BIOLOGY	FACTS
Adult Body Weight	20-40 grams
Approximate weight at birth	0.75 to 2.0 grams
Heart Rate	Adult: 632 +/- 51.3 beats per minute Newborn: 286 +/- 56.8 beats per minute
Respiratory Rate	85-200 breaths/minute
Life span	1-3 years
Food consumption	About 15g/100g body weight/day
Water consumption	About 15ml/100 g body weight/day
Breeding onset	About 50 days in males About 50-60 days in females
Estrus cycle length	4-5 days
Gestation period	19-21 days
Average litter size	10-12
Weaning age	21-28 days

Note: Strain variation can affect these values significantly.  As a general rule, inbred mice tend to have longer gestation periods and smaller litters than outbred and hybrid mice. 

Although female mice may have their first estrus at 28-40 days of age, they usually do not breed until 50 days of age or more.  The estrus cycle lasts about 12 hours, occurring in the evening.  Mating can be confirmed by the presence of a copulatory plug in the vagina up to 24 hours post-copulation.  Pregnancy can be detected by weighing the female daily.  Daily weight gains can be detected by about 13 days into gestation. Mice have a fertile estrus cycle 14-28 hours after parturition.  If they are not bred at this post-partum estrus, nursing will prevent them from cycling and mating again until weaning.       

Some mice are very susceptible to environmental stress.  Breeding difficulties may be overcome by evaluating overall mouse room conditions and trying to minimize exposure to sudden noises, excess handling, and vibrations from the surrounding areas.  Successful breeding can occur also by extending the light/dark cycle from 12/12 to 14/10.  Dietary fat content and nutritional makeup can affect reproductive performance. 

Reproductive performance generally decreases with age.  It is recommended to replace older breeders (older than 8 months of age) with younger mice (6-8 weeks of age) on a routine basis.  If breeder pairs do not produce progeny within 6-8 weeks, try switching males and female pairs.  If the females are not caring for their young and environmental stress has been minimized, consider fostering the litter to a proven surrogate mother.

LAMS Guidelines for Mouse Breeding Colonies:

Mice are housed according to LAMS husbandry SOPs  and UC IACUC policy #001 Mouse Husbandry and Breeding Colony Maintenance.   Weaning ages and housing limits may be exceeded if:

 Special Requests

If you wish to change the light cycle in your animal room or maintain breeding colonies on Breeder Diet (i.e. Picolab from Purina), please submit a LAMS Service/Equipment Request.