Dwarfism in Miniature Horses

Because the Miniature Horse is a “size” breed, early breeders were more concerned with size than anything else. Whenever you breed for a single trait at the expense of everything else, you’re bound to find some undesirable outcomes. With Miniature Horses, it was dwarfism.

Because of their tiny size, dwarfs were used as breeding stock in an effort to downsize the offspring, and the genes were passed along. Today, even with decades of careful breeding, dwarfs can pop up in even the most careful breeding programs, though genetic testing is beginning to take the guesswork out of the equation. Unfortunately, there are unscrupulous breeders and uneducated enthusiasts who think that the tiny size of dwarfs is desirable, and it is not uncommon for them to fetch top dollar at some exotics auctions. Dwarfs are tiny, but they have a myriad of health concerns due to their genetic disorder. They require a lifetime of careful care, are prone to painful joint issues, and have a dramatically shortened life expectancy. Dwarfs are not the right choice for a newcomer to horse care.

Signs of Dwarfism

Dwarfs generally have shortened limbs and neck, a distended abdomen, and a domed forehead. Their nostrils tend to be too far up their face, and they are prone to angular limb deformities, sometimes very severe. An underbite is very common. Some horses show minimal signs of dwarfism, but even these should not be bred to avoid producing a dwarf.

Types of Dwarfism

There are four identified and testable types of dwarfism in Miniature Horses, though there could still be more to discover. One of these results in mid-term abortion, but the other three can produce viable foals with dwarfism. The currently identified strains are all recessive, which means that they need to have a copy of a dwarfism gene passed on from each parent in order for the dwarfism to be expressed.

Health Concerns

In addition to the obvious issues of painful and eventually arthritic joints as a result of the limb deformities, a dwarf has an increased risk of developing breathing issues due to the deformed head shape and nasal cavities, as well as systemic problems caused by squishing normal sized organs into a small body cavity. Dental care is also a concern, with, as previously mentioned, a severely undershot jaw being a very common symptom that can cause issues with eating and dental maintenance. Dwarfs have a dramatically abbreviated life expectancy, and their quality of life must be carefully monitored. While dwarfs are known to be quite docile and friendly, it is not uncommon for people to mistake their good nature for the fact that they are simply not well enough to protest or move away. Despite their myriad health concerns and a common misconception to the contrary, dwarfs are fertile, their foals will also be dwarfs, and delivery will be hugely dangerous for them. There should be no possibility of pregnancy.

Prevention and Testing

In the past, breeders’ efforts to avoid producing a dwarf foal were limited to careful breeding of only those horses without any dwarf characteristics and hoping for the best. When dwarfs were produced, depending on the breeders, they would either not repeat the cross, or remove one or both horses from their breeding program. Today, we do have the option of testing for the known dwarfism genes, which allows us to make more educated breeding decisions. If you get your results back and your horse is positive for one of the mutations, that doesn’t necessarily mean you have to automatically eliminate the horse from your breeding program if there are lots of other desirable characteristics. What you will have to do is only ever cross with horses that are also tested and are negative for the any of the mutations. This way, you can be assured that your foal won’t be a dwarf. If you know that your foal has one parent that is a carrier, it’ll be necessary to test the foal as well, as the carrier parent will pass on that recessive gene 50 percent of the time and you’ll need this information for future breeding decisions. Testing for the dwarfism mutations is still a relatively recent development, but more people are starting to test, and more horses being advertised as N/N for the dwarfism panel. Testing is done through the University of Kentucky and will give you a lot of peace of mind when making your breeding decisions.

Tough Decisions

Should you have a dwarf foal born, you have a responsibility to ensure the horse has as pain-free a life as possible. Depending on the severity of the deformities, many dwarf foals are euthanized at birth, while others survive for only a few months before their physical ailments become so great that humane euthanasia is the only option. Some, with exceptional care, have a comfortable life for many years. Only you can decide what is right for yours, but it is your responsibility to protect a dwarf from people who don’t understand the special needs, and an auction is no place for a dwarf Miniature Horse.


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