Here you go!Here is a good article about riboflavin deficiency which can cause walking on hocks, curled under toes, and numbness: http://www.thepoultrysite.com/publications/6/diseases-of-poultry/217/vitamin-b2-deficiency/
I agree with Ronott about vitamins. A,E, and D are all fat soluble (unless using a water soluble E.) Those can be overdosed. I am not aware of the vitamin D used in rat poison, since I thought that was actually coumadin, a blood thinner. Vitamin D is used to counteract coumadin.
In dealing with a balance issue or walking on hocks, I would concentrate on B complex vitamins, which are hard to overdose because of being water soluble. Make sure that your vitamins contain riboflavin (B2,) and you can even dissolve 1/2 B Complex tablet into the food once a day. Beef liver chopped and kept in the freezer, and a small amount given once daily is a great source of B vitamins. If using NutriDrench the maximum dose is 3 ml once a day. Just read the labels.
Toxin
Cholecalciferol (Vitamin D Rodenticides)
Source
Quintox, True Grit Rampage, Ortho Rat-B-Gone, and cholecalciferol as a livestock feed additive. Vitamins contain Vitamin D, such as Viactiv. Cestrum diurnum (Day Jessamine) and Solanum malacoxylon plants also are a source of cholecalciferol.
General Information
Cholecalciferol poisoning can occur by ingestion of a pesticide, or in farm animals, by the ingestion of an overdose of a feed additive containing cholecalciferol. It causes a drastic increase in the calcium level, which causes heart problems and bleeding secondary to mineralization of the vessels, kidneys, stomach wall, and lungs. This mineralization can also cause kidney failure. This toxin is very lethal.
One IU of vitamin D3 is equivalent to 0.025 mcg of cholecalciferol.