Tips on care and handling
Minimize Environmental Stress
Inbred strains of mice are maintained by successive sister x brother matings. Reproductive performance and behavior are strain dependent and should be well researched before a mouse is imported. For example, strains like C57BL/6J are very susceptible to environmental stress, and breeding difficulties may be avoided by minimizing human activity, noise, handling, etc. in the rooms housing them. Often, changing the light/dark cycle from 12/12 to 14/10 improves breeding performance.
Feed Proper Diets
Dietary fat content and nutritional composition affect the overall health and reproductive performance of mice. Most of our mice are maintained on an NIH 31 6% fat diet from Research Diets, Inc.
Replace Old Breeders
As reproductive performance generally decreases with age, we usually recommend replacing old breeders (more than eight months old) with young ones (six to eight weeks old). Retirement age in our facility varies by strain. If breeders do not produce litters within six to eight weeks, try exchanging males and females between breeders. If females do not care for their young (even after environmental stress is minimized), consider fostering litters to a proven surrogate.
Litter Fostering
The litters of some mice need foster care to survive. For examples, females of some strains are poor mothers (
e.g., NZB/BlNJ, 000684) or cannot nurse, and a few mutations, such as toxic milk (
Atp7btx) and lethal milk (
Slc30a4lm), render the mother’s milk toxic to her pups. Fostering mice is relatively simple. The foster mother must have a healthy and well-fed litter of her own that is within one or two days of age of the fostered pups. It is very helpful if her pups are of a different color than that of the fosterlings. The foster litter should be no larger than the natural litter. Additionally, if the foster litter is larger than six pups, it should be divided between two foster mothers. Remove the proposed foster mother and place her in a holding pen. Place the fosterlings in her home pen and cover them with the nest material or bedding so they acquire the odors of the home pen. Wait 15 to 30 minutes, and place the foster mother back in her home pen with the fosterlings. She may better accept the new pups if you rub feces or damp bedding from her cage on them. Alternately, putting a heavy perfume scent on her nose before introducing her to the fosterlings may mask their scent. To be sure that the foster mother is feeding the pups, observe her and the pups carefully for a day or two. If litter survival is crucial, divide the litter among several foster mothers.
