Bovine embryos recovered 7-8 days after estrus were stored for 6-7 h at room temperature in BMOC-3 or Ringer's solution supplemented with 50% bovine serum which had been collected from superovulated heifers 7 to 8 days after estrus.
Single embryo was transferred to the uterine horn ipsilateral to the corpus luteum-bearing ovary 7-8 days after estrus using Cassou apparatus with 0.25 ml French straw. To prevent bacterial con-tamination, the Cassou gun was covered with a sterile plastic tube which was not punctured until the cervix was catched.
Pregnancy rate was not different between embryos kept in Ringer's solution supplemented with 50% bovine serum (8/14, 57.1%) and those kept in BMOC-3 (6/10, 60%).
Another group of bovine embryos were cultured at 37 C for 72 h in a stoppered test tube contain-ing 1 ml medium and air. Five embryos were cultured with Dulbecco's PBS plus 20% bovine serum and two embryos with Dulbecco's PBS plus 20% ovine serum (GIBCO). After 24 h of culture, all em-bryos were developed into expanding blastocysts. After 48-72 h, all embryos cultured with Dulbecco's PBS plus 20% bovine serum hatched from zona pellucida, and they did not degenerate after this time.
Whereas two embryos cultured with Dulbecco's PBS plus ovine serum degenerated after 48 h of culture.
These results suggest that supplementation of the serum of the same species is beneficial for the survival of the embryos cultured in vitro.

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Estrus behavior and ovulation of beef heifers were investigated after injections of prostaglandin F_2α (PGF_2a). Eight Japanese Shorthorn and one Japanese Black heifers received intramuscular injec-tions with 5 mg of PGF_2α per day in the morning of two successive days (Treatment I). Ten days later the same treatment was repeated and designated as treatment II. From the evening of the last injection of each treatment, behavioral estrus was assessed every two hours using a well trained bull until the end of estrus. The ovulation was judged by the rectal palpation at intervals of two hours after the disappearance of estrus behavior. The time of ovulation was estimated as one hour before the ovulation confirmed by the palpation. The time of the onset and end of estrus was defined at one hour before the first and one hour after the last estrus behavior. A heifer was considered to be in estrus when she showed the following behavior: (1) no refusal for being mounted, (2) she permitted chin-resting of the bull, (3) she permitted copulatory motion of the bull.
The results showed that, the time interval from the last injection of PGF_2α to estrus and ovula-tion became more uniform in treatment II than in treatment I, though the difference was not signifi-cant, and that estrus behavior and ovulation of beef heifers are much the same either induced by PGF_2α or occurred naturally.

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Macro- and microscopic observations were made on the cervix, vagina and vaginal vestibule of 39 piglets aged in 40 to 46 days (A group) and 18 porkers at 90 kg body weight (B group). The results obtained were as follows.
1. The longitudinal (C1) and horizontal prominences (C2), low hill (C3), flat surface (V1) and vaginal vestibule (V2) portions were macroscopically distinguishable in the genital organ of both groups.
2. As for the epithelium of the genital tract, characteristic differences were detected between vaginal vestibule and the other parts, but not between cervix and vagina.
3. The muscle layers that compose basement of the rounded prominences and rugged mucosa of the low hill were examined. The muscle fibers in the prominences and low hill were more conspicu-ous than that in Vl.
It is concluded that the border of the cervix and vagina is defined as that between C3 and Vl.

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Primary oocytes surrounded with cumulus cells were obtained from ovarian follicles of prepuberal mice of JCL: ICR strain (25-27 days old) which had been injected with 5 IU PMSG 46-47h previously. The oocytes were cultured for 12h to induce meiotic maturation and then inseminated in vitro with epididymal spermatozoa.
Fertilization was assessed 11-15h later. When the oocytes were matured and fertilized in the basic medium which is a chemically defined medium for in vitro fertilization of mouse oocytes, 38.4% (109/284) of the oocytes showed the evidence of sperm penetration into the vitellus but only 28.4% of these oocytes were found to have male and female pronucleus. The other penetrated oocytes showed either fertilizing sperm tail(s) only or incompletely enlarged sperm head(s) with chromosomes ar-rested or degenerating at metaphase II.
Addition of fetal calf serum (FCS, 1-20%) to the basic medium resulted in an increase in the number of oocytes fertilized (82.1-92.7%) and of the fertilized oocytes with male and female pro-nucleus (59.8-89.5%). Non-dialysable fraction of FCS (5-20%) was effective in increasing the fertiliza-tion rates (53.8-69.0%), while the ultrafiltrated fraction of FCS (5%, molecular weight<10, 000) was effective in increasing the proportion of fertilized oocytes that had male and female pronucleus (72.0%).

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In order to examine the effect of a cohabitant on the sexual maturation of the guinea pig, Har-tley strain females were cohabited with an adult female, an adult male, or an immature male from weaning (1 or 2-week-old).
These females were kept under daily observation for vaginal opening and body weight.
Following results were obtained.
1) Females cohabited with an adult male showed vaginal opening 8-10 days earlier than females reared without any cohabitants (P<O.01).
2) The average body weight at vaginal opening in females (weaned at 2-week-old) with an adult male was lighter than females without a cohabitant (P<O.01).
3) Some of females with an adult male mated during the first vaginal opening, and delivered normally.

