I'm not kidding when I say that Tonka is going on the equine version of the Atkins diet. There is a condition called EPSM or Equine Polysaccharide Storage Myopathy that is especially common in draft horses and crosses. We have no clue what type of horse Tonka is (when people ask I answer "a big grey one"), but his thick build suggests that he has draft blood. More importantly, he has some of the symptoms associated with EPSM -- poor hind end muscling relative to his front end, and a stiff hind limb gait. Once again, the culprit is carbohydrate. Unused sugars are stored a glyogens in the muscle, most of which is found at the front of the horse. Because horses rely mostly on their front half to get around, the front end musculature remains well-developed while the rear end wastes away in a vicious cycle. This photo shows an extreme case:
The suggested approach is to replace energy from carbohydrates with energy from fat. Lots and lots of fat in the form of plain old vegetable oil or fat-concentrated feeds. Again, hay/forage with minimal sugar is the foundation of an EPSM diet. For now I'm planning to buy a big 'ol bucket of canola oil at Costco so that I can pour a bit into his daily hay rations. Here is the same horse after a year of high-fat, low-carb dieting:
Photos and the gist of the information come from here. Thank goodness for the internets!