Do Equine Metabolic Diseases Affect Reproduction?
Having trouble getting your mare pregnant? It might be time to take a good look at her weight and metabolic condition. Some veterinarians now believe that metabolic diseases likely have a negative impact on equine reproduction.
At the 2013 Society for Theriogenology Conference, held Aug 7-10 in Louisville, Ky., Peter Morresey, BVSc, MACVSc, Dipl. ACT, ACVIM, presented a lecture on what we know about metabolic diseases and equine reproduction.
Knowledge from Other Species
At the moment, much of what veterinarians know about reproduction-related metabolic disorders in horses comes from human medicine and research in other species, Morresey explained. He touched on research first:
Metabolic Disease in Breeding Horses
So is there a parallel between the metabolic issues known to cause problems in human reproduction and those in horses? It's possible.
Veterinarians do know that metabolic syndrome in mares can negatively affect the insulin-like growth factors, which are key to follicle selection and dominance. These negative effects might ultimately impair ovarian function.
Additionally, he said, obesity has been shown to prolong estrous duration—leading to fewer usable breeding cycles each year—and ovulatory activity during the nonbreeding season. And while research has shown that a drug called metformin can help obese horses shed pounds and body systems return closer to normal, Morresey said it has not been uniformly effective in helping resolve obese mares' reproductive issues.
Another concern, he said, is gestational insulin resistance. All mares—even otherwise healthy ones—become insulin resistant during late pregnancy (generally after about 270 days, he said) and exhibit exaggerated insulin and glycemic responses when consuming high starch feeds compared to mares consuming a fat- and fiber-based diet. If already insulin resistant going into pregnancy the negative effects might well be amplified, he said.
It still isn't clear what impact metabolic disease has on stallion reproduction, Morresey said.
Managing Metabolic Disease in Breeding Horses
So how should owners and veterinarians manage breeding horses with or suspected of having metabolic disease?
First, Morresey said, make a good diagnosis: "Metabolic syndrome is a syndrome that's difficult to diagnose, a syndrome with profound effects, and a syndrome that's difficult to distinguish (from other endocrine disorders)."
He cautioned that while there are diagnostic options available, research has shown that none of the antemortem diagnostic tests are completely reliable. In fact, he said, they might be less reliable than clinical impression.
His advice: "Don't let a diagnostic test get in the way of a good diagnosis." He encouraged practitioners to rely on clinical impressions during the diagnostic procedures. He suggested they watch for abnormal fat distribution on the horse's body—especially in less common, but no less important, areas including in front of the mammary glands and sheath—and for hoof ridges as tell-tale signs of metabolic disease. He encouraged attendees to pay close attention to fat in the nuchal ligament (in the neck, which forms the "cresty neck"), which has been proven to have higher levels of pro-inflammatory cytokines (mediators of inflammation) than fat in other locations.
After making a diagnosis, Morresey said, it's time to implement a multifaceted treatment:
While researchers are making strides to understand metabolic disease's effects on reproduction, much is still a mystery. However, there is evidence to suggests that metabolic diseases could negatively affect equine reproduction.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.
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