Thrush consists in a congested condition of the sensitive frog associated with a discharge from the cleft and a ragged state of the horn. It is mostly seen in the fore-feet, although the hind ones now and again give evidence of the disease.
The causes of thrush are constitutional and local. In regard to the former the malady is found more especially in animals of a plethoric habit, and especially when too highly fed and allowed to lead a sedentary life. Old animals suffer more frequently from thrush than young ones, not so much on account of age itself as the diseases incidental to it. This refers more especially to navicular disease, during which thrush almost invariably •occurs from time to time at longer or shorter intervals. Long standing on hot, decomposing manure, or peat-moss saturated with moisture, is a fruitful cause of the disorder. Bad shoeing, in the course of which the frog is unduly pared and removed from contact with the ground, and allowed to become hard, dry, and shrunken, is perhaps the most common predisposing factor. It often follows a turn out to grass during wet weather.
Wherever it exists it indicates a disordered state of the vascular parts of the foot, and should receive prompt attention.
The presence of thrush is indicated by an offensive discharge from the cleft of the frog. The matter is grayish-white in colour, and varies in consistence from that of cream to that of soft cheese.
Rarely it is of a dark watery character. In the former condition it is chiefly made up of young horn cells mingled with varying small proportions of pus corpuscles, and occasionally with blood. Usually this disease is unattended with lameness, but in some instances it is very marked, and may be severe. Horses with thrush travel badly on rough roads, owing to the tender frogs being brought into contact with stones.
In all cases of thrush the system of shoeing should receive attention, and strict injunctions be given to the shoeing-smith to bring the frog gradually to the ground and remove no part of it save such portions as are ragged and disconnected with the parts beneath. A dose of physic or a course of saline medicine may be given in the case of plethoric animals, and the work should be increased.
As a means of assisting the discharge and bringing about a healthy state of the parts, astringent applications should be made to the frog, after the cleft has been thoroughly freed from dirt, by careful washing with carbolized water. The dressings most commonly used, and which are most effective for the purpose, are sulphate of copper or alum mixed with tar and a little carbolic acid. A solution of chloride of zinc is also a useful application; the ointment of the red oxide of mercury is equally beneficial. Tar dressing is sometimes applied by means of a pledget of tow, and covered over by a leather sole, and if it is required that the horse should work, this protection is in some instances necessary. Besides protecting the diseased part from injury, it has also the advantage of excluding dirt, but it forbids the removal of the application without the removal of the shoe. This difficulty may, however, be in some measure overcome by the use of movable leather pads.