General Husbandry Tips

General husbandry tips

  • Consult your institution’s Animal Care and Use Committee (ACUC) for guidelines to determine the best husbandry practices at your institution.
  • Obtain 2-4 breeding pairs to establish a new colony.  Additional breeders can significantly reduce the time needed to expand a colony.
  • Combining males from different litters is only appropriate at weaning (3-4 weeks).  Males combined later are likely to be aggressive and to fight, causing wounds and/or death to their male cage mates. Males shipped in separate compartments likewise should not be combined.
  • Mate mice early, at 6-12 weeks of age. Mice tend to gain weight and be less productive if mated later.
  • Replace non-productive breeders. If matings have not produced a litter within ~60 days, replace them to maximize your colony production.
  • Retire breeders at 7-8 months of age.  Rotating mice on a regular schedule will maximize colony production.
  • Breeding characteristics are strain- and environment-dependent.  Establish normative breeding data for each strain at your facility to detect colony changes, identify deviations and maximize breeding efficiency.
  • Genetic drift can alter strain phenotype over time. Cryopreserve your unique strains with The Jackson Laboratory and refresh inbred colonies regularly to protect against genetic drift, natural disasters, breeding errors or disease outbreaks. See our Disaster Planning for more information.
  • Expect seasonal changes in breeding performance. Some strains produce more litters in the spring and summer than in winter and fall.
  • Weather & air pressure changes can alter behavior and production. Reduced breeding performance and/or hyperactivity may coincide with changes in weather.
  • Hybrid mice generally breed more efficiently than inbred mice. F1 and F2 hybrids and mice with mixed genetic backgrounds display hybrid vigor, producing more, larger, and healthier litters than strains on a pure inbred background.
  • Anticipate changes in breeding performance when transferring a mutation (knock-out) or transgene to a new genetic background.  Breeding performance and phenotype of interest can change when a new background is introduced. 
  • Avoid selection pressure.  Be careful not to choose breeders that might select against your phenotype of interest. For example, if older mice develop a phenotype that limits their life span or breeding productivity, select breeders for the next generation from early 2nd or 3rd litters.  Similarly, don’t select breeders based only on good breeding performance; you may unknowingly alter their phenotype.

Strain breeding performance

Strain breeding performance (good, exceptional or challenging) is provided on each strain datasheet as a baseline for establishing your own colonies or for considering how long it will take, and how many breeding pairs you may need to produce cohorts of mice for your experiments.

Note: Mouse breeding performance can change under different environmental conditions, and first litters may not be representative of average pups per litter.

Good breeder
  • Regularly produces three to seven pups per litter
  • Reliably productive for seven or more months
  • Example: B6 Cd45.1, Stock No. 002014
Exceptional breeder
  • Regularly produces eight or more pups per litter
  • Exhibits good mothering instincts
  • Possesses a long, productive breeding lifespan
  • Example: FVB/NJ, Stock No. 001800
Challenging breeder
  • May require special maintenance, exhibit reduced productivity and/or experience some incidence of non-productive matings
  • See our tips for poor breeders section below
  • Example: 129P3/J, Stock No. 000690

Tips for poor breeders

  • Minimize noise. Keep in the quietest area possible, away from doors, sinks and heavy traffic.
  • Minimize handling, especially with females close to delivering or with new litters. Stressed mothers are more likely to cannibalize or abandon their young.
  • Keep males and females together whenever possible to maximize breeding and reduce stress. If a male needs to be removed, do not remove him when the female is about to give birth, and do not return to the cage until pups are weaned.
  • Handle mice gently with forceps. Disinfect forceps between cages and change gloves frequently, to avoid spreading scents. 
  • Maximize darkness. Move to the darkest location available, away from exit signs and other night light sources.  Ensure that the dark cycle is maintained once the lights are turned off.
  • Provide nesting materials. Nestlets, Kimwipes or other soft, fibrous material provide security and enrichment that may enhance productivity.  See ‘Enrichment’ suggestions in the Mouse room conditions section.
  • Consider changing diets.  Diets with a higher (or lower) fat or protein content, compared to your standard diet, may improve productivity of a challenging strain.

Fostering litters

Newborn litters are sometimes fostered onto nursing surrogate mothers for a variety of reasons. The following is a compilation of comments, suggestions and proven techniques for fostering a litter. Techniques used to ensure the foster mother will accept the new pups vary and the method that works may depend upon individual preferences and the reason for fostering. 

