Guidelines for Housing, Breeding & Weaning Rodents  | Rodent Genotyping  | Mouse Colony Management Seminar 


Animal Husbandry and Breeding

Housing and Husbandry Care for Laboratory Animals

The Animal Resource Program (ARP) employs veterinarians, veterinary technicians, animal caretakers, facility managers and administrative staff to perform all of the functions necessary to provide high quality care for the research animals housed in PSU facilities. ARP manages all of the laboratory animal facilities on the University Park campus. Mice and rats are the most commonly used laboratory animals in these facilities although PSU has the ability to house many other species, including rabbits, farm animals and non-human primates.

Investigators who have obtained approval to use animals in research at PSU must first work with the ARP office staff and facilities managers to select and order the appropriate type of animal for their research. Housing and care of the animals is then planned and arranged before they arrive at PSU. Laboratory animals may only be housed in ARP facilities. Investigator laboratories used for animal work must also be approved to ensure appropriate conditions for the animals. After completion of the appropriate training, including all required IACUC and ARP facility orientation training, principle investigators, their research staff and students are allowed to work within a laboratory animal facility. 

Several laboratory animal facilities of varying size are located on the University Park campus. The facilities are kept locked with alarms on the doors and access limited to approved personnel. There are several reasons why animal facilities are not open to the public:

  • Animals need a quiet, safe and secure environment to thrive. The presence of excessive noise, unfamiliar people and lots of activity can be disturbing for the animals. Limiting access to the facility reduces animal stress which leads to less statistical variability, more accurate research results and ultimately, the use of fewer animals.
  • Reliable and accurate research also requires the use of healthy animals. Limiting the flow of people in and out of the facility and requiring animal handlers to wear gloves, gowns and other protective gear reduces the chance animals will be exposed to infectious agents.
  • Laboratory animal facilities contain specialized and expensive equipment such as ventilated cage racks, x-ray machines and anesthetic equipment. Damage or theft of this equipment would compromise the ability of PSU staff to maintain the health and welfare of the animals and the accuracy of research taking place in the facility.


Each animal facility is unique but they all share certain features:

  • Secure Access: Research staff and students are provided with access to the specific facility in which they house animals. Entrance to a facility is either through key card or key. Approval for access must be obtained from the ARP office.
  • Climate controlled animal rooms: Animal rooms are maintained at ventilation, temperature and humidity levels appropriate for the species of animal in the room. All rooms have automatic timers to control when lights go on and off. Animal care technicians check the animals in the room at least once a day, seven days a week. Cages and other equipment are cleaned and replaced as often as needed to maintain clean, dry housing for each species. Food is supplied in the form and quantity appropriate for each animal species. Some animals require special diets or sterilized food to ensure adequate nutrition and good health. Water is also sometimes sterilized to prevent the introduction of disease causing organisms into certain groups of animals.
  • Room entry: Animal rooms within the facility are kept locked when not in use. This provides quiet and safety for the animals, in addition to helping prevent the spread of disease. Staff and students must comply with personnel protective equipment (PPE) requirements for each room. These requirements are usually posted on the animal room door. Do not wear the same PPE in more than one animal room.


Guidelines for Housing, Breeding & Weaning Rodents in PSU Facilities

Acclimation Periods

The shipping process is stressful for animals and results in a disruption of their normal environment. In the interest of animal welfare and experimental accuracy, ARP recommends that rodents not be used for any experimental procedures for at least 5 days after their arrival at the University Park animal facilities. Other species may require longer periods to acclimate after arrival. Please consult with an ARP veterinarian for more information.

Social Housing for Rodents

As social mammals, most rodents have evolved to co-exist with members of their own species. In fact, appropriate social interactions with conspecifics have been shown to be essential to normal development and well-being in many species. While single housing of laboratory rodents is sometimes necessary, the Guide for the Care and Use of Laboratory Animals (8th ed.) considers group housing the norm. Investigators are expected to pair or group house rodents unless the PSU IACUC has approved specified periods of individual housing as necessary for their experimental protocol or for the health and welfare of the animal. Investigators must consider the requirements for social housing when planning experiments. Modification of experimental design or procedures to accommodate pair or group housing is frequently possible without affecting data collection and accuracy. Individual housing is acceptable without specific scientific justification and IACUC approval in the following situations:

