Nutrition Biology

The rat's nutrition biology

These notes relate to the domesticated Norway rat, which is considered to be a tame and highly-intelligent pet rodent. The structure of the digestive tract, as well as the food intake and utilisation functions, is quite comparable to that of the house mouse. The food needs of the two species are fundamentally the same, and also resemble those of the golden hamster. All the rodents mentioned above need high-quality food of plant origin, together with components of animal origin since they depend on animal protein. Rats, hamsters and mice tolerate grain-based food quite well, and together with rabbits, guinea pigs and chinchillas are considered to be so-called 'concentrate feeders'. These animals have been bred under human supervision for many generations, resulting in a range of different colourings. However, but the basic conditions governing food utilisation have not changed. Modern feeding concepts take account of this in a natural manner. Our diagram shows the organs involved in digestion. The digestive tract starts with the mouth:

The incisors are sharp and chisel-like, serving to cut through food pieces and open seed husks. They grow continuously and must be constantly worn down. Ideally, this wearing-down process takes place through the abrasion and grinding involved when biting off and reducing hard, top-quality compound feeds, and when cracking shells or husks. The incisors are positioned in the front and centre of the mouth; there are two incisors each in the upper and lower jaws. It is very important to maintain the health of the incisors by proper feeding and by providing rough nesting material which the rodents need to reduce themselves. Particularly suitable nesting materials include straw, rough hay and small twigs. When selecting animals for breeding, strict attention should also be paid to dental health to ensure that dental anomalies are not passed on.

Further back in the oral cavity you will find the molars (three upper and three lower molars on each side of the jaw). The molars crush and grind the food pieces. The food is well-covered with saliva between the molars, ensuring that it slips down easily. The liquid required for this purpose is produced by the saliva glands. Initial saliva enzymes - which are also known as ferments, and are genuine bio-catalyst - start the pre-digestion process.

Rats do not have cheek vestibules. However, they are happy to carry any excess food in their mouths from the feeding point to their nest ... or, in domestic terms, from the feeding bowl to their cage. There, they can withdraw into their own space to eat in peace, or they may lay aside small stocks of food. These should be checked and removed at least twice a week.

The oesophagus is a pure transport organ. Food which has been well reduced and covered in saliva is transported from the mouth to the rest of the digestive tract. This fully masticated food is a sort of rough pulp known as chymus. At this point the chymus enters the actual utilisation process. The pharynx and the oesophagus also transport drinking water.

Rats have a single-chamber stomach which takes the form of a glandular stomach. This is responsible for producing hydrochloric acid and protein-splitting substances. Following the chewing and softening processes in the mouth, the actual digestive work starts here in the stomach, where initial nutrient components are separated. The food is heavily acidified with hydrochloric acid dispensed by special cells. In this acid environment, protein-reducing enzymes start the protein utilisation process, and stomach hormones are emitted as a signal. All hormones represent internal physical messenger substances, and are "transmitted" through the bloodstream.

The abdominal musculature surrounding the stomach ensures not only that the stomach contents are thoroughly mixed, but also that they the stomach is emptied. This refers to the transfer of the chymus by the ring muscle at the end of the glandular stomach section also known as the "gate-keeper" - to the rest of the digestive tract. However, the stomach musculature does not allow food which has been incorrectly swallowed to be regurgitated.

In the anterior small intestine, plenty of tissue liquid and enzymes are added to the chymus, ensuring that the chymus is a thin liquid before the rest of the utilisation process takes place.

About a centimetre behind the stomach, the excretory ducts of the pancreas and the liver enter the small intestine. The liver can store excess blood sugar for a short period in the form of glycogen, but its main task is central "detoxification". In addition, the liver produces bile which "buffers" the digestive juices, and provides the transition from an acid to an alkaline environment. The pancreas regulates blood sugar content, and dispenses both fat-splitting and carbohydrate-splitting ferments.

This is followed by the posterior small intestine, where the main digestive work takes place. The highly active intestinal villi tissue transmits the broken-down food products to the bloodstream. The nutritional substances can only pass through the intestinal wall once fully broken down, and are then made available for utilisation by the rat's other target organs. The posterior small intestine is the point where all nutrients and active substances already digested are transferred to the organism. The small intestine is also where most problems arise as a result of malnourishment with excessively fatty or sweet foot, or an excess of oily seeds. It is here that preventative animal health care, based on optimal feeding with the best contemporary animal food products, has the greatest effect. A good choice of food is essential for any rat! From this point on, the chymus contains almost only raw fibres, i.e. plant cell membrane components from the food.

The appendix branches off at the point where the small intestine merges into the large intestine area of the digestive tract. The appendix is known as the 'blind intestine' in German because it is essentially a blind alley or cul de sac. It is a fermentation chamber inhabited by a large number of specialised bacteria. Here, some residual energy can still be recovered from plant components rich in raw fibre and roughage, and the plant cell membrane components - especially dextrose obtained from cellulose - are also recovered. Rats have a relatively small appendix, but abrupt changes in feeding patterns must still be avoided to ensure that diverticular fermentation is not disrupted. In contrast to many purely herbivorous rodents, concentrate feeders such as hamsters, rats and mice do not generate diverticular faeces or soft faeces as separate excretion forms.

The remaining large intestine behind the transition area between the small intestine and the appendix is primarily responsible for recovering water from the "food pulp", which is now largely digested but still quite liquid. However, other bacteria can be found throughout the large intestine. Like their conspecifics or relatives in the appendix, these are able to carry out special fermentation and similar metabolic processes. They provide the intestinal wall cells with short-chained fatty acids from the food residues, but these can no longer enter the bloodstream from here. They nourish the tissue directly at this point. The faeces are pre-formed in the rear section of the large intestine.

The dry faeces particles are finally formed in the rectum, which as much residual moisture as possible is recovered from them. Rats also sometimes eat parts of their rectal faeces, but this is normal for all rodents. Diarrhoea and constipation are indications that the water regulation system has been impaired by malfunctions in the previous areas of the digestive tract.

The anus is the exit opening for the faeces. This solid excrement contains waste products which are not excreted in liquid form by the kidneys in the form of urine, as well as undigested food residues and any specific or temporary excess nutrients. The digestive tract terminates with the sphincter.