Accessory corpora lutea formation in pregnant Hokkaido sika deer (Cervus nippon yesoensis) investigated by examination of ovarian dynamics and steroid hormone concentrations

Abstract

Generally, sika deer conceive a single fetus, but approximately 80% of pregnant females have two corpora lutea (CLs). The function of the accessory CL (ACL) is unknown; moreover, the process of ACL formation is unclear, and understanding this is necessary to know its role. To elucidate the process of ACL formation, the ovarian dynamics of six adult Hokkaido sika deer females were examined ultrasonographically together with peripheral estradiol-17β and progesterone concentrations. ACLs formed in three females that conceived at the first estrus of the breeding season, but not in those females that conceived at the second estrus. After copulation, postconception ovulation of the dominant follicle of the first wave is induced by an increase in estradiol-17β, which leads to formation of an ACL. A relatively low concentration of progesterone after the first estrus of the breeding season is considered to be responsible for the increase in estradiol-17β after copulation.

Fig. 1.

Hormonal and ovarian dynamics in female sika deer that conceived at the first estrus (Group 1: A, B and C) and second estrus (Group 2: D, E and F) of the breeding season. P₄: progesterone. E₂: estradiol-17β.

Fig. 2.

Ultrasonographic and macroscopical images of an ovary in female sika deer A. (A) Ultrasonographic image of an ovary with a corpus luteum (CL) and dominant follicle of the first wave on day 8 of pregnancy. (B) Ultrasonographic image of the same ovary with two CLs on day 11 of pregnancy. (C) Macroscopical images of an ovary with two CLs on day 85 of pregnancy obtained after accidental death. Arrows indicate a CL. Bar = 1 cm.