Canine Dwarfism and Equine Dwarfism

To understand the nature of equine dwarfism we need look no further than the dog breeds. Centuries of animal husbandry and selective breeding have created several distinct breeds of dwarf dogs showing both the brachiocephalic and achondroplastic dwarfism.

Understand the parallels between equine and canine dwarfism will help you understand the issues involved with the health are breeding of miniature horses.

Brachiocephalic dwarfism in dogs

Brachiocephalic traits have been deliberately bred into many animal species, most notably the short-muzzled dog breeds. The brachiocephalic dog breeds include:

• Pug
• Basset hound
• Shih Tzu
• Boston Terrier
• Bulldog
• Pekinese
• Pomeranian

Over the centuries humans have developed dog breeds with distinct brachiocephalic traits, quite similar to the horses.
 

Facial anomalies in the brachiocephalic dwarf dog (Pug)

Physically, the domed head and the mashed-in look of the nose bridge of the Pug is distinctly similar to those of brachiocephalic dwarf horses. The characteristic “strong jaw” of the bulldog is the exact same trait as the monkey jaw in miniature horses.

It is also noteworthy that all of these dog breeds have reproductive problems associated with dystocia (difficult birth), just like the miniature horse breeds.

Achondroplastic Dog Breeds

In other dog breeds, we see the achondroplastic dwarf trait, most notably in the Dachshund, but also including the Welsh Corgi. The short limbs and tiny ears are a hallmark of this type of dwarfism.

Short limbs of the Facial anomalies in the achondroplastic dwarf dog (Dachshund)

Breeding parallels between canine and equine dwarfs

Sadly, some breeders of miniature horses report a typical loss of up to 50% of their foals each year. The foal losses are blamed in dystocia (abnormal placement of the fetus), red-bag deliveries and late-term abortions. We find the same types of birthing problems in dwarf dogs, suggesting that there are parallels in inter-species dwarfism and reproduction.

Dystocia is especially problematic in the dwarf dog breeds, especially the Boston Terrier, Bulldog, Welsh Corgi and Pekinese dog breeds.

Some miniature horse breeders can use the same techniques used by dog breeders to reduce the likelihood of loosing a miniature horse foal. These techniques include the creation of a clean room for field caesarian sections and the stocking of full equine hospital equipment. According to experts, some major miniature horse breeders invest in this equipment while the smaller breeders prefer to send their mares to an equine hospital shortly before foaling time.

The basset hound is another example of brachiocephalic dwarfism. Just like miniature horses, basset hounds physical anomalies make it difficult, if not impossible for them to deliver puppies normally.

The dwarf horse has far more observable anomalies than the achondroplastic dwarf, and this type of dwarfism is far more disabling, primarily because of the severe leg deformities and nasal constriction.

Equine brachiocephalic dwarfism

Like all forms of dwarfism, brachiocephalic dwarfism may range from very mild to life-threatening.  According to a long-time breeder, and some of the more severe dwarfs are killed by their breeders at birth because they are embarrassing to their breeding programs.  Equine dwarfism photos are published at Horsie Heaven. Common traits of the brachiocephalic dwarf include:

• Facial Anomalies – These problems include a bulbous head which gives the face a dished appearance and a flat nasal bridge with constrained passages, similar to the mashed-in face of a Pekinese dog.
   
• Bad legs – These problems include enlarged leg joints, twisted legs and severe fetlock and pastern deviations.
   
• Dental problems – The most common problems include a severe under-bite (monkey jaw), and retained caps, a condition where the baby teeth are retained after the adult teeth have erupted.
   
• Spinal Issues – Common traits include protruding spinal vertebrae, a roached (hunched) back or a very short neck.

A Brachiocephalic dwarf horse

The dwarf pictured above is a minimal dwarf horse. He has a severe under-bite and a protruding backbone, but has sound legs has the life expectancy or a normal horse.

Again, these traits are mutually exclusive and each trait may vary in severity. The factorial interaction of the 36 genes contributing to equine dwarfism creates thousands of variations on brachiocephalic dwarfism, ranging from a minimal dwarf with sound legs and a short neck, to a grossly-deformed “monster” with nostrils immediately under their eyes.

We also see severe lag deviations in these dwarfs and expensive surgery and farrier care are required to correct the condition.  Sadly, it is rumored that some breeders will kill their ponies rather than undertake the high expense of having them them treated.
 

Common leg deformities in a Brachiocephalic dwarf horse

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