The large intestine, named for its large diameter, is shorter in length: about 10-20% of the length of the small intestine. Functions of the large intestine include:

Water and electrolyte absorption
Fecal storage
Fermentation of ingested food fibers by beneficial bacteria
Inflammation of the large intestine, termed colitis, causes: straining to defecate and soft stool that may contain fresh blood and/or mucus. Dogs with colitis alone do not act sick beyond the soft stool. The most common causes of colitis in dogs include dietary indiscretion/intolerance and parasites.