- Email: [email protected]
Canker
C H A P T E R
Canker
198
MAARTEN OOSTERLINCK
E
quine proliferative pododermatitis, or canker, is a debilitating disease of the hoof characterized by chronic proliferation of horn-producing tissues, mainly in the frog region but sometimes also undermining the sole, heel bulbs, and, less commonly, the hoof wall. It is not a true neoplasm, but rather is a chronic inflammatory reaction with excessive dyskeratosis, resulting in exuberant horn of inferior quality. As opposed to thrush, which causes superficial degenerative keratolysis in the sulci of the frog, canker is a proliferative disease affecting the horn of the frog anywhere throughout its structure. Canker has been reported to have a higher prevalence in the hind limb, although forelimb involvement is also common. The disease has been considered to occur mainly in draft horses, but other breeds can equally be affected. Most horses have several hooves affected, although involvement of a single hoof can occur. Although horses often have local sensitivity at the level of the lesions, overt lameness is mostly associated with advanced infection or a concurrent hoof problem, such as a hoof abscess, laminitis, or other condition. Canker is generally regarded as a rare diagnosis in modern equine practice, with a higher prevalence seen in the semitropical climate of the southern United States. However, notwithstanding improvements in horse management and hoof care, the disease has not been eliminated, and some authors have even reported an increased prevalence that may in part be a result of increased awareness of the condition.
ETIOLOGY
The etiology of canker remains obscure: infectious agents such as anaerobic bacteria, viruses, fungi, and spirochetes have been isolated from diseased tissue, but the causal relationship between specific organisms and canker remains unclear, and wet or unhygienic environmental conditions have also been blamed as inciting factors. Moreover, an immunologic etiology has been hypothesized, which may be linked with a genetic predisposition. It cannot be excluded that canker may have several etiologies, which may explain differences in clinical presentation and response to treatment.
DIAGNOSIS
Diagnosis is generally made on the basis of history and the pathognomonic appearance of hoof tissue, most frequently foul-smelling, cheesy masses with filamentous or cauliflower-like epithelial proliferations, often extending from the caudal part of the frog to the heel bulbs and bleeding on manipulation; affected horses often also have upright hairs at the heel bulbs (Figures 198-1 to 198-3). In horses with moderate to severe stages of the disease, biopsy for histologic evaluation is unnecessary. Culture is generally unrewarding because the tissue typically yields a variety of organisms. It may be suggested that any case of thrush that
852
does not rapidly respond to a standard treatment should be considered canker. The disease remains underdiagnosed. Although equine veterinarians and farriers possess a common body of knowledge regarding hoof canker, diagnosis in the early stages of the disease is rarely made correctly, and inadequate treatments are used persistently. In a recent retrospective study, an initial presumptive diagnosis of thrush was made in 19 of 28 horses, and 10 of those 19 horses had been treated accordingly for several months. Overall, horses had been treated for weeks (5/28), months (16/28), or even several years (7/28) before being referred for further investigation and treatment. At first evaluation, differentiating between canker and thrush may be difficult for a farrier or veterinarian with limited experience because both conditions are associated with structural degradation and superficial bacterial contamination. However, lesions extending outside the sites where thrush is common or that arise in locations distant from the predilection sites for thrush (i.e., the sulci of the frog), the macroscopic appearance of underlying tissues that bleed profusely when manipulated, and the lack of response to standard treatment for thrush should alert caretakers and veterinarians to consider the possibility of canker. Better awareness of the condition and adequate education to recognize early stages of the disease are needed.
TREATMENT
Because no definitive single causative agent has been identified, a variety of treatments have been proposed. Treatment, which may be necessary for several weeks to several months, generally involves combinations of surgical debridement, medical treatment, and appropriate hoof care. Early recognition, prompt treatment by superficial debridement, a clean and dry environment, and long-term owner compliance are important factors for a successful outcome. Before embarking on treatment, all four hooves should be closely inspected and trimmed to ensure identification of all affected limbs. Preoperatively, horses generally receive antitetanus serum, systemic nonsteroidal antiinflammatory medication, and antimicrobials. Debridement can be performed under regional or general anaesthesia, depending on the severity of the disease and the number of affected hooves, by use of a tourniquet and a sharp hoof knife and scalpel blade to remove all abnormal tissue (Figures 198-4 and 198-5). Cautery is not used routinely. In the author’s experience, debridement is the most critical step. Insufficient debridement leaves diseased tissue in situ, mostly in the sulci of the frog. Adequate debridement should eliminate all clefts and should result in a visibly smooth transition from hoof sole or bars to the frog itself. However, care must be taken not to remove excessive corium because overaggressive debridement will drastically slow epithelialization. After most of the abnormal tissue has been
CHAPTER
198 Canker
853
Figure 198-3 Photograph of a more discrete, focal lesion with a cheeselike mass that bled easily when manipulated.
