HYPP

Hyperkalemic Periodic Paralysis

I was busy doing some research on horse feeds and happen to come across an article on black sunflower seeds and its nutritional value as a feed. In this article it was mentioned that horses with HYPP should not be fed it because it poses a health risk to those horses. Never before have I heard of HYPP and curiosity led me to doing some research on it. Here is what I found...

What is HYPP?

HYPP is a inherited muscular disease caused by a genetic defect (mutation of the sodium channel gene).

The muscle cell membranes have “pores” known as sodium channels and they control the contraction of the muscle fibers. Mutation of the sodium channel gene causes these channels to become “leaky” when potassium levels fluctuate in the blood. Excessive amounts of potassium in the blood will cause the muscles to contract more readily than normal. The horse then becomes more susceptible to episodes of muscle tremors or paralysis.

HYPP is a natural mutation that occurred as part of the evolutionary defect. This led to the production of an altered sodium channel. It is not caused by inbreeding.

Descendants of the American Quarter Horse sire Impressive are known to likely be carriers of HYPP. According to a UCDAVIS article, confirmed cases of HYPP have been restricted to descendants of this horse.

Inheritance of the gene

The gene can be both homozygous or heterozygous to have an effect on the horse. Homozygous horses, however, seem to be more severely affected. Research is still being done to determine why some horses show more severe signs of the disease than others.

Signs

Sporadic attacks of muscle tremors (shaking or trembling) is a characteristic sign of HYPP. Other signs includes weakness and collapse. Paralysis of the muscles of the upper airway may result in loud breathing noises. Severe paralytic attacks can lead to sudden death, most likely caused by heart failure and respiratory muscle paralysis.

HYPP attacks are often confused with that off Tying Up. One way to distinguish between the two is to observe the horse after the attack. A horse with HYPP will appear normal where as a horse with Tying Up will tend to have a stiff gait and painful/stiff muscles (hindlegs, rump and back).

HYPP attacks can also be confused with colic if the horse lies down or is unable to stand.

During attacks HYPP horses are conscious and aware of their surroundings. They may also appear to not be in pain.

Causes of attacks

Environmental factors can cause an attack. External stimulus and events can increase the chance of paralysis onset. Factors include changes to the diet (high potassium feeds), fasting general anesthesia, and concurrent illness and exercise restriction.

Prevention of HYPP attacks

1.Avoid high potassium feeds (alfalfa, canola oil, soybean meal/oil and molasses.

2. Feed twice a day.

3. Exercise regularly and/or allow frequent access to a large paddock.

4. Inform your vet prior to any anesthesia and medication.

5. When traveling provide plenty of water (every two hours).