Diet and Digestive Tract

In the wild, rabbits eat low level leaves, shoots, and grasses. The composition of the grass they eat is approximately 20-25% crude fiber, 15% crude protein, and 2-3% fat. [89] Strangely, rabbits digest cellulose poorly, which is a paradox for a herbivore. However, this results in the rapid elimination of large particles of cellulose, and consequently, allows for a smaller, lighter digestive tract, and a higher rate of food intake than would otherwise be possible. [90] Another feature of their digestive system is the production of two types of droppings. A dry black fecal pellet (often called a cocoa puff), and a soft green nutrient packed cecotrope. These cecotropes are essential to the good nutrition of the rabbit. [91] A rabbit's digestive tract is very complicated and makes up 10 to 20% of its bodyweight. [92] As food travels down the rabbit's esophagus, it passes through a junction between the esophagus and the stomach called the cardia. The cardia is a region that contains a valve called the cardiac sphincter. In rabbits this valve is well developed, and makes the rabbit unable to vomit. [93] [94] After passing through the cardia the food enters the stomach. The stomach is a thin-walled large organ, that almost always contains food, hair, caecal pellets, and fluid even after 24 hours of fasting. [95] [96] [97] After being mixed with stomach acid the food moves through a junction called the pylorus. This junction joins the stomach to the duodenum, which is the first of three parts that make up the small intestine. [98] The small intestine is where most of the nutrient extraction occurs. After the duodenum, the food passes through the second part of the small intestine, the jejunum. The last third of the small intestine is called the ileum. At the end of the ileum is the sacculus rotundus where the small intestine widens and its walls thicken. This dilated globule of the small intestine is rich in lymphoid follicles, and opens into a saucer shaped thickening of the walls of the large intestine or colon. As the food passes into the colon it passes by the ileo-cecal valve, which leads to the cecum. [99] Colonic contractions (also known as peristaltic waves) move fibrous particles rapidly through the colon, which extracts most its water content before excretion at the anus. At the same time, these waves separate out non-fibrous particles. Then anti-peristaltic (reverse) waves move fluid and non-fibrous particles back up the colon and through the ileo-cecal valve into the cecum for fermentation. Three to eight hours after eating, soft mucus-covered cecal pellets, looking very much like small clusters of grapes, appear at the anus. Instinctually, the rabbit will eat these without chewing, thus keeping the mucous coating intact. This coating protects the vitamin and nutrient rich bacteria from stomach acid, until it reaches the small intestine where the nutrients can be absorbed. [100]

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Rabbits have a very fast reproductive rate. [101] The breeding season for most rabbits lasts 9 months, from February to October. [102] Normal gestation is about 30 days. The average size of the litter varies but is usually between 4 and 12 babies, with larger breeds having larger litters. [103] A kit (baby rabbit) can be weaned at about 4 to 5 weeks of age. [104] This means in one season a single female rabbit can produce as many as 800 children, grandchildren, and great-grandchildren. A doe is ready to breed at about 6 months of age, and a buck at about 7 months. [105] Courtship and mating is very brief, lasting only 30 to 40 seconds. Courtship behavior involves licking, sniffing, and following the doe. Spraying urine is also a common sexual behavior. [106] Female rabbits are reflex ovulators. [107] Ovulation begins 10 hours after mating. [108] After mating, the female will make a nest or borough, and line the nest with fur from the dewlap, flanks, and belly. This behavior also exposes the nipples enabling her to better nurse the kits. [109] Kits are altricial, which means they're born blind, naked, and helpless. [110] Passive immunity (immunity acquired by transfer of antibodies or sensitized lymphocytes from another animal) is acquired by kits prior to birth via placental transfer. [111] [112] At about 10 to 11 days after birth, the baby rabbit's eyes will open, and they will start eating on their own at around 14 days old. [113] Although born naked, a soft baby coat of hair forms within a few days. At the age of 5 to 6 weeks, the soft baby coat is replaced with a pre-adult coat. At about 6 to 8 months of age, this intermediate coat is replaced by the final adult coat, which is shed twice a year thereafter. [114] Due to the nutritious nature of rabbit milk, kits only need to be nursed for a few minutes once or twice a day. [115]

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Written by Samuel Fall
Copyright © 2008 Rabbit Pictures & Facts

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Image Source for Eastern cottontail at top of page: William R. James, U.S. Fish and Wildlife Service.
Image Source for cottontail at bottom of page: Clinton & Charles Robertson / License under Creative Commons 2.0.