Hereditary equine regional dermal asthenia (HERDA) in Quarter Horses: A review of clinical signs,genetics and research

Hereditary equine regional dermal asthenia (HERDA) results from a genetic mutation which affects the skin and other tissues of Quarter Horses and horses with Quarter Horse lineage. The disease HERDA has an autosomal recessive mode of inheritance and has become a significant concern in the Quarter Horse industry due to the high frequency of heterozygote carriers. Affected homozygous horses appear normal at birth; however, within the first 2 years of life they usually acquire loose, hyperextensible skin and wounds which result in disfiguring scars either spontaneously or from minor trauma. Some severely affected horses also develop haematomas and seromas. Consequently, most affected horses are subjected to euthanasia at an early age. No treatment options other than palliative therapy currently exist. As part of a five panel test ( http://www.aqha.com/News/News-Articles/2013/April/04292013-Genetic-Testing.aspx ) the American Quarter Horse Association presently requires DNA testing for HERDA on all breeding stallions. There are currently no restrictions on registration of horses heterozygous or homozygous for the HERDA mutation. Due to the autosomal recessive nature of the disease, Quarter Horse mares and horses of all breeds from HERDA‐associated bloodlines should also be tested.     

Prevalence of the mutation in cyclophilin B (PPIB), a causal candidate gene for HERDA, among Quarter Horses in France

Hereditary equine regional dermal asthenia (HERDA) in Quarter Horses is an inherited degenerative skin disease. Initially reported as hyperelastosis cutis, HERDA has a phenotype of hyperextensible, fragile skin, with secondary seromas, haematomas, ulcers and scarring. It primarily affects the dorsal aspect of the body. An autosomal recessive mode of inheritance is considered likely, with affected horses more at risk to produce affected offspring. A mutation in cyclophilin B (PPIB) as a novel, causal candidate gene for HERDA has been described, and verified as segregating with carriers and affected horses. Screening of control Quarter Horses in the USA has indicated a 3.5% carrier frequency. The prevalence of this mutation among Quarter Horses in France was determined to be 1.6%.     

Hereditary equine regional dermal asthenia ("hyperelastosis cutis") in 50 horses: clinical, histological, immunohistological and ultrastructural findings

Data on fifty horses with hereditary equine regional dermal asthenia (HERDA; "hyperelastosis cutis") were collected on clinical, histopathological, ultrastructural and immunohistological findings. All horses were Quarter horses or of Quarter horse ancestry. Pedigree evaluation strongly supported an autosomal recessive mode of inheritance. The most common lesions were seromas/haematomas, open wounds, sloughing skin, and loose, easily tented skin that did not return to its initial position. Definitive diagnosis could not be made via histopathology, although the presence of tightly grouped thin and shortened collagen fibres arranged in clusters in the deep dermis was suggestive of the disease. Trichrome, acid orcein-Giemsa and immunohistochemical stains for collagens I and III showed no consistent abnormalities compared to control horses; an increase in elastic fibres was not a consistent finding. Electron microscopy showed no abnormalities in the periodicity of the collagen bundles; neither orientation nor variation of cross-section diameter of the collagen fibrils differentiated control from affected horses. The diagnosis of HERDA relies on clinical presentation, but may be supported by suggestive (although not pathognomonic) histopathological lesions.     

