Page 1160 - Adams and Stashak's Lameness in Horses, 7th Edition

1126 Chapter 11

sponges moistened in a solution of 10% benzoyl peroxide stimulates the normal physiology of the frog, ensuring
in acetone and sprinkled with metronidazole powder are its continued health. A well‐shaped frog that fills the
VetBooks.ir equally effective include a solution of tricide/gentocin/ cleaning mechanism such that when the foot is loaded,
space between the heels also promotes a natural self‐
used by the author. Other topical products that may be
the frog expands, expelling any accumulated dirt or
lincomycin or an oxytetracycline/metronidazole paste.
No caustic preparations should be used on the debrided debris from the frog sulci.
site as they will burn or damage the dermal tissue that is An unhealthy frog is markedly smaller in size and
necessary to restore healthy horn and cornify. recessed below the level of the ground surface of the
The use of systemic antibiotics such as chlorampheni­ hoof, thus creating a void in which debris can accumu­
col or oxytetracycline has been advocated, but the late. This can occur for a variety of reasons including
author questions this practice as the majority of cases many of the recognized hoof capsule distortions such as
resolve with local treatment only. All horses should be the low heel, club foot, or sheared heels along with inap­
treated orally with systemic prednisolone at a dose of propriate farriery practices. Other contributing factors
1 mg/kg q24h for 7 days, 0.5 mg/kg q24h for 7 days, and for thrush include wet, unhygienic stable conditions,
then 0.25 mg/kg q24h for 7 days. The author uses this especially when horses continually stand in urine and
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approach as an adjunct to the local treatment discussed manure‐soiled bedding, neglecting daily routine foot
above and has found it to be beneficial. care and lack of exercise. 1,3,34,41
Aftercare performed by the owner daily or at least A fundamental problem with palmar foot conforma­
every second day is extremely important for success. The tion involves the frog being below the level of the heels,
foot should be cleaned vigorously using a gauze pad which reduces the stimulation from the ground, causing
soaked with a suitable antiseptic solution, any suspected the frog to atrophy further. As the frog recedes within the
area of disease is debrided with a dry gauze pad, the foot hoof capsule, the frog losses its “self‐cleaning mecha­
is rinsed with saline, topical treatment is reapplied, and nism,” which allows material (dirt/manure, etc.) to accu­
the foot is rebandaged. The foot should remain bandaged mulate over the frog, creating excessive pressure. Over
until the affected area has cornified. A shoe with a treat­ time, this constant pressure on a compromised frog leads
ment plate has become popular with canker cases, but the to increased deterioration and atrophy. Weakened by the
author feels it is contraindicated as it neither keeps the reduced protective horn of the epidermis, the frog tissue
foot as clean or dry as necessary post‐debridement. Once becomes susceptible to penetration by bacteria and, con­
the surface has a complete layer of thin cornification, a sequently, development of the disease. Furthermore, the
treatment plate can be used if desired. A commitment accumulation of debris over the frog creates an environ­
from the owners is necessary for success, because after­ ment conducive to bacterial growth, especially for anaer­
care takes several weeks, depending on the stage of the obic bacteria. The recessed frog often loses its ability to
disease, until the affected tissue becomes cornified. act as an expansion joint and the heels begin to contract.
The diseased frog can no longer share in supporting the
horse’s weight, which shifts most of the load‐bearing
Thrush
function solely onto the heels of the hoof capsule.
Thrush is a degenerative condition that affects the No specific organism has been identified as the sole
body and base of the frog generally caused by a bacterial cause of thrush. Two anaerobic bacteria species,
infection. The disease begins when bacteria penetrate the Bacteroides sp. and F. necrophorum, are opportunistic
outer horn or epidermis of the frog and is characterized organisms found in the soil and are commonly isolated
by deterioration of the frog and the presence of black from the bottom of the horse’s foot. On the positive side,
necrotic exudate with a foul odor. 1,3,41 In severe cases, the when the necrotic tissue of the frog is debrided and the
bacteria can reach the frog dermis, causing pain and conformation of the structures in the palmar foot is
lameness. Blood may be encountered when the frog is improved, the anaerobic conditions will be improved, and
cleaned with a brush or on the end of hoof picking dur­ bacterial growth will be decreased. Furthermore, if
ing routine grooming. Severe cases of thrush must be dif­ antimicrobials are required, these organisms are quite
ferentiated from canker, which is a proliferative disease susceptible to most topical preparations.
where abnormal frog tissue increases in comparison with
thrush, which is a degenerative disease where the horn of
the frog deteriorates (Figure 11.47A and B). Clinical Signs and Diagnosis
The diagnosis of thrush is usually straight forward
Etiology and based on examination of the frog and surrounding
structures. There is usually an increased amount of mois­
The overall health of the frog is an important compo­ ture on the bottom of the foot and a black exudate in the
nent of the etiology of thrush as it does not occur in a sulci of the frog. This exudate, which varies in quantity,
healthy frog. A healthy, well‐formed frog is broad and usually has an offensive odor. 3,34 The affected sulci of the
firm and deforms with thumb pressure. The frog should frog are often deeper than usual and may extend into the
fill the space between the heels of the hoof capsule, and, sensitive tissues of the foot causing them to be painful.
when measured at its base (the widest part), the frog The frog will generally be small, recessed within the hoof
width should be at least 70% of its length. A large capsule, lack a solid firm consistency, and have a necrotic
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healthy frog acts as an expansion joint that holds the appearance. There may be a fissure present in the central
heels apart, shares the load‐bearing function with the sulci extending from the base of the frog to the hairline
other structures of the palmar foot, and helps to absorb at the bulbs of the heels (Figure 11.48). The frog may
concussion. Under normal conditions, weight‐bearing also be undermined, and areas of necrotic horn can often