TABLE 7-1 Reproductive and Developmental Indices of Voles

Species Name

Common Name

Adult Weight, g

Gestation, days

Litter Size

Birth Weight, g

Postnatal Growth, g/day

Approx. Weaning Age, Days

M. arvalis

Common vole

35

20

4.8

2.1

M. californianus

California vole

50

21

4.7

2.8

1.1

14

M. montanus

Montane vole

50

21

6.0

2.5

1.0

15–17

M. montebelli

Japanese field vole

41

21

4.7

2.7

0.9

21

M. ochrogaster

Prairie vole

40

20–22

3.9

2.8

1.0

14–21

M. oeconomus

Tundra vole

45

20.5

4.0

3.0

0.8

18

M. pennsylvanicus

Meadow vole

40

20–21

4.4

2.3

0.7

14

M. pinetorum

Pine vole

26

24

2.2

2.0

17

 

SOURCES: Lee and Horvath (1969), Richmond and Conaway (1969), Lindroth et al. (1984), Kudo and Oki (1984), Nadeau (1985).

HUSBANDRY AND FORM OF DIET

Vole colonies are usually founded by the capture of wild animals. Successful breeding colonies have been established for at least 10 species of voles in North America (Mallory and Dieterich, 1985) and several other species in Europe and Japan (Kudo and Oki, 1984). Different colonies of the same species may be genetically distinct because of substantial variation among the founding wild populations. Extensive morphological variation over the ranges of most species has resulted in the description of a plethora of subspecies. At the extreme, 27 subspecies have been described for Microtus pennsylvanicus (Hoffman and Koeppel, 1985). Populations of voles may vary in characteristics such as body mass and litter size, although the extent to which this variation is a result of genetic or environmental effects is not clear (Keller, 1985). Care must be exercised in generalizing from one colony to another; the values listed in Table 7-1 may not apply to all colonies.

Voles have been maintained in a variety of cages, but plastic mouse cages with solid bottoms and added bedding material are especially suitable (Richmond and Conaway, 1969; Mallory and Dieterich, 1985). Details of lighting, ambient temperature, social groupings, and other aspects of the husbandry of voles have been reviewed by Lee and Horvath (1969), Richmond and Conaway (1969), Dieterich and Preston (1977), and Mallory and Dieterich (1985).

NATURAL-INGREDIENT AND PURIFIED DIETS

After an initial adaptation period, voles adapt well to captivity and can be fed on various natural-ingredient diets. Pelleted natural-ingredient diets developed for rabbits, mice, rats, and guinea pigs are apparently the most commonly used diets, either with or without supplementation with succulent foods such as lettuce or apples. Of the 10 species listed by Mallory and Dieterich (1985), 7 have been maintained on rabbit diets and 7 on mouse breeder diets. Sole or heavy use of succulent items (such as barley sprouts, carrots, lettuce, and apples) or of unsupplemented seeds and grains (such as sunflower seed, grass seed, and oats) is not recommended because of the likelihood of unintended mineral or vitamin deficiencies (e.g., Batzli, 1986).

Purified diets based on vitamin-free casein, a purified cellulose source, a mixture of starch and sugars, and vitamin and mineral premixes and fed in the form of wafers supported adequate weight gains in short-term (6 to 10 days) experiments with weanling meadow voles as long as the cellulose source was at least 25 percent of the diet (Shenk et al., 1971). This may be too short a period to adequately assess response, however (Lindroth et al., 1984). Both prairie voles and tundra voles exhibited normal growth after weaning when fed either a purified diet (based on 20 percent casein and 40 percent cellulose) or a commercial natural-ingredient diet (formulated for rabbits); but the purified diet subsequently led to greater fat deposition, reduced production of litters, and reduced litter size (Lindroth et al., 1984). Sugawara and Oki (1988) noted that purified diets that contained less than 20 percent casein impaired female fertility in the common vole. It has yet to be demonstrated that a purified diet can maintain long-term reproduction in a breeding colony of voles.

DIET DIGESTIBILITY AND INTAKE

Voles exhibit a number of anatomical features that are associated with herbivory and fermentation of plant fiber. The cheek teeth are high-crowned and contain a complex array of cusps; the stomach is separated into two compartments, one of which (sometimes termed the esophageal pouch) is lined with stratified squamous epithelium and harbors anaerobic microorganisms; the cecum is enlarged and separated in pockets by projecting isthmuses; the colon is both elongate and arranged into spirals that facilitate particle segregation (Vorontsov, 1979; Kudo and Oki, 1984; Stevens, 1988). Although volatile fatty acids are produced



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