Inheritance of hereditary equine regional dermal asthenia in Quarter Horses

OBJECTIVE: To assess heritability and mode of inheritance for hereditary equine regional dermal asthenia (HERDA) in Quarter Horses. ANIMALS: 1,295 horses with Quarter Horse bloodlines, including 58 horses affected with HERDA. PROCEDURE: Horses were classified as affected or unaffected or as undetermined when data were insufficient to assess phenotype. Pedigree data were analyzed to determine the probable mode of inheritance. Heritability was estimated by use of Bayesian statistical methods. RESULTS: Heritability (mean+/-SD) of HERDA was estimated to be 0.38+/-0.13, with both sexes having an equal probability of being affected. Results for evaluation of the pedigrees were consistent with a single Mendelian autosomal recessive mode of inheritance. CONCLUSIONS AND CLINICAL RELEVANCE: HERDA in Quarter Horses is an inherited disease, and affected horses are more likely to produce affected offspring. An autosomal recessive mode of inheritance should be considered by people making breeding decisions involving Quarter Horses when a first-degree relative has been confirmed with HERDA or has produced affected offspring. In addition, breeders whose horses have produced affected offspring can reduce the likelihood of producing affected horses in the future by avoiding inbreeding.     

Ehlers-Danlos Syndrome in a Quarter Horse Gelding: A Case Report of PPIB-Independent Hereditary Equine Regional Dermal Asthenia

A Quarter Horse gelding presented with pathology consistent with hereditary equine regional dermal asthenia (HERDA) but without the familial association typically present with this disease. Grossly, lesions exhibited either a firm, scar-like appearance or a potential space between the superficial and deep dermis. Both lesioned and non-lesioned skin showed evidence of edema and collagen fragmentation, whereas lesions were also characterized by hemorrhage and inflammation. Genetic testing was performed by three independent laboratories, each using different methods to detect the mutation described in the PPIB gene, previously shown to be associated with HERDA. No mutations in the PPIB gene were revealed by genetic testing, either at the known location of the point mutation or at any other location in the coding sequence. These findings are suggestive of a diagnosis of HERDA or hyperelastosis cutis in the absence of the well-described, putatively causative mutation in the PPIB gene. We propose that, whereas HERDA refers specifically to a familial disease caused by a mutation in the PPIB gene, similar symptoms may in fact be caused by a syndrome resulting from either inherited or spontaneous mutations in any of a number of collagen-processing genes. We conclude that Ehlers-Danlos syndrome be diagnosed in horses of any breed with HERDA-like pathology without the causative mutation.     

Clinical and pathological findings in a HERDA-affected foal for 1.5 years of life

A Quarter horse filly bred from two horses affected with HERDA (hereditary equine regional dermal asthenia) was observed clinically and its skin histologically for the 1.5 years of its life. Severe signs of the disease did not manifest until 1.5 years of age, and were not temporally related to saddling. Histological comparison to an age-, breed- and sex-matched control did not show any consistent diagnostic features. Monitoring of the proband substantiated previous reports of (i) the autosomal recessive nature of the disease, (ii) mares affected with HERDA being able to foal without damage to the skin or reproductive tract, (iii) HERDA foals appearing phenotypically normal throughout the first year of life, and (iv) demonstrated that histological interpretation of skin specimens from grossly normal skin may be insufficient to differentiate HERDA-affected horses from controls.     

Superficial, nonhealing corneal ulcers in horses: 23 cases (1989-2003)

Objective To characterize superficial, nonhealing corneal ulcers in the horse and to assess the affect of age, breed, sex, inciting cause of the ulcer, and treatment on healing time of these ulcers. Design Retrospective study. Animals Twenty‐three horses with superficial, nonhealing corneal ulcerations. Procedure Medical records from 1989 to 2003 of horses diagnosed with superficial, nonhealing corneal ulcers were reviewed. Signalment, duration of clinical signs, ophthalmic abnormalities, treatment and response to treatment were recorded. Horses were treated, in addition to medical therapy, using debridement, debridement and grid keratotomy, superficial keratectomy, and superficial keratectomy with conjunctival graft placement. Results Mean age ± SD of horses was 13.7 ± 5.8 years. The mean time of presence of the corneal ulceration was 38.9 ± 21.3 days. Mean time to complete re‐epithelialization of the corneal ulcers after treatment was 20 ± 14.7 days. Horses treated with debridement alone, grid keratotomy and superficial keratectomy healed in a mean time of 15.3 ± 14.6 days, 16 ± 12.6 days, and 22.8 ± 6.7 days, respectively. Conclusions and clinical relevance Horses treated with a single debridement at initial evaluation healed in a significantly shorter time period than horses treated with grid keratotomy or superficial keratectomy. The latter two procedures may be beneficial in the treatment of nonhealing ulceration in horses, but the results of this study suggest that these procedures should only be performed following failure of the ulcer to heal after epithelial debridement.     

