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CARE, HANDLING AND SEXING LAB ANIMALS
Mice
Mice are omnivore’s animals, which feed on green vegetables, grains and pellet supplements. They eat most of their daily ration in the dark. Their incisors and molars wear down and regrow with use. It is important to check that each mouse has the required teeth in good order or else they risk under-nutrition or malnutrition.
They mature and mate when at the age of between 6-8 weeks old. At this time, they should be kept in threes (trios) per cage i.e. one male: two females. Avoid inbreeding as these may result in drop in average litter size
Their estrous circle last between 4-5 days with a gestation period of 19-21 days. They give birth to a litter size of 7-8 and have a litter frequency of 5 times yearly. The young ones should be weaned at 21 days.
Sexing is done by observing the distance between the anus and genitals. This distance is usually greater in the male than in females.
Avoid handling a postpartum female or her litter for several days after birth. Handling and transporting at this time could cause the mother to reject her young or eat them. This risk can be reduced by:
- Wearing plastic gloves, to eliminate human scent.
- Place the dam in a separate cage while the litter is handled.
- Rub the pups with bedding material from the home cage.
Taking a mouse by the tail is a common way of lifting the animal. However, this could be stressful and creates antagonism toward the handler. While the mouse is inside the cage, take the base of the tail between your thumb and index finger, then pick the animal up by the tail. Support the animal’s weight on your arm or the cage floor; never allow the animal to dangle.
Other methods for routine handling are to:
- Cup the mouse in your open hand, but note: the mouse will try to escape (and will sometimes succeed).
- Handle while inside a home cage tunnel.
- Collect the mouse using the tunnel and transfer to your open hand.
To restrain the mouse, place the animal on a rough surface such as a cage lid. Hold the loose neck skin between your thumb and index finger, and then lift the mouse securing the tail between the fourth or fifth finger and palm of the same hand. Your other hand is free for injections or other procedures. To pick up newborn or mice less than two weeks old, take the loose neck/shoulder skin into thumb and index finger or cup the pup in your open hand.
Rats
Rats take about 10-12 weeks to mature, this is their mating age. Their estrous circle last for between 4-5 days and have a gestation period of between 21-23 days .During this time it is advisable to isolate pregnant rats and provide with nesting materials.
Rats give birth to between 7-8 litters and can give birth up to 7-9 times yearly .These young ones should be left in densely populated cages for at least one week after weaning
To handle rats, pick them up by grasping them by the base of the tail, close to the body but do not suspend the rat by its tail or its upper body for a prolonged period. Support its body weight quickly, either on the cage top or on the arm of your lab coat.
Sexing is done by checking morphology and position of their genital organs
Rabbits
Rabbits mate at the age of between 6-9 months. They have no definite cycle. When the doe (female) is on heat, vulva and vagina become red, swollen and moist.
It is advisable to introduce the doe (female) into the buck’s (male ) cage and not vis versa then transfer the doe to larger cage with nesting materials after 24hrs.
They have a gestation period of between 28-31 days. During this period, it is advisable to isolate pregnant rabbits and to provide with nesting materials. They give birth to up to four litters and for up to 4 times yearly.
The rabbit is picked up from cage with the ears by one hand in a firm grip and another hand is placed under the hindquarters to support the weight and then lifted gently. After removing from cage, the animal is placed in a non-slippery place, as it otherwise feels insecure and becomes frightened.
One hand is placed across the back of the animal with the thumb behind the shoulders and the other fingers well forward on the opposite side. The animal is lifted gently supporting its weight with other hand placing the palm uppermost under the hindquarters.
Guinea pigs mate at the age of between 12-20 months. Their estrous circle can last for 16 days. Males should be placed in the cage with 5-10 females during mating.
Their gestation period takes between 59- 72 days .During this time Pregnant females should be isolated and placed in separate cages with nesting materials ,and fed with carrots, cabbages etc. apart from pellets.
They give birth to up to three young ones and up to 3 times yearly
Isolate pregnant rats and provide with nesting materials
Mating should be done at the age of between 7-9 weeks and should be done on the table under supervision to avoid female injuring the male genital after copulation. Their estrous circle last between 4-5 days
They have a gestation period of between 16 –17 days and give birth to six young ones in one birth (Litter size) their litter frequency is to up to 3-4 times yearly. Weaning should be done after 3-4 weeks.
They should be kept in metal cages because they gnaw plastic cages. But should be provided with wood to gnaw otherwise their incisors will over grow hence making it difficult to feed
Xenopus Frog (African Clawed Toad)
They are easy to maintain in the laboratory and breeding can be induced at any time of the year, but they do not breed until they are 2 years old. They are maintained in aquariums made from old plastic or metal tanks with minimum size of 50X40X15 cm for stock and 30x20x20 cm for breeding. The tanks should be carried with transparent sheet and reinforced with wire
Adult stock can be maintained at ambient temperatures so long as it does not fall below 10oc but for breeding and raring the larvae, the temperatures should be raised and maintained at 23oc using an aquarium heater
Adult toads should be feed on earthworms and fine chopped liver at least twice a week and the water should be exchanged afterwards. The toads should be marked by clipping one or two claws.
