White Line Disease: Recognize 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 hoof sole, visible as a light streak on the underside of the hoof. The tissue here is relatively soft and porous, making it a weak spot when conditions favor disease-causing organisms. Fungi and anaerobic bacteria can enter through small cracks or damage and then work their way up through the hoof wall. In severe cases, the infection sometimes reaches 3 to 5 centimeters high in the hoof wall — farriers call this significant 'undermining'.

Recognize the First Symptoms

White line disease often doesn't cause lameness in the early stages, which is why it's easy to miss. When cleaning out, watch for these warning signs:

• Dark or black discoloration along the white line
• Crumbly, brittle, or sandy material at the wall-sole transition
• A hollow sound when tapping on 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's rarely a single cause; usually it's a combination of factors that make the white line vulnerable. The most common triggers are:

• Prolonged wet or muddy conditions in pasture or stable
• Trimming intervals that are too long (more than 8 weeks), causing wall deterioration
• Mechanical stress from incorrect trim angle or uneven weight distribution
• Previous hoof injuries or white line cracks that weren't treated
• Biotin or zinc deficiency in the diet, reducing hoof quality

Treatment Step by Step

The farrier or veterinarian first removes all affected tissue ('débridement'): the loose, infected hoof wall is exposed until only healthy material remains. This sounds drastic, but it's necessary — simply covering it without débridement only gives the infection more room to spread. Afterward, the hoof is 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, the hoof can be protected with a special dressing or artificial resin. For a moderate-sized infection, expect a recovery period of 2 to 4 months — the affected hoof wall must grow out completely.

How to Prevent Recurrence

• Trim your horse every 6 to 8 weeks — regular trimming prevents brittle wall corners
• Ensure dry bedding areas and rotate pastures so horses aren't constantly standing in mud
• Clean hooves daily and visually inspect the white line at every grooming
• Support hoof quality through nutrition: biotin (minimum 20 mg per day) and adequate zinc
• Record trimming and treatment dates in your horse's file in EquiSight, so intervals don't become too long

When to Call the Veterinarian

Your farrier can usually guide the treatment themselves, but there are situations where a veterinarian is needed. Call immediately if your horse shows clear lameness on the affected leg, if the infection spreads toward the sensitive structures or live wall, or if the hoof hasn't improved after two weeks of daily treatment. A veterinarian can take X-rays to assess whether the coffin bone is involved. Use EquiCoach in EquiSight to document your findings — the AI feature helps you determine whether an emergency consultation is needed or if you can schedule a regular appointment.