The excess of organic matter in the soil seems to be a considerable factor. Both Thorburn and Sarginson mention the “mossy” soils and waters, and in Lanarkshire, Scotland, and Westmoreland, England, where they practised, black muck and peats abound. This is corroborated by the prevalence of the disorder in the damp lowlands of Belgium and Jutland, in the Swiss valleys, on the damp lands of New Jersey and the Carolina seaboard, and generally on damp pastures with rank, watery herbage.
When land has been better cultivated and enriched by manure, the disease has in many cases disappeared. This has been observed in England (Sarginson), Wurtenberg, Switzerland, etc. (Leclainche).
Succulent, watery food (potatoes, turnips), have been quoted as causes, as also rank, watery grasses, deficient in nutritious solids, but such food has invariably come from habitual osteo-malacia soils. On the rich, cultivated soils of the Lothians, Scotland, cattle are fed in large numbers on turnips alone, and osteo-malacia and pica are alike unknown. It is often noticed that the fodder grown on particular (osteo-malacia) soils will cause the disease when fed elsewhere, so that the inference is that some agent derived from these soils, and which is destroyed or rendered harmless by cultivation, is carried in the food. It cannot be a mere defect of nutritive matter, as this could be counter-balanced by the simple expedient of consuming a larger ration. Leclainche has seen the disease in its worst form in herds which received a rich and varied ration, while it spared adjacent herds that were kept on rather short rations. Even young plethoric animals suffered badly, though having all they would eat of natural fodders (hay) from districts where the disease was unknown, and in addition grain, linseed cake, cooked legumes and bread. In two neighboring stables, where the stock were kept in identical conditions, receiving the same food, in equal quantity, one was decimated by the malady, while the other was spared (Leclainche).
The affection often prevails on the higher lands, which, beside having the poorer soils, are specially exposed to cold storms and frosts, so that chill enters as an accessory condition. In Westmoreland, England, the river Eden divides the affected from the sound lands; the victims are found on the west bank which receives the cold, east winds, and not at all on the east bank where the warm, soft, west winds prevail. Thorburn noticed that the majority of cases start in spring, when the animals, debilitated by the winter’s seclusion, are exposed to severe vicissitudes of temperature and driving storms, to the strain of parturition, a fresh, heavy milk yield, and moulting.
The presence of a contagion has been suggested, but if this exists it must be habitually introduced in the food or water rather than transmitted from victim to victim. The healthy will often stand beside the diseased for an indefinite length of time without injury, and in certain recent cases a change to an uncontaminated farm, or an abundant ration drawn from such sound soil, will secure immediate improvement and recovery in a few weeks. In view of such prompt recoveries it would be quite as reasonable to suspect some ptomaine or toxin taken in with the food. The question of a microbe or a microbian poison is as yet a mere hypothesis.
Cows become more susceptible with advancing age, and Dengler alone claims to have seen the disease in calves. This is unfavorable to the idea of immunity, and rather favors that of debility or cachexia.
Lesions. These are confined to the bones. Decalcification in the Haversian canals and cancelli, reduces the bony tissue to a thin soft plate. Yet the condition is not constant. Grawitz found no special dilatation of the canals or cancelli in colts. Nessler and others found decrease of the lime salts, Bibra and Grouven detected no marked change, and Hoffmann and Begemann found an actual excess of phosphates. Doubtless the specimens selected and the stage of the disease, whether in active progress or during convalescence, may somewhat explain discrepancies. The fat cells increase in the cancelli, with more or less hyperæmia, and even blood staining as the disease advances, the bone cells become less branching, and there may be gelatinoid exudates. The resistance of the bone is diminished, it may be indented with the finger, or scraped off with the nail, or cut with a knife. It breaks under a slight strain, and is easily crushed under the weight of the animal so that fractures and distortions of all kinds are met with. In breeding cows the earliest and most marked lesions are in the pelvic bones, but fractures of the bones of the limbs are common.
Symptoms. Poor condition or even emaciation, with very visible projection of the bones is common. The coat is rough, the skin tense, inelastic and hide bound, appetite variable, sometimes impaired, and nearly always perverted so that the patient will lick the manger continually or pick up and chew all sorts of objects, bones, leather, articles of clothing, pieces of wood or iron, stones, etc. The amount of food consumed may, however, be up to the normal. The most marked feature is the difficulty and stiffness of locomotion. The patient lies most of the time, rises languidly and with difficulty and moves the limbs as if each were a rigid post without joints. The hocks will knock together, and the restricted movements of the joint are often attended by cracking. Yet appetite, temperature and yield of milk may remain normal.
Later appetite and milk secretion fail, temperature rises a degree or two, the animal refuses to rise, remaining down twelve to twenty-four hours at a time, and rising first on the hind parts, and remaining on the knees for a length of time, moaning and indisposed to exert herself further. Many cases at this stage begin to improve and may get well in five or six weeks. Some will remain down for several weeks and finally get up and recover. With constant decubitus however, the animal falls off greatly, becoming emaciated and weak, the appetite may fail altogether, and the patient is worn out by the persistent fever, nervous exhaustion and poisoning from the numerous bad sores. Abscesses, sloughs and fistulæ are common over the bony prominences.
It is in these last conditions above all that fractures and distortions of the pelvic bones and less frequently of the bones of the legs occur. They occur earlier as well in connection with falls, blows, crowding by their fellows and sudden active movements of various kinds.