In order to examine the implantation of the fertilized ovum in the bitch, 21 bitches were allowed to mate at varying intervals after ovulation.
The time of ovulation was estimated from the grade of maturity of follicles observed by laparotomy 3660 hours after the onset of acceptance of the male.
All the bitches were subjected to autopsy 15 to 24 days after mating and examined for fertilized ova or embryos in uterus. It was considered that implantation initiated when the blastocyst became fixed in position and floated no longer in the uterine lumen.
The results obtained are as follow.
Of the 21 bitches allowed to mate in estrus, seventeen became pregnant and four were infertile.
1. Development of blastocyst and the course of implantation.
The blastocyst on the 16th day after ovulation was a sphere 0.65mm in diameter outside the zona pellucida. It was floating freely in the uterine lumen.
On the 18th day after ovulation, the blastocyst was setted in the position of implantation in the uterine lumen. There was a floating blastocyst with the endoderm developing which was 1.5 mm in diameter outside the zona pellucida.
The free floating blastocyst on the 19th and 20th day after ovulation was deprived of the zona pellucida and assumed an oval shape 3.0×3.7 mm in size. Mesodermal cells interposed between the embryonic ectoderm and endoderm.
On the 21st day after ovulation, the uterine horn in the position of implantation increased slightly in size. The blastocyst took the shape of lemon 5.0×6.0 mm in size which agreed with the outline of the uterine cavity.
The blastocyst with a three-layered structure, consisting of endoderm, mesoderm and ectoderm, was attached partially to the uterine wall on the opposite edge of the mesometrium. The embryo attained a size of 1.5×6.0 mm by the 21.5th day, when the process of implantation was completed.
2. Time of implantation after ovulation.
Implantation took place 20.521.5 days after ovulation, when bitches were allowed to mate at one point of time within a range from 54 hours preovulation to 48 hours postovulation. Implantation also occurred in bitches allowed to mate between 72 and 84 hours postovulation in 22 days, and in bitches allowed to mate 96 and 108 hours postovulation in 22.5 and 23.0 days, respectively. Therefore, implantation was assumed to occur in bitches between 20.5 and 23.0 days postovulation.
When bitches were allowed to mate 54 hours preovulation, implantation took place 24.0 days after mating. It took place 22.0 days after mating in bitches allowed to mate 24 hours preovulation, 21.0 days at the time of ovulation, 20.0 days 12 or 24 hours postovulation, 19.5 days 36 hours post-ovulation, and 18.5-19.0 days between 72 and 108 hours postovulation.
In other words the time interval between mating and implantation was 18.5-24.0 days. From these results, the time of implantation was recognized to be almost definite in the bitches, falling in a range from 18.5 to 19.0 days after fertilization.

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[in Japanese]

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Histochemical demonstrations of 20α-hydroxysteroid dehydrogenase (OH-SDH) using 20α-hydroxypregn-4-en-3-one as the substrate and NADP as the co-factor, and of 20β-OH-SDH using 20β-hydroxypregn-4-en-3-one and NAD respectively were carried out with tubal hamster eggs at various preimplantation stages. The eggs were collected under following conditions: 2 hrs after ovulation for unfertilized eggs, 4 hrs for penetrated ones, 32 hrs for the 2-celled ones, 52 hrs for the 4-celled, 65 hrs for the 8-celled, and 76 hrs for blastocysts. The eggs at the earlier 4 stages were obtained from the oviducts, and the rest from the uteri. For the histochemical demonstration of the two enzymes, DICKMANN & DEY method was employed, the composition of the medium being 1.8 mg of the substrate, 4.0 mg co-factor, 2.0 mg Nitro-BT, and 10 ml 0.1 M phosphate buffer solution (pH 7.5).
In unfertilized and penetrated eggs were observed strong activities of 20α- and 20β-OH-SDH, and blue diformazan granules produced by these enzyme reactions were spread evenly throughout the cytoplasm. In eggs at 2-cell stage, the 20α-OH-SDH activity weakened to moderate, and the intensity was maintained as late as blastocyst stage. The 20β-OH-SDH activity was retained intense up to 8-cell stage, but somewhat decreased in blastocyst stage. In cleaved eggs, diformazan granules were located at perinuclear region and periphery of the cytoplasm, while in blastocysts the granules became uniformly spread in the cytoplasm of both inner cells and trophoblasts. From the results above was confirmed the presence of metabolic pathways in hamster eggs at preimplantation stage that convert 20α- and 20β-hydroxypregn-4-en-3-one into progesterone.