Industry Perceptions of HERDA in Performance Horses

Hereditary equine regional derma asthenia (HERDA), an autosomal-recessive trait, found in Quarter Horses, causes abnormal collagen structure. Owing to current breeding practices, 3.5% of registered quarter horses and 28.3% of the cow horse population are heterozygote carriers. Research demonstrated homozygote horses develop hyperextensible skin susceptible to injury and other abnormal tissues containing high fibrillar collagen content. No research exists determining the effects of the disease in heterozygote carriers. Currently, 30% of cutting sires are HERDA carriers, potentially increasing the number of heterozygous individuals when bred. The objective of the present study is to gauge knowledge of the disease, perception, and concerns of the diseases’ impact on horse performance and perceived value and breeding decisions. A Qualtrics link was distributed to horse owners via extension specialists and was available online on equine-related Facebook pages. Overall group means and standard deviations for constructs were reported. A total of 228 responses were collected. Most participants were involved in reining and cutting and 34.6% reported they were very familiar with the disease. Participants (78.5%) reported that HERDA status affects value of a breeding animal. Owners of HERDA carriers (62.5%) noticed no difference in performance or injury compared with noncarriers. Respondents (95.2%) believed that all breeding animals should have HERDA status available. Respondents are attempting to make informed breeding decisions based on HERDA status by pairing carriers with noncarriers; however, it remains to be seen if that is adequate to control the disease. Education regarding breeding practices and its impact on the genetic pool are warranted.     

Effects of Topical Application of Sunflower-Seed Oil on Experimentally Induced Wounds in Horses

The objectives were to evaluate clinical and histopathological aspects of topical application of sunflower-seed oil (Helianthus annuus) on the healing process of experimentally induced wounds in lumbar and metacarpal areas of healthy horses. Six adult horses were used. Eight wounds were surgically produced on each horse: two 6.25-cm² wounds cranial to the sacrum on each side of the lumbar region and two 2.89-cm² wounds close to the proximal epiphysis of the metacarpus on the lateral aspect of each forelimb. Left side was used for macroscopic observations and right side for histopathological analysis. The experimental lesions were treated daily with sunflower-seed oil, whereas saline solution was used in control lesions. Macroscopic and histopathological analyses were performed on tissue harvested at 3, 7, 14, and 21 days. Complete healing time for all wounds was recorded. For lumbar region’s wounds, a contraction of 90.78% was recorded for those treated with oil and of 79.27% for control wounds after 21 days of treatment. For metacarpal region’s wounds, a contraction of 47.63% was recorded for wounds treated with oil and of 30.21% for control wounds. Wounds in the sunflower-seed oil treatment group had an elevation of polymorphonuclear cells, a newly formed vascular bed during the inflammatory phase, and a better alignment of collagen fibers during the remodeling phase. In conclusion, topical application of sunflower-seed oil was beneficial in the healing process of experimentally induced skin wounds in horses, with best results for treatment of lumbar wounds, making it a therapeutic option in equine wound healing.     