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In our conventional breeding colony of Wistar-Imamichi rats, both 3, 756 dams with more than 6 pups (group A) and 63 dams with less than 5 pups (group B), at the first delivery, were used in this study. At the second delivery, litter size of two groups were compared between the two groups. Eightyfour dams sampled from 3, 756 animals in Group A according to the distribution of litter size at the 2nd delivery and all of the dams in Group B were killed and number of implantation sites and corpora lutea of pregnancy were counted on the next day of the second delivery. The results obtain-ed were as follows.
1) The mean values of litter obtained at the second delivery in Group A (12.3±0.05) and dams in Group B (9.1±0.5) were significantly different (P<0.001).
2) The numbers of unfertilized or fertilized ova lost before implantation (indicated by subtract-ing the number of implantation sites from the number of corpora lutea of pregnancy) were 1.3 (8.3%) in Group A and 2.2 (15.1%) in Group B. The number of ova lost in the latter group was signifi-cantly more than that in the former group (P<0.05).
3) The number of embryos or fetuses lost after implantation (the number of implantation sites minus the number of litters) was 1.9 (13.3%) in Group A and 3.3 (26.6%) in Group B. The number was higher in the latter group (P<0.001).
These results clearly demonstrated that the dams delivered of smaller size of litters at first de-livery were inclined to bring forth smaller number of pups at the second delivery, and that the major cause of the decrease in litter size at the second delivery was the loss of ova, embryos and fetuses before and after implantation.

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A micro-computer controlled freeze-thaw apparatus for embryo was developed. The apparatus can be freely programmed to choose the freezing temperature and the ice seeding can be smoothly performed with temperature increase held to within 1.0C. Eleven bovine embryos were recovered non-surgically 8 days after estrus from one superovulated donor. Four blastocysts were frozen by using the apparatus and then they were stored in liquid nitrogen for 55 days. They were thawed in a 25.0C waterbath for 10 seconds. After thawing, the embryos were examined under microscope and their morphological appearance was assessed being as good as before freezing. Four embryos were transferred to 4 recipients by the surgical method. One was diagnosed as a pregnancy by rectal palpation 60 days after transfer.

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The length of estrous cycle, duration of estrus and time of ovulation in swamp buffaloes were studied. Eight adult females in a lot were checked for estrus twice daily by a vasectomized buffalo bull for 3 months. Duration of estrus was estimat-ed by checking male-receptivity every 3 h and time of ovulation was determined by rectal palpation performed every 3 h after the end of estrus.
All females came into estrus 3 to 5 times during the experimental period of 91 days. The length of estrous cycle was 19.1±5.8 (Mean±SD) days with a range of 9 to 38 days. The duration of estrus was 17.3±4.6 h (range: 9-24) and time of ovulation was 13.5±3.7 h (range: 6-18) after the end of estrus. External signs of estrus examined were not evi-dent enough to detect estrus and homosexual behavior was seldom observed.
These results indicate that characteristics related to estrus and estrous cycle in swamp buffaloes are analogous to those in cattle except for the uncertainty of external signs of estrus.

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The protein compositions of luminal fluids and mucosal tissue extracts of the rabbit uterus and cervix were investigated with the aid of horizontal polyacrylamide slab-gel electrophoresis, as a part of a study on the preimplantation loss of eggs in the rabbit. The daily samples were obtained from normally mated and superovulated does up to the 6th day of pregnancy. Protein profiles in the uterus and cervix changed almost synchro-nously. Some protein fractions which were absent in blood serum were detected in the uterine and cervical fluids, and a few of them were present also in their tissue extracts. Based on a quantitative fluctuation of uteroglobin as an indicator, daily changes in protein patterns of the secreta of both organs in superovulated does were apparently ad-vanced by 3 days compared with those in normally mated does, and accumulated-uterine-fluid flow descended through the cervical canal from at least 3-4 days after normal mat-ing or just before mating in the superovulated does. The results of these studies suggest that the asynchronously advanced changes in the protein composition of uterine fluid of supervulated does, relative to embryo development, may be one of the causes for high embryonic mortality.

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The function of the cervix in holding embryos in the uterine cavity during early pregnancy was re-evaluated in rabbits in which cervical devices had been installed to expand the cervical lumen. The cervical device, consisting of either intact (Type A) or fenestrated (Type B) polyethylene tubing (intracervical part) attached to a base of sili-cone rubber, was inserted into a unilateral cervical canal. The animals were mated and given an iv injection of hCG (20 IU), and examined for fertilization, implantation and loss of eggs.
The devices installed in the cervix did not interfere with fertilization, implantation and sperm transport, although the implantation rate was low on the side in which Type-B devices had been installed. At autopsies performed 3 to 5 days post coitum (p.c.), the reproductive tract was flushed and the embryos were examined. A significant (P<O.05) loss of ova on day 5 p. c. was observed on the side containing Type-B devices. In vivo vaginal washing conducted in intact does 48 to 168 h p. c. revealed that about 10% of the eggs ovulated had been expelled into the vagina during the preimplantation stage.
The present findings indicate that a structural characteristic of the cervix, namely the narrow lumen, contributes to prevention of egg expulsion, and that the expulsion mecha-nism may depend on some function of the cervical epithelium, probably ciliary action.

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