Clinical signs of colic are usually referable to pain, although the horse may appear depressed rather than painful in cases of necrosis (tissue death) of the gastrointestinal tract, inflammation of the intestines, endotoxemia, or significant dehydration.[38] Pain levels are often used to determine the need for surgery (See Surgical intervention). Horses are more likely to require surgery if they display severe clinical signs that can not be controlled by the administration of analgesics and sedatives, or have persistent signs that require multiple administrations of such drugs.[23] Heart rate is often used as a measure of the animal's pain level and a heart rate >60 bpm is more likely to require surgery.[21] However, this measure can be deceiving in the early stages of a severe colic, when the horse may still retain a relatively low rate.[23] Additionally, pain tolerance of the individual must be taken into account, since very stoic animals with severe cases of colic may not show adequate levels of pain to suggest the need for surgery.[7] High heart rates (>60 bpm), prolonged capillary refill time, and congested mucous membranes suggest cardiovascular compromise and the need for more intense management.[23] Decreased or absent gut sounds often suggest the need for surgical intervention if prolonged.[7][23][39]
A horse showing severe clinical signs, followed by a rapid and significant improvement, may have experienced gastrointestinal perforation.[38] While this releases the pressure that originally caused so much discomfort for the horse, it results in a non-treatable peritonitis that requires euthanasia. Soon after this apparent improvement, the horse will display signs of shock, including an elevated heart rate, increased capillary refill time, rapid shallow breathing, and a change in mucous membrane color. It may also be pyretic, act depressed, or become extremely painful.[35]
Gas distention usually produces mild clinical signs, but in some cases leads to severe signs due to pressure and tension on the mesentery.[38] Simple obstructions often present with a slightly elevated heart rate (