Detection of early pregnancy in Caribou : Evidence for embryonic mortality

Abstract

To investigate relations between body condition and fecundity, we determined pregnancy status of arctic caribou (Rangifer tarandus granti) from presence or absence of pregnancy-specific protein B (PSPB) and progesterone concentration in blood sera or plasma. We drew peripheral blood samples from female caribou 3-5 (n = 142) and 20-23 (n = 44) weeks after the breeding season. We then weighed and estimated the fat content of each caribou, and we radiocollared 115 of 184 individuals. We verified parturition status for 96 of these radiocollared females in June. In addition, we determined presence of PSPB for captive caribou in autumn and early winter. Progesterone concentration was superior to PSPB as a predictor of pregnancy during early gestation, and a threshold value of 1.5 ng/mL was used to separate pregnant from nonpregnant females in autumn and winter. Pregnancy status was strongly related to body condition in both autumn and winter, and fatter or heavier caribou were more likely to be pregnant. Use of both PSPB and progesterone concentration allowed detection of early embryonic mortality among lactating caribou that were in poor condition.