Thrush: understand it, prevent it, know when to call in a professional

A strong smell when picking out, a central groove getting deeper: the frog is often the first part of the hoof to suffer from wet conditions. How it works, why it deteriorates, and what can be done in the stable and what is a job for a professional.

A key part of the underside of the hoof

With the hoof lifted, the frog is recognisable by its V shape, opening towards the heels. It is framed by the bars and by two grooves, the collateral grooves; down its centre runs the central groove. Like the sole and the bars, it is produced by the living tissue of the foot and grows in thickness.

Its role is mechanical. When the horse puts its foot down, the heels take the weight and spread apart: the frog then touches the ground and helps to absorb the impact of the stride. A firm, clean frog works with every step.

What is known as thrush

The IFCE describes deep thrush, sometimes called a “heated frog”, as the result of too much moisture: softened horn allows germs to take hold, which break down the central groove, first on the surface, then more deeply if nothing is done.

When picking out, several signs should ring alarm bells: a very strong smell, a blackish discharge deep in the grooves, a central groove getting deeper, a frog that bleeds, a horse that is lame. Daily picking out is the best time to look, and to smell.

Moisture, the main culprit

Muddy fields, boxes with soiled bedding, legs hosed and badly dried: the frog sits in water and manure, and the horn macerates. Winter makes things worse, as the sole and frog stay soft all the time; the IFCE notes that at this time of year horses are more prone to thrush, hoof abscesses and corns. Narrow or deep frogs, which are hard to keep clean, are the most exposed.

Picking out, the basic task

Picking out removes what builds up under the hoof, manure, soil, stones, sand, and lets you check there is no wound or foreign object. The IFCE recommends doing it every time, before and after work. Clear the frog first, then the collateral grooves, then the sole; next brush the whole hoof, including the heel bulbs, and finish with a sponge if needed. If the hoof is to be greased, let it dry first: grease on a wet hoof would trap water against the horn.

Picking out is also a moment to observe: by picking out every day, you notice straight away when something changes under the hoof.

Prevention starts in the stable

• Pick out the hooves every day, ideally before and after work, clearing the frog and its grooves thoroughly.
• Keep the bedding clean and dry: droppings removed and box mucked out every day, straw added as soon as needed, stable well ventilated.
• In winter, turn out in the healthiest fields, with a dry shelter, and move the hay rack regularly to avoid poached areas.
• Do not hose the legs out of habit: often, a brush once the mud has dried is enough; after hosing, dry carefully.
• Have the hooves trimmed regularly by the farrier, whether the horse is shod or barefoot.

Protecting the underside of the hoof in wet weather

On a clean, dry hoof, a water-repellent product reduces the time the frog spends soaking. Stockholm Tar and Cade Oil, two wood distillates traditionally used in farriery, are applied to the sole and into the grooves. The method does not change: clean, let dry, apply, then wait until it is dry before the horse goes back on its bedding.

The IFCE points out that tar should be used sparingly, when conditions call for it: it is not a product to apply all year round for no reason. When the weather dries up, go back to your usual hoof ointment and space out applications. And no product replaces daily picking out or dry bedding.

When to call in a professional

Maintenance products support a healthy hoof. As soon as a frog smells very strong, shows a black discharge, bleeds, or the horse is lame, call the farrier and, if necessary, the vet. The farrier will examine the hoof and may recommend a suitable product; the vet decides what happens next. Avoid home-made preparations: misused, they sometimes do more harm than good. Our The Horse’s Hoof page describes the anatomy of the hoof in detail.

Sources: IFCE équipédia (in French), “Le pied du cheval” (J.-M. Goubault, N. Genoux, F. Cavé, 2019), “Maux de l’hiver : vigilance accrue !” (N. Genoux, L. Le Masne, M. Delerue, J. Etiemble, 2025); directions for use of Stockholm Tar and Cade Oil.

Gamme du Maréchal