OSTEOPOROSIS— OSTEOMALACIA 211 



Occurrence. — ^The disease is not uncommon among horses in 

 certain regions of the United States. Along the river valleys 

 of the Middle West numbers of cases occur. On the higher 

 ground and especially in the limestone districts it is of rare 

 occurrence. It is probably more frequently seen among city 

 than coimtry horses. Cattle are also affected especially dairy 

 cows. In Europe the disease seems most common among 

 cattle. It is occasionally seen in sheep and swine. Osteo-- 

 porosis is a disease of adults resembling rachitis in the young 

 animals. 



Etiology. — ^The causes of osteoporosis are not well under- 

 stood. It is probably due to infection as the anatomical 

 changes present in the affected bones are of the character of 

 infectious inflammation. Predisposing causes are pregnancy, 

 excessive lactation in cows, lack of lime in the food and soil, 

 darkness, dampness and poor ventilation in the stables. 



Necropsy. — The postmortem changes consist in an inflam- 

 matory hyperemia with decalcification and softening of the 

 bone and marked dilatation of the Haversian canals. The 

 bones affected are brittle and fracture spontaneously. They 

 are also enlarged, extremely light in weight, the cortical sub- 

 stance abnormally thin and the medullary cavity greatly 

 increased. The medulla appears as a reddish, gelatinous mass. 

 The bones chiefly involved are the pelvis, femur, facial 

 bones and mandible. However, it may affect any bone of 

 the skeleton. Healed fractures are not uncommonly noted. 



Symptoms. — While in some cases the affection of the bones 

 is preceded by digestive disturbances and symptoms of viti- 

 ated appetite ("licking disease"), most commonly the first 

 symptoms are disturbance in locomotion, the patient becom- 

 ing lame or stiff and experiencing difficulty in getting up or 

 lying down. If the maxillae are involved there may be diffi- 

 culty in mastication. Quite commonly the horse is thought 

 to be suffering from rheumatism which usually affects the 

 stifle or fetlock joints. After rest the symptom of lameness 

 may disappear to recur again, but in a different joint, when 

 the animal is retm-ned to work. In other oases the owner 

 complains of the horse eating slowly and losing flesh~ and 

 requests that its teeth be dressed. In advanced cases a 



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