Figure 198-1 Photograph of a hoof with advanced canker, showing the appearance that can be considered pathognomonic for this condition. Marked filamentous epithelial proliferation has affected the complete caudal part of the frog and has extended to the heel bulbs. (From Oosterlinck M, Deneut K, Dumoulin M, et al. Retrospective study on 30 horses with chronic proliferative pododermatitis (canker). Equine Vet Educ 2011;23:467.)
Figure 198-4 Thorough trimming of the complete hoof, especially at the level of the heels, is followed by debridement with a hoof knife. Curettage should be performed without removing excessive corium because this will retard healing. (From Oosterlinck M, Deneut K, Dumoulin M, et al. Retrospective study on 30 horses with chronic proliferative pododermatitis (canker). Equine Vet Educ 2011;23:468.) Figure 198-2 Photograph of upright hairs growing at the level of the coronary band at the heel bulbs. This finding is commonly seen in addition to the vegetative hoof lesions.
removed, gentle curettage may be superior to further use of a scalpel blade or hoof knife. After debridement, the sole should be rinsed with 0.05% chlorhexidine solution and dried with gauze sponges. Topical medication like chlortetracycline hydrochloride spray or metronidazole is frequently applied (see later). Finally, the defect is packed with gauge sponges and a dry hoof bandage. Adequate pressure on the affected area, especially in the sulci of the frog, is necessary to prevent bulging of dermal tissue. After the procedure, the hoof bandage should be changed on a regular basis, and various types of topical medication can be applied to the exposed dermal tissue. A wooden
tongue depressor is useful to medicate and pack the sulci of the frog. The use of caustic substances, such as sulfates or formaldehyde, and cautery are to be avoided. Use of oxytetracycline, trimethoprim-sulfadiazine, doxycycline powder, dimethylsulfoxide (DMSO), chloramphenicol, 10% benzoyl peroxide in acetone combined with metronidazole, and many other topical treatments has been described. It is clear that more scientific information on the etiopathogenesis of canker is needed to develop more targeted treatments. Several treatment protocols are empirical or based on low-number case reports, whereas in some larger case series, trimethoprim-sulfadiazine and metronidazole have been applied successfully. Empirically, use of an emulsion1
1
Dog Eczema/Dermacure, KelaLaboratoria, Hoogstraten, Belgium.
854
SECTION
XVII Musculoskeletal
Figure 198-5 The hoof sole is rinsed with 0.05% chlorhexidine solution, and final debridement at the level of the sulci of the frog is performed with a scalpel blade. All clefts in the sulci are removed until a smooth transition from the sole or bars to the frog is obtained. (From Oosterlinck M, Deneut K, Dumoulin M, et al. Retrospective study on 30 horses with chronic proliferative pododermatitis (canker). Equine Vet Educ 2011; 23:468.)
containing prednisolone, precipitated sulfur, zinc oxide, and neomycin sulfate has yielded favorable results, a response that may be associated with the effects of the prednisolone. The optimal medical treatment strategy may be influenced by local regulations because potential human health risks and the classification of the horse as a food-producing animal have limited the number of available formulations in veterinary medicine in several countries. Besides adequate debridement, topical medical treatment, and dedicated hoof care, additional long-term oral treatment with prednisolone significantly shortens the duration of care and therefore can be considered as part of the treatment protocol for equine proliferative pododermatitis. One should not substitute a more potent corticosteroid, such as dexamethasone, because of the anecdotally reported risk for laminitis. The prednisolone dose regimen is 1 mg/kg once every 24 hours for 7 days, followed by 0.5 mg/kg once every 24 hours for 7 days, and then 0.25 mg/kg once every 24 hours for 7 days. Given the circadian rhythm of endogenous cortisol release, administration of corticoids in the morning may be preferable. In most horses, systemic antimicrobial and nonsteroidal antiinflammatory therapy is continued for only 2 to 7 days. In severely affected horses, systemic antimicrobial treatment (e.g., oral trimethoprim-sulfadiazine at 30 mg/kg every 12 hours) may be instituted for another 1 to 3 weeks, although the efficacy of systemic antimicrobials may be questionable. Local treatment and bandaging are repeated until dermal edema and exudation have decreased. At that time, a hoof cast or a plate shoe is applied. As soon as cornification has developed, an astringent cream can be applied topically. The author uses a preparation2 containing copper acetate, zinc sulfate, and honey.
