Serum Progesterone and Estradiol-17.BETA. Concentrations in Captive and Free-Ranging Adult Female Japanese Black Bears (Ursus thibetanus japonicus).

Abstract

ABSTRACT. Progesterone (P4) and estradiol-17β (E2) concentrations were measured in serum samples obtained from 23 captive and 23 freeranging adult female Japanese black bears. We then determined the relationship between changes in these sex steroid hormones and pregnancy. In all captive bears, which included animals of both known and unknown reproductive status, serum P 4 concentrations were low from April to July, then tended to become higher after August. The levels then became much higher still in November and December, but returned to low levels in March. Serum P 4 concentrations in eight captive pregnant bears, which had parturitions the following spring, increased gradually from August (0.5-2.4 ng/ml) to October (0.9-3.6 ng/ml), and achieved significantly higher maximum levels in December (7.2-18.0 ng/ml). Thereafter, serum P 4 concentrations tended to decrease (3.5-6.4 ng/ml in January and 0.3-0.7 ng/ml in March). In all captive bears, serum E 2 concentrations varied from April to October but showed low levels in November and December, and became high in January. Serum E 2 concentrations in the eight pregnant bears were high in May (95.6-191.4 pg/ml) and varied from August to October (35.6-143.3 pg/ml). Subsequently, serum E 2 concentrations in December dropped to significantly lower minimum levels (5.3-11.9 pg/ml) and increased again in January (67.6-153.1 pg/ml). Among the free-ranging bears, the data on serum P 4 concentrations in eight bears led to expectations of pregnancy, whereas serum E2 concentrations showed no distinct evidence related to pregnancy. These results, particularly in captive pregnant bears, indicate that a marked increase of P 4 in December might be accompanied by reactivation of the corpus luteum preceding implantation. Furthermore, changes in E 2 concentrations suggested the possibility that a decline in December and an increase in January are associated with implantation and parturition, respectively.-KEY WORD: bear, estradiol-17β, pregnancy, progesterone.

Reproductive Pattern of the Sun Bear(Helarctos malayanus) in Sarawak, Malaysia.

“…Alternatively, the measurement of estrogen concentration will help detecting delayed implantation indirectly. During delayed implantation, no increase or tendency to decrease of estrogen levels was reported in several species [13,15,17,18,21,24]. Observation of estrogen values in the serum, urine, or feces of mated female sun bears for at least one year is essential to find possibility of delayed implantation.…”

Factors Affecting Date of Implantation, Parturition, and Den Entry Estimated from Activity and Body Temperature in Free-Ranging Brown Bears

“…The mating season of most bear species occurs in spring or early summer and lasts approximately 2–2.5 months. Fertilized eggs undergo diapause at the blastocyst stage for 4–5 months until delayed implantation occurs [11], [17], [19], [20]. The duration of embryonic diapauses varies, because the time of implantation and birth is uncoupled from the mating season [8], [10].…”

Changes in expression of hepatic genes involved in lipid metabolism during prehibernation period in captive adult female Japanese black bears (Ursus thibetanus japonicus)

“…Additionally, in contrast to other hibernators, bears give birth to cubs and nurse them during hibernation (Nelson 1973). The mating season is from mid-June to August, and implantation occurs between late November and early December (Sato et al 2000) when the bears enter hibernation in the wild. The energy required for fetal development, parturition, and lactation comes almost entirely from the fat reserves accumulated before hibernation (Nelson et al 1983).…”