Livestock breeding programs are designed to select for and maintain certain genetic traits that suit the breeder’s needs. In rare situations, this can mean supporting the existence of a genetic disorder. Such is the case for the myotonic goat, also known as Tennessee fainting or fainting goat.

Myotonia congenita affects skeletal muscles, the muscles that move and support the skeleton. When a myotonic goat is startled, it stiffens up, much like you or I would stiffen should someone sneak up from behind and yell, “BOO!” The difference between the goat and us is that in a split second our muscles begin to relax; the goat’s muscles do not. The animal either remains standing, frozen in one position, or falls to the ground to lie on its side with legs extended, or on its back with hooves stretched to the sky, hence the name. But, fainting is a misnomer. The nervous system is in no way compromised; the animal remains conscious and alert the entire time, and once no more than 20 seconds have passed, it will begin to recover and return to whatever it was doing before the startle, albeit a bit stiffly.

A considerable amount is known about the condition, not necessarily for the goat’s sake, but for mankind’s: roughly 1 in 100,000 humans around the world are believed to be born with the same condition. Studies have shown that a gene, named CLCN1, lies at the core of this disorder. It bears the recipe for a protein essential to normal skeletal muscle function. Chloride ions help muscle cells relax after a contraction, and this protein manages their flow. On a mutated gene, the protein’s recipe is “scrambled” and the flow of chloride ions is not regulated properly. As a result, sodium ions, which activate muscle contractions, build up inside the cells and repeatedly discharge electrical signals, telling the cells to contract.

Relaxation is slow in coming, but eventually arrives. Some goats are only mildly affected by the condition and can remain standing during a startling episode. The more severely affected fall to the ground and remain there until the episode has passed. A goat’s age also plays a role; older animals tend to develop some control and are often observed bracing their legs so as to remain upright.

There is a touch of mystery with this breed, as far as how it came to be. As the story goes, in the 1880s a man by the name of John Tinsley arrived in Tennessee. It’s thought he may have been from Nova Scotia due to his manner of dress and accent, but we don’t know that for sure. Accompanying him were four goats, three does and a buck, that appeared to faint when surprised. Tinsley sold the four to a Dr. H.H. Mayberry and left town, never to be seen or heard from again. Mayberry, curious, made certain the buck was kept busy. Before long his suspicions were confirmed; the strange behavior exhibited by those four was indeed heritable.

At present, myotonic goats are a diverse lot, with variation primarily demonstrated through coloration and size. In the 1940s, a number of comparatively large individuals were transported from Tennessee to Texas and bred for traits that enhanced their meat quality. Today, this Texas strain is renowned for heavily muscled, large individuals (mature does weigh 90 to 130 pounds, bucks up to 200 pounds) with a meat-to-bone ration of 4-to-1 (other breeds average a 3-to-1 meat-to-bone ratio). The standard eastern strain is also considered rather brawny for its size, with mature does weighing 80 to 110 pounds and bucks weighing up to 175 pounds. A miniature strain has been developed as well, with mature individuals weighing as little as 50 pounds and measuring 17 inches at the withers. These mini versions have reportedly been bred to suit a novel pet demand.

The myotonic goat’s heavily muscled conformation is attributed to the disorder, because prolonged muscle contractions lead to skeletal muscle hypertrophy, or an increase in muscle mass. So, it turns out that not only do these animals provide entertainment when you chase them with an umbrella, they are also capable of producing a considerable amount of meat per head.

If you are considering raising and breeding meat goats, myotonic goats might be for you. They are known for their mild temperaments and their unwillingness to climb or jump over fences. The does consistently bear twins or triplets, and many are capable of producing two kiddings per year. They appear to have a strong resistance to parasites and are well-adapted to low-input, forage-based feeding systems. Some folks have crossed the Myotonic goat with the Boer, considered to be the premier meat goat, and have been quite happy with the offspring’s conformation. Of note: hybrids can have myotonia congenita because it is a dominant trait.

The American Livestock Breeds Conservancy (www.albc-usa.org) has placed this breed on its watch list due to its limited geographic distribution and an estimate of less than 10,000 of these goats in the world. If you would like to learn more about this barnyard novelty, visit the International Fainting Goat Association at www.faintinggoat.com or the Myotonic Goat Registry at http://myotonicgoatregistry.net to learn more.

The author, a regular contributor to Farming, is a biologist who lives and farms in Vermont’s Northeast Kingdom.