Strict carnivores, cats have a digestive system that has evolved to suit a diet of small animals such as mice. They have sharp teeth designed to kill and cut up prey, and relatively short intestines for digesting meat.
The kidneys clean the blood, removing wastes and eliminating them from the body. Queens tend to give birth in spring and summer when food is likely to be plentiful for the kittens once they are weaned.
Cats have one of the narrowest diets of all carnivorous mammals. Their diet must include certain vitamins, fatty acids, and amino acids, as well as a chemical called taurine, which is found only in meat.
Cats cannot make these nutrients, or taurine, themselves nor get them from other sources of food, such as plants, and they cannot survive without them. Unlike vegetable matter, meat is relatively easy to break down into nutrients in the intestines.
Cats, therefore, have a relatively short, simple digestive tract compared to that of herbivores such as sheep and horses.
Digestion
The domestic cat’s digestive tract is a little longer than that of its wildcat ancestor. This suggests that the cat’s digestive system has been adapting to the increased plant matter in its diet (probably from scavenged scraps of human food containing both meat and cereal) since it first began to associate with humans several thousand years ago.
Kittens have 26 milk teeth, which erupt before 2 weeks of age and begin to fall out at about 14 weeks. Cats have 30 permanent teeth. Small incisors at the front of the jaws are used for grasping prey, while the canines, or fangs, kill prey by severing the spinal cord.
Cats cannot chew very well; instead, their back teeth chop up food into smaller pieces before it is swallowed. The carnassial teeth (the upper jaw’s back premolars and the lower jaw’s molars) are especially effective in slicing through food with a scissorlike action. When eating, the cat’s rough tongue—which is covered in little barbs—can rasp meat from the bones of prey animals.
Cats eat little and often. The transit of food—from eating to defecating—takes about 20 hours. The first stage of digestion is the physical breakup of food in the mouth by the teeth. The mouth produces saliva to lubricate the food, which, on being swallowed, passes down the esophagus into the stomach, where further physical digestion as well as some chemical breakdown by enzymes occurs.
The strong acid in a cat’s stomach is powerful enough to soften swallowed bones. (Any bones, hair, and feathers that cannot be digested are usually regurgitated later.)
Partly digested food leaves the stomach through the pyloric sphincter and enters the first section of the small intestine, the duodenum, where most of the chemical digestion takes place. Bile, produced by the liver and stored in the gall bladder, and a mix of enzymes from the pancreas enter this small loop of intestine and digest fats, proteins, and carbohydrates.
Nutrients are then absorbed across the wall of the small intestine into the bloodstream. They travel to the liver to be processed into useful molecules. Water is absorbed in the colon, and waste matter is passed out through the anus as feces.
Elimination of wastes
Besides solid feces, waste from the liver is processed by the kidneys. Their major role is to cleanse the blood, removing potentially harmful metabolic wastes, such as urea. The kidneys also control the composition and volume of fluids in a cat’s body.
Waste substances leave the kidneys, dissolved in water as urine. The urine flows along narrow ureters—one from each kidney—to be stored in the bladder. This balloon like organ holds up to 3½fl oz (100ml) of urine, which exits the bladder through the urethra. The urine of unneutered cats can be especially pungent and is used to mark territory and advertise sexual status.
Reproduction
Cats usually become sexually mature between 6–9 months, although in some Oriental breeds it may be earlier. As daylight hours increase during spring, hormonal changes in an unaltered female, or queen, make her receptive to finding a mate. She is then said to be “in heat” or “in season.”
She produces scents that attract intact males, or toms, and she may also call to them. Sexual intercourse is painful for the female. A tom’s penis has a band of 120–150 backward-pointing hooks that abrade the female’s vagina as he withdraws, causing her to yowl loudly and lash out. However, this does not seem to have a lasting effect because she mates many times while in heat, often with several toms.
The pain also triggers the release of eggs from the ovaries about 25–35 hours after the first mating. The eggs travel along the two “horns” of the uterus. The period of heat then eases off. If no pregnancy occurs, the queen will go into heat again a couple of weeks later. If mating is successful, pregnancy lasts for about 63 days. The average litter size is 3–5 kittens and can be as many as 10.