Causes.—­This condition is purely a physiological, and not a pathological one, and the words of its more common name, ‘grass rings,’ sufficiently indicate one of the most common causes.  Anything tending to an alternate increase and decrease in the secretion of horn from the coronet will bring it about.  Thus, in an animal at grass, with, according to the weather conditions, an alternate moistness and dryness of the pasture, with its consequent influence on the horn secretion, these rings nearly always appear.  The effects of repeated blisters to the coronet make themselves apparent in the same way, and testify to the efficacy of blisters in this region in any case where an increased growth of horn is deemed necessary.  From this it is clear that the condition depends primarily upon the amount and condition of the blood supplied to the coronary cushion.  Thus, fluctuations in temperature during a long-continued fever, or the effects of alternate heat and cold, or of healthy exercise alternated with comparative idleness, will each rib the foot in much the same manner.

Treatment.—­The condition is so simple that we may almost regard it as normal.  Consequently, treatment of any kind is superfluous.  Where constitutional disturbance is exerting an influence upon either the quality or quantity of the blood directed to the part, then, of course, attention must be paid to the disease from which it is arising.

F. THE HOOF WITH BAD HORN.

(a) THE BRITTLE HOOF.

Definition.—­As the name indicates, we have in this condition an abnormally dry state of the horn.

Symptoms.—­These are obvious.  The horn is hard, and when cut by the farrier’s tools gives the impression of being baked hard and stony, the natural polish of the external layer is wanting, and there is present, usually, a tendency to contracted heels.  With the dryness is a liability to fracture, especially at points where the shoe is attached by the nails.  As a consequence, the shoes are easily cast, leading to splits in the direction of the horn fibres.  These run dangerously near the sensitive structures, giving rise in many cases to lameness.  Even where pronounced lameness is absent the action becomes short and ‘groggy,’ and the utmost care is required in the shoeing to keep the animal at work.

Causes.—­To a very great extent the condition is hereditary, and is observed frequently in animals of the short, ‘cobby’ type.  In ponies bred in the Welsh and New Forest droves the condition is not uncommon, especially in the smaller animals.  Animals who have had their feet much in water—­as, for instance, those bred and reared on marshy soils—­and afterwards transferred to the constant dryness of stable bedding, are also particularly liable to this condition.  It is noticed, too, following the excessive use of unsuitable hoof-dressings, more especially in cases where coat after coat of the dressing is applied without occasionally removing the previous applications.