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Physiologically, rats are similar to other single-stomached animals, except for their lack of a gall bladder and their diffuse pancreas, an organ that is well-formed in other monogastric animals. Three bile ducts lead directly from the liver to the duodenum. The best research results are obtained from uniformly sized rats that are produced in closed colonies. By using rats from the same source you can ensure uniformity of size, good reproduction, and fewer genetic variations.
Physiologically, rats are similar to other single-stomached animals, except for their lack of a gall bladder and their diffuse pancreas, an organ that is well-formed in other monogastric animals. Three bile ducts lead directly from the liver to the duodenum. The best research results are obtained from uniformly sized rats that are produced in closed colonies. By using rats from the same source you can ensure uniformity of size, good reproduction, and fewer genetic variations.
Cattle, sheep and goats, as well as other ruminant animals, are useful as subjects in certain special research projects. Polygastric animals utilize large populations of microorganisms, which break down cellulose to form short-chain, volatile, fatty acids commonly called VFA. These volatile fatty acids provide the ruminant with 60-80% of its energy needs.
Break down of the cellulose walls of plants by bacteria makes the other cellular food constituents such as fat, starch and protein available for further digestion as they move through the gastrointestinal tract. Ruminants are not popular laboratory research animals because they are expensive to maintain.
The size of the animals increases their cost of maintenance due to:
However, these domesticated animals are easy to work with because of their gentle dispositions and consistency of their biological performance. They are also more conducive to long-term research studies because they have a much longer life span than rats and mice.
The similarity of the biochemical and physiological processes of monkeys and human beings makes the non-human primate an extremely valuable research animal species. The monkey's mental capacity, which goes far beyond that of all other research animals, must be a primary consideration in its care and handling.
Most of the monkeys used in research studies have been imported from their natural habitats. This practice is in the process of being discontinued. Breeding colonies are being established in more controlled environments, but the cost of producing them in quantities will be greatly increased. Monkeys are difficult to handle and can be dangerous. Special handling procedures must be employed to properly care for the monkey.
The monkey's living environment is extremely important. If it is carefully prepared, the cage will not be a restraining device to the monkey, but "home." Without the home condition, the monkey's mental and physical health will be adversely affected. Proper conditions in the cage depend upon the type of primate, although most are able to adapt to some variations, especially temperature changes, if they are gradual.
Sunlight is one of the "extra" considerations monkeys require. Sunlight increases the monkey's level of contentment and "at-homeness." If at all possible, an effort should be made to include natural sunlight in the monkey's environment.
As well as having good physical facilities, the monkeys must be managed well to ensure reliable research results. Routine care and cleanliness are essential for the monkey's welfare. The cage should be large with appropriate play objects and good feeding and watering conditions. Extra attention should be paid to cage door fasteners to prevent escapes. As an extra precaution, windows and vents in the surroundings should be screened.
Kind handling by humans can help to make the monkey's temperament more gentle and cooperative. But there is a definite danger in handling animals that are new to captivity. The instinctive response of the frightened monkey is to bite or scratch. If the monkey happens to be a carrier of monkey B-virus or some other virus, the wound can be fatal. Handlers going into gang cages should be fully covered and should wear face masks.
Because of the primates' advanced brain capacity, technicians need to attend to the monkey's responses more carefully. Monkeys are capable of anticipating a routine, of being amused, angered or bored. Their group and individual responses should be observed to gain the most knowledge from these valuable laboratory animals.
Ferrets have become increasingly important in biological research. In fact, they are now being used in physiology, pharmacology, virology/immunology, behavior, parasitology, toxicology and many other areas of research.
Man's domestication of the ferret can be traced back to the 4th century B.C., when the animals were used to exterminate rats and snakes in Europe and Asia. Over the past 40 years, breeding stock has been developed with gentle temperaments, so most can be handled without gloves.
Ferrets adapt well to caging and can be kept individually or communally. Space requirements for exercise are minimal. They habitually use one toilet location in an area opposite of where they sleep, making it easy to collect fecal samples. Common litter materials and automatic waterers make caring for ferrets conveniently similar to caring for other laboratory animals such as rabbits, guinea pigs, mice, etc.