  • When required to prevent injuries and stress associated with aggression (e.g., unfamiliar adult male mice). Housing socially incompatible rodents in the same cage will lead to unrelieved stress and (often) physical injury and pain for those animals; in addition to increased variability as research subjects.
  • During temporary periods associated with breeding activities (e.g., pregnant females housed individually prior to and when giving birth). Although commensal nesting is normal for mice and rats, there may be research requirements for temporary single housing.
  • Rarely, when a compatible animal of the same line/status is unavailable. Whenever possible, investigators should plan accordingly to prevent this from occurring.
  • All mice must be provided with nesting material (exceptions to this policy require IACUC approval).


Environmental Enrichment

Environmental enrichment is intended to facilitate the expression of species typical behaviors and promote psychological well-being in captive animals. In addition, mice and other small animals may suffer from cold stress when housed alone. Appropriate nesting material must be provided to all mice unless the IACUC has specifically approved withholding enrichment for experimental purposes. Rats are typically provided with material to gnaw on. In addition to nesting material, individually housed rodents must be provided with a secondary form of enrichment such as a tube to hide in.

Special Care Indicator Cards

The investigator is responsible for clearly indentifying laboratory animals with unusual or unique research or husbandry requirements. ARP provides investigators with "special care indicator cards" that are placed on cages of animals requiring food and/or water restriction, unique food and/or water sources (e.g., medicated water or specific nutritional formulations) or other research needs. These cards must be dated and clearly indicate the special care requirements to all personnel working in the room (i.e., lab staff, ARP vet staff and husbandry technicians). Cards must include all relevant information for those animals, including the date/time range of special care (especially important for food/water restriction) and the name of any medication, substance or specific feed that is used. These cards may be obtained by contacting the Animal Resource Program.

Animal Room Environmental Assessment Sheet (AREA)

In certain circumstances, the PSU IACUC may grant approval for an investigator to provide specific husbandry care for research animals listed on their protocol. Research personnel who perform husbandry duties must document the care they provide on the Animal Room Environmental Assessment Sheet (AREA) each time these duties are completed. AREA sheets are located inside the animal room or on the entry door (for restricted or reverse light cycle rooms). If a research lab is providing any form of husbandry for research animals, they must initial the dark green “PI Husbandry” box located at the bottom of the AREA sheet at the time care is provided. ARP monitors these sheets to ensure that husbandry duties are completed. Initialing in advance is not permitted. Note that failure to properly document husbandry care via the AREA sheet may lead to IACUC action.

Housing and Care of Breeding Mice

Housing and Husbandry for Laboratory AnimalsThe ARP provides a training seminar for PSU research personnel, Basic Principles of Mouse Breeding Colony Management that is available online.

For permanently paired breeding mice, the number of animals is limited as follows:

  • Shoebox caging (small cages): 1 male and 1 female with their current litter
  • Gang caging (larger cages): 1 male and 2 females with current litters 

Alternate configurations involving larger breeder groups may be acceptable if pregnant females are removed prior to giving birth. Breeding cages should be observed by research staff a minimum of three times a week. Breeding animals must be supplied with appropriate nesting material. Consult the ARP veterinary staff for more information.

The number, age and activity level of mouse pups, as well as the general cage environment, breeding characteristics and/or reproductive performance of the colony may influence decisions on the number of mice to place within a cage. Under certain circumstances, it may be necessary to reduce the cage population or increase the floor space (by moving animals to a larger cage) to ensure the health and welfare of animals. Breeding colony managers, in consultation with the ARP animal care staff, are responsible for decisions regarding cage space and frequency of cage changes for breeding animals. Investigators who wish to decrease the frequency of cage changes (below normal levels) must first obtain IACUC approval.

Weaning Mice

In general, mouse pups should be weaned from their mother between 21-26 days of age. At this time, male and female pups must be separated into same-sex groups to avoid accidental breeding when mice reach puberty at 6-8 weeks of age. If litters are not weaned promptly, the cages will become overcrowded. If a litter is not weaned by 28 days of age, an ARP animal care technician will wean the animals and the investigator will be charged a fee.