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The present study was attempted to induce the parturition in swine with prostaglandin F_2α (PGF_2α) and investigated its effects on lactation and reproductive performance.
Eleven pregnant sows and gilts including Land race, Humpshire, Duroc and crossbred were injected intramuscularly with 10mg of PGF2a at 5 am on the day 110, 112, 113, and 114 of gestation (day 1=the last day of artificial insemination). Four control animals received 2ml of vehicle at the same time on the day 112 and 113.
After the treatment of PGF_2α, clinical observation was incessantly maintained to record the time of initial birth, interval between piglets, total farrowing time and dystocia etc.
The mean time intervals (M±S.D.) from the injection to birth of the first piglet and total farrowing time (M±S.D.) in control and PGF_2α treated animals were 58:25±17:17; 4:19±1:56 and 30:09±3:58; 4:59±4:06 hours, respectively.
Mean gestation length (days) of PGF_2α treated animals was clearly shorter than that of the controls.
No significant differences between PGF_2α treated and control animals were found in number and weight of live piglets at birth and weaning. Also, no harmful effects of PGF_2α were noted with respect to lactation following the induced parturition.

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It is well known that the abrupt increase of uterine weight accompanied by the "ballooning" with the accumulation of inner fluid occurs in rats before the time of first ovulation.
To clarify the relationship between uterine development and blood gonadotropin levels during the first ovulation period, rats were killed by decapitation under light ether anesthesia at 10:00, 15:00, 17:00 or 19:00 h on 5 weeks of age. Serum gonadotropin (LH and FSH) levels were measured by radioimmunoassay.
The animals were classified into two groups, ovulated and unovulated: Unovulated group was subdivided into three subgroups by the degree of the uterine development as follows;
a) "Non-ballooned uterus": less than 100 mg with no fluid.
b) "Semi-ballooned uterus": 100150 mg with a small amount of fluid.
c) "Ballooned uterus": more than 150 mg filled with fluid.
There was little change in serum gonadotropin levels during the time of "Non-ballooned", "Semi-ballooned" and the morning of "Ballooned".
In the "Ballooned uterus" group serum levels of both LH and FSH in the afternoon were clearly classified into two types, remarkable high levels ("Activated"), and low basal levels ("Non-activated") similar with the other anovulated groups. In the "Activated" group, LH levels reached a peak at 17:00 h followed by a significant decrease at 19:00 h, while high FSH levels were maintained through 15:00 h to 19:00 h.
When the uterine weights during 15:00 to 19:00 h were pooled, the uterine weight of the activated group was significantly heavier (p<0.01) than that of non-activated group.
In "Ovulated" group, LH had already decreased to the basal levels while FSH were still higher than the levels before GTH surge occurred.
The authors acknowledge the gift of rat LH and FSH radioimmunoassy materials from the Rat Pituitary Hormone Distribution Program of the National Institute of Arthritis, Metabolism and Digestive Diseases.

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In seven anestrous bitches, estrus was experimentally induced by a specially designed hormonal treatment, which has been modified from the original method developed by TAKEISHI et al., in 1973, and all of these females were soon inseminated naturally or artificially.
The result of this experiment was as follows :
1. In each bitch, vulval bleeding was observed 3 to 9 days after the intramuscular injection with estrone of 300 to 30000 μg dose.
2. A duplicate gonadotrophic injection, consisted of HCG 1000 MU and PMSG 200 to 400 IU was given on the day, after the sexual bleeding was withdrawn, and the second gonadotrophic administra-tion was done on the day, the vaginal smear showed estrus phase.
3. Insemination was carried out on the day, when the minor axis of vulva in each estrous bitch became shorter.
4. Six of the seven bitches treated became pregnant, and parturition occured 60 to 63 days after insemination. Average litter size was 4.25.

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