The better management of horses has greatly reduced the number of cases met with, but the condition can scarcely be forgotten by anyone who has witnessed it. It is an almost precisely opposite state of the blood to that described under the heading of ansemia. The subject is usually fat, or else has been so suddenly placed upon a too liberal diet that the circulatory fluid has become rapidly loaded with red corpuscles, and what has probably more to do with the symptoms presently to be described is the accumulation of effete material in the blood which the emunctories fail to eliminate. Urea and other deleterious products of combustion circulate in the blood stream, producing effects varying with the quantity, and the idiosyncrasy of the individual.
Idleness conjoined with over-feeding upon highly nitrogenous food. Close stabling and want of exercise. Inactivity of the liver, kidneys, and skin; but these latter are usually secondary and dependent on bad hygienic conditions.
Trembling and blowing are sometimes present, but closer inspection shows, in addition, engorgement of the vessels of the conjunctiva and more or less cerebral disturbance, denoted by excitement, followed sooner or later by a dull, heavy expression. The pulse is full and hard at one time and quick and irritable at others. The extremities are variable as to temperature, but the ears are commonly hot and the appetite fastidious or altogether in abeyance.
This is one of the few disorders for which the veterinarian may, with advantage, resort to venesection. It is attended with immediate relief of the more pressing symptoms. Where the disorder is not of an urgent character, bleeding will be dispensed with, and reliance placed upon an aloetic ball, a spare diet, and, as soon as permissible, exercise followed by regular work. There can be little doubt that this malady is often mistaken for pulmonary congestion. A horse that has once suffered from plethora should receive special care as to diet when his services are not in demand, and laxative foods, as bran, more frequently given; for in keeping the bowels active safety is found.