Wednesday, February 1, 2012

Genetic Defects and Model Horses: Part Two

Here's part two of my posts on genetic defects and model horses.

I'm going to continue talking about the same horse here. If you'll remember, I mentioned he had Impressive in his pedigree multiple times, and was himself HYPP N/H.

The bottom of the horse's pedigree was nice, with some Three Bars in there (I like Three Bars, just not through Impressive), but there was something scary lurking back there among all the nice stuff: Poco Lena.

But what's wrong with Poco Lena?

Poco Lena comes from the Poco Bueno line. Poco Bueno and Poco Lena carried a defect known as HERDA. This is a recessive mutation that basically causes weakness in the skin. A recessive mutation requires two copies of the mutation to have an effect, so Poco Lena more than likely got it from both her sire and her dam, which means that whole line is very suspect in a pedigree. Current thinking is that the original mutation goes back through a mystery horse line involved in the Poco line, either coming through, or starting at, a horse named Traveler.

There are seven conditions that cause similar problems to HERDA in humans, and they're all very problematic for sufferers. The weakness of the skin caused by these disorders makes it very easy to tear. When skin is opened up, there is a risk of infection. When the skin is easy to tear, that means more opportunities for infection. Simply saddling or riding a horse with HERDA can cause horrific damage to the horse. Sunburn too is a big problem, as the peeling can spread a lot further than it would in healthy skin.

HERDA is usually lethal in 2-4 years in horses.

This is classic HERDA scarring. This is the least disgusting and squicky picture I can find. Everything else is very graphic.

In a way, HERDA is a bit like Vinegar Syndrome if OF model horses, or lifting, in vintage custom model horses.

What does HERDA mean for model horses?

Thankfully, it doesn't mean much. Our plastic horses, unless they have vinegar syndrome, or suffer from lifting, aren't going to fall apart if we happen to have their pedigrees give us a HERDA positive horse.

However, I think for pedigree assignment enthusiasts, HERDA is something to keep in mind. If you wouldn't breed for it in real life, why are you breeding it in your models?

That concludes my Genetic Defects and Model Horses mini-series for now. I don't know enough about other genetic disorders in horses to write about them.

I hope you've enjoyed it, and that it's given you something to think about.

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