166 COMMON DISEASES. 



HEAVES. 



Definition. — A disturbance of the process of respiration, char- 

 acterized especially by easy inspiration and difficult expiration, the 

 latter being accomplished by two distinct movements. It is usual- 

 ly conceded to be an indirect result of a disturbance originating 

 in the stomach, and affecting the lungs through the pneumogastric 

 or tenth cranial nerve, from which nerve both these organs receive 

 a portion of their nerve supply. 



This disease very materially lessens a horse's value and use- 

 fulness. Horses so affected are often unthrifty by reason of 

 chronic indigestion. Light feeders are usually free from this dis- 

 ease. The air vesicles are gradually dilated, losing their elasticity, 

 and even rupturing together so as to produce small cavities from 

 which the air is expelled with great difficulty. The air may in 

 this way escape into the interlobular tissues. 



Cause. — Generally conceded to be a reflex disturbance 

 through a stomach branch of the tenth cranial nerve, which nerve 

 also supplies in part the heart and lungs. We may say that the 

 direct cause of this disease is excessive eating of bulky food, 

 especially hay that is over ripe and dusty. Tame hay that is cut 

 very ripe, and dusty clover hay are both prone to cause this 

 trouble. Heaves rarely, if ever, develops on horses in pasture or 

 that have only wild hay, or reasonable quantities of earlv cut tame 

 hay. 



Symptoms. — A peculiar explosive cough usually appears be- 

 fore respiration is much disturbed. Later on it is noticed that 

 exercise produces marked difficulty in breathing, the inspiration 

 being quite normal and the expiration being difficult. The air is 

 expelled in two efforts, the latter portion of the tidal air being ex- 

 pelled by a special effort of the abdominal muscles. Over feed- 

 ing increases the difficulty. Some cases of heaves may he dis- 

 guised temporarily by the use of drugs and feeding on concen- 

 trated food. The trick may be detected by allowing the horse a 

 hearty feed and then giving violent exercise, or even by the ex- 

 ercise without the special feed. 



It is usually easy to distinguish between heaves and roaring. 

 The latter is a disorder of the larynx due to paralysis of one of 

 the laryngeal cartilages. It is shown by the abnormal sounds 



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