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Equine HYPP[edit]
Symptoms and presentation[edit]
This inherited disease is characterized by violent muscle twitching and substantial muscle weakness or paralysis among affected horses. HYPP is a dominant genetic disorder; therefore, heterozygotes bred to genotypically normal horses have a statistic probability of producing clinically affected offspring 50% of the time.

Horses with HYPP can be treated with some possibility of reducing clinical signs, but the degree that medical treatment helps varies from horse to horse. There is no cure. Horses with HYPP often lose muscle control during an attack.

Some horses are more affected by the disease than others and some attacks will be more severe than others, even in the same horse. Symptoms of an HYPP attack may include:

Muscle trembling
Prolapse of the third eyelid — this means that the third eyelid flickers across the eye or covers 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 — because the muscles of the voicebox are affected as well as other muscles
Death — in a severe attack the diaphragm is paralyzed and the horse can suffocate
HYPP attacks occur randomly and can strike a horse standing calmly in a stable just as easily as during exercise. Following an HYPP attack, the horse appears normal and is not in any pain which helps to distinguish it from Equine Exertional Rhabdomyolysis (ER), commonly known as "Azoturia," "Monday Morning Sickness" or "tying up." Horses that are tying up usually suffer attacks in connection with exercise and may take anywhere from 12 hours to several days to recover. Muscle tissue is damaged in an attack of ER, and the horse will be in pain during and following an attack. A blood test will reveal elevations in certain muscle enzymes after an episode of ER and so the two diseases, while superficially similar, are easily distinguished from one another in the laboratory.

Unlike with seizures, horses with HYPP are fully conscious and lucid during an attack. Horses may suffocate during an HYPP attack due to paralysis of the respiratory system. Horses that collapse during an episode are clearly distressed as they repeatedly struggle to get to their feet. If this occurs while the horse is being ridden or otherwise handled, the human handler or rider may be at risk of being injured by the movement of the horse.
 

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HYPP is an autosomal dominant genetic defect, meaning both sexes are equally affected, and dominant means that there are no silent carriers-if the horse gets one copy of that defective gene, he is hypp pos
Also, just because a hypp parent has no episodes, does not mean if he passes that defect on, an offspring can't be more severely affected
It is hardly a non issue, as many halter breeding programs are built around HYPP positive horses, and since AQHA is an outcross for both Paints and Appaloosas, those stock horse breeds also have HYPP in them
All HYpp horses trace back to Impressive, so it is pretty much confirmed that when he was conceived, a genetic mutation occurred, creating a dominant genetic defect, which became known as HYPP, and which he then passed on to many of his offspring (50/50 chance)
AQHA has moved very slowly in also excluding HYPP heterozygous horses from registration, for the very reason they fear a back lash , from those halter programs, built around HYpp heterozygous horses
Since it is a dominant defect, thus no carrier state that is asymptomatic, as in HERDA, which is a recessive genetic defect, thus needing to have two copies of the defect, for clinical disease, no horse with a dominant genetic defect should be bred
Excellent and well written explanation Smilie. Thank You.

I remember seeing an advertisement in a QH magazine many years ago by the owners of Impressive. This was after HYPP had been scientifically proven to originate with Impressive. They were still offering breedings to him, and if the resulting foal tested H/H, they offered to take the foal back,AND give another breeding to him. I WAS APPALLED by the greed and deliberate attempts to gloss over this horrible disease. And people took them up on the offer!
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HYPP is an autosomal dominant genetic defect, meaning both sexes are equally affected, and dominant means that there are no silent carriers-if the horse gets one copy of that defective gene, he is hypp pos
Also, just because a hypp parent has no episodes, does not mean if he passes that defect on, an offspring can't be more severely affected
It is hardly a non issue, as many halter breeding programs are built around HYPP positive horses, and since AQHA is an outcross for both Paints and Appaloosas, those stock horse breeds also have HYPP in them
All HYpp horses trace back to Impressive, so it is pretty much confirmed that when he was conceived, a genetic mutation occurred, creating a dominant genetic defect, which became known as HYPP, and which he then passed on to many of his offspring (50/50 chance)
AQHA has moved very slowly in also excluding HYPP heterozygous horses from registration, for the very reason they fear a back lash , from those halter programs, built around HYpp heterozygous horses
Since it is a dominant defect, thus no carrier state that is asymptomatic, as in HERDA, which is a recessive genetic defect, thus needing to have two copies of the defect, for clinical disease, no horse with a dominant genetic defect should be bred
Very clear and well written Smilie. HYPP is FAR from a dead issue, at least down here in the US and the halter world. There are programs whose entire breeding plan center around HYPP horses and they feel that the risk of having an H/H foal is acceptable in the pursuit of a World Champion halter horse. Having worked in that barn with those horses, I absolutely won't breed an N/H horse. Period. Full Stop.

When Boo was still in foal to the stallion she'd been bred to before I bought her, I absolutely could not understand WHY on God's green earth anyone would breed a Frame Mare (turned out she wasn't but her previous owner thought she was) to a Frame Overo Stallion who ALSO was N/H. The mare is N/N, so they knew that they couldn't get an H/H foal but still...Why on earth would you run the risk of having a foal that if it didn't need to be euthanized for being homozygous Frame, would also have a chance of being N/H for HYPP? I guess if there was an Arab in the wood pile somewhere the foal could have come out a carrier for SCID and LFS just for fun. Good Grief!
 

