Dwarfism

One of the disorders associated with horses is Dwarfism. Right now it's a hot topic of conversation with the Friesians because the KFPS has developed a test that is about 98% accurate to determine if a Friesian is a carrier. Because the test is not 100% conclusive and is based on gene markers, not a single gene it's not a widely used test. But 98% is better than not knowing. The KFPS will test any pure Friesian horse (even if it's not mainbook/fhana) as long as it's pure Friesian (b- book 1 or 2 or D or C books, out of non approved sires) they will test it for you for a small fee.

Here is the form for the FHANA horses to be tested FORM (email me if the link doesn't work)
to contact the KFPS directly for non approved stallion offspring (bb1,2, C and D books) please go to www.kfps.nl and contact them.


Dwarfism is not a new thing or a Friesian only thing. Miniature horses have had several Dwarf genes and they were selected for to create the breed. Here is a general article on Dwarfism in horses, including mini's, so not specific to Friesians but there is a Dwarf Friesian photographed on that page so worth a look for information Dwarfism in Horses. Friesians have a specific type called Diastrophia Phenotye.

Breeding and why you should know if your mare is a carrier before picking a stallion for her to mate with
Dwarfism is a recessive gene meaning that the affected horse has to have both Dwarf genes to exhibit symptoms.
Genetically speaking if you breed a non carrier (BB) to a carrier (Bd) each offspring can get 1 of the 2 genes from each parent. So with BB x Bd  you have the ability to get offspring that are BB, Bd, BB, and Bd. So 50/50 chance of having a carrier (Bd) offspring and 50/50 chance of a non carrier (BB).

If you breed 2 carriers (Bd) x (Bd) you have a chance of getting BB, Bd, dB,dd  so you would have a 25% chance of non carrier (BB) 50% chance of carrier (Bd), and 25% chance of affected (dd). It's never recommended to breed carrier to carrier because you have that 25% risk of having an affected/symptomatic offspring. But it's not to say it has never been done, or that it's not going on right now. Testing is very recent and with only a %25 chance of affected foal there is also a chance that 75% of the time the foals were born appearing to be healthy. The only 100 % positive test to know if a Dam and Sire are carriers is to produce an affected (dd) foal.

Dwarfism is not lethal to the horse, it is more inconvenient to that horse. They have shorter limbs with tendon laxity that gets worse with age, rather than getting better after birth. They appear to have larger heads, but they are similar in size to a full grown horse, just on a smaller body. They sometimes have issues with the abdominal cavity sizing and shape that can cause problems as the horse grows to a mature age.  The growth plates of dwarf horses are also affected so they don't achieve full height. The breed standard for a Friesian is 154 min for a mare and have been at and above 170 for some. There are some friesians that are 150cm without carrying the dwarf gene, but a dwarf affected foal will be about 110cm (can vary, records are not kept very well on dwarf average heights). But full expected height will not be achieved by a dwarf affected horse, and other physical abnormalities stated above will also be present.

There is a photo of a 7yo dwarf mare that has a regular size foal at foot as recent as 1995 (there may be other cases of breeding dwarf mares).  So they can grow to be adult horses and as the photo implies, carry foals to term. If breeding  dwarf mare she would be (dd) affected, so you would want to make sure 100% that the stallion is (BB) non carrier. All the offspring would be Bd, so 100% carriers with no affected foals. So mathematically speaking it's possible to breed, but very questionable ethically and scientifically given the rib cage abnormalities, the tendon laxity of the limbs and all the stress of adding the extra weight of a full sized foal.

Here is a link to an article about the gene mapping of the Dwarf gene and some added information about Dwarf Friesians. If the link no longer works please e-mail me for a pdf, I can't upload pdf's to the blog??  ARTICLE

Historically
Firstly, approved stallions are given #'s after their name indicating the order that they were approved in. Friesians are from a very small gene pool that in recent times can trace back to 3 stallions. Tetman 205, Age 168, Ritske 202 P so the gene pool is very small.
But lets go back a bit further and focus on Darfism, the topic of this converstaion.  The following stallions have been known to have produced 1 or more dwarf foals. Prins 109,  Alva 113, Friso 117, Paulus 121, President 123, Nemo 51, Frits, Cramer 136, Elvis 138, Corbus 248, Remmelt 323, Lukas 324.

Some non approved stallions and pure Mares that have produced Dwarf foals but it's un known if the gene comes from their sire or their dam line so it's not conclusive if their sire carries or their dam, but they got the gene from one of them and have produced 1 or more dwarf offspring -  Lyckle B (son of Ulrik 168) and Maurits Friso (son of Dagho 247), 4 mares (by Yjsbrand 238). 2 Mares (by Jochem 259) If you have information on any dwarf offspring or positive mares or stallions please help us share that information.

Current stallions (starting with # 483) have all been tested and reported. Stallions before that are not being reported unless the stallion owner posts it. Mostly because of the EU privacy laws, but also because the last big dna reveal, Red Gene, caused 1000's of loosed breedings for carrier stallions so there is a lot of fear of repercussions of public posting. The tested approved stallions are on my blog pages by stallion #, not all are tested. .

The KFPS IS, yes IS, still approving carrier stallions. It's up to the mare owners to also test so that they know what their breeding risk is. Check out the STALLION LIST to see who of the 483# and higher carries and who doesn't.

 I'm also putting together a list of carrier horses. SO if you have a carrier horse please message me a copy of the papers and what they are carriers for. I will not post the papers just the lineage. Or send the Sire, Dam sire, grand dam's sire, and great grand dam's sire. There is still a small chance the gene came from further back but statistically the carrier would be in that list. For example there is a Carrier A, he's a Sape 381(-) x Thomas 327 x Djurre 284 x Corbus 248. Sape is negative for dwarf, so we know the gene had to come from one of the others. It just so happens that history shows Corbus 248 as a carrier, but that doesn't mean that Thomas and Djurre are not the one's that gave it to the dam. So it would be important for people with mares with Corbus, Thomas and Djurre to get tested. It is still important to test all breeding horses, however some people who are sitting on the fence about testing may get the push when they see their mare's lineage on the list.

The only true + test is a dwarf foal. I would love for people to share those results with us also, but I also hope there are not many out there. If anyone has any first hand photos of a dwarf Friesian horse please share that with me, so we can share as much information as we can. The new tests are great, but the only 100% proof of being a carrier is producing and affected offspring.

Non KFPS dwarf information -
Here is another page with more information on Dwarfism. The one main thing that I would point out is that they state that by crossing Friesians with other breeds we are "spreading" the dwarf risk HOWEVER, other breeds are carriers of the dwarf genes. We just have more people talking about the Friesian's right now. A Friesian x TB produced a Dwarf foal, that is only possible because the TB was a carrier of the same gene disorder as the Friesian. so it will not "spread" it's already out there. PAGE
Even the American Morgan Horse Association is working on Dwarfism testing, showing it's a concern in that breed also LINK