Taken from an article from Dr Phil Sponenberg which I felt explained the Myotonic goat well, he writes:
The unique myotonic breed first enters historical note in the 1880s, when a farm labourer arrrived in the middle of Tennessee with four of these goats and a zebu cow in tow. The labourer, Tinsley worked in the area for a few years and then moved on. His employer, Dr Mayberry, purchased the goats and their offspring. This is the beginning of the breed, although the ultimate origin of them is likely to always remain a mystery. They don't appear to have surfaced elsewhere in the world, but certainly must have originated somewhere.
In Tennessee these goats were developed as a local meat source, valued for their environmental adaptability. They were easy to fence in because they jump and climb poorly,if at all. This alone makes then unique among goats. In the 1950s a few Texas ranchers bought some, moved them home to Texas, and began using them as a local source of meat. The Tennessee and Texas goats spring from a single source; remarkable similarities are present throughout both of these major branches of the breed.
A trend in American agriculture in the 1980s began to seek out and popularise a number of exotic breeds and species of animals- including myotonic goats. As popularity increased, it became prudent to have registries to track the breed and its breeding. A few registries remain, and the main ones today are the Myotonic Goat registry and the International Fainting Goat Association. These were both developed to track purebred goats, which is an important goal as not all goats with myotonia are purebred myotonic goats. For the breed to be useful it must protect its purity; this is the goal of the registries.
The registries are reasonably inclusive, and recognise that many foundation herds of excellent goats lie behind the present breed. No single strain is able to claim to be the oldest, best or purest any more strongly then could proponents of the remaining strains.While size has and does vary, ethical breeders have never resorted to crossing to decrease or increase size, but has instead worked within the breed to achieve a purebred that fits different desires across breeders.