If a mouse gives birth to a second litter before her first litter is weaned, research staff must remove the older litter from the cage. If after 48 hours, the older litter has not been weaned, the cage will be considered overcrowded and the litter will be weaned by an ARP animal care technician. The investigator will be charged a fee for weaning services.

Overcrowding of a cage may occur prior to weaning age if there are a large number of pups in the litter or if there are multiple dams/litters in one cage. Investigators should monitor large litters and move them with their dam(s) to a larger (gang) or separate cage if needed. This typically occurs when pups are around 10-14 days of age. If an ARP animal care technician is required to perform this duty, the investigator will be charged a fee.

Recently weaned mice should not be individually housed unless required for immediate experimental purposes. All recently weaned mice (and any individually housed mouse) must be provided nesting material. ARP supplies shredded paper nesting material in each mouse room. Individually housed mice should also be provided with a plastic tube or other approved structure.

Rodent Genotyping

Genetic identification of research rodents is often accomplished through the use of PCR analysis of DNA extracted from tail or ear punch tissue. DNA may also be obtained from other samples, such as hair, blood and oral swabs. Deviations from PSU IACUC genotyping guidelines must be approved by the IACUC. Personnel must receive sufficient training to perform the procedures in a safe and humane manner.

Guidelines for tissue collection

Ear punch/ear snip: Tissue for genotyping may be collected by ear punch or snip at any age and does not require anesthesia. This is the preferred method of tissue collection for genotyping of rodents.

Ear punch - The amount of tissue collected from a 1-2 mm sterile ear punch is usually adequate for genotyping and may be performed on any age mouse without general anesthesia. Ear punches must be cleaned and disinfected between animals.

Ear snip - Using a sharp, sterile scissors, 2-3 mm may be snipped from the tip of the ear to collect tissue for genotyping. Scissor tips must be cleaned and disinfected between animals. This procedure may be performed on any age mouse without general anesthesia.

Tail Tip Amputation: Animals must be less than 3 1/2 weeks of age at the time of tail tip amputation for genotyping. DNA yield from tail tissue has been shown to be highest in 10-21 day old rodents. Tail tissue analysis and identification of desired mice prior to weaning may allow more efficient use of resources. In addition, cutting through the soft tissue in the tail of a young mouse is likely to be less painful than cutting through more extensively mineralized bone and mature tissue in older animals. Tail tip collection should be performed at as young an age as feasible.

Animals less than 3.5 weeks of age: Collection of tail tissue may be performed without general anesthesia. Local anesthetic methods are available. Please contact an ARP veterinarian for more information.

Animals greater than 3.5 weeks of age: Samples for genotyping must be collected by ear punch or ear snip.

In most cases, 2 mm removed from the tip of the tail is adequate for genotyping. No more than 5 mm of tissue may be removed from an animal. DNA yield does not proportionally increase as larger amounts of tail tissue are collected. Tail amputation should be done using a sharp, sterile scissors that is cleaned and disinfected between animals. Note: all tissue must be removed from the scissors after each animal for accurate DNA analysis via PCR.

Blood loss should be minimal from animals less than 3.5 weeks of age when proper procedures are used. If needed, bleeding may be controlled by applying direct pressure to the tip of the tail. Styptic powder/pencils and silver nitrate are chemical cauterizing agents that may be used if necessary. Use of heat to cauterize the tail end is not allowed.

If it is necessary to collect a second sample from an animal, the second sample must be collected via ear punch or ear snip.

Mouse Colony Management Seminar

The ARP provides an online mouse breeding colony management training seminar for PSU research personnel. The information presented in this seminar and on the ARP website is intended as a resource for Pennsylvania State University research investigators. No guarantee of efficacy or safety is made nor must information obtained from this site be substituted for professional veterinary advice. Please contact the ARP if you have additional questions on mouse colony management or breeding.

Please note that presentation format is best viewed full screen but hyperlinks will not work in full screen mode unless you right click on the link and open it in a new window.

Part 1: Guidelines and starting out, record keeping, nomenclature, housing and weaning, identification.

The ABCs of Breeding Colony Management Part 1

Part 2: Mouse reproductive biology, breeding strategies and tips, health issues and euthanasia.

Breeding Colony Management Part 2