Rabbit Digestive System

The teeth of the rabbit are very well adapted to its normalfoods. The teeth consist of two pairs of incisors (or cutting 'teeth) on the upper jaw and one pair on the lower, threepre-molars and three molars (both grinding ' teeth) oneither side of the upper jaw, and two pre-molars and threemolars on either side of the lower jaw. The incisors in thetipper jaw appear from the front to be two pairs side by side,but only a single pair, with a groove clown the centre of eachtooth, can be seen from the front. A much smaller pair ofint isms lie lichind the main incisors, and together with these,I erns a V shaped groove into which the chisel edge of the1.w•i ill, isms noinially lit.

The cheek teeth, that is the pre-molars and molars, arerather smaller than the incisors, but have flattened ends withprominent ridges, thus forming a most efficient grindingmechanism.

All the teeth of the rabbit grow continuously throughoutlife, the surfaces constantly wearing down in order to maintainthe correct length and either the chisel edge of the incisors orthe grinding surface of the cheek teeth.

Leading into the mouth are several ducts from the especiallywell developed system of salivary glands which secrete salivawisest the rabbit is eating. From the mouths, a slender tube,the oesophagus, carries food to the stomach, which is a thinwalled organ having little power of contraction. Food passesfrom the stomach through a muscular band of tissue knownas the pylorus, which controls the entrance of the food into thesmall intestine. The first part of the small intestine is loopedto form the duodenum, and within this duodenal loop liesthe pancreas. This is a diffuse irregular organ which suppliescertain fluids to the duodenum. Also entering into theduodenum from the gall bladder in the liver, is a bile ductwhich carries bile from the liver where it is produced.The small intestine continues until it enlarges into thesacculus rotundus, an enlarged sac peculiar to the rabbit.From the sacculus rotundus arises the large intestine, consistingof the caecum, the colon and the rectum. The caecum meetsthe colon at the sacculus rotundus, and is a relatively verylarge organ, with the appendix attached to the end.

Digestion takes place in stages, and consists of the breakingdown of the complex food substances into relatively simplesubstances which the animal can absorb into its body. Theprotein of the food must be broken down into amino-acids, thecarbohydrates into sugars, and the oils or fats into fatty acidsand glycerides (although the animal can absorb some verysmall fat particles.)

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

After food material is cut up by the incisors of the rabbit,and whilst it is being ground by the cheek teeth, the firstenzyme (in the saliva) is mixed with the food. The rabbit,when not unduly hungry, masticates its food a good deal, andtherefore when the food reaches the stomach it is in a finelydivided state. When an animal is excessively hungry it maynot masticate its food sufficiently, with the consequent pro-duction of digestive disturbances.

The walls of the stomach produce fluids which are of anacid nature and contain further enzymes. Digestion thereforeproceeds a stage further, the food being stored in that portionof the stomach nearest the pylorus. The walls of the stomach,having little power of contraction, cannot force the foodthrough the pylorus, and this only occurs when there isadditional pressure from more food (or coprophagous pellets(see below) ), coming into the stomach.

When the partially digested food is passed into the first partof the small intestine, a further series of enzymes mix with it,in addition to bile from the liver. The bile acts upon the fatof the food, which until this stage remains undigested, andbreaks it up into minute droplets. This process assists otherenzymes to break most of it down into fatty acids andglycerides. During the remainder of its passage through thesmall intestine, the food is finally digested and absorption ofthe digested materials takes place. The inner surface of thesmall intestine is covered with minute knob-like projections,whirls increases the surface area of the intestine very con-siderably. The food passes through the surface of theseprojections (villi) into the blood system inside them and thencethroughout the blood stream to all parts of the body for furtheruse. The digested materials from the fat portion of the foodpass 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 consistsboth of undigested and fibrous material, passes into thecaecum, 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 thismaterial through the colon and rectum, thus forming thepeculiar type of pellet eaten by the rabbit during coprophagy.The final residue of the twice digested food passes throughthe colon wherein much of the moisture is removed, and thenormal faecal pellets formed, these latter passing through therectum and being excreted.

The simple products of digestion, having passed into theblood stream are transported to the various parts of the bodyrequiring them. Any surpluses are stored in various placesfor later use.