Breeding Better: Strategies for Increasing Reproductive Performance in Laboratory Mice
Are you experiencing suboptimal breeding performance in your mouse colonies? Navigating mouse husbandry requires specialized knowledge. In this article we offer expert, JAX-approved guidance, in alignment with the 3Rs principles, to help you with mouse breeding strategies and explore factors that can significantly influence reproductive success, including:
Excessive handling and frequent cage disturbances and their impact on breeding performance
The critical importance of male-female interactions during breeding and pregnancy
Environmental factors that influence mouse reproduction
The role of habitat enrichment in mouse well-being and breeding efficiency
Optimal environmental conditions for maximizing reproductive outcomes
Key Factors Affecting Breeding Success
Minimizing Stress
Laboratory mice are remarkably sensitive to environmental disruptions. Frequent handling, cage changes, and invasive procedures can significantly compromise breeding performance. Mice can experience stress from seemingly minor disturbances that humans might not even notice, such as cage changes more often than 1-2 times per week, repeated welfare checks, or unexpected loud noises.
To mitigate stress, it is best to implement defined handling protocols: limit cage interventions, position breeders away from high-traffic areas like doors or sinks, and train caretakers to work with mice gently, slowly, and quietly. Consider adding white noise or background music to buffer unexpected loud noises, creating a more stable and conducive breeding environment.
Social Dynamics
The timing of male-female interaction can also impact breeding success. Removing males from breeding cages can significantly disrupt reproductive performance, potentially causing their pregnant mates to resorb in utero, abandon, or cannibalize their litters due to increased stress.
At JAX, we maintain males with females throughout pregnancy and nursing periods. If a male must be removed, it is best to wait until the pups are delivered, and do not return him to the cage until the litter is weaned.
Maintaining males alongside females increases a colony's overall productivity by leveraging postpartum estrus. Females enter estrus and are receptive to mating immediately after delivering a litter. If the male is present, a female may become pregnant with a second litter while nursing her first, delivering it 3-4 weeks later. If the postpartum estrus window is missed, females will not be receptive to mating until after weaning.
However, consult facility managers about cage capacity and litter management. A second litter born before the first is weaned may require screening, culling, or early weaning. Larger cages can also help accommodate multiple litters more effectively.
Environmental Stressors
Light
As nocturnal animals, mice mate only in the middle of their dark cycle. At JAX, our mouse rooms maintain a 14-hour light and 10-hour dark cycle, though a 12-hour light/dark cycle is also acceptable. The key is ensuring at least 10 hours of uninterrupted darkness. Once the lights go off, they must remain off and eliminate any additional light sources from equipment that might disrupt this critical breeding period.
If you need to enter the vivarium during dark hours for procedures like injections or measurements, use night-vision equipment to avoid disturbing the mouse breeding cycle. Even minimal light exposure can interfere with their reproductive processes!
Odor
Odors can induce stress, increase aggressive behavior, and reduce mating productivity in mice. Mice possess a highly developed sense of smell, making them sensitive to odors from perfumes, skincare products, and cross-cage pheromones. To mitigate the latter risk and avoid pathogen transmission, it is best practice to disinfect gloves and forceps between cage interactions.
Enrichment
Mice instinctively love to nestle and burrow in their nests. Without environmental enrichment, many strains exhibit problematic behaviors like barbering, reduced eating, and diminished breeding. Enrichment options such as Shepherd Shacks®, nestlets, igloos, and biotunnels can significantly improve the mental well-being and breeding efficiency of your mice.
At JAX, our commitment to the 3Rs principles of ethical animal research guides our approach to mouse husbandry. By prioritizing environmental enrichment and stress reduction, we not only improve breeding performance but also enhance animal welfare.
Even our most commonly used strains, like C57BL/6J (000664) and NSG (005557), are housed with enrichment to enhance wellness and psychological stimulation.
Diet Considerations
Different mouse strains require unique dietary approaches. For instance, our most popular C57BL/6J mice thrive on a 6% fat diet, while CAST/EiJ mice perform better with 10% fat. "Breeder chow" diets typically contain 10-12% fat, but caution is needed, as some strains like C57BL/6J may become obese, potentially diminishing breeding performance.
JAX investigators have developed a dietary supplement called "Love Mash" (recipe below) to enhance breeding performance. For those unable to prepare it themselves, BioServ offers a pelleted version with similar ingredients.
“Love Mash” Ingredients:
42 oz oatmeal
200ml wheat germ
200ml brewer’s yeast
150ml cod liver oil
Health Status
Health status critically impacts breeding performance. Immunodeficient strains like NODscid (001303), Nude (007850 and 002019), Balb/c scid (001803), and the most immunodeficient mouse strain, NSG (005557), require meticulous environmental cleanliness. Some strains, such as B6.129P2-Il10tm1Cgn/J (002251), B6.129P2-Il2tm1Hor/J (002252), and B6.129S7-Rag1tm1Mom/J (002216), may be less obviously sensitive to environmental pathogens, but their breeding success and phenotypes can be significantly compromised by insufficient room hygiene.
JAX maintains rigorous animal health standards through our comprehensive Animal Health Program. Our approach includes preventative measures to avoid infectious agent entry, monitor for potential infections, and minimize transmission through microisolator caging and strict health practices. Detailed pathogen monitoring information is available in our Animal Health reports, accessible under the "Health & Care" tab of each strain datasheet and on our "Animal Health Program" webpage.
Bonus Tip: Understand Your Strain's Reproductive Potential
Despite best practices, some mouse strains inherently breed poorly. Knowing your strain's fecundity helps set realistic expectations. The Mouse Phenome Database provides comprehensive insights, including superovulation rates, percentage of productive matings, and overall reproductive performance for several popular strains.
At JAX, our Genetic Quality Control and Genetic Stability (GQC) Programs ensure the highest standards of genetic integrity through rigorous monitoring, genotyping, and carefully executed breeding protocols. This commitment guarantees that researchers receive reliable and reproducible mouse models. Learn more about the GQC programs here.
Need More Guidance?
If you cannot find the specific information you need, contact our Technical Information Services (TIS) team for expert, personalized guidance on mouse husbandry and breeding. Our Technical Information Scientists are ready to answer in-depth breeding questions and help resolve technical challenges. Visit the TIS Help Center for additional resources to support and optimize your mouse breeding performance. your mouse breeding performance.
Contact Us: micetech@jax.org 1-800-422-6423 (US) +1-207-288-5845 (International)
For researchers seeking a comprehensive solution, JAX can also manage your entire breeding program, offering superior logistics and guaranteed on-time delivery of high-quality mouse models. Learn more by visiting our Mouse Breeding Services webpage or request a consultation today.