RABBIT NUTRITION AND DIETARY REQUIREMENTS

Rabbits are herbivores and nibblers as well. They do not see the area below the mouth, and so rely upon smell and tactile information from the whiskers of the upper lip as well as the cleft in the upper lip.

Energy requirements determine food intake for the rabbit; however other factors do come into play. Food intake decreases with a rise in environmental temperature above the preferred optimal temperature of 62 F. 

The digestive tract of the rabbit is adapted to a diet high in fiber. Rabbits are part of a group of animals known as "hind gut fermentors", meaning that much, if not most digestion takes place in the cecum and colon (digestion in the small intestine is via hydrolysis). The cecum is critical to the digestive process, making up about 40% of the tract, and is much larger than the stomach. The cecum and colon have haustra, which are large outpouchings along the walls. The haustra function to separate particles of fiber from liquid.

After a rabbit ingests fibrous foods, the proximal colon separates indigestible from fermentable materials, and eliminates the indigestibles as firm fecal pellets. Fermentable (digestible) materials are actively moved back into the cecum, where bacterial fermentation takes place. This is where volatile fatty acids are released (by bacteria), to be used as an energy source. Cecotrophs (known commonly as "night feces") are actually cecal contents that are periodically released to be consumed by the rabbit to recover amino acids and vitamins.  Cecotrophs are soft and mucoid, and are eaten directly from the anus. They are produced 4 to 8 hours after eating, and contain about twice the level of protein of the standard rabbit pelleted feed. The nutrients from the cecotrophs are absorbed by the small intestine.

In the world of rabbits, fiber intake is very important. The proximal colon separates fiber into small and large particles. Particles measuring >0.5mm are not digested, and do not enter the cecum. This indigestible fiber is necessary to stimulate GI motility, which moves fermentable products into the cecum.  Indigestible fiber also helps to maintain dental health and proper wear, in addition to stimulating appetite.  Particles measuring <0.3mm are digested in the cecum via bacterial fermentation. Chemical composition of the fermentable (digestible) fiber also plays a large role in its bacterial degradation.

Diets high in carbohydrates and low in fiber have long been implicated in enterotoxemia seen in young rabbits. Young rabbits seem to digest starches less efficiently than adults (stomach and small intestine are responsible), with residual starch reaching the cecum, resulting in bacterial flora imbalance. The causative organism for enterotoxemia is Clostridium spiroforme, which uses glucose as a substrate, which of course is a result of bacterial fermentation of carbohydrates.

Additionally, rabbits metabolize dietary calcium in a unique way. Most mammals regulate calcium uptake in the small intestine via parathyroid hormone (PTH) and vitamin D, calcitriol (1,25-dihydrocholecalciferol). When blood calcium levels drop, most mammals (but not rabbits) experience a rise in PTH from the parathyroids, which activates alpha hydroxylase in the renal tubule cells, which in turn increases calcitriol synthesis. Calcium and phosphorous absorption is therefore increased for 24 – 48 hours. However, rabbits are not most mammals.  Rabbits’ serum calcium instead fluctuates with dietary calcium. Why? Rabbits nearly completely absorb dietary calcium in the intestine. They excrete excess calcium in the urine as a precipitate after filtering it through their kidneys, while most mammals excrete excess calcium in bile and intestinal secretions. It also appears that vitamin D acts within the kidneys to regulate calcium excretion. 

What to feed the pet rabbit? Around the world, rabbits have been in commercial production for a very long time. As a result, the nutritional requirements for breeding, pregnant, lactating and weaning rabbits are well researched. Note that these animals all have short life spans. What is less clear, then, is the nutritional requirement of the pet rabbit, who it is hoped, will live a full, long life. Incorrect feeding can cause many problems for the pet rabbit. To compound the problem, owners are often provided incorrect information regarding rabbit nutrition. What, then, is an owner to do?

Generally, the adult rabbit should be offered free access to a high-quality grass hay, such as timothy. Examples of other grass hays are oat, brome, and orchard.  Alfalfa is a legume hay, along with clover, pea, and peanut, and has been associated, because of its' high calcium content, with urinary calculi, crystals, and/or sludge. Note the word "adult" above. Young rabbits, due to their growth requirements, may be offered alfalfa hay, in conjunction with timothy.

A good quality pellet should also be provided. Most stores carry only alfalfa-based pellets, however timothy-based pellets are also available. The calcium found in alfalfa, and the calcium carbonate found in most commercial pellets is highly absorbable. Calcium oxalate, on the other hand is found in many vegetables (spinach, cabbage, beet leaves, peas, among others). Most mammals (including rabbits) do not absorb, for all practical considerations, calcium oxalate. 

Ideally, pelleted diets should have a fiber content of 15–20%, a fat content of 1–3%, a protein level of 12–13%, and a calcium level of 0.5-1.0%. The calcium : phosphorous ratio should be 1.2-2 : 1. The diet should also contain vitamin D.  Recommendations regarding quantity range from 1/4 cup pellets per 2 1/2 pounds of rabbit per day to 1/4 cup pellets per 5 pounds of rabbit per day. Additionally, rabbits may be offered up to one cup of fresh vegetables per day.  The offerings should be consistent, to avoid upsetting those ever-temperamental microbes. Suggested offerings may include collards, dandelion greens, romaine, parsley, and kale, among others. Fruits should be kept to a minimum.

Nutrition has a great impact on the overall health of any creature, including the rabbit. Proper nutrition may prevent dental problems, behavioral problems, gastrointestinal problems, growth deficiencies, and urinary tract problems, among others. Proper nutrition will also help the immune system ward off disease, and lead to a longer, healthier life for the pet rabbit.

Below you will find a list of references and resources for additional information:

Antinoff, N:  Physical examination and preventive care of rabbits, Vet. Clin. of North America, Exotic Animal Practice 2:405-427, 1999

Harcourt-Brown, Frances:  Textbook of Rabbit Medicine. Butterworth-Heinemann, 2002

Hillyer & Quisenberry:  Ferrets, Rabbits and Rodents clinical medicine and surgery. WB Saunders, 1997

Jenkins, JR:  Feeding recommendations for the house rabbit, Vet. Clin. of North America, Exotic Animal Practice2:143-151, 1999

Johnson-Delaney, CA:  Rabbits. In Johnson-Delaney CA: Exotic Companion Medicine Handbook. Lake Worth, FL. Wingers Publishing, 1996

Kupersmith,  David S:  A Practical Overview of Small Mammal Nutrition, Seminars in Avian and Exotic Pet Medicine, Vol  7,  No 3 (July), 1998: pp141-147

Oxbow Pet Products, "Feeding the Pet Rabbit"

Redrobe, Sharon: Calcium metabolism in rabbits, Seminars in Avian and Exotic Pet Medicine,  Vol 11, No2, (April), 2002: pp 94-101