Rectum and Defecation
several times daily, strong and extensive mass movements of the colon move fecal material into the rectum. Distension of the rectum stimulates the need to defecate. The act of defecation requires contractions of smooth muscle in the wall of the rectum, and these result from a spinal reflex stimulated by distension of the rectum.
Conscious control of defecation involves inhibition of the spinal reflex and contraction of the external anal sphincter, which is composed of skeletal muscle. Contraction of abdominal muscles increases intra-abdominal pressure, which also assists with emptying the rectum.The variability in character and shape of feces among species is primarily a function of the structural and functional features of the more distal segments of the colon. in horses relatively strong segmentation contractions form the characteristic fecal balls.
Equine colic is a general term for any painful condition associated with the abdomen of the horse. Conditions associated with any segment of the gastrointestinal tract may result in colic, and clinical signs indicate that the degree of pain can vary from mild to severe. Causes of colic include ulcers; inappropriate diet, such as overload of grain or concentrates; infection; obstruction due to parasites or foreign bodies; impaction of feed or foreign material, such as sand; twisted segments of intestine; and alterations in intestinal motility. Management, including parasite control, proper diet, access to water, and attention to environmental hazards, is helpful in preventing the incidence of colic. Some causes of colic can be readily treated medically, but other causes threaten life and require prompt surgery.