Handling Breeding Problems

It is not uncommon to experience problems when breeding mice. Problems may occur with first time mating or with colonies that have been breeding well. It is often difficult to determine why a breeding colony suddenly breeds poorly. The following are things which can cause problems. Check each situation, keeping in mind that sometimes it can be a combination of two or more.

1. Check the environment of the breeding room. Loud noises from a nearby area can cause problems. Move the mice away from high traffic areas. It is helpful to have music or a radio playing in the room to provide a constant “white noise” level to reduce sudden noises.

2. Make sure the mouse rack does not vibrate. Check to see that it is sturdy and is not up against a wall with HVAC equipment on the other side. Solid bottom cages are necessary for breeding mice.

3. Maintain temperatures between 65-750F. Humidity can range from 40-70% relative humidity, but is recommended to be between 45-55%.

4. Check the age of the mice being mated. Mice will continue to breed until approximately 9 months of age, depending upon the strain or mutant gene. Mice first mated when older than 3 months probably will not breed.

5. If breeders do not deliver a litter after six to eight weeks, try a different mature male or female. Another suggestion is to separate the pair completely and re-mate after a week.

6. When mice breed poorly, it is recommended that the mice be handled less frequently. Change the cage once/week. If the female is due to deliver or has newborn pups, skip changing the cage until the pups are 3-4 days old. Resist the urge to take the cage off the shelf repeatedly to observe the mice. Use forceps or a clean-gloved hand to handle the mice, avoid putting a bare hand into the cage. Don’t wear perfume or cologne when handling mice.

7. If it appears dams are not taking care of newborns, it is helpful to provide nesting material. Nestlets, two kimwipes rolled into a ball, or fluffy pine shavings are all possible nesting materials.

8. Check the health status of the mice for any recent changes. Also check for anatomical abnormalities in the colony. Check the diet the breeders are being fed. Sometimes a change in the diet to either a higher or lower fat content will help.

Housing

Weight # Per Cage Floor Area Per Animal Small Mouse Cage: 70 square inches of floor space < 10 grams 11 6 sq. in. space required 10-15 8 8 15-25 5 12 > 25 4 15 Tecniplast Ventilated Mouse Cage: 82 square inches of floor space < 10 grams 13 6 sq. in. space required 10-15 10 8 15-25 6 12 > 25 5 15 Large Plastic Mouse Cage: 153 square inches of floor space < 10 grams 25 6 sq. in. space required 10-15 19 8 15-25 12 12 > 25 10 15

IACUC Cage Population Densities for Breeding Mice

Category 1: A single male and a female with litter. Preferred method. Breeder males should be removed from cages when they are not needed for pup care or re-breeding in the postpartum period.

Category 2: Two females in a cage with not more than a total of 12 pups from 12 days of age to weaning. (Mouse strains that require communal care.)

Category 3: Trio breeding (one male and two females) with not more than a total of 12 pups from 0-14 days and not more than 6 pups from 15 days to weaning. (Postpartum mating needed for production and communal care required.)

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