The diseases affecting bony tissues may broadly be divided into local and general. Local diseases like ostitis, periostitis, necrosis, fracture, etc., are somewhat rare, and are less important in cattle than such general diseases as rachitis and osseous cachexia.
Rachitis is a disease of young animals, and occurs during the growing period. Osseous cachexia is a disease of adults. Nevertheless, there is a relationship between these two morbid conditions, for they frequently co-exist in one family. Moreover, brood mares and cows suffering from osseous cachexia give birth to foals and calves, which, if left with their mothers, almost inevitably become rachitic.
The general characteristic common to both rachitis and osseous cachexia consisting in diminution in the normal proportion of mineral salts entering into the constitution of the bone, numerous theories have been advanced to explain this irregularity in nutrition.
The theory of insufficiency is one of the oldest. It presupposes that the young animals’ food contains insufficient mineral salts necessary for building up the skeleton, hence rachitis; or again, that the daily food of the adults does not afford sufficient mineral salts to compensate for the normal transformation which is continually going on within the organism, and for the direct losses which occur through the medium of the urine, milk, etc.
This extremely simple theory appears perfectly logical, but unfortunately does not fit in with all the observed facts. In reality, rachitis attacks children whose supply of milk, from a chemical point of view, leaves nothing to be desired. The same is true of animals, particularly of young pigs. The so-called “acid theory” has therefore been advanced to explain the points left obscure by its predecessor.
The acid theory. According to this theory, the food may contain more than sufficient mineral material without, however, preventing the development of rachitis or of osseous cachexia.
In animals suffering from digestive disturbance the alimentary tract may become the seat of excessive fermentation or of changes in secretion. There is thus produced an excess of lactic acid which passes into the circulation and accumulates in the tissues, checking the processes which end in ossification or, in the case of adults, even leading to decalcification.
It seems fairly well established that experimental administration of lactic acid to animals causes diminution in the quantity of calcium salts contained in the bones (Siedamgrotsky, Hofmeister). On the other hand however Arloing and Tripier failed to produce rachitis experimentally.
Bouchard revived this theory in a somewhat modified form. He considers that calcium salts are absorbed as carbonates and chlorides and phosphoric acid as phospho-glyceric acid. The reaction which these compounds undergo within the organism ends in the formation of the phosphate of calcium necessary to ossification, but this “phosphate of ossification” cannot be deposited if the organism contains an excess of lactic acid.
Theory of inflammation. A third theory which until now has received very little support is that called the theory of inflammation. The general lesions which characterise rachitis are regarded as resulting from primary attacks of ostitis and osteo-periostitis. The cause of these forms of inflammation is not suggested.