2
Egyptischezalf, Ecuphar, Oostkamp, Belgium.
The choice to apply a bandage, cast, or a hospital plate shoe is made on an individual basis, depending on the breed, extent of the lesions, contamination of stable bedding, and stage of healing. In some reports, use of regularly changed bandages is preferred over casting because the former method may maintain a drier environment. Indisputably, wet and unhygienic environments, especially those caused by the presence of urine or manure, should be avoided. However, maintenance of a clean, moist wound environment encourages a higher rate of epithelialization and decreased healing time compared with dry wound healing. Warmth, restriction of movement, and maintenance of a moist healing envi ronment in conjunction with application of a cast may be optimal for hoof wound healing. However, hoof casts are unlikely to remain intact and uncontaminated in draft horses, and a hospital plate shoe may be preferable in those breeds. To prevent contamination inside the plate shoe, the hoof is carefully wrapped with impermeable adhesive tape, which is renewed daily after the hoof care. Horses are stall-rested and monitored intensively until adequate cornification has occurred and bandaging or treatment plate application is no longer required. After this, owners are advised to provide normal daily hoof care and to arrange for periodic inspection by the farrier or veterinarian. In case of recurrence, early and adequate intervention is indicated.
PROGNOSIS
Although some reports have claimed a favorable prognosis for complete resolution if treatment is instituted early, others have stated that recurrence is common and the prognosis is guarded. Direct comparison between studies is difficult because of confounding variables (e.g., the stage of disease at presentation; choice of topical treatment; use of a bandage, cast, or hospital plate; and duration of follow-up period, among others). In the authors’ experience, the prognosis for severely affected horses is at least guarded, with about 75% of horses having an acceptable long-term outcome, with either no recurrence or recurrence limited to minor, manageable lesions. Recurrence is usually seen within 1 year of the initial episode in horses in which the condition returns. There does not seem to be a significant association between the recurrence of problems and number of affected hooves or the presence or absence of any systemic treatment. Hoof conformation characterized by deep or narrow sulci and high heels may be a negative prognostic factor. All parties involved in the caretaking of horses need increased awareness of the disease because delaying adequate treatment has been associated with a thirteenfold increased risk for recurrence.
Suggested Readings Baxter GM, Stashak TS. Canker. In: Baxter G, ed. Adams and Stashak’s Lameness in Horses. 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2011:519-520. Booth L, White D. Equine canker. In: Floyd AE, Mansmann RA, eds. Equine Podiatry. 1st ed. St. Louis: Saunders Elsevier, 2007: 246-249. Fürst AE, Lischer CJ. Degenerative and neoplastic diseases of the foot: canker. In: Auer JA, Stick JA, eds. Equine Surgery. 4th ed. St. Louis: Saunders Elsevier, 2012: 1277-1279. Goble DO. Lameness in draft horses. In: Ross MW, Dyson SJ, eds. Diagnosis and Management of Lameness in the Horse. 2nd ed. St. Louis: Saunders Elsevier, 2011:1221-1222.
O’Grady SE. Canker. In: Baxter G, ed. Adams and Stashak’s Lameness in Horses. 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2011:1206. O’Grady SE, Madison JB. How to treat equine canker. In: Proceedings of the 50th Annual Convention of the American Association of Equine Practitioners, 2004:202-205. Oosterlinck M, Deneut K, Dumoulin M, et al. Retrospective study on 30 horses with chronic proliferative pododermatitis (canker). Equine Vet Educ 2011;23:466-471.
CHAPTER
198 Canker
855
Parks A. Canker. In: Munroe GA, Weese JS, eds. Equine Clinical Medicine, Surgery, and Reproduction. 1st ed. London: Manson Publishing, 2011:68. Reeves MJ, Yovich JV, Turner AS. Miscellaneous conditions of the equine foot. Vet Clin North Am Equine Pract 1989;5: 221-242. Whitton RC, Hodgson DR, Rose RJ. Canker. In: Rose RJ, Hodgson DR, eds. Manual of Equine Practice. 2nd ed. Philadelphia: Saunders Elsevier, 2000:122-123.