Grid keratotomy as a treatment for superficial nonhealing corneal ulcers in 10 horses

OBJECTIVE: To describe the clinical symptoms of 10 cases of superficial nonhealing corneal ulcers in horses and to evaluate the results of grid keratotomy in these patients. DESIGN: Retrospective study. ANIMALS: Ten horses with superficial nonhealing corneal ulceration in one eye. PROCEDURE: The signalment, history and clinical symptoms are reported of 10 patients with superficial nonhealing corneal ulcers during the period from August 2003 to February 2005. Grid keratotomy was performed in all cases. In addition, the surgical procedure of grid keratotomy and response to therapy are described. RESULTS: Horses generally responded well to grid keratotomy (eight cases healed after one grid keratotomy and one horse healed after a second grid keratotomy; one case was not available for follow-up). Only 2/10 had discomfort after treatment and only 2/9 had some degree of scarring after treatment. The healing time, which was known in seven cases, averaged 8.4 days (+/- SD 4). CONCLUSIONS AND CLINICAL RELEVANCE: Grid keratotomy is an appropriate option for treatment of superficial nonhealing corneal ulcers in horses. The procedure is simple to perform. It generally induces a rapid and uncomplicated healing of the cornea. Only in a limited number of cases does a small amount of scarring occur.     

Microbiology of equine wounds and evidence of bacterial biofilms

Horse wounds have a high risk of becoming infected due to their environment. Infected wounds harbour diverse populations of microorganisms, however in some cases these microorganisms can be difficult to identify and fail to respond to antibiotic treatment, resulting in chronic non-healing wounds. In human wounds this has been attributed to the ability of bacteria to survive in a biofilm phenotypic state. Biofilms are known to delay wound healing, principally due to their recalcitrance towards antimicrobial therapies and components of the innate immune response. This study describes the presence of bacterial biofilms within equine wounds. Thirteen 8-mm diameter tissue samples were collected from (n=18) chronic wounds. Following histological staining, samples were observed for evidence of biofilms. Fifty one wounds and control skin sites were sampled using sterile swabs. Control skin sites were on the uninjured side of the horse at the same anatomical location as the wound. The isolated bacteria were cultured aerobically and anaerobically. The biofilm forming potential of all the isolated bacteria was determined using a standard crystal violet microtitre plate assay. Stained tissue samples provided evidence of biofilms within 61.5% (8 out of 13) equine wounds. In total 340 bacterial isolates were identified from all the equine wound and skin samples. Pseudomonas aeruginosa and Enterococcus faecium were the most predominantly isolated bacterial species from equine wound and skin samples respectively. Staphylococcus was the most commonly isolated genus in both environments. Bacteria cultured from chronic and acute wounds showed significantly (P<0.05) higher biofilm forming potential than bacteria isolated from skin. This paper highlights preliminary evidence supporting the presence of biofilms and a high microbial diversity in equine chronic wounds. The presence of biofilms in equine wounds partly explains the reluctance of many lower limb wounds to heal. Non-healing limb wounds in horses are a well documented welfare and economic concern. This knowledge can be used to shape future treatments in order to increase the healing rate and decrease the costs and suffering associate with equine wounds.     

Second-intention repair in the horse and pony and management of exuberant granulation tissue.

Second-intention repair is faster in ponies than in horses and faster in body wounds than in limb wounds. To a large extent, the differences between horses and ponies can be explained by differences in the local inflammatory response, which are a result of the functional capacity of leukocytes. In ponies, leukocytes produce more inflammatory mediators,resulting in better local defense, faster cellular debridement, and a faster transition to the repair phases, with more wound contraction. In horses,leukocytes produce fewer mediators, initiating a weak inflammatory response, which becomes chronic. This inhibits wound contraction and gives rise to the formation of exuberant granulation tissue. The anatomic environment that influences the inflammatory response and wound contraction most probably determines the differences between body and limb wounds. In body wounds, better perfusion results in faster initiation of the inflammatory phase. The weaker local resistance results in a greater degree of contraction. In limb wounds, particularly of horses, the initial inflammatory response is weak and wound contraction is restricted. Both factors give rise to chronic inflammation, which further inhibits wound contraction and promotes exuberant granulation tissue. The high incidence of exuberant granulation tissue in limb wounds of horses can thus be explained by the chronicity of the inflammatory response as well as by the common use of bandages during treatment. Chronic inflammation is often not recognized as a cause of exuberant granulation tissue. It must be prevented and treated to promote the healing process. Bandages and casts stimulate the formation of exuberant granulation tissue; however, they are advantageous in many respects and play an important role in support of the overall healing process.     

