White line disease: recognise and treat it in time

What exactly is the white line?

The white line is the narrow connecting layer between the hoof wall and the sole, visible as a light strip on the underside of the hoof. The tissue here is relatively soft and porous, making it a weak point when conditions favour pathogens. Fungi and anaerobic bacteria can enter through small cracks or damage and then work their way upward through the hoof wall. In serious cases the infection can reach 3 to 5 centimetres up into the hoof wall — farriers refer to this as a significant 'undermining'.

Recognising the first symptoms

White line disease does not always cause lameness in the early stages, which means it can easily be overlooked. When picking out the hoof, watch for the following signs:

• Dark or black discolouration along the white line
• Crumbly, friable, or gritty material at the wall-sole junction
• A hollow sound when tapping the hoof wall (sounds 'empty')
• Visible cracks or holes on the underside of the hoof
• Mild lameness when pressure is applied to the affected area

What causes it?

There is rarely a single cause; it is usually a combination of factors that makes the white line vulnerable. The most common triggers are:

• Prolonged wet or muddy conditions in the pasture or stable
• Excessively long trimming intervals (more than 8 weeks), causing the wall to crumble
• Mechanical stress from an incorrect hoof angle or uneven weight distribution
• Previous hoof injuries or white line cracks that were left untreated
• Insufficient biotin or zinc in the diet, leading to reduced hoof quality

Treatment step by step

The farrier or vet first removes all affected tissue ('debridement'): the loose, infected hoof wall is opened up until only healthy material remains. This sounds drastic, but is essential — covering the area without debridement only gives the infection more room to spread. The hoof is then treated daily with an antifungal or disinfectant such as copper chloride or iodine. Keep the area dry and check it every day. Depending on the extent of the infection, the hoof can be protected with a special compound or acrylic resin. For a moderate infection, expect a recovery period of 2 to 4 months — the damaged hoof wall must grow out completely.

How to prevent recurrence

• Have your horse trimmed every 6 to 8 weeks — regular trimming prevents crumbling quarters
• Ensure dry resting areas and rotate pastures so horses are not standing in mud consistently
• Pick out hooves daily and visually inspect the white line at every session
• Support hoof quality through diet: biotin (at least 20 mg per day) and sufficient zinc
• Record trimming and treatment dates in your horse's profile in EquiSight so that intervals do not run too long

When should you call the vet?

Your farrier can manage treatment in most cases, but there are situations where a vet is needed. Call one immediately if your horse is clearly lame on the affected leg, if the infection is spreading towards the white zone or sensitive laminae, or if the hoof shows no improvement after two weeks of daily treatment. A vet can take X-rays to assess whether the pedal bone is already involved. Use EquiCoach in EquiSight to describe your findings — the intelligence helps you judge whether an emergency consultation is needed or whether you can calmly book an appointment.