The first step in fostering is the selection of a suitable foster mother. Try to choose a mother that has successfully weaned a litter in the recent past. For best results, it is important to match the age of the litter to be fostered with the age of the foster mother's natural litter. The foster mother's litter should be a different coat color than the litter to be fostered so that the pups from the two litters can be separated at weaning. If, however, the entire natural litter is removed and replaced with the foster litter this is not necessary. 

Among inbred strains, we typically recommend FVB/NJ (Stock# 001800) as foster mothers. F1 hybrids and outbred mice (like CD1), also, are commonly used. If you want to use a foster mother that is pigmented (because your foster pups are albino), F1 hybrid mice, such as B6129SF1/J (Stock# 101043) and B6C3F1/J (Stock# 100010) may be useful as well. 

Always be sure the that foster mother has finished delivering her young before using her as a foster mother because one or two pups may be born as long as 6 hours after the majority of pups are born. It is critical to have the litter size as equal to the natural litter size as possible. If the litter to be fostered is especially large (more than 10 pups) the litter may need to be divided up and given to two foster mothers. A change in litter size of +/- 2 or more pups can affect the milk supply of the foster mother. 

It is best to keep the foster mother in her cage, remove the natural pups, and add the foster pups to the cage. She and her foster litter can be transferred to a clean cage the next day. Disturb the foster mother and her new litter as little as possible for the first 24 hours, but do check during the first 24 hours to be sure the litter is being cared for. 
In addition, we typically leave the male in the cage as well, because we would not want to sacrifice a proven and established breeder to foster pups that may or may not survive. Usually the strains used for fostering are more docile so there is a lesser chance the male would be aggressive to the fostered litter. However, depending on the cage size, the number of pups that are being fostered, and your institutions' policy on rodent housing, you may need to remove the males in order to be in compliance with the Guide's recommendation on rodent housing. 

Remove entire nest with the foster mother's pups in it. Place under heat lamp or some source of heat. Place pups that are to be fostered in nest, gently mingle pups together to spread scent. Rub feces from foster mom on the backs of all pups. This should stimulate the foster mother to clean the pups, will increase the likelihood that she will accept the foster pups as her own. Place nest back in cage of the foster female. 

Aggression and fighting

  • Males may be combined at weaning age (3-4 weeks), but should not be combined at older ages. They may fight, cause wounds and/or death of male cage mates.
  • Males shipped in separate compartments of the same shipping box or in individual boxes should not be combined upon entry into your facility as they may fight.  Wounded mice may not be useable for your research.
  • Separate group-housed males which are fighting; at the very least remove the dominant male (the mouse lacking wounds).
  • Males from some strains (e.g. SJL/J) are naturally aggressive toward their female mates and offspring and may need to be removed until pups are weaned.
  • Housing density of mice can affect aggressive tendencies.  Consult your institutional ACUC for housing density guidelines.
  • Change gloves frequently and use forceps disinfected between cages to reduce scent transfer that can lead to increased aggression.
  • Providing environmental enrichment such as nesting materials, Nestlets (Animal Specialties and Provisions, LLC), NestPaks (WF Fisher and Son), and Shepherd Shacks (Shepherd Specialty Papers) can help alleviate stress and aggression.

Additional mouse breeding resources and references

Jackson Laboratory resources
Online mouse husbandry links and downloads
Chapters for download

Conner DA. 2005. Transgenic mouse colony management. Curr Protoc Mol Biol, Chapter 23:Unit 23.10.  PMID: 18265361.

Conner DA. 2002. Mouse colony management. Curr Protoc Mol Biol, Chapter 23:Unit 23.8. PMID: 18265310.


Institute of Laboratory Animal Resources. 1996. Guide for the care and use of laboratory animals. National Academy Press, Washington, D.C.

Inglis, JK. 1980. Introduction to Laboratory Animal Science and Technology. New York, New York: Pergamon Press

Stark, D.M. and Ostrow, M.E. (eds.) 1991. American Association for Laboratory Animal Science Training Manual Series, Volume One, Assistant Laboratory Animal Technician. Tennessee(AALAS): Cordova

Fox J, Barthold S, Davisson M, Newcomer C, Quimby F, Smith A, eds. 2006. The Mouse in Biomedical Research, 2nd edition, Vol. III. Normative Biology, Husbandry and Models. Elsevier Academic Press, San Diego, CA