Jz. Adamczewski et al., THE INFLUENCE OF FATNESS ON THE LIKELIHOOD OF EARLY-WINTER PREGNANCY IN MUSKOXEN (OVIBOS-MOSCHATUS), Theriogenology, 50(4), 1998, pp. 605-614
Among wild ruminants, muskoxen have an exceptional ability to fatten,
but their pregnancy rates are variable and often low. To test whether
the likelihood of pregnancy in muskoxen is associated with exceptional
ly good body condition, we used logistic regression analysis with data
from 32 pregnant and 18 nonpregnant muskoxen greater than or equal to
1.5 yr of age shot in November (1989 to 1992) on Victoria Island in A
rctic Canada. We assayed their serum for insulin-like growth factor-1
(IGF-1). All fatness and mass measures were positively related to the
likelihood of pregnancy (P < 0.001), with the strongest associations f
or estimated total fat mass (80% of outcomes predicted correctly) and
kidney fat mass (77%), and weaker models for body mass. Pregnancy was
less likely to occur in lactating females than in nonlactating ones (P
= 0.03). Although IGF-1 concentrations were higher (P = 0.001) in non
lactating females than in lactating ones (28.7 +/- 1.7 vs. 22.5 ng/ml)
, no association with pregnancy was detected (P = 0.57). Fatness assoc
iated with a 50% probability of pregnancy in muskoxen (22% of ingesta-
free body mass or 32 kg fat in females > 3.5 yr old) is much higher th
an in caribou and somewhat higher than in cattle, and this may partly
account for the low calving rates often observed in this species. (C)
1998 by Elsevier Science Inc.