Characteristics of reproductive physiology during conception period and maintenance of pregnancy in Hokkaido sika deer (Cervus nippon yesoensis)

There are many species of boreal or temperate deer (Lincoln 1992) and they are short-day breeders (Sadleir 1987, Lincoln 1985, Loudon and Brinklow 1992) mating in autumn and fawning in early summer (Kaji 1988, Koizumi 1991, Matsuura et al. 2004a). Their seasonal reproductive pattern ensures that fawns are born at a time of year when food is available for lactating and the weather is favorable for survival of offspring (Loudon and Brinklow 1992). Although most of parturition takes place during period of about one month (Guinness et al. 1978a, Koizumi 1991, Birgersson and Ekvall 1997, Bowyer et al. 1998), range of 83 to 135 days for birth date due to late parturitions were reported in sika deer (Koizumi 1991, Matsuura 2004). Late conception leads to late parturition (Matsuura et al. 2004a) and late parturition results in decline in reproductive success of females, defined as the number of fawns a mother reared to one year old over a specified period of time (red deer: Clutton-Brock et al. 1982), due to increase in mortality rate of fawn (Guinness et al. 1978b) or decrease in female conception rate in the following mating season (Clutton-Brock et al. 1983). Therefore, conceptions at the appropriate breeding season and subsequent maintenance of pregnancy throughout gestation are required for females to enhance their reproductive success. Since most of female conceive at the first estrus of the season (Matsuura et al. 2004a), the change in physiological condition from the anestrous season to the estrous season is important factors which responsible for determining the time of conception. However, there is no insight into mechanism for the successful conception and physiological factor influences to the conception date, and even basic information about the reproductive physiology such as ovarian dynamics and changes in hormones around the conception are not well known in sika deer. Therefore this study was conducted to clarify the characteristics of reproductive physiology of sika deer with special interest in around conception and gestation period by revealing the changes in reproductive organs and steroid hormones. There are two approaches to study about the issue; using carcasses and using live animals. Carcasses are available from nuisance control, sport hunting and hunting for the research purpose, and provide information on morphology and histology of reproductive organs in which animals are needed to be killed. Although abundant carcasses can be obtained, information from carcasses reflects the condition only at the time they were sampled. On the other hand, studying live animals provides the temporal changes in reproductive physiology in animals. However, number of captive deer available for physiological study is limited due to lack of institution holding animals, insufficient equipment, and financial problem in Japan. Therefore, combination of these two approaches is essential for further improvement for understanding reproductive physiology of sika deer. Carcasses provide the physiological data such as occurrence of ovulation (Suzuki and Ohtaishi 1993) and steroidogenic ability of corpus luteum (CL; Matsuura et al. 2004c). In the study using carcasses, the reproductive status must be estimated from the condition of the female, and when they are pregnant, gestational ages are estimate from fetal weight in sika deer (Suzuki et al. 1996). However, present method of gestational age estimation will contain an intrinsic error at early gestational stage. The accurate estimation of early gestational age of the samples contributes to revealing characteristics of reproductive physiology around early pregnancy. Study using live animals is advantageous in understanding temporal changes in the individuals and noninvasive examination, such as behavioral observation and fecal progesterone analysis (Matsuura et al. 2004a), provided the important insight in sika deer. However, data of noninvasive examination are limited to indirect changes in reproductive physiology. To know the characteristics around the first estrus and conception more in detail, invasive methods as it has be done in other cervid species, such as blood collection for hormone assay (Plotka et al. 1977, Kelly et al. 1982, Adam et al. 1985, Garcia et al. 2003) and transrectal ultrasonography for follicular and luteal dynamics (Asher et al. 1997, McCorkell et al. 2004, 2006, 2007) of captive animals under restrain or immobilization are also needed. In sika deer, there is a unique reproductive characteristics observed from early pregnancy. It is multiple CLs formation in spite of having singleton (Yamauchi et al. 1984, Suzuki et al. 1992, Suzuki and Ohtaishi 1993). Since both CLs have ability to synthesis progesterone, it is assumed that forming surplus CL have an important role for establishment and maintenance of pregnancy (Matsuura et al. 2004c). However, significance and function of surplus CL is not obvious, and even the origin and the timing of formation of surplus CL are not known. For understanding the conception and maintenance of pregnancy in this species, these questions must be revealed. In present thesis, the author focused on conception and pregnancy period in sika deer. In chapter 1, the temporal ovarian dynamics and changes in steroid hormones were investigated from anestrous to estrous season to know the characteristics during the seasonal transition and to discuss the factor influence to the successful conception. In chapter 2, the temporal ovarian dynamics and changes in steroid hormone during conception and early gestation were investigated and the significance of multiple CLs was discussed. In chapter 3, description of fetal development and estimation of fetal age during early pregnancy was reported. In chapter 4, distribution of steroid hormone receptors in uteri derived from the wild deer were examined to know the steroid hormone action site at the each stage of pregnancy.