Spring vaccinations are an important part of keeping your horse healthy. The routine spring vaccine includes protection for:
Eastern and Western Equine Encephalomyelitis (also called “Sleeping Sickness”)
Rhinopneumonitis (also called “Equine Herpes”, EHV)
West Nile Virus
These are diseases that are commonly encountered in horses. Here in Colorado, the highest risks of exposure are for West Nile virus and Rabies, as well as the respiratory viruses. We immunize for these in the spring because the encephalitis and West Nile viruses are spread via mosquito bites. Protection persists through the entire mosquito season. If your horse travels to the deep south or the coasts, a second encephalitis booster is recommended in the fall to provide year round protection for these diseases. Rabies vaccine should be boosted once yearly in the horse.
PPID (Equine Pituitary Pars Intermedia Dysfunction) is a disease of the horse’s brain. It is caused by damage to the nerves that control secretion of hormones by the pituitary gland. Pituitary hormones include regulation for Cortisone, Thyroid Hormone, Hair growth, Urination, Lactation, and Reproduction. Loss of control usually causes elevation of the various hormones, although sometimes it just mean loss of the normal up and down cycles that occur daily.
The signs of PPID are related to which hormones have gone out of control. The most commonly observed ones are ACTH, which regulates body cortisone levels, MTH, which regulates hair growth, and ADH, which regulates production of urine. As you might expect, the horse shows these problems by urinating too much, growing too much hair, or getting a large abdomen or foundering. Horses that show the typical long dreadlock type hair are obvious. The urination and reproductive issues must be tested for , indirectly, by looking at kidney, urine, and reproductive hormone levels. Cortisol is best evaluated indirectly by measuring ACTH levels, although there are older tests such as the dex suppression test that can also be used. Detecting cortisol elevations is vital because of the increase in insulin resistance it causes, as well as the direct suppression of the immune system and liver damage.
Once diagnosed, the treatment of PPID is medical, and the goal is to return hormone levels to normal. Fortunately, we now have available a prescription medication to treat the disease called Prascend. Prior to the availability of Prascend, we were forced to use compounded pergolide, which was shown in multiple studies to be very unreliable and unstable. Prascend causes ACTH to go down to normal levels when dosed correctly in over 90% of the horses. It is important to monitor the ACTH level at least twice yearly to be sure the ACTH is staying in the normal range. There is a fall rise in the normal level of ACTH in August through December, and it is exaggerated in PPID patients. This elevation causes an increase in insulin resistance, and is responsible for the fall laminitis episodes that occur each year.
Equine Metabolic Syndrome Basics
Equine Metabolic Syndrome (EMS) is a disease similar to Type 2 Diabetes in humans. Normally, when horses eat a meal, they absorb sugars from their intestines, causing an increase in blood sugar levels. In response, the pancreas secretes insulin, a hormone that helps glucose get into the cells where it can be used for energy. The circulating blood sugar thus goes back to a lower level. This is an active balancing mechanism.
In the EMS patient, the body becomes much less sensitive to insulin, and ever increasing amounts are required to return the blood sugar to normal. This lack of sensitivity to insulin causes a number of problems. First and foremost, there is significant evidence that chronically elevated insulin levels directly damage the lamina in the feet, causing founder. In addition, there is strong evidence of immune system damage, and increased fat deposition both externally (the crest, loin, and tail head), and internally, particularly in the liver. The internal fat is particularly damaging, because it releases various other compounds that amplify the insulin resistance.
Management of EMS in the horse is centered on dietary changes and increased exercise. Exercise is the best insulin sensitizer available. Riding 4-5 days a week for an hour is great therapy for both horse and owner. Each session should work up a sweat.
Modification of the diet to limit intake of soluble sugars is very helpful. There are broadly two types of sugars available in the horse’s diet. These sugars are classed as soluble and insoluble. Soluble sugars are things like glucose and fructose and taste sweet. Insoluble sugars are more like pasta. It is possible to measure the soluble sugars in hay and grain samples. The goal is to have less than 10% soluble sugars in the horse’s diet. Hays with more than 10% soluble sugars can be soaked for 30 minutes to remove the soluble sugars. Remember to pour out the water before you feed the hay! There are sources of low soluble sugar hay pellets and pre-formulated rations available from Purina, Nutrena, and others.
The other essential part of dietary management is total caloric intake. EMS horses need to be a little on the thin side. Normal recommendation for total caloric consumption is 1.5 pounds of feed (total hay and grain) per day per hundred pounds. If your horse is over weight, a weight loss program should be devised to get his weight down. Remember, less fat = less insulin resistance.