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rates of short-term survival to discharge of 83% (10/12) and 58% survival at 13 months post-operatively (Archer et al. 2006). However, a separate study suggested that these lesions could be left in situ, with resection and anastomosis only performed in 1/28 cases of IFEE in which 100% of cases survived to hospital discharge (Perez Olmos et al. 2006). In the authors’ hospital, IFEE cases now routinely undergo manual decompression only and are not resected unless intestinal viability or severe luminal obstruction is a concern. This suggests that IFEE lesions would appear to have different characteristics with regard to mucosal barrier function and progression of lesion necrosis when compared with eosinophilic lesions of the small or large colon. Resection of the affected portion of small colon was


performed in four out of five of the horses in this series. Due to the degree of mural thickening and concerns about focal necrosis already developing at the site, leaving the affected portion of colon in situ was considered likely to result in a poor prognosis for survival. Several factors should be considered when undertaking resection of small colon including the frequent large amounts of adipose tissue in the mesentery making vessel identification and ligation more difficult and the need to ensure that the mesenteric portion of the anastomosis is secure to prevent leakage occurring (Rakestraw and Hardy 2012). High concentrations of collagenase and bacteria within the bowel, along with the mechanical stress endured by movement of hard faecal balls within the lumen post-operatively may also result in the potential for leakage of the anastomosis to occur (Rakestraw and Hardy 2012). In man, small colon bacterial populations are rich in aerobic and anaerobic bacteria and contain a high level of matrix metalloproteinases (MMPs), with abnormal upregulation of MMPs and disturbances in the extracellular matrix identified in patients with anastomotic leakage following colorectal surgery (Stumpf


et al. 2005).


Complications following enterotomy or resection and anastomosis of the small colon in horses, however, are rare, being reported to occur in just under 5% of cases (Prange et al. 2010), including dehiscence of part of the anastomosis which occurred in one case in the present study. Median survival times following small colon resection have been reported at just under 3 years, which is lower when compared with horses with a primary lesion of the small colon not requiring resection, reported at just under 8.5 years (de Bont et al. 2013). The histopathological


findings reported in focal


eosinophilic lesions affecting the large colon (Edwards et al. 2000), are similar to the lesions of the small colon described in


the present case series, but there are some contrasting findings compared with histopathological features of focal lesions affecting the small intestine. Necrotic mucosa in the small colon cases contained neutrophils and eosinophils, with bacterial colonisation on the surface of devitalised mucosa, consistent with similar lesions in the large colon (Edwards et al. 2000). In contrast, IFEE lesions typically had a moderate diffuse inflammation of the lamina propria of the mucosa, with mild to moderate changes associated with the lamina epithelialis mucosae, represented by short, stubby or shattered villi and focal necrosis or erosion of villous tip epithelial cells (M€


akinen et al. 2008). In the latter lesions,


lymphocytes dominated the inflammatory infiltrate, followed by macrophages, eosinophils, plasma cells and neutrophils in decreasing numbers (M€


akinen et al. 2008). The submucosal


regions of the large colon lesions reported by Edwards et al. (2000) were again similar to the lesions of the small colon described in the current study and were characterised by oedema, fibrinous exudation, lymphatic dilatation and thrombosis, with eosinophilic infiltrates of varying intensity. In addition, variable features included small numbers of neutrophils, submucosal fibroplasia and granulation tissue formation (Edwards et al. 2000). In contrast, the transmural inflammatory infiltration within the submucosa of IFEE lesions was dominated by eosinophils and macrophages, with smaller numbers of lymphocytes, plasma cells and neutrophils (M€


akinen et al. 2008). Diffuse oedema and hyperaemia was


often noted, with occasional focal areas of necrosis representing degenerate eosinophils (M€


akinen et al. 2008).


The muscularis of the large colon was generally well preserved in eosinophilic colitis lesions with variable focal necrosis, oedema and fibrinous exudate (Edwards et al. 2000). The transmural inflammatory infiltration within the muscularis of IFEE lesions was dominated by eosinophils and macrophages (M€


akinen et al. 2008), similar to findings in the


muscularis of the small colon in the current series. In addition, swelling, vacuolation and necrosis of the muscularis was evident in IFEE lesions (Archer et al. 2006). Histologically, the serosal surfaces of large colon lesions were hyperaemic, oedematous and infiltrated by variable numbers of eosinophils (Edwards et al. 2000), again similar to the lesions described in the current study, which were intensely hyperaemic. Focal inflammatory infiltrates were reported to often, but not always, extend to the serosal layer of IFEE lesions (M€


akinen et al. 2008). The cause of the focal lesions in the current series and


those affecting the large colon (Edwards et al. 2000) and small intestine (Archer et al. 2006, 2015; M€


akinen et al. 2008),


remains unknown and requires further research. There was no evidence of a primary cause for the eosinophilic infiltrate in the current series based on histopathological examination. Eosinophilic gastrointestinal disease (EGID) is uncommon in man and characterised by either focal or diffuse eosinophilic infiltrate within the gastrointestinal tract, without evidence of known causes of eosinophilia including parasitism, drug reactions and malignancy (Rothenberg 2004; Sheikh et al. 2009). Gastroduodenal involvement is most commonly seen, with cases rarely affecting the colon (Sheikh et al. 2009). Indeed, eosinophilic colitis represents the least frequent manifestation of EGID, irrespective of whether or not other segments of the gastrointestinal tract are involved (Guajardo et al. 2002). The disease has been classified into mucosal, submucosal (transmural) and serosal forms, based on the predominant location of eosinophilic infiltrates (Klein et al. 1970; Talley et al. 1990). Gastrointestinal obstruction is uncommon and associated primarily with the transmural form of the disease, manifesting as gastric outlet or duodenal obstruction and intestinal thickening (Sheikh et al. 2009). The transmural form has also been associated with intussusception, volvulus and perforation (Fraile et al. 1994; Box et al. 1997; Velchuru et al. 2007) and may therefore be most similar to the lesions seen in the small and large colons in horses. The serosal form is distinguishable by the presence


of eosinophilic ascites, with up to 88% eosinophils seen on fluid analysis (Kravis et al. 1982). Peripheral eosinophilia has also been reported in up to 80% of cases (Khan and Orenstein 2008). Mucosal predominant disease results in mucosal dysfunction and manifests clinically as protein-losing


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