If you would like more  information on HyPP here is a link to Judith A. Reynolds  HyPP overview
and management strategies
Managing Horses with HYPP   
It is most important to minimize the amount of potassium from the diet that reaches the blood at any given
time. Also, until more research can be done, do not work horses during peak post-prandial plasma K+
concentration times (about 2-5 hours after large meals), since they are unlikely to perform well during those
times.

In the Texas A&M studies, when the mares were fed two meals per day which contained approximately 33
g of potassium per meal, they remained asymptomatic. However, when fed 58 g/meal and 89 g/meal they
had symptoms 52% and 67% of the time, respectively. Therefore, the objective is to feed less than 33 g
per meal of potassium and also to feed in multiple meals, or allow horses to eat continuously, so that only
small amounts of potassium are available for absorption into the bloodstream at any given time

Management suggestions include:

Balance the total ration for all other nutrients including fiber.

Keep total dietary potassium below 1.1% and meals below 33 g potassium.

Allow access to paddocks and pastures with low potassium forages.

Give small, frequent meals.

Change diet components slowly.

Supplement with vitamin E, selenium, salt, and balanced minerals with no added potassium (research has
shown them to be important in other muscle disorders).

When choosing feeds and feeding programs:

Do not use electrolyte supplements that contain large amounts of potassium.

Use low and medium potassium feeds.

Minimize the use of ‘sweet feeds’.

Use vegetable oils as energy sources.

Analyze feeds for potassium content and check labels.

Use continuous rather than meal feeding of fiber sources.

Feed small, frequent meals of concentrates.


Click to View.......Example Ration for a  Horse with HYPP*
Click to View.........Potassium Content of Common Horse Feeds


Management at a Glance

What you should do for horses with HYPP:

Consult with your veterinarian to develop plans for chronic maintenance and acute treatment during attacks.

Feed a low potassium diet (<1.1% in total diet and < 33 g potassium per meal). This means you need to
know how much potassium is in everything you feed, which is not an easy task.

Feed as many evenly-spaced meals as possible, at least three. (This means 6 a.m., 2 p.m., and 10 p.m.; not
8 a.m., noon, and 5 p.m.).

Allow turnout, grazing (low potassium pasture) and exercise as much as possible.

Do not train or work the horse during peak post-prandial plasma K+ concentration times (usually about 2-5
hours after a large meal).

What you should NOT do with horses with HYPP:

Confine to a stall for 23 hours per day.

Feed two meals consisting of large amounts of alfalfa, sweet feed, protein supplements, and electrolytes
(containing potassium).

Have no management plan or treatment plan for attacks

What are the signs of an HYPP attack?
As with any genetic disease, HYPP has different degrees of what is termed penetrance in different horses.
Penetrance is a term that is used to describe the extent to which a genetic trait can be seen in a particular
individual. Some horses will be severely affected (and this will be exacerbated if they are homozygous for
the trait), and others may look normal for the majority of their lives.
Signs that you may see during an attack of HYPP are:
Muscle trembling
Prolapse of the third eyelid - this means that you may note the third eyelid flickering across the eye, or
covering more of the eye than normal
Generalized weakness
Weakness in the hind end - the horse may look as though it is 'dog-sitting'
Complete collapse
Abnormal whinny - this is because the muscles of the voicebox are affected as well as other muscles

What diseases could be mistaken for HYPP?
When HYPP was first seen in horses, it was often confused with:
Tying Up Syndrome
Seizures
Cardiac problems
When a horse is having an attach of HYPP, he usually remains very alert - this helps us to distinguish
HYPP from a seizure, in which the horse is not aware of who or where he is.
After an HYPP attack is over, the horse appears normal - he does not show signs of stiffness or muscle
pain. This helps us to distinguish HYPP from Tying Up Syndrome, which is characterized by painful, stiff
muscles that may last for days to weeks after an episode. The horse often sweats profusely, and appears to
be painful. Tying Up Syndrome is also accompanied by high muscle enzymes, such as CPK. This is
because muscle cells are actually breaking down. A horse having an HYPP attack will have normal muscle
enzymes. HYPP attacks can also occur at any time - even when a horse is standing quietly in his stall.
Tying Up Syndrome is usually precipitated by exercise.
Cardiac abnormalities severe enough to cause collapse are usually accompanied by other signs of cardiac
failure, such as weakness, abnormal jugular pulsations, or peripheral edema - even when an attack is not
occuring. These horses will also often have murmurs or cardiac arrhythmias - this is not seen with HYPP
unless the horse has more than one problem.

