Equine pelvic flexure impaction. A model used to evaluate motor events and compare drug response

Pelvic flexure fistulas (2.5 cm diameter) were established in eight 160 kg Shetland X ponies. Impaction was induced at the pelvic flexure 25 times in the 8 animals through partial obstruction by a 1 litre rubber rebreathing bag fixed at the fistula site. Blood flow probes were implanted on the dorsal and ventral colic arteries (right colic artery and colic branch of ileocolic artery) in two of the ponies. Intraluminal pressure changes were measured at 8 different locations in the large colon during episodes of colic and following administration of flunixin or xylazine. Episodes of colic characterized by pawing, anxiety, anorexia, and attempts to lie down during impaction correlated with longer, louder sounds on auscultation and multiple contraction (closely grouped series lasting 3-5 minutes) of greater than 40 mm Hg as interpreted from simultaneous intraluminal pressure recordings. Flunixin and xylazine relieved clinical signs for 30-60 minutes. Xylazine resulted in cessation of intraluminal pressure changes for 30 minutes, Flunixin relieved signs but did not interfere with intraluminal pressure changes. Mean arterial blood flow through the colic arteries doubled during episodes of colic. Following administration of flunixin during colic, blood flow remained elevated; however, following administration of xylazine during colic, blood flow decreased.