<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><!-- saved from url=(0055)http://www.miami.edu/research/training/Biometh_rat.html --><!--This file created 11/30/98 9:29 AM by Claris Home Page version 3.0d321.3-->
Biomethodology of the Rat
· Behavior
· Handling
· Occupational Health/Zoonosis
A. Nomenclature and Breeds
· The Norway rat or laboratory rat (Rattus norvegicus), is a mammal of the order Rodentia. The laboratory rat was the first animal where the primary reason for domestication was for use in scientific endeavors.
· "Out-bred" rats are bred to maintain genetic diversity by mating unrelated rats (less than 1% inbreeding per generation) and are referred to as “stock”. To be designated as outbred, these rats must be maintained in a closed colony for a minimum of 4 generations.
· "Inbred" rats (such as Fischer 344, Wistar) are bred to maintain genetic homozygosity by utilizing a brother X sister breeding scheme for a minimum of 20 generations. Inbred animals are referred to as “strains”.
· The "F1 hybrid rats" are produced by crossing two inbred strains for one generation.
B. Unique Biological Characteristics
· The acute hearing of rats makes them sensitive to ultrasounds and high pitched sounds.
· The vision of rats is very poor and they are unable to detect color and are blind to long-wave (red) light.
· The tail of the rat is the principal organ for heat exchange.
· Rats are nocturnal.
· Rats have no tonsils, water taste receptors, sweat glands or gall bladders.
· Rats do not vomit.
· Malocclusion (mal-alignment of the teeth) may occur in rats due to trauma, genetics or feeding a soft diet that prevents proper wearing of teeth.
· Aging studies
· Oncology
· Toxicology
· Teratology
· Inbred, outbred, hybrid, or mutant rats are available from many commercial sources. The DLAR office staff is familiar with many of the commonly available strains and will assist in locating animals available for purchase.
· Commercially available rats from Charles River or Taconic must be ordered by Tuesday at 9:00 am for delivery by Thursday of that week. Animals should be held for a minimum of 48 hours before experimental use to allow recovery from the stress of shipping.
· The rat can become accustomed to handling providing they are not upset by the experience.
· Rats will bite without warning, but usually not repeatedly. Males tend to be more aggressive than females.
· Unlike mice, groups of the same sex can be housed together without fighting.
· Rats are active primarily during the night at which time they feed; the light hours are used primarily for rest, sleep and digestion. Handling animals during the night phase can be more difficult due to this increase in activity.
· The diurnal rhythm can be changed by a 12 hour shift in the light cycle. It takes approximately two weeks for rats to adjust to this shift.
· Rats are coprophagic (ingest their own feces).
Biological Data
|
<TBODY> Adult body weight: male |
450-520 gm1 |
|
300-800 gm2 |
|
|
Adult body weight: female |
250-320 gm1 |
|
250-400 gm2 |
|
|
Body surface area |
10.5 (wt. in grams)2/31 |
|
9.1 kg0.66 B.W.2 |
|
|
Life span |
2-3.5 years1 |
|
Food consumption |
10 g/100 g/ day1 |
|
Water consumption |
10-12 ml/100 g/day1 |
|
Breeding onset: male |
65-110 days1 |
|
Breeding onset: female |
65-110 days1 |
|
Gestation Period |
21-23 days1 |
|
Body Temperature |
38-39 C2 |
|
35.9-37.5 C1 |
|
|
Heart rate |
320-480 beats per minute2 |
|
250-450 beats per minute1 |
|
|
Respiratory rate |
85-110 per minute2 |
|
70-115 per minute1 |
|
|
Tidal volume |
0.6-2.0 ml1 |
|
1.6 (1.5-1.8 ml)2 </TBODY> |
· Breeding systems can be monogamous (one male and one female) or polygamous (one male and one to two females).
· Gestation is 21-23 days. Litter size varies widely with stock/strain, ranging from 3-18 pups. Birth weights are normally 5-6 grams. Pups are weaned at 21 days of age.
· Female rats have a post-partum estrus.
· Male and female rats can be differentiated by observing the distance from the anus and genital papilla (anogenital distance) which is greater in males.
· This difference is also present in neonatal rats.
· Rats can be grouped by their microbial colonization.
- Specific Pathogen Free (SPF) rats are free from known bacterial, viral, and parasitic rat pathogens. To insure the maintenance of the SPF microbial status requires that rats be housed in more stringent conditions that prevent the introduction of rodent pathogens (i.e. maximum isolation housing).
- Conventional rats are not known to be free of pathogens. Standard housing (i.e. conventional housing) cannot prevent the introduction of rodent pathogens
- Other less common categories are axenic rats (i.e free from organisms) and gnotobiotic rats, which have a defined microbial flora.
· Choosing the proper housing conditions for rats is very important, especially those used in immunological studies. Rodent pathogens often do not produce clinical signs in affected animals but often have an immunomodulating effects. Conventionally housed animals are exposed to room air and therefore may readily contract viral, bacterial and/or parasitic diseases.
