engleski

Measuring the conception rate via embryo recovery from uteruses of brown bears after embryonic diapause

In brown bear females the fertilized ovum remains free-floating in the uterus (embryonic diapause) for up to five months, only attaching to the uterine wall at the beginning of hibernation when the “real” pregnancy begins. Reproductive cycle of brown bear is slow with exact effects on ultimate reproductive success rate is still unknown. Major processes of the reproductive cycle include ovulation, implantation, fetus development, parturition and neonate nurturing. It is of interest to know which of these processes has the greatest effect on the success of the whole cycle. One way to gain insight is to compare the success rates of each of the processes. In majority of domestic mammals, major cause of reproductive failure is early embryonic mortality with a mortality rate up to 40% of fertilized eggs. We examined female sexual organs immediately after being shot in legal hunting. The uterus was flushed with 60 ml of Ringer lactate solution and embryos were microscopically searched in Petri dish. We also searched for presence of corpora lutea (CLs) on ovaries as indicator of mating and ovulation, and compared it with number of recovered embryos. Study was performed in November 2017 when implantation and active development of conceptus should begin since active fetal growth in bear lasts for 60 days and parturition in den is usually in January. Study included 4 adult females that altogether had 8 embryos and 8 CLs. One female had 3 CLs and 3 embryos, two had 2 CLs and 2 embryos each, while one had one CL and one embryo. All embryos were active with significantly more than 200 cells per embryo (activated stage). According to our findings, there was no proof of any embryonic mortality in observed bears after embryonic diapause stage, since number of recovered embryos corresponded with number of CLs. Hence, the conception rate was 100%! Further research is needed to detect precise mechanisms involved in embryonic and fetal development of brown bears.

Ursus arctos, diapause, embrio

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