Canker
198
MAARTEN OOSTERLINCK
E
quine proliferative pododermatitis, or canker, is a debilitating disease of the hoof characterized by chronic proliferation of horn-producing tissues, mainly in the frog region but sometimes also undermining the sole, heel bulbs, and, less commonly, the hoof wall. It is not a true neoplasm, but rather is a chronic inflammatory reaction with excessive dyskeratosis, resulting in exuberant horn of inferior quality. As opposed to thrush, which causes superficial degenerative keratolysis in the sulci of the frog, canker is a proliferative disease affecting the horn of the frog anywhere throughout its structure. Canker has been reported to have a higher prevalence in the hind limb, although forelimb involvement is also common. The disease has been considered to occur mainly in draft horses, but other breeds can equally be affected. Most horses have several hooves affected, although involvement of a single hoof can occur. Although horses often have local sensitivity at the level of the lesions, overt lameness is mostly associated with advanced infection or a concurrent hoof problem, such as a hoof abscess, laminitis, or other condition. Canker is generally regarded as a rare diagnosis in modern equine practice, with a higher prevalence seen in the semitropical climate of the southern United States. However, notwithstanding improvements in horse management and hoof care, the disease has not been eliminated, and some authors have even reported an increased prevalence that may in part be a result of increased awareness of the condition.
ETIOLOGY
The etiology of canker remains obscure: infectious agents such as anaerobic bacteria, viruses, fungi, and spirochetes have been isolated from diseased tissue, but the causal relationship between specific organisms and canker remains unclear, and wet or unhygienic environmental conditions have also been blamed as inciting factors. Moreover, an immunologic etiology has been hypothesized, which may be linked with a genetic predisposition. It cannot be excluded that canker may have several etiologies, which may explain differences in clinical presentation and response to treatment.
DIAGNOSIS
Diagnosis is generally made on the basis of history and the pathognomonic appearance of hoof tissue, most frequently foul-smelling, cheesy masses with filamentous or cauliflower-like epithelial proliferations, often extending from the caudal part of the frog to the heel bulbs and bleeding on manipulation; affected horses often also have upright hairs at the heel bulbs (Figures 198-1 to 198-3). In horses with moderate to severe stages of the disease, biopsy for histologic evaluation is unnecessary. Culture is generally unrewarding because the tissue typically yields a variety of organisms. It may be suggested that any case of thrush that
852
does not rapidly respond to a standard treatment should be considered canker. The disease remains underdiagnosed. Although equine veterinarians and farriers possess a common body of knowledge regarding hoof canker, diagnosis in the early stages of the disease is rarely made correctly, and inadequate treatments are used persistently. In a recent retrospective study, an initial presumptive diagnosis of thrush was made in 19 of 28 horses, and 10 of those 19 horses had been treated accordingly for several months. Overall, horses had been treated for weeks (5/28), months (16/28), or even several years (7/28) before being referred for further investigation and treatment. At first evaluation, differentiating between canker and thrush may be difficult for a farrier or veterinarian with limited experience because both conditions are associated with structural degradation and superficial bacterial contamination. However, lesions extending outside the sites where thrush is common or that arise in locations distant from the predilection sites for thrush (i.e., the sulci of the frog), the macroscopic appearance of underlying tissues that bleed profusely when manipulated, and the lack of response to standard treatment for thrush should alert caretakers and veterinarians to consider the possibility of canker. Better awareness of the condition and adequate education to recognize early stages of the disease are needed.
TREATMENT
Because no definitive single causative agent has been identified, a variety of treatments have been proposed. Treatment, which may be necessary for several weeks to several months, generally involves combinations of surgical debridement, medical treatment, and appropriate hoof care. Early recognition, prompt treatment by superficial debridement, a clean and dry environment, and long-term owner compliance are important factors for a successful outcome. Before embarking on treatment, all four hooves should be closely inspected and trimmed to ensure identification of all affected limbs. Preoperatively, horses generally receive antitetanus serum, systemic nonsteroidal antiinflammatory medication, and antimicrobials. Debridement can be performed under regional or general anaesthesia, depending on the severity of the disease and the number of affected hooves, by use of a tourniquet and a sharp hoof knife and scalpel blade to remove all abnormal tissue (Figures 198-4 and 198-5). Cautery is not used routinely. In the author’s experience, debridement is the most critical step. Insufficient debridement leaves diseased tissue in situ, mostly in the sulci of the frog. Adequate debridement should eliminate all clefts and should result in a visibly smooth transition from hoof sole or bars to the frog itself. However, care must be taken not to remove excessive corium because overaggressive debridement will drastically slow epithelialization. After most of the abnormal tissue has been
CHAPTER
198 Canker
853
Figure 198-3 Photograph of a more discrete, focal lesion with a cheeselike mass that bled easily when manipulated.