· Immunocompromised animals (i.e. athymic rats) are very sensitive to opportunistic agents, and must be housed under maximum isolation conditions to allow for their long term survival. Valuable animals and animals that may need to be transported to other institutions should also be housed under maximum isolation conditions.
· Conventional Housing
- Most rats are housed in shoebox cages composed of polypropylene (opaque) or polycarbonate material (clear) with a wire bar lid used to hold the water bottle and feed. Bedding is placed directly into the shoe box cage allowing the absorption of urine and the animal to burrow. This type of cage will hold 1-3 adult rats depending on the size of the cage.
- When removing the lid from this type of cage, it is important to remove the water bottle to prevent spillage. If the cage is to be transported the bottle should be turned sipper tube up to prevent spillage during transport. However, you should remember to turn the bottle back over to allow access to water after transport.
- The husbandry staff changes cages twice per week, thereby providing the animal a clean cage with new bedding, food and water. Water bottles and feed hoppers are checked daily by animal caretakers to insure the provision of food and water.
· Maximum Isolation Housing
- Rats housed under maximum isolation conditions are housed in sterilized, polycarbonate cages with microisolater bonnets. Bedding is sterilized within the cage and allows the absorption of urine and the opportunity for the animal to burrow. This type of cage will hold 1-3 adult rats depending on the size of the cage.
- Animals are provided irradiated food and hyperfiltrated water.
- Personnel are required to wear protective clothing (sterile gowns, gloves, mask, head covers and foot covers) while working in the room.
- All experimental work and husbandry care must be conducted within a laminar flow hood.
- If animals are removed from the housing area and taken to the investigators laboratory, they may not be returned (terminal procedure only).
- Access to maximum isolation housing areas is limited to prevent inadvertent fomite transmission of rodent pathogens by personnel.
- All research personnel must be trained by the DLAR Assistant Director before working in this area.
· Suspended cages – conventional housing
- Some rats are housed on wire mesh bottom cages to allow collection of feces and urine or to prevent contact with bedding.
- This type of housing is not preferred and is used only when dictated by experimental design (i.e. for toxocilogy studies)
- Most suspended cages have water bottles but occasionally are equipped with automatic watering. Typically a nipple valve (lixit valve) is located in the back of the cage which can be operated by contact. When replacing a suspended cage that is provided with automatic watering it is important to push the cage fully into the rack to insure that the lixit valve fully extends into the cage, allowing the animal access to water.
- Occasionally a rat will jam the nipple open resulting in constant dripping of water from the nipple, saturating the bedding material. Upon observation the bedding will appear much darker. This problem should be reported to husbandry personnel immediately to allow correction.
· Pelleted natural ingredient diets are used to feed all rodents and are composed primarily of cereal grains which are supplemented with additional protein, vitamins and minerals. Due to the nature of this type of diet the exact composition can vary substantially from lot to lot.
· Environmental Parameters
- Room temperature 64-79F
- Humidity 30-70%
- Ventilation 10-15 air changes per hour
· Cage cards are utilized to identify the strain of rat, sex, number, principal investigator, and research protocol.
· Cage cards should not be removed from the cage to avoid misidentification of the animals.
· Temporary identification of individual rats can be accomplished by pen marks on the tail, hair clipping or dyeing the fur. Pen marks will only last 1-2 days whereas hair clipping may last up to 14 days.
· Permanent identification methods can be achieved by tail tattooing which will be performed by veterinary personnel upon request. Ear tag or punch identification can be utilized but may be obliterated by fighting between individuals. Subcutaneous microchip transponders are easy to implant and work well but are expensive.
· Tail and toe clipping are not recommended.
· When handling rats it is advisable to wear latex gloves to prevent the development of allergies due to direct contact with animal allergens.
· Rats typically become accustomed to repeated handling. In a naive animal the temperament of the animal can be determined by placing the hand into the cage to allow exploration by the animal prior to touching. Initial gentle stroking of the animal followed by gradual grasping the animal will prevent startling the animal and initiating an aggressive response.
· Avoid approaching the animal from the front.
· Rats are normally lifted by grasping the whole body with the palm over the back, with forefinger behind the head and the thumb and second finger under opposite axilla. This extends the rat's forelimbs so that they may be controlled.
· Holding with one hand is usually adequate for control, but the tail, rear legs or lower part of body may be held by the other hand for close control, treatment or examination. The use of both hands is often necessary for rats weighing over 350 gms.
· Young rats may be handled like mice when body size does not permit ease of handling within the hand.
· Investigators should avoid lifting by the tail as they may strip the skin from the tail. This is particularly likely for heavy rats (>450 gms), rats that "spin," and when the tail is grasped more than a couple of centimeters from its base. However, the "base" of the tail may be grasped with the thumb and forefinger. With this simple method of holding, they may be transferred to another cage or a balance, identified, examined casually or sex may be determined.
· For transporting short distances it may be helpful to support the rat with your arm or hand while holding the tail.
