Since rickets is one of the manifestations of a deficiency of vitamin D, it is perhaps a fitting time to discuss its causation and, so far as possible, its treatment, mainly preventative.
Vitamin D plays an important part in the assimilation of calcium and phosphorous from the intestine and their transfer to and from the body and the bones. Although Vitamin D exerts a degree of control over phosphorus and calcium balance within the body, it cannot operate successfully when the relative proportion of these two substances is grossly disturbed. In growing puppies the intake of each—the Ca: P ratio—should be 1•2:I.
When the calcium is in excess of the phosphorus to the extent of 2:I, the calcification of bone in dogs under 18 such cases the administration of vitamins D2 or D3 may exert a moderate degree of control.
The fact remains, however, that cakiferol, as the commonly used form of the vitamin is termed, is not specific against the development of rickets unless the Ca: P balance is kept at the correct level.
An excess of calcium in a puppy's diet may be more harmful than a deficiency, and the custom of feeding more and more calcium to a rickety puppy is far more likely to do harm than good.
The minimum amount of vitamin D2 necessary to avoid rickets when the diet is correctly adjusted, is approximately 20 I.U. per kilogram of bodyweight daily. A kilogram is roughly about 2 lb.
Pure cod-liver oil contains ,about 6,000 I.U. of vitamin D in each fluid ounce of oil.
It seems likely that, apart from dietary discrepancies, a tendency to rickets may have a hereditary background, and in certain strains and circumstances the condition may appear when puppies are correctly fed and exercised and kept in suitable environment. Sometimes these cases become so exaggerated that the puppy cannot stand at all on its forelimbs and nothing appears to be in any sense a remedy.