How does my veterinarian make a diagnosis of HYPP?
In addition to the clinical signs, if your veterinarian is able to obtain a blood sample at the time of an attack,
analysis will show a very high potassium level. Blood potassium levels are usually normal in between.
Veterinarians used to diagnose HYPP by challenging the horse with a test dose of potassium given orally.
This test is generally no longer done. Why? Well, it did give us some false negatives, meaning that the test
would say that a horse was not affected when it actually was. It also was a rather dangerous test - horses
stood a risk of having a severe episode of HYPP because of the test.
There are also specialized neurodiagnostic tests that can help to confirm a diagnosis of HYPP. For instance,
although we don't see outwardly abnormal signs during an attack, the muscles are actually still functioning
abnormally. This is detectable using an electromyogram, or EMG. This test usually must be done in a
referral hospital that has specialized equipment. What the examiner will notice is that the muscle has
abnormal spontaneous activity, due to small fluctuations in potassium and sodium.
The definitive test, however, is a genetic test that allows us to determine whether the affected horse carries
the gene for HYPP. All that this requires is a blood sample - and it is a very accurate test.

How can my horse be treated if he has a severe attack?
It is important to be able to recognize whether your horse is having a mild attack or a severe attack. A
moderate to severe attack requires veterinary care, whereas a mild attack may often be treated at home by
the owner. If you are not experienced with this disease, it is wise to call your veterinarian in all cases, until
both of you feel comfortable with your ability to make the right decision.
A mild attack would consist of mild muscle trembling, but no signs of recumbency, abnormal whinny, or
generalized weakness.
In the case of a mild attack, there are several things that seem to help.
Very light exercise - this means hand-walking, not barrel racing!
Get some carbohydrates into your horse - plain corn, light corn syrup, or even sugar will help. Avoid feeds
with molasses added, as molasses is high in potassium. Sugar prompts the body to release insulin, which in
turn has the effect of moving potassium back into the cells.
If you have already consulted with your veterinarian about your horse, she may recommend that you give
your horse a dose of a drug called acetazolamide. This is a diuretic (makes your horse urinate) that also
promotes the loss of potassium in the urine.
In the case of a moderate to severe attack, emergency treatment by a veterinarian is needed.
The goal of treatment is to decrease the amount of potassium in the blood stream - only by doing this will
the muscles regain their ability to contract normally.
What can your veterinarian do to reduce the blood potassium?
One of the first things that your veterinarian will do is to give your horse dextrose (a sugar) intravenously.
As with oral adminstration of sugar, this will help to drive potassium back into the cells.
Oftentimes, your veterinarian will combine the dextrose with bicarbonate, which has an additive effect with
the dextrose.
If your horse is severely affected, your veterinarian may administer calcium intravenously - this may help
to counter the effects of the potassium.
If none of this is helping, your veterinarian may choose to give insulin to boost what your horse is
producing on its own in response to the dextrose.
Finally, your veterinarian will probably give acetazolamide, to encourage your horse's body to waste
potassium.

How can I prevent attacks of HYPP?
Many people keep HYPP-positive horses on acetazolamide all the time. It seems to have little adverse
effects on the horse, and is relatively inexpensive. Most owners of HYPP horses report that this reduces
the number and severity of attacks.
It is sensible to keep your horse on a low potassium diet.
Foods that are very high in potassium include:
Molasses
Alfalfa and timothy hay
Foods that are low in potassium include:
Most grains (but avoid sweet feed, that is mixed with molasses)
Oat hay
Make sure that your horse has a regular exercise schedule - if you are not going to ride your horse one day,
make sure that he has plenty of turn-out. In general, turnout with good shelter from the elements is a better
housing choice for these horses than being confined to a stall.
Avoid sudden exposure to extremes of heat or cold
Maintain a regular feeding schedule. High potassium hays such as alfalfa and timothy are more likely to
precipitate an attack if they are suddenly introduced into a previously low potassium diet.
Feed at least three small grain meals (such as oats, barley, or corn) per day.

Now that we know about the inheritance of HYPP, can we eliminate it?
Well, the problem is that horses with the gene for HYPP tend to be highly muscled, with the ideal physique
for a show Quarterhorse. Because this desireable look accompanies the defect, people will still want to
breed these horses for show. The only way that this disease will every be entirely eliminated is if all owners
have their horses genetically tested before breeding AND agreeing not to breed horses who are positive for
the HYPP gene.