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Ask The Veterinarian
By Ellen Yungmeyer, DVM
Q:I have one horse that is a very easy keeper and one horse that has been diagnosed with Cushing’s Disease. Every spring, I get nervous about turning them out on the green grass. What tips do you have to help prevent them from foundering?
A:You are absolutely correct to be cautious about turning out horses like yours to graze on new spring grass. This month we will discuss why certain horses are at particular risk of laminitis this time of year and what you can do to prevent problems.
A sudden diet change from hay all winter to spring grass high in non-structural carbohydrates (aka simple sugars and starches) can make even the healthiest of horses have problems. But a horse with metabolic or endocrine problems is particularly at risk.
First, let’s review the two most common endocrine disorders of horses. One of these disorders, Equine Metabolic Syndrome (EMS), has three hallmark characteristics. These horses have insulin resistance; have regional fat deposits along the crest of the neck, tail head, etc.; and are prone to laminitis. Many horses with EMS are the classic “easy keepers” that stay chubby despite being put on a diet and being exercised regularly.
Insulin resistance has some similarities to Type II Diabetes in humans. The horse’s pancreas produces plenty of insulin, but their tissues (fat, muscle, organs, etc.) are not able to absorb the insulin and, therefore, are not able to break glucose into small units of energy that the cells can use. As a result, the horse may have abnormally high levels of blood glucose and blood insulin, and becomes even more prone to obesity. Why these horses are more prone to laminitis is not entirely understood.
The key to managing horses with EMS is to manage their weight. Horses with EMS are often put on special low starch diets; have their hay soaked to remove non-structural carbohydrates; are turned out on dry lots instead of grassy pastures, and may be placed on thyroid supplementation to aid weight loss.
The other endocrine disorder that horses commonly develop is Cushing’s disease, or Pituitary Pars Intermedia Dysfunction (PPID). This is a disease that affects older horses, and the most obvious clinical signs are laminitis and an excessively long hair coat that does not shed well in the spring (the term for this is hirsutism). Other problems that may be seen in horses with Cushing’s are recurrent infections, such as hoof abscesses, slow healing wounds, and loss of muscle mass. Equine Cushing’s is caused by an abnormal growth of cells in part of the pituitary gland, and the result is the pituitary gland secreting too much ACTH, and, therefore, the adrenal gland secreting too much cortisol.
Cushing’s disease is most often treated with a drug called Pergolide, as well as with dietary changes. Most horses with Cushing’s can be managed well and live a relatively normal life. Just like horses with EMS, it is important to make sure their nutritional needs are met without overloading them with non-structural carbohydrates.
There is some degree of overlap between Equine Metabolic Syndrome and Equine Cushing’s Disease. Many horses that have signs of EMS during their teen years will suddenly drop weight and fail to shed in the spring, signaling that they have likely developed Cushing’s disease. Some horses with Cushing’s Disease remain insulin resistant, making their nutritional management even more important.
So, now to the nitty gritty of limiting the simple starches being fed. For grain, horses that are easy keepers or have been diagnosed with EMS or Cushing’s should absolutely not be given sweet feed or corn. There are several quality pelleted grain products that have low starch levels and provide adequate calories, vitamins, minerals, and amino acids, even for working athletic horses. Hay can be soaked for 30 minutes in clean cool water to remove some of the non-structural carbohydrates. If you have a horse with these needs, work with your veterinarian to design an appropriate feeding plan.
Limiting intake of simple starches is absolutely more of a challenge during the months when pasture is lush. Here are a few tips to allow your horses some turnout and grazing time without putting them at risk for laminitis:
When pastures first green up, increase the amount of time your horses graze very gradually. Adding grazing time in increments of 30 minutes per day would be reasonable. This is also important if you have just moved your horse to a location with better grass, or if your horse has been kept in the stall for an extended period due to bad weather or an injury.
Turnout on grass needs to be very limited or completely eliminated during times of fast grass growth (when it is first turning green in the spring; when it is first drying out at the beginning of a drought; or for about a week after a heavy rain). Pay attention to how often your yard needs mowing as a way to gauge grass growth.
Turn out during the early morning hours (some research suggests no later than 10 a.m.) when grasses have the lowest sugar content.
Put a grazing muzzle on your horse. These devices have built in safety releases in case of getting caught on fencing, and they allow the horse to get a few blades of grass but not large mouthfuls.
In horses with a history of laminitis, watch closely for any foot soreness and have your veterinarian teach you how to feel digital pulses and hoof temperature to detect early signs of laminitis. If you do see these signs, do not let your horse graze until it has been examined by a veterinarian.
Remember: when in doubt, it is probably safest to let your horse have some turnout in a dry lot or dirt arena rather than a grassy pasture.
If you are concerned that your horse has an endocrine issue or is sensitive to spring grass, call your veterinarian for a consultation and possible testing to determine if he is just an “easy keeper,” or if he has EMS or Cushing’s Disease, and to find out the best possible management techniques.
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