Impaction, Colonic - Horse

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Medical Treatment of Colic in Horses

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Pathophysiology

Anatomy

Impactions of the large colon occur where the luminal diameter narrows, especially the pelvic flexure and the right dorsal colon (RDC) (83 in Bliks)

Risk Factors

Sudden restriction in exercise associated with musculoskeletal injury (84) Twice daily feeding of concentrate - large fluxes of fluid into and out of colon, associated with readily fermentable carbohydrate in the colon and increases in serum aldosterone. Fluid fluxes may cause dehydration of ingesta during aldosterone-stimulated net fluid flux out of the colon (32). Amitraz - acaricide associated with clinical cases of colon impaction (85,86) - may alter pelvic flexure pacemaker activity resulting in uncoordinated motility patterns between the left ventral and left dorsal colon and excessive retention of ingesta. Absorption of water from ingesta increases with time, dehydrating the contents of the colon and resulting in impaction Parasite migration in the region of the pacemaker (87) Limited exercise Poor dentition Coarse roughage Dehydration

Clinical Signs

Slwo onset mild colic Reduced defaecation Faeces hard, dry and mucus-covered because of delaed transit Heart rate mildly elevated during painful episodes but often normal Colic signs typically well controlled with analgesics but become increasingly more severe and refractory if impaction not resolved