Treatment of suppurative facial cellulitis and panniculitis caused by Corynebacterium pseudotuberculosis in two horses

Two horses were examined for large head wounds suspected to be the result of trauma and characterized by extensive necrosis of the skin and subcutaneous tissue, with abundant purulent exudate. Corynebacterium pseudotuberculosis was isolated from the facial wounds in both horses. Histopathologic examination revealed severe suppurative cellulitis and panniculitis with fistulous tracts and granulation tissue in 1 horse. Both horses were treated with local wound care, nonsteroidal anti-inflammatory drugs, and administration of antimicrobials. The concept of moist wound care was used in the second horse, with products that have recently become available for veterinary wound management. Outcome in both horses was good.     

The modified Meek technique as a novel method for skin grafting in horses: evaluation of acceptance, wound contraction and closure in chronic wounds

REASONS FOR PERFORMING STUDY: The acceptance of skin grafts in horses is unpredictable and the final cosmetic result can be disappointing. Besides movement and infection, graft failure is often caused by chronic inflammation, inherently present during second intention healing of limb wounds in horses. In human burns affected by infection and inflammation, the acceptance of the island skin grafts of the modified Meek technique appeared to be better than meshed sheet skin grafts. HYPOTHESIS: The percentage take of Meek micrografts is higher than of other techniques; and rates of both wound contraction and epithelialisation are increased. METHODS: Large traumatic limb wounds of 13 horses healing by second intention were grafted using the modified Meek technique. Photographs of the wounds were taken at set intervals. Wound areas, and areas of acceptance and rejection were determined using a digital image post processor (Scion Image). The percentages of take, wound contraction and epithelialisation were calculated. RESULTS: The initial mean wound area was 7500 mm2. Graft acceptance was mean +/- s.d. 93.7 +/- 5.9%. Wound closure was due to contraction (55.2 +/- 11.1%) and epithelialisation (44.8 +/- 11.1%) and resulted in a 96.7 +/- 3.6% reduction of the initial wound area 29.1 +/- 6 days after grafting. All wounds showed functional and cosmetic healing. CONCLUSIONS: The method for skin grafting in horses achieved higher percentages of take than reported previously and consistent cosmetic and functional results. The grafts increased not only the rate of epithelialisation but also had a strong positive effect on wound contraction, resulting in rapid closure and smaller scars. POTENTIAL RELEVANCE: The modified Meek technique proved to be a novel technique for skin grafting equine wounds in clinical practice, which can be performed easily. The molecular background of the increase of wound contraction by the grafts may provide a clue in the search for medicinal stimulation of wound contraction during second intention healing.     

Nonhealing corneal ulcers in cats: 29 cases (1991-1999)

OBJECTIVE: To compare mean healing times after debridement, debridement with grid keratotomy, and superficial keratectomy in cats with nonhealing corneal ulcers. DESIGN: Retrospective study. ANIMALS: 29 cats with 36 nonhealing corneal ulcers. PROCEDURE: Medical records of cats with nonhealing corneal ulcers were reviewed. Signalment, duration of clinical signs, ophthalmic abnormalities, and response to various treatment protocols were recorded. RESULTS: Mean age of affected cats was 7 years, 8 months. Affected breeds included domestic shorthair (17 cats), Persian (9), Himalayan (2), and Siamese (1). Clinical signs were evident for approximately 2 weeks prior to referral. Both eyes were affected in 4 cats. Mean healing time of ulcers treated with superficial debridement was 30 days. Mean healing time of ulcers treated with superficial debridement and grid keratotomy was 42 days. Superficial keratectomy was performed on 2 eyes and resulted in a healing time of 2 weeks. Formation of a corneal sequestrum was evident in 2 of 21 eyes treated with superficial debridement. Formation of a corneal sequestrum was evident in 4 of 13 eyes treated with superficial debridement and grid keratotomy. CONCLUSIONS AND CLINICAL RELEVANCE: Brachycephalic cats appear to be predisposed to developing nonhealing corneal ulcers. The combination of superficial debridement and grid keratotomy did not decrease mean healing time of nonhealing ulcers, compared with superficial debridement alone. Grid keratotomy may predispose cats with corneal ulcers to develop a corneal sequestrum.     

