Sciuromorpha

Last modified on June 5, 2010

Richardson's ground squirrel

Woodchucks

Richardson's ground squirrel (Spermophilus richardsoni){3999}

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Woodchuck (Marmota monax)

Woodchucks are also called groundhogs, whistle pigs, or just "chucks". They have been used to study hibernation, control of food intake, and circannual cycles such as thyroid activity and testicular development. The only other wild sciurid that has been bred in captivity is the 13-lined ground squirrel.{3955} As hibernating animals, their body weight fluctuates from 2-3kg in the spring to 4.5-7kg in the fall. They have strong front claws for burrowing.{3560}

Husbandry: Keep woodchucks in natural light and local photoperiods, with some artificial light supplementation. House them in 1½ sq meter pens in groups of 2-4 females with one male, or in ½ sq meter individual cages with solid flooring.{3955} Dietary requirements may be met using rabbit feed{3560} or Agway woodchuck chow{3955}, but not commercial rodent chow. Woodchucks will eat 200-300 gram of feed in a single feeding (in the summer), and drink large quantities of water.{3560}

To restrain a woodchuck, the head is pushed to the cage floor with one gloved hand, while the other hand picks the animal up by the tail. They may become accustomed to being carried with the tail in one hand and the other hand supporting the thorax against the person's body.{3560}

Hibernation can be induced in woodchucks kept in the laboratory under the proper conditions. There must be adequate body fat stores, cool temperatures (6-8ºC), and controlled day length. Torpor is initiated over several weeks, in increasingly long periods ranging from 4-5 days at first to 10-12 days. During brief (24 hr) arousal periods, the woodchucks warm up and urinate. Minor disturbances will not generally arouse them. Although natural hibernation lasts about 3-4 months, in the laboratory this period can last as long as 8 months. The final arousal stimulus is unknown.{3560}

Reproduction: Breeding season begins in January or February. Adult body weights range from 2-3 kg for females and 3-4 kg in males early in the season. Half a year later body weights are at their peak, 4-5 kg for females and 4-6 kg for males. Swelling of the vulva is an indicator of estrus; when it gets to 7-9 mm they're in early estrus. Males get testicular swelling during the breeding season. Females are usually induced ovulators, ovulating 24 hours after mating, and vulvar swelling decreases over 5-10 days after a fertile mating. They should be mated several times while receptive, once to induce ovulation and later to deposit fertile sperm where they're needed. The mating season is about 10-20 days. Implantation is on the antimesenteric side of the uterus, but the placenta develops on the mesenteric side. Implantation occurs on day 6-7. Embryo transfer was successful as late as day 5 after mating. Pregnancy can be confirmed by palpating vesicles 10-40 mm across. Gestation period is 31-32 days. Place nesting boxes with females 5-8 days before parturition. Litter size is about 3 pups weaned.{3955} For a comparative table of reproductive values in several non-traditional rodents, click here.

Use in research: Woodchucks, because of their weight fluctuations, have some similarities to man such as obesity and vascular diseases. They are interesting to study for their appetite changes, endocrine and metabolic function, and physical activity levels. There is an unusually high rate of dietary atherosclerosis, aortic rupture, cerebrovascular and cardiovascular disease. Finally, woodchuck hepatitis virus and the related development of hepatocellular carcinoma have been considered as models for hepatitis B of man.{3560}

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©1999, Janet Becker Rodgers, DVM, MS, DipACLAM, MRCVS

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Comments? Send an email to janet.rodgers@vet.ox.ac.uk