Peromycus maniculatus Deer Mouse-BW Stock
Peromyscus maniculatus (American Deer Mouse)
BW. Subspecies P. m. bairdii originally from Washtenaw County, Michigan.
The BW stock originated from about 40 animals wild-captured near Ann Arbor, Michigan between 1946 and 1948. Van T. Harris and Lee R. Dice originated the stock. About 1954 a substock was established at Ohio State University, and in 1962 the University of South Carolina colony was founded using animals from Ohio State. The present stock is decended from 19 individuals and has an inbreeding coefficient in excess of 0.30.
The animals are typical for the species, and typical of the "prairie" ecotype described by Blair (1950). The dorsal pelage is dark brownish gray, and the underside is white, with dark bases to individual hairs. Mean adult (6 months) weight is 18 grams. Head and body length averages 85 mm and the tail length 54 mm.
Animals are sexually mature by 60 days age. The estrous cycle is five days. Gestation is 22 days, except in lactating females where it is delayed by 4-5 days to 26 or 27 days. Breeding is optimized when animals are continuously retained in breeding pairs. The females enter postpartum estrus about 12 hours after delivery and remate. Thus, serial litters are born at 26-27 day intervals. About 80% of the pairs are productive within 3 months. There may be a lag in breeding during midwinter under natural lighting. Mean number per litter is 4.2. Usual litters are 3-6 and rarely exceed 8. Mean newborn weight is 1.6 grams.
Peromyscus can be maintained using standard laboratory mouse methodology. A maximum of six animals can be house in a 7" X 10" plastic cage. Feed and water are presented ad libitum. Nutritionally complete commercial laboratory rodent feed is advised. Do not use rabbit or guinea pig feed. Supplements of fresh vegetables, raisins, sunflower seed, etc., are unnecessary, and may be detrimental. Except for breeding, sexes should be house separately. Peromyscus are reasonably cold tolerant, but ambient temperature should never exceed 33C. Optimum temperature is 22-25C.
Pairs are established individually, and checked regularly for pregnancies or litters. Copulatory plugs are inconspicuous in Peromyscus and are not a reliable indication of mating. Lighting is very important, with a 16:8 light-dark cycle satisfactory. Continuous light will produce anestrus. Breeding difficulties are sometimes overcome by reducing the light cycle to 12:12, then advancing it to 16:8 over a 3 week interval. The male should be retained with the female throughout. Introduction of a strange male to a pregnant female may block the pregnancy. Litters should be removed by 25 days of age, and may be ear or toe marked at this time. It is convenient to tag each mating cage with a card to maintain a record of breeding performance.
BEHAVIOR AND HANDLING:
Peromyscus are considerably more active than laboratory mice and will readily escape if not properly guarded. A handling table with a 10 inch high barricade is useful. Although the animals will bite if improperly handled, they rarely bite without provocation. Gentle handling is advised, and the animals become accustomed to regular gentle handling. The skin at the neck is loose and the animals may be held by the scruff of the neck. The animals may also be restrained by cupping the palm of the hand over the animal, without applying pressure, and picking the animal up by the tail. Peromyscus are much more active at night than during the day. Their repertoire of behavior is greater than that of laboratory mice, and they exhibit many activities and routines of circling, jumping, climbing, etc.
GENETICS AND PHYSIOLOGY:
Baseline data on several genetic and physiological parameters of the BW stock have been generated.