OSTEOPOROSIS, OR BIGHEAD. 557 



become swollen and deformed, which, together with the bulging of 

 the bones under the eyes, gives a good illustration of the reason for 

 the application of the term bighead. 



Other bones of the body will undergo similar changes, but these 

 alterations are not so readily noted except by the symptoms they occa- 

 sion. The alterations of the bones of the spinal column and the limbs, 

 while difficult of observation, are nevertheless indicated by the reluc- 

 tance of the animal to get up and the desire to remain lying for long 

 periods of time. The animal easily tires, moves less rapidly, and if 

 urged to go faster may sustain a fracture or have a ligament torn from 

 its bony attachments, especially in the lower bones of the leg. An 

 affected horse weighing 1,000 pounds was seen by the writer to frac- 

 ture the large pastern bone from rearing during halter exercise. 



The animal becomes poor in flesh, the coat is rough and lusterless, and 

 the skin tight and harsh, producing a condition termed "hidebound," 

 with considerable "tucking up" of the abdomen. The horse shows a 

 short, stilted, choppy gait, which later becomes stiffer and more 

 restricted, while on standing a position simulating that in founder is 

 assumed, with a noticeable drop to the croup. The animal at this 

 stage usually lies down and remains recumbent for several days at a 

 time. Bed sores frequently arise and fractures are not uncommon in 

 consequence of attempts to arise, which complications, in addition to 

 emaciation, result in death. 



The disease may exist in this manner for variable periods extend- 

 ing from two or three months to two years. The termination of the 

 disease is uncertain at best, but is likely to be favorable if treatment 

 and a change of feed, water, and location is adopted in the early stages 

 of the malady. 



LESIONS. 



As has been stated, the bones are the pnncipal tissues involved. 

 The nutrition of the bone is disturbed, as is indicated by the dimin- 

 ished density or rarefaction of the bony substances, the increase in 

 the size or widening of the Haversian canal and the medullary cavity, 

 and the enlargement of the network of spaces in the spongy tissue, the 

 absorptive changes following the course of the Haversian system. In 

 this process of absorption there are formed within the substance of the 

 bone areas of erosion, indentations, or hollow spaces of irregular shape. 

 These spaces increase in size and become confluent, causing an appear- 

 ance resembling some varieties of coral. The affected bone may be 

 readily incised with a knife, the cut surface appearing finely porous. 

 This porous area is soft, pliable, and yields easily to the pressure of 

 the finger. It has been shown by chemical analysis that the bone of 

 an osteoporotic horse, when compared with that of a normal horse, 

 shows a reduction in the amount of fat, phosphoric acid, lime, and 

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