Plasma Protein Profile as an Index of Pregnancy in the Black Bear

We analyzed plasma protein profiles in an attempt to identify physiological parameters associated with pregnancy in black bears (Ursus americanus) that might be used as early confirmation of this reproductive state. We collected serial blood samples from 2 animals over 3 consecutive fall periods. Both females were pregnant during the 1st and 3rd years; cubs from the 1st litters were removed early so females were in a nonpregnant, anestrus state during the 2nd year. We qualitatively analyzed the plasma proteins using polyacrylamide gel electrophoresis. Several distinct differences were apparent between samples from pregnant and non-pregnant animals and the protein profile changed during pregnancy as the time of implantation approached. Results suggest that 1 or more plasma proteins are associated with early stages of pregnancy in the black bear. Int. Conf. Bear Res. and Manage. 6:221-224 Many physiological changes occur in association with pregnancy that provide support and regulation of embryonic development. One such well-documented change is the appearance of human chorionic gonadotropin (hCG), a hormone of embryonic origin, in the blood of pregnant women (Saxena et al. 1974). This glycoprotein has been used as an antigen to which specific antibodies have been produced in the development of pregnancy testing kits. Pregnancyspecific antigens that are blood-borne have also been described in mink (Larsen et al. 1971), rat (Lin et al. 1974), mouse (Lin et al. 1974; Morton et al. 1974, 1976), and sheep (Cerini et al. 1976a, b; Morton et al. 1979). Many of these antigens appear late in pregnancy and are associated with placental function; however a few, such as hCG in humans and those in sheep, appear very early. With the exception of mink, where an antigen was identified during the latter half of pregnancy, up to now no report of such blood components has been made for a species that exhibits an obligate delay in embryonic development. The black bear is 1 such species that exhibits this reproductive phenomenon. Pregnancy in black bears is characterized by 5 months of embryonic quiescence after conception in June, with implantation in late November, and a 2-month postimplantation development period before parturition in late January (Fig. 1, Wimsatt 1963, Foresman and Daniel 1983). Concomitant with studies designed to identify plasma levels of progesterone during pregnancy (Foresman and Daniel 1983) studies were performed to address the question of the existence of pregnancy-specific plasma proteins in this species. During this study support was graciously provided by the Appalachian Zool. Soc. and the Knoxville Zool. Park, Knoxville, Tenn. Technical assistance from Keith G. Dayhuff and Drs. David J. Black and Suzanne Kennedy was appreciated. The illustrative work of Ms. Donna DeCarlo was also much appreciated.