I have talked about equine metabolic syndrome and equine Cushing's disease in horses and today I am going to talk about reproduction in mares affected with these conditions. If you have a mare that has equine metabolic syndrome or Cushing's disease, there is some evidence these horses may be less fertile than other horses. First of all, it's really not a good idea for these mares to carry a foal anyway because they are susceptible to laminitis and founder, and the added weight of a foal will not help.
Also, it has been shown that older horses have a persistent low-grade inflammation caused by production of some inflammatory mediators and increased body fat may be a contributor as fatty tissue increases production of the inflammatory chemicals. Although it is not known what effect these chemicals have on fertility, many of these overweight horses tend to cycle throughout the winter whereas healthy horses stop cycling from October to February. Also, the cycles on these overweight mares can be abnormal as the interval between cycles is much greater. The hormone progesterone is elevated longer in these horses and this fact, coupled with the decreased immunity in horses with Cushing's disease, makes them more susceptible to infections. Since uterine infections are a major cause of infertility in mares, these mares in general are less fertile. So if you have an older mare that you would like to breed that is overweight and has equine metabolic syndrome or Cushing's disease, it is important to address these problems before considering breeding.