Effects of induction versus prevention of hibernation on reproduction in captive male and female woodchucks (Marmota monax).

Reproductive performance and gonadal function were studied in two groups of woodchucks containing 16 females and 8-9 males each. The control group was maintained indoors under conditions that do not induce hibernation, including fluctuating temperature of 6-12 degrees C, ad libitum feed, and exposure to natural and incandescent light. The hibernaculum-housed group was, in addition, provided conditions that do induce hibernation, including temperature reduced to 5.6 +/- 1.7 degrees C, no food, and no light from 19 November to 21 February. Hibernaculum housing caused 67% of males and 94% of females to hibernate with reduced body temperature for significant periods of times. Compared to control conditions, hibernaculum housing caused (p less than 0.05) a delay in testis recrudescence, a reduction in mean peak testis size (1.8 vs. 3.0 cc) and its mean date of occurrence (14 March vs. 15 February), a reduction in mean testosterone concentrations in February, and a reduced incidence of fertile matings (22 vs. 88%). In females, hibernation resulted (p less than 0.05) in a greater loss in body weight and a reduced pregnancy rate (31 vs. 82%), which was related to post-hibernation body weights that, in turn, were related to prehibernation body weights. Among hibernaculum-housed females, the pregnancy rate was lower in smaller females (0%; 2.0 +/- 0.1 kg) than in the larger ones (63%; 2.9 +/- 0.1 kg). The results demonstrate that the experimental imposition of hibernation-inducing conditions for 3 mo prior to the expected breeding season can alter subsequent reproductive performance in laboratory-maintained woodchucks, whereas a reproductive rate of 88% can be obtained in animals prevented from hibernating during their first year in captivity.