EMS. PPID is reported to have an effect on reproductive activity, including abnormal oestrus cycles [3] and reduced fertility [4]. The exact pathophysiology underlying these clinical signs is not known, however, there is evidence that increased concentrations of glucocorticoids can have an adverse effect on ovarian function. Repeated administration of glucocorticoids to mares in dioestrus has been suggested to inhibit follicular development, oestrus behaviour and ovulation [5]. Ferris and McCue [6] reported suppression of luteinising hormone (LH) and ovulation failure (40% ovulation rate compared with 100% in controls and 83% in prednisolone-treated mares) in mares receiving dexamethasone for 5 days in early oestrus ...