In England broken wind is much less prevalent than on the European Continent and it is deserving of notice that lucerne and sainfoin hold no place among the British green crops, that red clover hay is only exceptionally met with owing to the amount of land that is clover-sick, that natural hay is largely used, and that when horses are largely fed on hay it is qualified by such laxative agents as turnips, carrots, beet, etc.
All this throws light on the immunity of horses on our western prairies and plains. Feeding on the indigenous grasses fresh or made into hay, they are saved from the noxious influence of those artificial products which are found in all countries to determine the development of broken wind. It needs not that we adopt the popular notion that any special plant growing in these pastures ensures the safety of the equine races. It is merely a repetition in the Western Hemisphere of the experience so long before obtained in the case of Spain. Parallel with the progress of cultivation in our western lands, we see this malady advancing. Fifty years ago it was virtually unknown in Michigan and adjacent states whereas now these states can almost emulate New York in the relative number of their victims. It must not however be supposed that this cultivated fodder is the sole cause of the westward march of this malady. With improved agriculture have come better roads, spring wagons and driving at a pace which was comparatively unknown to the early settlers.
In California the condition of Spain was for long pretty accurately repeated. With no winter worthy of the name, troops of horses were left at pasture throughout the whole year and those that were stabled subsisted chiefly on natural hay in which the indigenous grasses were commingled with white—but no red—clover. California long retained the reputation of having no broken winded horses.
In our Eastern states where the disease was thirty years ago so notoriously prevalent, the fields of luxuriant red clover might well have excited the envy of the English farmer. The hay made from this, full of seed and dust was given without stint to the farm horses, which during the rigor of the winter were often shut up in stable for a length of time continuously and dangerously gorged themselves with this provender. In the Eastern States with a steady falling off in the red clover, there is also a corresponding reduction in the number of cases of heaves. The grain allowed them, a mixture, supposed to consist of Indian corn, oats and buckwheat, given as a dry coarse flour, was little calculated to counteract the effects of the clover hay, and the entire absence of turnips and other succulent roots as a farm crop precluded their use as a preventive of the malady. We need not forget the prevalent ambition to possess a fast trotter, nor the effect of the climate on the air passages (See chronic bronchitis) in estimating the causes of this malady in the Eastern states.
The mere overloading of the stomach is a potent cause of the development of heaves. The horse is above all other animals compelled to undergo hard work on a full stomach. Coleman cites the experience of the coaching days when each horse had 20 lbs. of oats daily and not more than 5 lbs. of hay with no water before work. These horses were driven fast for long stages yet they never contracted broken wind under this treatment. Farmers’ and millers’ horses on the other hand were most subject to the disease because gorged continually with hay chaff and mealy food, and worked in this condition. “Nimrod” who confirms Coleman’s statement says “I have taken some pains to ascertain this fact by my own personal inquiries. One proprietor who has nearly fifty horses at work—many of which are in as fast coaches as any that travel on the road—assured me lately that he had not a broken winded horse in his yard; whereas before he stinted them in their hay he generally had one to five in that state.” Percivall testifies to its comparative infrequency in the English cavalry horses, which have their diet carefully regulated. Hay musty from bad harvesting or other cause and such as is rank from growing in low wet localities are caeteris paribus more injurious than good hay.
Every day observation shows that driving a horse upon a full stomach often causes broken wind and nothing will more surely aggravate it, when it does exist. The same remark may be made of the drinking of large quantities of water after feeding and just before going to work. Gross feeders are above all others the subjects of the complaint.
The question arises how a disturbing cause operating directly upon the digestive organs should affect the respiratory, in such a marked and permanent manner. It cannot be because of the gastric and abdominal distension since pregnant mares though in a state of much greater plentitude, are not thereby rendered liable to broken wind, and if they have previously suffered from this infirmity, the symptoms are usually less marked when breeding. The explanation first advanced by Dupuy appears to be the correct one. The lungs, the stomach, and certain other organs derive innervation from the vagus nerve, and certain disturbances of the stomach and intestines so impair the function of this nerve that the lungs are affected, at first functionally and afterwards structurally. In support of this view is the fact that broken wind is usually associated quite as much with digestive as respiratory derangement. The horse though a heavy feeder becomes unthrifty, hidebound and emaciated; his dung is passed in an undigested state like so much chopped straw, and flatus is continually passed from the bowels. Indeed the almost incessant passage of wind and fæces, during the first mile or two of a journey, is a disgusting evidence of the malady. The power of doses of shot, fat and other agents to temporarily allay the symptoms may be held to point in the same direction.
Beside causes operating on the side of the digestive organs others undoubtedly superinduce the disease, and among these severe exertions and chronic bronchitis ought to hold prominent positions.
Overexertion induces overdistension and rupture of the air cells by the forced retention of air within the lungs, by the closure of the glottis, while the chest is strongly compressed by the respiratory muscles. It is an essential condition to all severe exertion in man that the breath should be held, and though the horse appears equal to the same efforts of draught after the operation of tracheotomy has deprived him of the power of holding the breath, yet he would seem to be sooner exhausted (Goubaux, Colin, Bouley), from which it may be inferred that this power is frequently exercised, and it probably always is in any sudden severe effort as in starting a heavy load, or jumping a five-bar gate. This retention of air in the lungs during violent compression of the chest walls is precisely the condition met with during an access of coughing, and in both cases alike there is the tendency to overdistension of the minute tubes and air cells until they have lost their power of contraction, or they may even give way and allow the air to pass out and lodge in the lung tissue.
Another mode in which violent effort injures the lungs is by the rapid and continued inhalation of great quantities of air during rapid breathing, so as to dilate the lungs suddenly to their fullest extent. Sometimes from irregular distribution of the ærial current or from the want of tone in a particular part of the lung that gives way under the pressure and the air cells become overdistended or ruptured. This condition is especially met in the more rapid paces. It is well exemplified in the results of the deep breathing after cutting the vagi nerves.