Figure 198-1 Photograph of a hoof with advanced canker, showing the appearance that can be considered pathognomonic for this condition. Marked filamentous epithelial proliferation has affected the complete caudal part of the frog and has extended to the heel bulbs. (From Oosterlinck M, Deneut K, Dumoulin M, et al. Retrospective study on 30 horses with chronic proliferative pododermatitis (canker). Equine Vet Educ 2011;23:467.)
Figure 198-4 Thorough trimming of the complete hoof, especially at the level of the heels, is followed by debridement with a hoof knife. Curettage should be performed without removing excessive corium because this will retard healing. (From Oosterlinck M, Deneut K, Dumoulin M, et al. Retrospective study on 30 horses with chronic proliferative pododermatitis (canker). Equine Vet Educ 2011;23:468.) Figure 198-2 Photograph of upright hairs growing at the level of the coronary band at the heel bulbs. This finding is commonly seen in addition to the vegetative hoof lesions.
removed, gentle curettage may be superior to further use of a scalpel blade or hoof knife. After debridement, the sole should be rinsed with 0.05% chlorhexidine solution and dried with gauze sponges. Topical medication like chlortetracycline hydrochloride spray or metronidazole is frequently applied (see later). Finally, the defect is packed with gauge sponges and a dry hoof bandage. Adequate pressure on the affected area, especially in the sulci of the frog, is necessary to prevent bulging of dermal tissue. After the procedure, the hoof bandage should be changed on a regular basis, and various types of topical medication can be applied to the exposed dermal tissue. A wooden
tongue depressor is useful to medicate and pack the sulci of the frog. The use of caustic substances, such as sulfates or formaldehyde, and cautery are to be avoided. Use of oxytetracycline, trimethoprim-sulfadiazine, doxycycline powder, dimethylsulfoxide (DMSO), chloramphenicol, 10% benzoyl peroxide in acetone combined with metronidazole, and many other topical treatments has been described. It is clear that more scientific information on the etiopathogenesis of canker is needed to develop more targeted treatments. Several treatment protocols are empirical or based on low-number case reports, whereas in some larger case series, trimethoprim-sulfadiazine and metronidazole have been applied successfully. Empirically, use of an emulsion1
1
Dog Eczema/Dermacure, KelaLaboratoria, Hoogstraten, Belgium.
854
SECTION
XVII Musculoskeletal
Figure 198-5 The hoof sole is rinsed with 0.05% chlorhexidine solution, and final debridement at the level of the sulci of the frog is performed with a scalpel blade. All clefts in the sulci are removed until a smooth transition from the sole or bars to the frog is obtained. (From Oosterlinck M, Deneut K, Dumoulin M, et al. Retrospective study on 30 horses with chronic proliferative pododermatitis (canker). Equine Vet Educ 2011; 23:468.)
containing prednisolone, precipitated sulfur, zinc oxide, and neomycin sulfate has yielded favorable results, a response that may be associated with the effects of the prednisolone. The optimal medical treatment strategy may be influenced by local regulations because potential human health risks and the classification of the horse as a food-producing animal have limited the number of available formulations in veterinary medicine in several countries. Besides adequate debridement, topical medical treatment, and dedicated hoof care, additional long-term oral treatment with prednisolone significantly shortens the duration of care and therefore can be considered as part of the treatment protocol for equine proliferative pododermatitis. One should not substitute a more potent corticosteroid, such as dexamethasone, because of the anecdotally reported risk for laminitis. The prednisolone dose regimen is 1 mg/kg once every 24 hours for 7 days, followed by 0.5 mg/kg once every 24 hours for 7 days, and then 0.25 mg/kg once every 24 hours for 7 days. Given the circadian rhythm of endogenous cortisol release, administration of corticoids in the morning may be preferable. In most horses, systemic antimicrobial and nonsteroidal antiinflammatory therapy is continued for only 2 to 7 days. In severely affected horses, systemic antimicrobial treatment (e.g., oral trimethoprim-sulfadiazine at 30 mg/kg every 12 hours) may be instituted for another 1 to 3 weeks, although the efficacy of systemic antimicrobials may be questionable. Local treatment and bandaging are repeated until dermal edema and exudation have decreased. At that time, a hoof cast or a plate shoe is applied. As soon as cornification has developed, an astringent cream can be applied topically. The author uses a preparation2 containing copper acetate, zinc sulfate, and honey.
