Feeding a rabbit: its omnivorous diet and nutritional needs
There are many different classifications of diet compositions for animals. Diets that are composed of plant material are grouped as herbivorous, diets that are composed of animal material are grouped as carnivorous, and diets comprised of both plant and animal material are considered omnivorous. Animals that must eat material from one of these specific categories are considered obligates of that food type. Rabbits are classified as obligate herbivores, meaning that they must consume plant material in their diet in order to be healthy and thrive.
There are many reasons why animals evolve to require certain food types. Natural selection ensures that animals adopt traits that are most beneficial to their survival. In order to survive and combat predation, rabbits have many adaptations that increase their likelihood of escape. Along with having their eyes situated on the side of their head, thereby creating a good visual field to survey their surroundings; having upright ears adept at funneling sound; and having an unguligrade foot structure to ensure the longest stride possible; diet also plays an important role in a rabbits' defense strategy. Diets of dry, fibrous material enable rabbits to eat in open plains, a habitat that allows early and easy detection of any approaching predators. At the sighting of such a threat, a highly fibrous diet also aids a rabbit in its fast flight response. With its muscular hind legs, and a body skeleton which comprises a mere eight percent of its entire body weight, a rabbit is capable of very fast flight, an ability which will not be hindered by a stomach filled with a meal of fiber. A meal with a high fat or water content would sit significantly heavier in a rabbit's stomach, potentially slowing it down and making it victim to a faster predator.
In their natural wild habitat, rabbits are able to fend for themselves and eat meals that fulfill their dietary requirements. However, in captivity, it is easy to feed rabbits in such a way as to deprive them of certain nutrients and the high fiber content they have evolved to require. When such deficiencies occur, there are detrimental affects on the animal's health. Gastrointestinal problems are common in pet rabbits, and most "are related to inappropriate diets (low fiber; high protein; high carbohydrate) and infrequent feeding of treats to which the rabbit is not accustomed" (Davies). Other problems arise from an imbalanced diet as well. Feeding young rabbits too many carbohydrates causes enteritis characterized by overgrowth of undesirable bacteria, excess calcium can cause kidney disease, pregnancy toxemia occurs when by pregnant does are not fed the right nutrients and can result in seizures, and urolithiasis is a condition involving the formation of urinary stones due to the consumption of too much calcium. The dietary requirements of rabbits are not well understood, except that they do best when fed a combination of foods they would normally eat in the wild, and "problems can be avoided if captive rabbits are fed a diet consisting primarily of fibrous vegetation, such as grass, hay and fibrous weeds" (Davies).
Another evolutionary dietary characteristic of the rabbit is the practice of coprophagy. This refers to the production of both hard and soft feces and the ingestion of the latter type directly from the anus. The purpose of this particular behavior is to gain access to "water, protein, and B vitamins that the rabbit needs" (Gendron 41), all of which are contained in their soft feces. Problems arise when raising rabbits in captivity if owners consider this behavior abhorrent and attempt to stop it. Coprophagy is necessary in the health of a rabbit, and "when you try to keep a rabbit from eating this stool or if your rabbit is impacted and not passing stool, he will become ill from missing these nutrients" (41). Due to their anatomic limitations, rabbits are unable to absorb all the needed nutrients from their meals during the first digestion; and food must be processed multiple times to derive the utmost benefit of its contents.
Evolution has shaped the dietary requirements of the rabbit. The ingestion of feed of high fiber has allowed the rabbit to survive and flourish, and it has evolved many characteristics that complement and depend upon this diet. This dependence should be taken into account when rabbits are raised in captivity and their food source is provided for them solely by their caretakers. In order to have ideally healthy pets, diets should mimic a rabbit's natural food intake as much as possible, as most deviations from natural feed result in severe health problems.
The veterinary clinics of North America. Exotic animal practice [1094-9194] Davies, RR
yr: 2003 vol: 6 iss: 1 pg: 139
Gendron, Karen. The Rabbit Handbook. Barron's Educational Series, Inc. Hauppauge, New York 2000.