High-Protein Diet Okay for HYPP Horse?

Q:I have a 16.1-hand Quarter Horse who is HYPP +/-. He is 13 years old and gets moderate work once or twice a week. He is on turnout with access to grass and hay. I have just switched him to Ultra Dynamix (Seminole), but I am concerned that it contains 14% protein. I was always told that high levels of protein would make a horse "hot." Is this true?

Rosemarie, via e-mail

A:Your question is an excellent one, but unfortunately not one to which there is an easy answer. (This area of) equine nutrition remains a hotly debated topic with very little in scientific literature to support much of the anecdotal evidence noted by the equine community. There are surprisingly few studies that examine the effects of diet on equine behavior.

When looking at the factors that make a horse "hot" (excitable, full of energy), many issues need to be taken into account, such as lack of adequate stimulation, lack of exercise, and excess amount of energy reserves, to name a few. The feeds that have been associated with making horses more energetic have often been feeds with high starch content, including many grain concentrates.

Studies in humans have demonstrated that children fed breakfast foods with high glycemic indexes (high sugar) demonstrate lower performance and shorter attention spans than peers who were fed a lower glycemic index breakfast. Extrapolating to horses, we can see that the amount of sugar in a feed may influence the behavior of the horse.

Some studies in horses have also suggested that aggressive behavior in horses receiving a high starch diet was decreased if the starch was replaced by fat. Another explanation is that concentrates fed twice a day may ferment improperly, causing gastrointestinal discomfort and leading to unruliness. These studies are far from conclusive, but the effect of diet on a horse's behavior cannot be ignored.

There is not much scientific evidence that the amount of protein within the feed would increase excitability in the horse. Whenever a horse is fed excessive energy, whether it is in the form of starch or protein, this may cause the horse to be more excitable. In those cases, the amount of total energy (most often, the amount of concentrate) the horse receives should be reduced.

Hyperkalemic periodic paralysis (HYPP) is an inherited disease in which horses have abnormal sodium channels within their muscles that become sensitive to changes of potassium in the blood. When potassium blood levels change due to diet or stress (due to trailer rides, for example), these horses can suffer from muscle stiffness that causes a constellation of clinical signs. When thinking of diet and the HYPP horse, the most important factors to prevent episodes from occurring center around keeping horses in a steady level of work the majority of the time and offering them a diet that is low in potassium. Feeds such as alfalfa hay, brome hay, canola oil, soybean meal/oil, and molasses should all be avoided.

Horses diagnosed with HYPP should instead be offered timothy or Bermuda grass hay, beet pulp, oats, corn, or barley. These recommendations are especially critical in horses that are +/+ (otherwise known as H/H or homozygous carriers, which have a double copy of the defective gene) because they will display more severe clinical signs when having an HYPP attack than a horse with +/- (N/H or heterozygous carriers, which carry one copy of the gene). However, even a heterozygous horse can suffer from mild clinical signs. You should consult your veterinarian before making any changes in feed that may negatively impact your horse.

About the Author

Maeva Louis May, DVM, Dipl. ACVIM

Maeva Louis May, DVM, Dipl. ACVIM, is a lecturer at the University of Pennsylvania.

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