Effects of 25% propylene glycol hydrogel (Solugel) on second intention wound healing in horses

OBJECTIVE: To evaluate the effect of a commercially available 25% propylene glycol hydrogel preparation (Solugel; Johnson and Johnson Medical, North Ryde, Australia) on healing of full-thickness skin wounds on the distal aspect of the limb in horses. STUDY DESIGN: Experimental. ANIMALS: Eight Standardbred horses. METHODS: Standardized (2.5 x 2.5 cm) full-thickness skin wounds were created over the mid-dorsomedial aspect of both metacarpi in 8 horses. One wound in each horse was dressed with saline solution (0.9% NaCl) soaked gauze, and one was treated with Solugel under dry regular gauze; wounds were then bandaged with gauze-coated cotton wool and elastic adhesive bandages. Wounds were videorecorded and rebandaged twice weekly until healed. Wound healing variables were measured from the videorecordings using a computer software package and analyzed as a randomized complete block design with repeated measures. Where necessary variables were made positive for analysis; significance was set at P <.05. RESULTS: The area of the wound at the first bandage change did not vary between treated and untreated wounds. Treatment had no effect on the total rate of healing, rate of healing during the retraction phase of healing, rate of healing after the retraction phase was complete, or the amount the wounds retracted. CONCLUSIONS: Using this model of wound healing, Solugel had no effect on second intention healing of distal limb wounds in horses. CLINICAL RELEVANCE: Solugel does not appear to have any beneficial effect on healing of small full-thickness skin wounds to the distal limb of horses.     

Pathomorphological study on gastroduodenal ulceration in horses: localisation of lesions

Gastroduodenal ulceration is a prevalent disease in foals and adult horses. Decreased performance as well as fatal complications relate to this syndrome. The objective of our study was to determine the prevalence of gastric ulceration in a mixed population of horses by postmortem examination and to evaluate a possible association between equine gastric ulcer syndrome (EGUS) and sex or age of the examined horses, to evaluate the localisation of lesions in the proximal part of the gastrointestinal tract and to determine the occurrence of gastric parasites. Postmortem examinations were performed on 71 horses over a period of 24 months. Gastric ulcers were found in 52 horses (73.2%). There was no significant association between age or sex and occurrence of gastric ulcers. In all horses the squamous mucosa lesions were localised near the margo plicatus (100% of the cases), whereas in 23 horses the lesions were near the margo plicatus and lesser curvature and in 7 horses at the greater curvature. In 18 horses the mucosa was affected in the whole extent of the margo plicatus and in 1 horse diffuse lesions of the squamous mucosa were noted. Lesions of the glandular mucosa were localised in 11 horses at the fundic area, in 1 horse they occurred in the pylorus, and in 10 horses diffuse lesions of the glandular mucosa were recorded. A low prevalence of Gasterophilus intestinalis infection was detected (1 horse, 1.4%). We have confirmed that gastric ulcers are a common problem in horses and duodenal or oesophageal ulceration is rare (not a single case of the latter was found in this study). Lesions in the glandular mucosa of the stomach are more frequent in suckling foals than in older animals. Lesions of the glandular mucosa are also common in adult horses, and a complete gastroscopic examination including examination of the pylorus is advisable to evaluate this syndrome.     

