It is not uncommon after a horse defecates for a small ring of red rectal lining tissue to evert (turn outward or inside out) from the anus for a second after manure is passed, but then almost immediately disappear. It is abnormal for this to persist any longer than a second after the fecal ball is passed. If this sign is particularly prevalent in a horse, it could indicate that the manure is especially fibrous or dry and it might warrant an assessment by your vet.

Horses that strain to defecate for prolonged periods may force rectal tissue out through the anus. Severe abdominal pushing and straining can occur as a response to chronic diarrhea, constipation, and especially after prolonged labor (dystocia). This turning inside out (eversion) of the rectal tissue is known as rectal prolapse. Prolapsed tissue quickly becomes a swollen and will look like a firm red ball.

Gruesome aside: This finding in a dead horse is also not uncommon. Dead horses bloat and the pressure inside the belly forces the rectum to turn inside out. The presence of this finding does not say much about the cause of death.

Diagnosis of prolapse is obvious, via visual assessment. The severity needs to be determined though; How much of the rectal wall has prolapsed? The underlying cause needs to be diagnosed and managed.

In the case of simple prolapse, the tissue can be replaced manually. Often this procedure requires sedation and sometimes an epidural to prevent continued straining. Above all, the underlying problem causing the prolapse must be managed or resolved, and measures may need to be taken to ensure that the replaced tissue does not re-emerge.