The gestation period of the ferret is a uniform 42 days, with litter sizes ranging from 6-10. They are weaned at 6 weeks and at 9 weeks of age, they are one-half of their mature size. Mature weight for male ferrets is 1800 grams, with body length at 16 inches (without tail). Female ferrets are considerably less formidable at 900 grams and 14 inches in length (without tail). Ferrets are nocturnal creatures, usually spending a great deal of time sleeping.
Unique anatomical variants include the large intestine, which has no anatomical division between the ileum and the colon, making it appear as one undifferentiated tube. Another interesting variant in the ferret is the existence of a single central ascending artery instead of the more common bilateral carotid arteries.
Finally, the respiratory system of the ferret is adapted to its burrowing nature. The ferret's chest walls are extremely compliant and the total lung capacity and inspiratory reserve are very large in relation to body size. The long trachea and larger diameter airways in ferrets result in a much lower pulmonary and central airway resistance than is seen in other laboratory animals of comparable size.
The disadvantages of using the ferret for research are few. They are susceptible to and should be vaccinated for canine distemper, and like cats, lack easily accessible veins, making intravenous drug administration virtually impossible.
Sources: Laboratory Management of the Ferret for Research, K.D. Moody, T. A. Bowman and C. M. Lang, Lab Animal Science 35:272-279 (1985)
Many pharmaceutical companies use cats in their laboratories to develop drugs for the treatment and prevention of feline diseases. Cats are also used extensively in basic research. Because their brain has been thoroughly mapped, cats are widely used as models in neurophysiologic research. In addition, the cat's eye is extremely well-defined and well-developed, making it a perfect model for basic visual research as well.
Most researchers prefer to use purpose bred cats because many confounding variables are controlled. Purpose bred cats are obtained from suppliers who breed cats specifically to supply research laboratories. Cats from these sources have known genetic histories, sometimes as far back as 20 generations. They have accurate and complete vaccination records and are accustomed to living in laboratory conditions, making them less stressed by a research laboratory environment than random source cats.
Unlike most other laboratory animals, felines are strict carnivores, requiring high protein and low carbohydrate content in their diets. A typical cat diet should provide 20-30% of the ration as a high-quality animal protein. In addition to the essential amino acids required by all animals, the cat requires a dietary source of taurine, a b-amino sulphonic acid. Without dietary taurine, many cats develop eye abnormalities, most commonly central retinal degeneration. Another unique nutritional quality of the cat is its inability to convert carotenes to vitamin A. A feline diet must supply preformed vitamin A for proper nutrition.
Cats may be housed either individually or in groups. The environment should be clean, dry and free of wide variations in temperature or humidity levels. The Institute of Laboratory Animal Resources publishes guidelines for the amount of space and the type of facilities appropriate for housing cats in laboratories. These guidelines are also regulated by the Federal Animal Welfare Act (9 Code of Federal Regulations Part 3). Cats require two unique features in their habitat. They must have litter boxes with litter fill and solid resting surfaces. The resting surfaces must be elevated with enough space to accommodate all of the cats in the enclosure.
Guinea pigs are valuable research animals because of the variety of experiments in which they can be used. They are often used to test lotions and ointments because their skin resembles human skin. Long use of the guinea pig in bacteriological and serological research has resulted in a sizeable accumulation of information on blood values, cell counts, elementary analyses and physical constants. Guinea pigs have been used frequently in nutritional research and in immunology experiments.
Guinea pigs became known to research scientists after sailors brought them to England from Peru as pets. The Dunkin-Hartley strain, developed by the British, is the most widely used in laboratories. It is almost always an albino with short, smooth hair. A second type of guinea pig, the Abyssinian, has short, rough hair that grows in rosettes. The present day Peruvian type of guinea pig, with long hair, is seldom used in research.
Of all of the commonly used lab animals, guinea pigs are one of the most nervous and high-strung species. The guinea pig needs to be approached quietly and confidently. It will seldom scratch a human when it is picked up if it is supported well. If it does become alarmed, however, the whole colony can detect the fright and become apprehensive. To pick up the pig, grasp behind its head and in front of its forelegs with the thumb and forefinger. With the remaining fingers, hold the pig behind its front legs and rib cage. Use the other hand to support the hindquarters.
Good sanitation is extremely important in the guinea pig colony. The animals are very susceptible to paratyphoid infections. Cages need to be cleaned often to keep the animals as free of microorganisms as possible.