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I've been around two.

First one, Karo syrup every time. Always pulled through fine.

Second one, owner thought I was nuts. She called me from work to come help be she thought the horse was having a bout of colic. Turned out she was. But the stress of that triggered an episode. I called the BO and vet. They both confirmed I wasn't off. We lost her. Both issues going on at once in a very young horse just didn't go well.


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Horrible :(

Smilie while I COMPLETELY agree, it is my understand that NH as opposed to HH do tend more towards asymptomatic and if symptomatic tend to have less severe symptoms. Lesser evil of course- completely unacceptable either way and unfortunately the new rules still do not prevent HH's being bred correct (as parents)? Also, has this ever followed through to other affected breeds (APHA?)

That's the worst part to me, the panic the poor horses must have. Can you imagine? How much worse can it get.
 

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Horrible :(

Smilie while I COMPLETELY agree, it is my understand that NH as opposed to HH do tend more towards asymptomatic and if symptomatic tend to have less severe symptoms. Lesser evil of course- completely unacceptable either way and unfortunately the new rules still do not prevent HH's being bred correct (as parents)? Also, has this ever followed through to other affected breeds (APHA?)

That's the worst part to me, the panic the poor horses must have. Can you imagine? How much worse can it get.
far as I know HYPP pos/pos horses are so severely affected, that most are in research facilities.

No, there is no way of knowing how severe symptoms in an HYPP pos/neg horse will be, and whether one might fall into the lucky few that are asymptomatic, and that asymptomatic hypp pos horse can produce ones that can be severely affected

Actually since homozygous hypp pos horses can't be registered, , they could not be used in a program that produces registered horses. No, those breeding programs are now built around heterozygous HYPP horses, and if tow are bred together, both passing on that HYPP gene, then that offspring can't be registered, even if it survives
Yes, both ApHC (Appaloosa ) and APHA (Paints ) have AQHA as an allowable outcross,and also have halter programs centered around HYPP heterozygous horses
 

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I don't believe that they pulled registrations, just made it so you can't register new H/H foals. Not going far enough, but at least it's a step in the right direction. Paints and Pintos don't have that restriction I don't believe. Don't know about Apps.
 

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Has anyone else seen evidence of change in behavior in HYPP positive horse? Our horse was so docile and loving for first 3 years before he had first of his seizures. Now he has become aggressive- biting, kicking, raring at humans, and trying to run over humans. We are trying to determine why he is having this drastic change in his personality. Do you have any suggestions about how to care for him to improve his attitude? It is dangerous to groom him or clean his hooves. We are fearful to even be in corral with him.
 

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Some of the horses I handled behaved like that and I honestly believe if they'd been given the same training as the NON HYPP horses, they would have come around. They wouldn't do it though, because stress can bring on an attack. I have to wonder which is worse, having to put the horse down for his aggression or dealing with an episode or 2 while you teach him some manners?

My answer for the op, sadly is, I wouldn't handle him, not for all the tea in china. I'd recommend you get a trainer in there to help you.
 

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Since his episode (not a seizure as it's not epilepsy) have you changed how you handle him, perhaps sympathetic. If so this could be what has bro't on his behavior. Be sure to keep him on a low potassium diet (oats for grain is good) as is senior pellets. These horses should be on turnout to keep them moving. Provide loose coarse salt as well as a lick. And plenty of water. No apples or carrots as they are too high in potassium. My n/h has never been symptomatic with his previous owner, a vet, nor the 9 yrs with me. Treats are either part of an alfalfa cube or senior pellets. My NH is the kindest "old" soul you could ever hope to meet.
 

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Hypp does not cause change in disposition like OP describes:sad: the N/H horses I owned were quiet & all great to work with. :D can read horse forum& websites but I'll go with Personal experience & the experiences of that of my peers & vets dealing with HYPP horses .That is the info I find most creditable.:wink:
 
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Hypp does not cause change in disposition like OP describes:sad: the N/H horses I owned were quiet & all great to work with. :D can read horse forum& websites but I'll go with Personal experience & the experiences of that of my peers & vets dealing with HYPP horses .That is the info I find most creditable.:wink:
Is my computer messing up? Where is the OP saying her horse has a disposition change? I only see that she is curious to learn more about HYPP as she is writing about it.
 

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Is my computer messing up? Where is the OP saying her horse has a disposition change? I only see that she is curious to learn more about HYPP as she is writing about it.
OOPs,No I'm sorry not OP:cry: but I was replying to another post from
Sandy B a question about behavior changes in HYPP horse:wink:
 
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Has anyone else seen evidence of change in behavior in HYPP positive horse? Our horse was so docile and loving for first 3 years before he had first of his seizures. Now he has become aggressive- biting, kicking, raring at humans, and trying to run over humans. We are trying to determine why he is having this drastic change in his personality. Do you have any suggestions about how to care for him to improve his attitude? It is dangerous to groom him or clean his hooves. We are fearful to even be in corral with him.
FWIW, HYPP attacks are not seizures. Has he been actually tested?
However as air can be cut off for extended periods of time, I see no reason why a horse COULDN'T have some sort of brain damage from a SEVERE attack.

I'd consult with your vet and a very good trainer on where to go from here.
 
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