We have hitherto spoken of the one principal cause of roaring, but, as we have already pointed out, there are others of a less serious character, and some of them amenable to treatment. It will be understood that any obstruction to the free ingress and egress of air in the respiratory passage, and especially that portion of it which extends from the nostrils to the lungs, may have the effect of producing a roaring noise. A horse will roar when any tumour or obstructive thickening exists in the nasal chambers, or from any undue pressure on the windpipe. Roaring may also be induced by pressure on the larynx, by an accumulation of "matter" in the guttural pouches, by an enlargement of the glands of the throat, or by a spasmodic contraction of the muscles. Moreover, it may, and does, too frequently result from distortion of the larynx following the abuse of the bearing rein, but whether this is the explanation or not it is difficult to say.
That grunting is a common accompaniment of roaring is so well known among horse-dealers that they may be seen, in auction sale-yards and other confined places, threatening the animals with a stick to see if they grunt with fear, and pinching the throat to provoke a cough, the quality of which is in a certain measure, and to an experienced man, a guide to the existence of the disease. Though roarers very frequently have this deep cough, which is a mixture of groan and cough, there are many horses only moderately affected with the malady, who do not, and will not, cough when the larynx is pressed, as there are also whistlers who do not grunt on a feint being made to strike them. It has also to be borne in mind that many horses of nervous temperament, and others when out of condition, will grunt on being threatened with a stick, although perfectly sound in the wind.
In this affection the patient, while at rest, shows no symptoms, nor are any awakened, save in bad cases, in the slow paces, and it is not until the animal is galloped, or, in the case of a harness-horse, compelled to draw a load uphill, or move at a quick pace, that the respiratory trouble becomes apparent.
Paralytic roaring usually comes on gradually, and shows but little variation in its severity, and in this respect it differs from spasm of the larynx, which is sudden in its onset, remains only for a brief period, and as suddenly disappears.
If roaring is the result of paralysis of the laryngeal muscles treatment is not hopeful, and to steady its further progress and palliate the symptoms is as much as we may look for.
Various attempts, surgical and otherwise, have been made to afford relief to the disabled organ. The most recent of these consisted in the removal of that part of the larynx (arytenoid cartilage) over which the muscles had ceased to exercise control, and whose displacement constituted the immediate cause of obstruction to the ingress of air in the act of breathing. Although the operation referred to cannot be said to have been followed by an encouraging measure of success it cannot be regarded as an unqualified failure, as in the hands of the writer it has had the effect in several instances of restoring useless animals to a state of usefulness. The method most commonly adopted for aiding respiration in these cases is that of inserting a tube into the windpipe about one-third of the distance down the neck. Through this artificial channel respiration can be efficiently carried on without the objectionable noise and premature distress resulting from the disease, and by its use the animal's services may be considerably prolonged and his comfort under exertion very materially enhanced. It is, however, at the best an unsightly expedient, and not altogether unattended with pain, while sooner or later the irritation induced by the tube will provoke an outward or inward growth of " proud flesh", rendering a further operation, necessary, or maybe the destruction of the animal. All horses suffering from this disease should be kept in high condition. Throwing them out of work and " letting them down" adds considerably to the embarrassment of the breathing, if it does not also expedite the disease. In those cases where the breathing is left defective after an attack of cold, influenza, or strangles, no time should be lost in applying a counter-irritant to the throat, such as mustard or turpentine liniment, and a repetition of the application should be made at intervals for several times. Moreover, paralytic roaring should be anticipated by the early administration of full doses of nux vomica.