Like monkeys and human beings, guinea pigs need daily doses of vitamin C to prevent the development of scurvy. Scurvy can develop within seven to ten days without dietary vitamin C. Normally a daily intake of 10 milligrams of ascorbic acid will be adequate to keep the guinea pig free from scurvy.
Poultry play a valuable role in the research laboratory. Chicks are used mainly to measure the biological availability of various nutrients. Because of their extremely fast rate of growth, chicks are used in nutritional biochemistry investigation in which metabolic pathways are of interest. To some degree they are valuable in assays for vitamins. Laying birds are valuable for producing eggs for virus cultures and related materials used in the production of biologicals.
Few research labs breed their own chicks. They are much more easily and inexpensively obtained from commercial hatcheries. The meat-producing chicken, a heavier breed, is most often used because they grow much faster than the lighter, egg-laying strains. But with the assay work for vitamin D3, where consistency of response is essential, the egg-laying purebred Leghorns are used.
Chicks are usually ordered from the hatchery already sexed, if that distinction is necessary. Unless the sex of the chick has been genetically linked with some other characteristic, such as a wing feather, chicks cannot be sexed reliably in the research laboratory.
Chicks need a well-ventilated, clean and uniformly lighted environment. Temperatures should be regulated according to their ages. When they first arrive at the lab, chicks should be put in battery brooders that have thermostatically controlled heating units. The brooder temperature should be decreased by five degrees each week, beginning at 95°F until the room temperature of 70 to 75°F is reached. The heat in the brooder can then be turned off. Temperatures in the chick's surrounding area should not vary more than half a degree form ceiling to floor.
The optimum relative humidity is 45-50% for chicks. At humidity levels below 40% the mucous lining of the chick's respiratory tract dehydrates, making the chick more susceptible to infection. Overcrowding, overheating or excessive lighting can lead to feather picking and cannibalism.
Rabbits of all strains are used in laboratory research, especially in studies of bacteriology, physiology, and nutrition. Researchers also use them in clinical laboratories to conduct hormone studies and to produce biologics.
Rabbits are usually obtained from an outside source in the size and number required for a particular experiment. To make sure you have a good supply of uniform animals, it is best to plan well ahead and order from one supplier. This eliminates having to introduce undesirable variations into the experiment.
Except for future breeders, rabbits should be handled as little as possible. It is easy to injure the rabbit's back unless proper support is provided. Occasionally handling the breeders will accustom them to the cage transfers required for mating. To hold them, firmly grasp the loose skin over the shoulders with one hand and support the weight by placing the other hand under the hindquarters. Rabbits usually will not resist handling by someone they trust. If they need to be restrained, wrapping them in a cloth will help prevent scratching.
The rabbit eliminated two kinds of feces. The "day" feces are hard, round and dry. The "night" feces are soft and encased in a membrane. These night feces are consumed by the rabbits as an important source of nutrients. Fasted rabbits with empty stomachs are difficult to gain because of this practice of coprophagy. The day droppings should be cleaned out regularly by the caretakers.
Newly purchased rabbits should be isolated for at least 21 days. When the rabbit is caged, it should have enough room to stretch out full length to its normal resting position. The cage also should be high enough to permit the rabbit to sit up on its haunches.
As a biomedical research model, swine have physiological similarities to man. Crossbred strains, developed mostly as food animals, grow fast and develop into large animals. The size and weight of these animals often makes it difficult to handle and house them for laboratory purposes. In response to this drawback, smaller animals -- miniature pigs -- have been developed. The adult mini-pig weighs approximately 70 kilograms, about the size of an average person.
The body size, skeletal size, skin, teeth, gastrointestinal tract, heart position and blood supply are strikingly similar in humans and miniature pigs. Nutrient requirements and dietary ingredients have many parallels. These animals have a long life span, making them appropriate for studies of cardiovascular disease, gerontology and toxicology. Animals born by cesarean section can be used for germ-free or gnotobiotic studies. Other important applications include studies on reproductive physiology, endocrinology, dental research, effects of radiation and many others. Hairless strains have been developed for use in skin sensitivity tests.
The miniature swine can be handled under laboratory conditions, in appropriate cages and climate controlled facilities.