Rabbit Digestive System

The teeth of the rabbit are very well adapted to its normal foods. The teeth consist of two pairs of incisors (or cutting 'teeth) on the upper jaw and one pair on the lower, three pre-molars and three molars (both grinding ' teeth) on either side of the upper jaw, and two pre-molars and three molars on either side of the lower jaw. The incisors in the tipper jaw appear from the front to be two pairs side by side, but only a single pair, with a groove clown the centre of each tooth, can be seen from the front.

The cheek teeth, that is the pre-molars and molars, are rather smaller than the incisors, but have flattened ends with prominent ridges, thus forming a most efficient grinding mechanism.

All the teeth of the rabbit grow continuously throughout life, the surfaces constantly wearing down in order to maintain the correct length and either the chisel edge of the incisors or the grinding surface of the cheek teeth.

Leading into the mouth are several ducts from the especially well developed system of salivary glands which secrete saliva wisest the rabbit is eating. From the mouths, a slender tube, the oesophagus, carries food to the stomach, which is a thin walled organ having little power of contraction. Food passes from the stomach through a muscular band of tissue known as the pylorus, which controls the entrance of the food into the small intestine. The first part of the small intestine is looped to form the duodenum, and within this duodenal loop is the pancreas. This is a diffuse irregular organ which supplies certain fluids to the duodenum. Also entering into the duodenum from the gall bladder in the liver, is a bile duct which carries bile from the liver where it is produced. The small intestine continues until it enlarges into the sacculus rotundus, an enlarged sac peculiar to the rabbit. From the sacculus rotundus arises the large intestine, consisting of the caecum, the colon and the rectum. The caecum meets the colon at the sacculus rotundus, and is a relatively very large organ, with the appendix attached to the end.

Digestion takes place in stages, and consists of the breaking down of the complex food substances into relatively simple substances which the animal can absorb into its body. The protein of the food must be broken down into amino-acids, the carbohydrates into sugars, and the oils or fats into fatty acids and glycerides (although the animal can absorb some very small fat particles).

The breakdown of food into these simpler substances is accomplished by enzymes, or special chemicals, of which there are a number produced in various parts of the digestive system.

After food material is cut up by the incisors of the rabbit, and whilst it is being ground by the cheek teeth, the first enzyme (in the saliva) is mixed with the food. The rabbit, when not unduly hungry, masticates its food a good deal, and therefore when the food reaches the stomach it is in a finely divided state. When an animal is excessively hungry it may not masticate its food sufficiently, with the consequent production of digestive disturbances.

The walls of the stomach produce fluids which are of an acid nature and contain further enzymes. Digestion therefore proceeds a stage further, the food being stored in that portion of the stomach nearest the pylorus. The walls of the stomach, having little power of contraction, cannot force the food through the pylorus, and this only occurs when there is additional pressure from more food (or coprophagous pellets), coming into the stomach.

When the partially digested food is passed into the first part of the small intestine, a further series of enzymes mix with it, in addition to bile from the liver. The bile acts upon the fat of the food, which until this stage remains undigested, and breaks it up into minute droplets. This process assists other enzymes to break most of it down into fatty acids and glycerides. During the remainder of its passage through the small intestine, the food is finally digested and absorption of the digested materials takes place. The inner surface of the small intestine is covered with minute knob-like projections, whirls increases the surface area of the intestine very considerably. The food passes through the surface of these projections (villi) into the blood system inside them and hence throughout the blood stream to all parts of the body for further use. The digested materials from the fat portion of the food pass through the surfaces of the villi into the lymphatic system and by way of this into the blood stream.

The remains of the food left after absorption, which consists both of undigested and fibrous material, passes into the caecum, wherein bacteria attack and to some extent digest it.

The contents of the mecum is normally a thick fluid, and at certain periods contractions of the caecum force some of this material through the colon and rectum, thus forming the peculiar type of pellet eaten by the rabbit during coprophagy. The final residue of the twice digested food passes through the colon wherein much of the moisture is removed, and the normal faecal pellets formed, these latter passing through the rectum and being excreted.

The simple products of digestion, having passed into the blood stream are transported to the various parts of the body requiring them. Any surpluses are stored in various places for later use.