Rabbits are an herbivore, which means rabbits are designed to eat only plant material. Rabbits have a simple one-chambered stomach, a large cecum, and a rather complex digestive physiology that features fermentation in the cecum to break down plant fiber and starch. In addition herbivores need to have food constantly moving through their digestive system. Wild rabbits eat about 30 times per day.
A diet that contains a large amount of fiber from grass hay is vital to maintain the health of a pet bunny. The fiber from the grass hay helps to prevent two of the most common health problems of pet bunnies: dental disease and gastrointestinal disease.
All 28 teeth of the rabbit are continuously growing (elodent). These teeth can be divided into two main types. The teeth at the front of the mouth are called incisors, and the cheek teeth are the premolars and molars. When a rabbit eats, he uses the incisors to cut the grass or vegetation and then uses the cheek teeth to grind up the plant material. This normal grinding of the food also causes the teeth to grind against each other in a side to side fashion instead of an up and down direction. The rabbit’s jaw may move side to side as much as 120 times per minute while grinding plant material. This side to side grinding of the teeth also wears the teeth down and prevents the constantly growing teeth from becoming too long.
When pet rabbits eat mostly low fiber material, such as carrots and pellets, or soft foods like bread, cereal and treats, they do not do the normal side to side chewing and grinding of the teeth. This allows the teeth to become too long, which can cause serious dental problems like fractured teeth, infections and abscesses above the roots of the teeth (periapical), cuts to the tongue and inner cheek, and infection of the jaw (osteomyelitis). These dental problems can make it painful to eat and lead to reduced food intake, anorexia and even starvation.
The other serious and potentially fatal problem from a low-fiber diet is gastrointestinal disease. If a rabbit eats a low-fiber diet there will not be enough fiber to keep the regular wavelike movement of the gastrointestinal tract normal, and the movement of the GI tract will decrease. This can lead to impactions of the stomach from hair (hairballs), changes in the cecum pH and changes in the bacteria in the cecum. The normal “good” bacteria of the cecum that is required for fermentation of fiber is replaced by “bad” pathogenic bacteria, such as Clostridium and Escherichia coli. Overgrowth of these “bad” bacteria can cause diarrhea, dehydration and death. In addition a low-fiber diet typically has a high carbohydrate level. Carbohydrates also decrease the mobility of the gastrointestinal tract, increase the amount of bad bacteria, and can cause death from a toxin produced by Clostridium (enterotoxemia).
A diet that contains mostly grass hay like timothy hay, oat hay, fescue, and/or ryegrass is a must for maintaining a rabbit’s health. Grass hay also helps to prevent obesity. A rabbit should eat a pile of hay that is roughly the size of the bunny every day and should have fresh, clean hay available at all times. Alfalfa hay is only recommended for young growing bunnies, pregnant and lactating does, and for sick bunnies. Alfalfa should not be fed routinely to healthy, adult rabbits because it may cause obesity and bladder stones (calcium oxalate) from the excessive amount of calcium in alfalfa.
Fresh vegetables such as carrots, beets, broccoli tops, romaine lettuce, cauliflower, celery leaves, cabbage, kale, and leafy greens like clover, collard, mustard, and dandelion greens should also be offered in small amounts daily. High-fiber (greater than 18 percent fiber) pellets should be a small portion of the diet. Low-fiber pellets and mixed rations that contain seeds, nuts, corn, and fruit should be avoided. Also avoid high carbohydrate foods, such as beans, peas, corn, bread, breakfast cereal and sugary treats. Small pieces of fruit can be used as an occasional treat or as a reward for good behavior.