Prevent an EHV Outbreak by Protecting Your Horse's Immune Function

By Juliet M. Getty, Ph.D.

When there are equine herpes virus (EHV) outbreaks, it causes great concern among horse owners. Did you know that your horse is already likely to be infected with this virus? Virtually all horses carry this opportunistic organism and it remains latent until something (usually stress) triggers it and it has an "opportunity" to show symptoms, producing respiratory and even neurological distress. Ever have a cold sore? That's also herpes and it remains dormant in our systems until we get physically or mentally stressed.

Some stress is inevitable

Traveling long distances, strange settings, unfamiliar horses, performance intensity, different smells and noises … the list is long. Heavy travel seasons are coming up this summer -- July and August are popular horse fair months. And stress suppresses the immune function, making it difficult for your horse to combat illness. Now is the time to get your horse’s immune system in tip top shape so he is less, much less, likely to succumb to a stress-related illness such as EHV. The key to prevention is twofold: Reduce stress and boost immunity.

An empty stomach = Stress

One of the most stressful situations for any horse, regardless of the horse’s schedule and environment, is an empty stomach. Not being permitted to graze continually on pasture and/or hay goes against a horse’s instincts and innate physiology. This is because the horse’s stomach, unlike our own, continuously secretes acid, even when empty. Chewing produces saliva, a natural antacid, which neutralizes that acid. Left without anything to chew, and the horse will suffer, both physically and mentally. Furthermore, the motility of the gastrointestinal tract (which is made of muscles) depends of a steady supply of forage flowing through it in order to prevent colic. And finally, exercising on an empty stomach can lead to an ulcer as the acid sloshes around to the unprotected areas of the stomach’s lining.

Horses are “trickle feeders,” designed to continually and freely roam and graze. But in addition to 24/7 turnout and free choice access to pasture and/or hay, there are many helpful nutrients that can protect your horse, especially while training, traveling, and performing. Vitamins E and C, in particular, as well as vitamin A (beta carotene), magnesium, adequate protein, and Omega 3 fatty acids stabilize the immune system, allowing your horse to be less susceptible toward developing infections.

How much supplementation, you ask?  

  • Vitamins E and C are potent antioxidants and are best increased to higher levels during intense physical and mental stress. Offer 5 IUs of vitamin E and 5 mg of vitamin C per pound of body weight (10 IUs of vitamin E and 10 mg of vitamin C per kg of body weight). Slowly wean your horse down to lower levels of these vitamins (especially vitamin C) during maintenance periods (unless you have an older horse, who will need extra vitamin C due to reduced production).
  • Selenium needs also increase during intense physical activity – the diet should contain 1 to 3 mg per day during maintenance, and up to 5 mg of selenium per day for heavily active horses .
  • Hay has little, if any, beta carotene (used to make vitamin A). Most vitamin/mineral supplements and feeds are fortified with this vitamin.  Offer 60 to 120 IU/kg body weight for performance; 30 IU/kg bw at maintenance.
  • Omega 3 fatty acids are best provided by flaxseed meal -- provide 1/2 cup per 400 lbs (180 kg) of body weight. Chia seeds are also high in omega 3s (1/4 cup per 400 lbs of body weight).
  • Protein should be 14-16% of the diet, and be of high quality. Offer a variety of sources (grass plus alfalfa, for example) so they can complement each other’s amino acid profile.
  • Don’t forget the magnesium – important for muscle and nerve function. Borderline deficiencies can affect your horse’s behavior and stamina. An appropriate dose is 5,000 mg of magnesium per 500 lbs (227 kg) of body weight.

It’s amazingly simple

All this may sound complicated, but it's actually just the opposite. It's amazingly simple. Allow your horse to nibble on hay all day and night, and never let him perform without some hay in his digestive tract. Fill in the nutritional gaps that exist in hay with a good vitamin/mineral supplement, offer omega 3s and extra antioxidants during stressful times, and your horse will not only perform better, calmer, and more gracefully, but will come home healthy and ready to learn more.


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