HYPP: TO BE OR NOT TO BE?
By Karen Berk
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HYPP, or as properly addressed Hyperkalemic Periodic Paralysis,
has become a topic in the stock horse industry that has virtually
divided it’s membership. In 2004, The American Quarter
Horse Association, in a well documented and debated decision,
passed a bill to discontinue the registration of homozygous
(H/H) foals born in 2007 and beyond. Additionally passed would
be the non registration of heterogygous (N/H) foals, 20 years
hence, 2027.
Both sides of the issue have fought and defended their positions
with great fervor. Yet upon researching this article, I discovered
the majority of people I interviewed had only general knowledge
of HYPP, and a much lesser degree in regard to specific characteristics
and idiosyncrasies significant to the genetic disorder. So,
let’s attempt to distinguish between the facts and myths
of HYPP.
To begin, HYPP is a genetic flaw. It has been identified to
have originated from the stallion Impressive, as a mutated gene.
He did not inherit this from either parent. Impressive had 3
full siblings and seven half siblings out of his dam. There
is no evidence of the disorder in any of their history. Due
to the fact that Impressive sired N/N foals, he could only have
been N/H himself. HYPP also occurs in humans and swine, along
with other species. A mutation of this nature can occur at any
time, in any given individual. If this had generated itself
in a stallion of lesser quality and demand, it may never have
been brought to public attention, thereby wiping it out due
to lack of interest in propagating the bloodline. Impressive
was so sought after as a sire, that inbreeding and line breeding
became the rule rather than the exception. Each generation of
champions from these crosses, continued the breeding trend,
shrinking and intensifying the genetic pool.
HYPP is a muscular disease that is by all means hereditary,
but not a mutation of inbreeding. The genetic defect affects
a protein called a sodium ion channel. The defect disrupts the
channel’s ability to open and close, causing uncontrolled
muscle twitching or intense weakness. Roaring respiratory noises
often accompany a severe attack due to the tightening of muscles
in the Larynx and Pharynx. Not all attacks are severe, and often
pass with little or no notice. Some horses are non symptomatic
their entire lives, with no special management at all. When
one does occur, a blood test identifies high levels of potassium
present. Therefore a low potassium diet is strongly recommended
for positive horses. Alfalfa, originally thought to be a problem,
is now accepted and has a lower potassium content than that
of grass hay, in the volume needed to support a horse. Many
major feed companies are doing research and offering special
low potassium products to accommodate the HYPP horse. Traditionally
oats have been the feed of choice. Another no no is red salt
blocks, as it is extremely high in potassium levels, while white
salt is highly recommended. Management has been the key to providing
these horses with a normal and happy life. Diet, exercise, lots
of available water and a daily stress free routine, with medication
if necessary, can lead to a totally non symptomatic life.
Historically, N/H horses have been sought after for their excessive
muscling by trainers and owners who dream of trophies and large
shiny buckles. To achieve this, many sought to breed horses
with at least one H in his DNA. H/H to H/H will always produce
H/H. N/N to N/N will never produce a carrier. But any combination
that includes at least one H, will have the ability of producing
an N/H foal. N/H to H/H can produce H/H.
Interestingly enough, as much as has been achieved by N/H horses
in the pen, H/H stallions have never dominated competition or
the breeding shed. Breeders repeatedly spoke and wrote to me
of their commitment to breed for a great horse, not a positive
horse. Few professional breeders reported having any problems
due to their proper management and regiment of affected horses.
New developments on the horizon include research into a potassium
rich semen extender that would effectively incapacitate only
sperm cells carrying the mutated gene. This lofty goal may not
be realized in the near future as research grants may need to
be privately funded. Dr. Sam Prien, Ph.D Associate Professor
from Texas Tech University is spearheading the project along
with Clayton Dehn of YL Ranch in Texas.
The produce of Impressive can now be seen in all disciplines
of horses. Although his major impact has been on the Halter
Horse industry, Impressive’s stamp of beauty, elegance
size, muscling and athletic ability, have influenced everything
from Pleasure Horses to Ropers.
It has been often warned that Impressive bred horses should
never be ridden, as there is concern of having a seizure with
a rider on. In fact, exercise is the major contributor to positive
horses leading a normal useful life. At the first sign of an
attack, one should aggressively walk or lunge the horse. Administering
Karo syrup or the drug Acetozolamide, is also highly recommended,
both as a daily supplement and during an attack. Acetazolamide
increases potassium excretion from the kidney and also affects
glucose metabolism, while exercise stimulates adrenalin, which
helps replace potassium inside the cells.
According to Dr. Sara Caldwell. DVM, Ocala Florida, a graduate
of Florida State University, College of Veterinary Medicine,
“The non riding myth is propagated by the veterinary teaching
schools, We are actually taught and directed in school to discourage
clients from riding HYPP horses in order to protect ourselves,
veterinarians, from possible legal action, should an accident
occur. Not at all for reasons of veterinary health or management,
it is strictly a legal issue.”
This discrepancy, to ride or not to ride, brought a flurry of
e mails. Nearly a hundred exhibitors and pleasure riders contacted
me in a one week period with loving stories of their fabulous
mounts. From World Champions to Back Yard Heroes, these Americans
are riding and showing positive horses. There appears to be
no more incidence of injury or evidence of danger than any other
horse. No one reported any attack while under saddle. Some over
a period of as much as 16 years. HYPP attacks are often confused
with riding horses tying up or exhibiting Equine Polysaccharide
Storage Myopathy, which is prevalent in several bloodlines.
Many contributors spoke of their concerns of not having a market
to sell their positive horses, and what would be their fate.
All communications were sentimental, upbeat, yet tinged with
sadness. Their horses encompassed all age groups and disciplines,
making it an excellent sampling.
It is with great interest that we will be able to follow the
fate of HYPP horses in the future. It is with great hope and
expectation that science will render a solution to those horses
carrying the defect. It is with great pride these horses have
helped developed the looks and athletic ability of today’s
stock horse, whether AQHA, APHA or ApHC. It is with great promise
that our registries, trainers and judges will give us unanimous
direction. It is with great anticipation that we look to the
marketplace to be an influence in developing healthy preferences.
And finally, it is with great respect that we acknowledge an
individual’s right to make educated and personal choices
in regard to their own horses.
I wish to thank everyone who responded to my inquiries with
such wonderful information and insight, and the following for
their wisdom and contributions to this article.
Candace Jussen, owner of World Champion Mr GQ, N/H
Zoerado Mills, Owner of World Champion Noble Tradition, N/N
Penny Steward, Siesta Quarter Horses
Sara Caldwell, DVM, legal issues
Sharon Spier, DVM UC Davis published research
About the author: Karen
Berk owns and operates Equine Reproduction Services (ERS) Stallion
Station in Ocala Florida. Along with Bryan Huggins she stands
9 stallions and travels nationwide as a speaker and clinician.
Her published articles have appeared in over 30 publications
in 4 languages, worldwide. She can be contacted through
www.frozen-semen.com. mailto:ERSmobileAiLab@aol.com |
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