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THE CAUSE OF THRUSH, AS WITH MOST OTHER HOOF PROBLEMS, LIES IN REDUCED CIRCULATION AND THUS RESTRICTED BLOOD SUPPLY TO THE HOOF.
Even in the old books on hoofcare, thrush was depicted as a contracted hoof. In a contracted hoof, the lateral walls are parallel to one another, ie. they do not diverge groundward, as would be the case in a healthy hoof. When a healthy hoof becomes contracted, the sheets of sole horn are compressed laterally, at the expense of the frog, which is pinched.
A cross-section through a healthy and a contracted hoof show the changes inside the hoof. The horn pressure against the transition between sole and frog corium (where, in the area of the heel, the bars are formed) flattens the corium and so impedes circulation in the region of the frog sulci. Too little oxygen and nutrient rich blood reaches the frog corium, and too little horn is produced in relation to the constant decomposition of the soft horn by bacteria. The frog becomes weaker and weaker. With dehydration of the hoof, cracks appear in the thin sheet of soft horn, possibly in as far as the corium, which then become infected. Wound discharge is a slightly alkaline environment and further helps the putrefactive agents. Because of the poor blood supply, the corium cannot heal. The frog region is sensitive to pressure to the point of lameness. The situation cannot, of course, be improved by drying and immobilisation (stall rest), but rather only by the removal of the cause, ie. the contraction of the hooves. The contracted hoof must therefore be brought to a normal, open shape, in which the frog corium will again be optimally supplied with blood. It does not help--as is commonly done--to use circulation-enhancing or anit-infectious agents, intravenously or through the alimentary tract, because they do not reach the problem area on account of the reduced blood supply.
To achieve the opening of contracted hooves, optimal living conditions for the horse are necessary (freedom of movement 24 hours/day), as well as frequent, knowledgeable hoofcare and proper trimming.
IT IS OBVIOUS THAT THRUSH CANNOT BE HEALED THROUGH SHOEING.
With friendly permition by DVM H. Strasser
Copyright 2005 Dr. vet. med. H. Strasser
Ed & Trans. Sabine Kells
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