2
Egyptischezalf, Ecuphar, Oostkamp, Belgium.
The choice to apply a bandage, cast, or a hospital plate shoe is made on an individual basis, depending on the breed, extent of the lesions, contamination of stable bedding, and stage of healing. In some reports, use of regularly changed bandages is preferred over casting because the former method may maintain a drier environment. Indisputably, wet and unhygienic environments, especially those caused by the presence of urine or manure, should be avoided. However, maintenance of a clean, moist wound environment encourages a higher rate of epithelialization and decreased healing time compared with dry wound healing. Warmth, restriction of movement, and maintenance of a moist healing envi ronment in conjunction with application of a cast may be optimal for hoof wound healing. However, hoof casts are unlikely to remain intact and uncontaminated in draft horses, and a hospital plate shoe may be preferable in those breeds. To prevent contamination inside the plate shoe, the hoof is carefully wrapped with impermeable adhesive tape, which is renewed daily after the hoof care. Horses are stall-rested and monitored intensively until adequate cornification has occurred and bandaging or treatment plate application is no longer required. After this, owners are advised to provide normal daily hoof care and to arrange for periodic inspection by the farrier or veterinarian. In case of recurrence, early and adequate intervention is indicated.
PROGNOSIS
Although some reports have claimed a favorable prognosis for complete resolution if treatment is instituted early, others have stated that recurrence is common and the prognosis is guarded. Direct comparison between studies is difficult because of confounding variables (e.g., the stage of disease at presentation; choice of topical treatment; use of a bandage, cast, or hospital plate; and duration of follow-up period, among others). In the authors’ experience, the prognosis for severely affected horses is at least guarded, with about 75% of horses having an acceptable long-term outcome, with either no recurrence or recurrence limited to minor, manageable lesions. Recurrence is usually seen within 1 year of the initial episode in horses in which the condition returns. There does not seem to be a significant association between the recurrence of problems and number of affected hooves or the presence or absence of any systemic treatment. Hoof conformation characterized by deep or narrow sulci and high heels may be a negative prognostic factor. All parties involved in the caretaking of horses need increased awareness of the disease because delaying adequate treatment has been associated with a thirteenfold increased risk for recurrence.
Suggested Readings Baxter GM, Stashak TS. Canker. In: Baxter G, ed. Adams and Stashak’s Lameness in Horses. 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2011:519-520. Booth L, White D. Equine canker. In: Floyd AE, Mansmann RA, eds. Equine Podiatry. 1st ed. St. Louis: Saunders Elsevier, 2007: 246-249. Fürst AE, Lischer CJ. Degenerative and neoplastic diseases of the foot: canker. In: Auer JA, Stick JA, eds. Equine Surgery. 4th ed. St. Louis: Saunders Elsevier, 2012: 1277-1279. Goble DO. Lameness in draft horses. In: Ross MW, Dyson SJ, eds. Diagnosis and Management of Lameness in the Horse. 2nd ed. St. Louis: Saunders Elsevier, 2011:1221-1222.
O’Grady SE. Canker. In: Baxter G, ed. Adams and Stashak’s Lameness in Horses. 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2011:1206. O’Grady SE, Madison JB. How to treat equine canker. In: Proceedings of the 50th Annual Convention of the American Association of Equine Practitioners, 2004:202-205. Oosterlinck M, Deneut K, Dumoulin M, et al. Retrospective study on 30 horses with chronic proliferative pododermatitis (canker). Equine Vet Educ 2011;23:466-471.
CHAPTER
198 Canker
855
Parks A. Canker. In: Munroe GA, Weese JS, eds. Equine Clinical Medicine, Surgery, and Reproduction. 1st ed. London: Manson Publishing, 2011:68. Reeves MJ, Yovich JV, Turner AS. Miscellaneous conditions of the equine foot. Vet Clin North Am Equine Pract 1989;5: 221-242. Whitton RC, Hodgson DR, Rose RJ. Canker. In: Rose RJ, Hodgson DR, eds. Manual of Equine Practice. 2nd ed. Philadelphia: Saunders Elsevier, 2000:122-123.