Oesophageal obstruction in an aged pony associated with squamous cell carcinoma

An aged miniature pony was referred for chronic recurrent oesophageal obstruction. Endoscopic examination demonstrated distal oesophageal constriction and radiography confirmed an irregular soft tissue mass in the region of the distal intrathoracic oesophagus. The pony was subjected to euthanasia and post mortem examination confirmed squamous cell carcinoma of the distal oesophagus and stomach. Oesophageal squamous cell carcinoma is a rare condition in horses, but should be considered as a differential diagnosis in cases of chronic recurrent obstruction, particularly in older horses.     

Effects of hyperbaric oxygen on full-thickness meshed sheet skin grafts applied to fresh and granulating wounds in horses

OBJECTIVE: To determine the effects of hyperbaric oxygen therapy (HBOT) on full-thickness skin grafts applied to fresh and granulating wounds of horses. ANIMALS: 6 horses. PROCEDURES: On day 0, two 4-cm-diameter circular sections of full-thickness skin were removed from each of 2 randomly selected limbs of each horse, and two 4-cm-diameter circular skin grafts were harvested from the pectoral region. A skin graft was applied to 1 randomly selected wound on each limb, leaving the 2 nongrafted wounds to heal by second intention. On day 7, 2 grafts were harvested from the pectoral region and applied to the granulating wounds, and wounds grafted on day 0 were biopsied. On day 14, 1 wound was created on each of the 2 unwounded limbs, and the wounds that were grafted on day 7 were biopsied. All 4 ungrafted wounds (ie, 2 fresh wounds and 2 wounds with 1-week-old granulation beds) were grafted. The horses then received HBOT for 1 hour daily at 23 PSI for 7 days. On day 21, the grafts applied on day 14 were biopsied. RESULTS: Histologic examination of biopsy specimens revealed that grafts treated with HBOT developed less granulation tissue, edema, and neovascularization, but more inflammation. The superficial portion of the graft was also less viable than the superficial portion of those not treated with HBOT. CONCLUSIONS AND CLINICAL RELEVANCE: The use of HBOT after full-thickness skin grafting of uncompromised fresh and granulating wounds of horses is not indicated.     

The effect of equine recombinant growth hormone on second intention wound healing in horses

OBJECTIVE: To evaluate the effect of intramuscular administration of recombinant equine growth hormone on healing of full thickness skin wounds on equine limbs. STUDY DESIGN: Experimental. ANIMALS: Nine Standardbred horses. METHODS: In study 1, standardized full thickness skin wounds (2.5 x 2.5 cm) were made over the dorsomedial aspect of the mid-cannon bone of 1 forelimb and 1 hindlimb in 9 horses. Wounds were bandaged without treatment (control subjects) and videorecorded twice weekly until healed. Then, in study 2, similar wounds were created on the opposite limbs; 6 horses were administered intramuscular recombinant equine growth hormone (10 microg/kg daily for 7 days, then 20 microg/kg daily for 49 days), and 3 horses (control subjects) were administered equivalent volumes of sterile water. Wounds were videorecorded twice weekly until healed. Wound healing variables were measured from the videorecordings using a computer software package and analyzed as a randomized complete block design factorial analysis of variance; significance was set at P <.05. RESULTS: No differences in the measured variables were detected between wounds in study 1 and the control wounds in study 2. In recombinant equine growth hormone-treated horses, wounds retracted more during treatment and contracted faster after treatment stopped when compared with wounds from untreated horses. No other treatment effects were detected. CONCLUSIONS: Recombinant equine growth hormone seemingly increases wound retraction. After treatment ceases, wound contraction increases. CLINICAL RELEVANCE: Intramuscular administration of recombinant equine growth hormone (10 microg/kg daily for 7 days, then 20 microg/kg daily for 49 days) does not appear to have any beneficial clinical effect on healing of equine limb wounds.