LECTURE XLVII 

 HEAVES 



This is a disease of horses. It is characterized by a peculiar 

 disturbance of respiration, in which although inspiration is 

 about normal, there is difficult expiration, the air being expelled 

 by two distinct movements instead of the normal one. 



True heaves is usually associated with the feeding of consid- 

 erable quantities of timothy and clover hay — especially dusty 

 hay — and it lessens very materially the value and usefulness 

 of horses affected by it. Light feeders are as a rule free from 

 this disorder, while horses that eat hay greedily are most 

 liable to have it. 



In the lungs of horses so affected, the air vesicles are gradually 

 dilated, losing their elasticity; they may even rupture together 

 so as to produce small cavities, from which the air is expelled 

 with great difficulty. During forced expiration, the air may 

 escape into the surrounding tissue. This escape of air from the 

 air cells into the lung tissues (emphysema) usually occurs in 

 connection with heaves, but its relation to the disease is quite 

 problematical. Plainly a horse may have such air leakage with- 

 out heaves. This condition is probably to be regarded as an 

 effect rather than a cause. 



Cause. — Any chronic irritation of the bronchial mucous mem- 

 brane may cause heaves — chronic bronchitis and severe cough, 

 for example, or repeated violent exercise by a horse not in 

 condition. But we may say that the usual direct cause of 

 heaves is the excessive eating of bulky food, especially hay that 

 is overripe and dusty, — or worse, musty. Tame hay cut very 

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

 which rarely, if ever, develops in horses on pasture or that 

 have only bright, wild hay or a reasonable quantity of early-cut 

 tame hay. This disease is said to be almost unknown in arid 

 regions where timothy and clover hay are grown by irrigation, 

 and where such hay is never exposed to dew or rain and there- 

 fore does not develop fungi to a serious extent. Mere bulk and 



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