Page 886 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Gastrointestinal system: 4.2 The lower gastrointestinal tr act 861

VetBooks.ir rupture can either occur during parturition or 4.175
result from type 3 or 4 rectal prolapse. During
the first stage of labour, the small colon may get
trapped between the uterus and the body wall
as the foal vigorously positions itself and rotates
from a ventral to a dorsal position. The mesocolon
may stretch and rupture during this manoeuvre.
During type 3 or 4 rectal prolapses, the mesoco-
lon vasculature becomes disrupted if >30 cm of the
distal small colon and rectum prolapse. Rupture
of the mesocolon and mesocolonic vasculature
results in infarction, causing segmental ischaemic
necrosis and functional obstruction of the small
colon. Progressive signs of colic and septic perito- Fig. 4.175 Typical post-mortem appearance of an infarct
nitis occur as a consequence. lesion of the peritoneal rectum and distal small colon.
The lesion in this broodmare resulted from a rupture of
Clinical presentation the mesocolon, which had occurred during parturition.
In the broodmare affected with segmental ischaemic
necrosis of the small colon, mild signs of colic occur Management
within 24 hours of parturition. Affected horses fail Exploratory coeliotomy and resection of the isch-
to pass faeces. If the condition is not treated, car- aemic segment of the small colon and anastomosis
diovascular status slowly deteriorates, and signs of should be performed. However, because of the loca-
septic peritonitis and shock develop. tion of the lesion, this procedure is rarely feasible
and end colostomy is the only procedure that may be
Differential diagnosis attempted to save the life of the affected horse.
Early signs of segmental ischaemic necrosis of the
small colon need to be differentiated from the mild Prognosis
abdominal pain associated with uterine contractions. The prognosis is directly correlated with the loca-
Differential diagnoses also include conditions asso- tion of the lesion: if it is orad enough that resection
ciated with small-colon obstruction, septic perito- and anastomosis can be performed, the prognosis is
nitis and parturition-associated reproductive tract fair; if the lesion is too aborad for an anastomosis to
disease. be performed, the prognosis is grave.

Diagnosis RECTAL TEARS
A history of recent parturition or rectal prolapse
with reduced or lack of faecal production can be Definition/overview
indicative of segmental ischaemic necrosis of A rectal tear occurs when at least one of the rectal
the small colon in horses displaying mild signs wall layers is disrupted. Most rectal tears occur dur-
of colic. Rectal examination may not be initially ing transrectal palpation; they are generally located
diagnostic, but as the condition progresses, one 20–30 cm from the anus, in the dorsal portion of the
or several firm, tubular and digesta-filled loops rectum, and have a longitudinal direction. Young
of small colon can be palpated. Abdominocentesis horses, males and Arabian horses are more fre-
initially reveals abdominal haemorrhage, with an quently affected than other horses.
increased WBC count and protein level as the
condition progresses. Exploratory coeliotomy will Aetiology/pathophysiology
often be the only way definitively to diagnose the Rectal tears are most commonly iatrogenic in origin.
condition (Fig. 4.175). The aetiology includes transrectal palpation, enema