· Rats will bite and certain strains are more aggressive than others (e.g., F344 rats tend to be more aggressive than Sprague-Dawley), so care and experience are essential to rapid handling. Various restraint devices are available for use with rats.
· Neonatal rats can be handled from the day of birth but care should be taken to carefully replace the newborn in the nest with the remaining pups.
· Numerous types of restraint devices are commercially available to restrain rats. Quality devices prevent the animal from turning around yet allow easy access to the tail or legs. Devices should also be easy to clean and provide adequate ventilation.
· For tail vein injections in small rats, a wire box cage top can be turned over and the tail gently passed through the wire bars preventing the rat from turning.
· Rats that are moved indoors can be transported in a rat cage. A clean rat cage can be obtained from the cage wash area and one half inch of bedding material added. If you cannot locate a clean cage ask a supervisor or caretaker in the area for assistance.
· A wire bar lid should be placed over the cage to secure the animal during transport. If the animal is going to be in the laboratory for more than an hour a water bottle should also be obtained.
· During transport the water bottle should be placed upright in the cage lid to prevent spillage.
· Transport always results in some stress to the animal, however, animals should recover from indoor transport within their own cage within an hour. No recovery time may be needed if the animals are moved with care and have become accustomed to routine transport.
· It is recommended that a permeable drape be placed over the cages to darken the cage and prevent over arousal of the rats during transport.
· Only DLAR husbandry or veterinary staff members may transport rats to other buildings or to other animal facilities. Investigators should request animal transportation by contacting the business office at 444-2194. Transport requests should be made 48 hours in advance to allow scheduling of staff.
· Group housing, to allow social interaction, is a primary source of environmental enrichment. All rat cages also have an additional shredded paper material (Enviro-dri ™) added to their cage to encourage nest building.
· Chewing items such as Nylabones™ can be used to augment enrichment.
· Frequent handling by personnel is important and increases the ease of working with these animals.
· If animals cannot have environmental enrichment opportunities because of the nature of the research please contact the DLAR Director or the Clinical Veterinarian (444-2194).
· Zoonoses are infectious diseases that can be passed from animals to humans.
· Potential zoonotic diseases are associated with rats.
- Rat Bite Fever is caused by one of two bacteria, Streptobacillus moniliformis or Spirillium minus. Transmission of these agents is by a bite wound.
- Tapeworms (Hymenolepis nana) are transmitted by the fecal-oral route.
- Ringworm, caused by Trichophyton mentagrophytes, is a fungal infection of the skin and is transmitted by physical contact.
· Personnel can receive severe bites from rats and these bites can easily become infected. As always, it is important to clean the wound promptly and seek medical attention, when appropriate.
· A tetanus vaccination is required for all personnel working with animals.
· Allergy to rat dander and urine is not uncommon and usually develops within a few years of working with the animals. Sensitive personnel should wear face masks and/or respirators (properly fitted), gloves and a lab coat. Personnel should alert Occupational Medicine during their annual health risk assessment and if allergy is a problem, obtain advice and treatment from the Occupational Medicine physician.
A. Monitoring
· Investigators should monitor their animals routinely for common signs of illness such as
- loss of appetite,
- weight loss,
- diarrhea,
- nasal discharge,
- ocular discharge (brownish-red in color; known as poryphyria),,
- lethargy,
- swelling around the jaw,
- vocalization (“chattering” of teeth),
- unkempt appearance, and
- subcutaneous masses
· The frequency of monitoring of the animal by the investigator is stated in their approved IACUC protocol. Early endpoints are also defined in the protocol and the investigator is responsible for euthanize their animals when these early endpoints are reached.
B. Reporting Sick Animals
· If an animal is identified with either experimental or non-experimentally related illness, the investigator should notify the DLAR veterinary staff at 444-2194 between the hours of 8:00 a.m. and 5:00 p.m., Monday through Friday.
· If the investigator needs to contact a veterinarian on the weekend, the veterinary “on-call” list is posted in the main entry area of all DLAR facilities and provides the name, home phone number and pager number of the veterinarian on duty.
· When contacting the veterinarian, please provide the following information:
- Investigators name/ your name
- Species of animals and animal ID number
- Location of the animal (building, room #, rack or cage #)
- Signs of illness
- Description of any experimental manipulations performed
- Phone number where you can be reached.
· In emergency situations, if an animal needs immediate veterinary care, call the main DLAR office at 444-2194. The DLAR office will send an emergency (911) page or radio the veterinarian. If the emergency occurs after hours, call the veterinarian directly.
1) Harkness JE, Wagner JE.The Biology and Medicine of Rabbits and Rodents; 3rd Edition, Lea and Febiger, Philadelphia, PA, 1989.
2) Poole TB.The UFAW Handbook on the Care and Management of Laboratory Animals, 6th edition, Longman Scientific & Technical; England, 1987.
3) Sharp PE, La Regina MC. The Laboratory Rat, CRC Press, Boca Raton, NY, 1998.