White Line Health

 

The white line is the junction between the solar horn and wall horn. A healthy white line is tight and narrow forming a seamless connection between wall and sole. An unhealthy white line might be stretched and wide. The normal white line on an average sized foot (4 ½ inches across widest part of the sole) is approximately 1/8 of an inch or less. With a stretched white line sometimes a gap develops between the sole and wall, leaving a depression around part or all of inner hoof wall. For you to inspect it properly, the foot must be free of any dirt. The white line might need to be lightly rasped in order to bring its detail into view.

This photo shows a close-up view of a healthy white line with good integrity. Individual epidermal laminae are visible. The hoof wall outside of the white line has a few cracks but they are not extending to the white line and are not large enough to cause any problems in this hoof.

If your horse is shod, make a point to look at the feet during a farrier appointment after the shoes are pulled. In shod feet the white line might appear separated around the nail holes. If the feet are otherwise healthy this is a superficial blemish and not a sign of weakness. The separation is rasped or nipped off before the next set of shoes is nailed on.

One warning sign of ill health, possibly laminitis, is a stretched white line that does not improve once the foot has been trimmed. This means the damaged, separated horn is not merely superficial. A hoof with white line stretching is subject to infection and further weakening. Another warning sign is blood staining in the white line, which, when combined with stretching, can indicate more severe imbalance. Sometimes chronic imbalance can be a contributing factor to laminitis.

This photo shows stretched laminae with separation between the sole and wall across the toe and extending back all the way to the quarters. This photo was taken after the foot was trimmed, illustrating that with severe laminar weakening, the problem does not resolve after one trim.

The term white line disease has been used to refer to various problems that appear as deterioration of the white line. But the term white line disease is also used for disease in the hoof wall that is outside the white line. In either case (white line or outer hoof wall disease) research has shown there can be fungus and/or other microorganisms involved. Usually these organisms are not highly pathogenic so they may be a consequence of a previously weakened white line or wall rather than the cause. If you notice white line or wall separation with soft chalky horn and in some cases black exude oozing from the cracks talk to your farrier and veterinarian about possible solutions. Topical antimicrobial medication can sometimes help. A wall resection might be necessary if the damage involves large amounts of wall.

But regardless of topical application or how much of the damaged horn your farrier can dig out, the problem is likely to recur if the underlying cause is not addressed. I have seen two general categories of underlying cause: mechanical or metabolic. Mechanical is usually caused by imbalance that leads to separation or stretching. Metabolic causes may involve a systemic problem that weakens the horn (even if balance is good). Nutritional causes can lead to weak horn and thus a reduced local immune response in the foot which is what allows these normally non-pathogenic organisms to cause a problem.

The white line is a useful early warning of problems as well as an indicator of healing deeper inside the foot. It is worthwhile for you to pay close attention to this area. If you know the normal width and quality of your horse’s white line, you might catch a potential problem before the clinical signs become obvious. For example, if the toe is slightly too long, bruising can develop in the white line. If caught early, balance can be adjusted and by the next appointment signs of bruising may have disappeared. Additionally, if your horse currently has a hoof problem, monitoring the horn quality in the white line can give you some indication of how well the hoof is healing.

 

Copyright © 2012 ~ Dr. Lisa Lancaster DVM, WDAA Blog Author

 

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