THE MERCK VETERINARY MANUAL
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White Line Disease in Horses

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White line disease is a condition of the hoof wall in which the hoof wall separates from the underlying laminae (stratum internum) at the level of the stratum medium (tubular horn) of the hoof wall. The separation likely starts as a result of abnormal wall stress due to poor foot conformation or trimming (eg, long toe, underrun heels), and can start at the toes, quarters, or heel. Opportunistic bacteria and fungi may be present in the fissures in the hoof wall, sometimes resulting in purulent drainage. The outer surface of the wall may appear sound, but on dressing the palmar surface of the hoof, the inner surface of the wall is mealy, and there may be a cavity due to loss of horn substance. Tapping on the outside of the wall at the toe elicits a hollow sound over the affected portion. Lameness may be present in severe cases, in which loss of support of the distal phalanx occurs.

The diagnostic workup includes a thorough physical examination and lateral and dorsopalmar radiographs to assess the extent of separation of the hoof wall. For treatment, corrective trimming is critical to remove abnormal stresses on the hoof wall, followed by removal of the entire extent of the separated hoof wall to the point that firm, healthy adhesion of the hoof wall to the underlying stratum internum can be observed. This hoof wall debridement is performed with a combination of hoof nippers, hoof knives, and a rotary tool. With proper debridement, there is probably no need for antiseptic or astringent treatment. Corrective shoeing is critical to provide adequate support to the remaining foot, while removing stress from the affected regions; a heart bar or egg bar shoe in combination with a resilient putty in the caudal two-thirds of the sole (to provide distal phalanx support) is recommended.

Last full review/revision March 2012 by Stephen B. Adams, DVM, MS, DACVS; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; James K. Belknap, DVM, PhD, DACVS; Jane C. Boswell, MA, VetMB, CertVA, CertES (Orth), DECVS, MRCVS; Peter Clegg, MA, Vet MB, PhD, CertEO, DECVS, MRCVS; Andrew L. Crawford, BVetMed, CertES (Orth), MRCVS; Jean-Marie Denoix, DVM, PhD, Agregé; Marcus J. Head, BVetMed, MRCVS; C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS, DACVSMR; James Schumacher, DVM, MS, DACVS, MRCVS; John Schumacher, DVM, MS, DACVIM; Roger K. W. Smith, MA, VetMB, PhD, DEO, DECVS, MRCVS; Chris Whitton, BVSc, FACVSc, PhD

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