Friday, January 10, 2014

Genetic Disorders

I am a bit of a nerd.  I have always enjoyed reading and learning and as a young teenager, I began stumbling upon the building blocks of genetics in science.  I immediately delved into equine color genetics and genetic disorders.

As I familiarized myself with such studies, I was asked time and time again by fellow equine hobbyists why it was worth my time or effort as I wasn't a breeder.

Color genetics perhaps, but I think all horse people should have a basic idea of equine genetic disorders, how they occur, what it means, how it is genetically transferred, and so forth.

But if you just have a performance horse or a pasture pet why should it matter?

Sadly, I have seen horses with genetic disorders stripped of papers and sold.  HYPP +/- stallions bred to grade horses with no information to the mare owners on what can occur.

Even the best intentioned person could be enjoying their young horse and then notice something isn't quite right later on.

There are quite a few well known genetic disorders:
Severe Combined Immunodeficiency
Hyperkalemic Periodic Paralysis
Hereditary Equine Regional Dermal Asthenia
Overo Lethal White Syndrome

Some not as well known

Glycogen Branching Enzyme Deficiency
Hoof Wall Separation Syndrome
Warmblood Fragile Foal Syndrome
Fell Foal Syndrome

And so forth.

One recent genetic disorder that came across my lap recently was hoof wall separation syndrome (HWSS).  It is believed to be an autosomal recessive trait. 

What does "autosomal recessive" mean?

Autosomal means a gene that is located on an autosome, which is a chromosome that doesn't determine gender.  In a simplistic view of things, there are two parking "spots" for genes at each location (loci).  

A dominant autosomal gene would be on the autosome, but you would only need one "defective" copy of the gene in that loci to be afflicted with the disorder.  An autosomal recessive requires both loci to have defective copies.

So with HWSS, perfectly normal Connemara ponies were having offspring with these tragic feet.

But I have to give kudos to Connemara people.  It has been acknowledged that this is a genetic issue.  Funding is being done for further research at UC Davis.  

A blog for people communicating about HWSS is set up with information and stories from breeders.

Be warned that some of the stories are quite sad though.

But still why should someone care?  

I guarantee you that this is just not limited to Connemara horses.  Connemara crossbreds are popular, handy little horses.  This crossbreds, if excellent examples, are often bred on which is fine by me.

However, for that person buying that young event prospect out of the field and there is a little toe chipping off on that nice pony cross, it may be worth keeping this in mind.  Possibly nothing, but with education, additional heartbreak can be prevented.

For the breeder that doesn't know why so many young horses have "white line disease", perhaps the knowledgeable barn friend or farrier could pass this along.

They are looking for more examples of unaffected and affected Connemara ponies to pinpoint down the exact location of this genetic defect in the genome.  Once this is done, a test can be developed.  

Knowledge is key.  I think knowing a basis of equine genetic disorders is a good piece of knowledge to have, right next to saddle fitting and nutrition. How about you?  Any genetic disorders that you are familiar with?  Any personal stories?


  1. I have not dealt with any, but I have heard of the more common one. Drafts can get CPL (chronic progressive lymphedema) which the simple explanation is elephantiasis in the leg. Its a bit more complicated than that though and leads to premature death.

    1. I saw that listed online a couple weeks ago! I don't have a lot of experiences with draft horses and thought that would be very tragic and difficult to deal with. :(

  2. My friend picked up a grade ranch horse several years ago,they were out trail riding when it had an episode and fell on her, they were stuck on the trail for about a day. Horse was diagnosed with HYPP. :/

    1. Very sad. I ended up handling and dealing with a HYPP stallion one very bitterly cold day in January. We at least knew he was HYPP but it didn't make it any easier.

      Sad for your friend. I wouldn't be surprised if he originally had papers and they were "lost" with his status. I have unfortunately heard a few too many stories where this has occurred and it frustrates me when the horses end up with novice/unknowing owners or youth riders. How incredibly dangerous by former owners/breeders who want to profit from this mistake. :(


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