Xenopus toads can be induced to breed by injecting them with pregynyl hormone, which will cause them to begin to sprawn. If sprawning does not occur, then temperatures in the aquarium need to be raised to 28 oc. After sprawning, the adults should be removed and the eggs distributed between containers so that at least each egg is in contact with the surrounding water and no eggs are left in the surrounding solid mass. Aeration of the tank is done by means of aquarium pump fitted to a diffuser block, these must be done gently
The newly hatched tadpoles may be feed on dried nettle powders. Metamorphosis occurs approximately after seven weeks, during these period, the larvae may be fed on microforms, daphnia etc. but after wards they can be feed on liver
Locust
Locust is also relatively easy to maintain in the laboratory as permanent stock. Cages should be made of glass-fronted containers of approximately 15 x15x 20 inches with a false floor of perforated zinc. The cages should be heated by means of electric bulbs one below the false floor and one above the floor i.e. in the locust compartment. The floor should be arranged such that containers of sand for egg laying may be placed underneath. The minimum size of the egg containers should be 4inches deep and 1.25 inches diameter
It is essential to provide each cage with twiggy branches or a cylinder of large mesh wire netting to provide perching space to reduce chances for deformed adults i.e. Unless the instars can hang freely when molting, most of them will deform
Locust can tolerate a wide range of temperature but should be within the range of 28- 34oc. Excess humidity should be discouraged because these can favor diseases. Excess humidity can be noticed if condensation appears on the cages or if feces are soft or hard.
Locust should be provided with grass and sometimes wheat bran to feed on in cage. Do not overfeed them because this makes cleaning difficult
Eggs are laid in frothy pods in holes excavated in moist sand each pod contain between 30-300 eggs .The sand must be soft and sterilized in ovens and should always be sterilized after every period. It should have good moisture content and should be 4inches deep beneath the floor of the cage. Do not use porous containers as they lose water easily .after checking for the presence of pods, cover them to avoid excessive evaporation and set to incubate at 28- 32 oc where they will hatch after 11-17 days
- Some people are allergic to locust therefore avoid overexposure to them
Earthworms
Earthworms are obtained by watering the ground with KMnO4 (aq) and allowing it to spread. These will attract earthworms. Collect the worms that come to the surface and rinse them before placing them in a wormery. The wormery is made to act in the form of a typical soil profile
Drosophila
Drosophila are small flies, typically pale yellow to reddish brown to black, with red eyes. Many species have distinct black patterns on the wings. The plumose (feathery) arista, bristling of the head and thorax, and wing venation are characters used to diagnose the family. Most are small, about 2–4 millimeters long are larger than a housefly.
Male and female drosophila differ in many ways: Only males have a sex comb, a fringe of black bristles on the forelegs. The tip of the abdomen is elongate, somewhat pointed in females, and more rounded in males. The abdomen of the female has seven segments, whereas that of the male has only five segments.
Drosophila melanogaster is a popular experimental animal because it is easily cultured in mass out of the wild, has a short generation time, and mutant animals are readily obtainable. Drosophila species are widely used in studies of genetics, embryogenesis, and other areas. Drosophila are grown in media which is prepared by adding about 6g of agar to 35g black treacle and 75g of oat meal to 560cm3 of distilled water and boiling while stirring. Nipagin is added which inhibit mold growth. This quantity is distributed into about 60 specimen bottles and allowed to cool.
When the culture media have set, add few drops of baker’s yeast suspension, plug the container with cotton wool as soon as steam escapes. A piece of folded filter paper or non-medicated paper be placed in the container before the introduction of the flies. Optimum temperature for experimental mating is 25oc, prolonged exposure at 10oc or below will kill the flies and a temperature of 28-30oc will result in sterile progeny.
Parasitic mites and molds are the major problems but they can be completely controlled by regular sub culturing if the flies are kept at 25oc because at this temperature, the life cycle of the flies is shorter than that of the pest
Insect Larvae
Take about 1kg meat and tie it using a string to hang on a tree branch for about 1 week until it rot, insects will feed on it and will deposit their eggs in it, which shall hatch into larvae
Amoeba
Amoeba is cultured in shallow glass containers containing about 2 cm deep culture solutions e.g. chackleys media, which is prepared as a stock solution and diluted for use. It contains
NaCl =16g
NaHCO3 = 0.8g
KCl =0.4g
NaHPO4=0.2g
NB: Never use deionized water because it contains phenol, which is harmful. In addition, extreme cleanness should be emphasized
For use, take 5cm3 of stock solution and dilute to 1dm3 with distilled water. Distribute the medium to culture dishes and about four boiled wheat grains in each dish and allows bacteria and molds to grow and finally colpedium, which will become food for Amoeba. Now inoculate with Amoeba
Paramecium
Add 30g of boiled wheat grain to about one liter of chackeys media and inoculate with Bacillus subtilis then inoculate with paramecium 24 hours latter