This is a disease in which the air-cells of the lungs are abnormally dilated; the lungs themselves are consequently enlarged or ruptured and their elasticity impaired, as a result of which breathing is carried on with much difficulty and distress.
While the proximate causes are not known with certainty, the remote or contributory ones are generally agreed upon. Hereditary predisposition no doubt conduces to its origin. It is observed to affect heavy or coarse-bred animals more frequently than the better-bred ones. This may be in part due to the fact that the former are more likely to live and work under conditions conducive to the development of the disease than those more carefully housed and fed and maintained for pleasure and sport.
It frequently originates in the excessive use of coarse innutritious bulky food, and especially in connection with greedy feeders. The exclusive use of damaged fodder contributes largely towards bringing about this disease, more particularly in the case of old animals. It is of common occurrence in ponies leading a life of idleness while receiving a superabundance of nutritious and bulky food.
All these facts go to show the disease to be, in a great measure at least, the result of dietetic causes.
The cough is characteristic and different from any other in its prolongation - a double effort in expiration, which is easily seen in a well-developed case but may in others be mistaken for the quick breathing induced by exertion and excitement. When the patient is at rest and subjected to no excitement the cough is rarely heard, but it often occurs at the time of feeding, or follows a full meal and copious draughts of water. The chest sounds are very variable, but in nearly all cases those of the trachea and larger bronchi are exaggerated, and over different areas there is a fine crepitus as well as an increased sound or resonance on percussion. In advanced cases flatulency is a marked symptom, and wind is frequently ejected from behind in the act of coughing. As the disease progresses, and the lungs undergo expansion, the walls of the chest become rounded in consequence of the ribs being forced outward. Premature distress invariably attends upon exertion, and the capacity for work is much abridged. Where work is enforced the body shrinks, while the abdomen becomes perceptibly larger than normal.
In no disease can so much be done for a horse by judicious dieting as in broken wind. Many a subject of it will perform useful work without undue distress for years in the care of a good horseman, the same animal being practically useless when transferred to the care of one who does not prepare and administer the food secundem artem. In these cases it is especially desirable to give nutritious food in small bulk and at comparatively short intervals, so that the patient may be well nourished but never distended. Every particle of dust should be separated from the corn by the sieve or other means, and no hay with a suspicion of must allowed, and even the best should only be given in small amount and always in the form of chaff previously damped in order to ensure proper grinding of the corn. Long hay may be dispensed with altogether, or, if given as an occasional treat, should be first steamed and the animal allowed to eat it at night or at a time when his services will not be required soon afterwards. Linseed is the food par excellence for a broken-winded horse, and although it is found that many tire of it, it must be dished up in different ways and a taste for it cultivated. It is often spoiled in the cooking, being allowed to cake in the bottom of the saucepan, and the novice invariably putting too much linseed in proportion to water and hurrying the process. Linseed-oil and cod-liver-oil in small quantities may be mixed with the food once or twice daily, or every other day; some horses become very fond of both, and show a distaste for their food without it. With regard to medicinal agents, these should be reserved for occasions when climatic conditions or other causes have induced unusual distress. The sedative agents recommended for asthma may be resorted to in this disorder, and usually result in abatement of the symptoms, but the digestive system must be our principal care, and those agents should be chosen which are most likely to disencumber the bowels, restore tone, and increase constitutional vigour. An occasional dose of aperient medicine has a most beneficial effect in relieving the embarrassed breathing, retarding the progress of the disease, and the same may be said of allowing ample time for digestion between feeding and working. The mineral acids and vegetable bitters are especially employed for this purpose, and for allaying the difficulty in breathing much benefit is often obtained from a course of nux vomica and arsenic, the latter being given in solution and in combination with bicarbonate of potash. The good effects of arsenic are apt to cease with its discontinuance, and it is well to resume it again as occasion requires at suitable intervals.