Present study was carried out to determine the factors causing poor implantation rates in adult rats treated with high doses of PMSG and hCG. Two handred ninety two rats were housed under artificial lighting (light from 07:00 to 21:00 h), and injected with 10, 20, or 40 IU of PMSG at 11:00 h on the day of early diestrus. Then the females were injected with the same dose of hCG 54h later (corresponding to the time of LH surge of normal proestrus), and mated with a male overnight. Both ovaries were removed from 24 to 120h after hCG injection (or 12 to 108 h after mating) at 24h inter vals, and were sectioned. Healthy and atretic follicles larger than 250μm in diameter were classified in each sizes of 50μm. For radioimmunoassay of progesterone, estrone and estradio1-17β, blood was collected from the abdominal aorta at the time of hCG injection and various times after hCG.
1) In untreated rats, the number of healthy follicles larger than 500μm in diameter increased with time after mating. In 40 IU-treated rats at 24 and 48 h after hCG injection, the number of healthy follicles of this sizes was significantly more than that of untreated rats (P<0.01). 2) The serum concentration of progesterone in untreated, 10 and 20 IU-treated rats increased gradually until 96 or 120 h after hCG injection, whereas in 40 IU-treated rats, progesterone level reached a peak at 72h after hCG injection, then decreased rapidly to control level by 120h. 3) At the time of hCG injection, estradio1-17β value was high in all groups, and decreased rapidly 24 h later. The low levels were maintained in untreated and 10 IU-treated groups until 120h after hCG injection. But in 40 IU-treated rats, estradiol-17β level was significantly higher than that of untreated rats at 72 h after hCG injection (P<0.01).
These results suggest that the low rates of implantation in adult rats treated with high doses of PMSG and hCG may be due to the abnormal hormonal environment in the oviducts and uterus. It may result from the high level of estradiol-17β at 72h after hCG injection and dramatic decrease in the concentration of progesterone from 96 to 120h.

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This study was carried out in order to make clear the changes of the reproductive performance with the increase of the calving number in Japanese Black cows. Forty cows were classified into the four groups 1 (1st), 2 (2nd), 3 (3rd to 5th) and 4 (6th to 10th) according to calving number shown in parentheses.
Ovaries and uterus were regularly examined twice a week by rectal palpation, and estrus sign was checked twice daily. Calves were weaned at 6 months of age. The results obtained are as follows.
1. The days required for uterine involution after calving ranged from 23 to 48 days. The aver-age values were 31.8±4.5 days in Group 1 and 44.7±3.1 days in Group 4 which was significantly longer than any other group.
2. The interval from calving to first ovulation was the shortest in Group 3 with a mean of 29.3±9.1 days, and was the longest in Group 1 with a mean of 83 8±43.0 days. The average days requried for recurrence of estrus in Group 1-4 were 102.3±43.6, 69.9±43.3, 42.2±16.9 and 41.7±20.6 days, respectively. The intervals from calving to first ovulation, second ovulation and first estrus in Group 1 were significantly longer than those of Groups 3 and 4. The intervals from first to second ovulation were significantly shorter than second to third ovula-tion, and the chance of exhibiting first estrus at first ovulation was lower than that of the second and third ovulation in all groups and not related to the calving number.
3. The average days requried for conception after calving was the shortest in Group 2 with a mean of 78.6±41.2 days, and the next shortest was Group 3 with a mean of 85.3±64.0 days and in Groups 1 and 4, the values were more than doubled. The cumulative conception rate from the first to third insemination for conception in Group 4 was significantly lower than in Group 1 or 2, and the insemination for conception had to be repeated in Group 4 more frequently than in the other groups.

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Nonsurgical transfer and survival of frozen-thawed bovine embryos by one step straw method using sucrose
Exp 1. Bovine embryos were classified microscopically as A (Excellent), B (Good), C (Poor) ac-cording to the standard of GARY et al.²⁾ Glycerol was added to the culture medium at room tempera-ture in three steps of 10 minutes each (3%, 6%, 10% respectively). After equilibration, the 0.25 ml straws were filled with three compartments, each separated by small air bubbles. The embryo was placed in the middle compartment containing PBS and 10% glycerol as cryoprotectant. The upper and lower compartments contained 0.3 mole or 0.6 mole sucrose solution in water supplemented with 20% bovine serum.
Then, the upper air bubble was removed by giving light pat to the straw by the finger and the upper and middle compartments were mixed. Then the straw was kept at 38C for ten minutes, meanwhile the lower compartment kept unmixed.
Ten minutes later the embryos in the straw were cultured for 24 to 72 h with Ham's F-10 +20% BS. All embryos classified as A and B were developed into blastocyst or hatched blastocyst after being mixed with 0.3 mole sucrose solution (10/10 and 2/2 respectively) or 0.6 mole sucrose solution (2/2 and 3/3 respectively).
Exp 2. After 1 to 300 day of preservation at -96C, the contents were thawed at 38 C and mixed by same method as Exp 1. Ten minutes later the embryos in the straw were cultured for 24 to 72 h with Ham's F-10+20% BS. A higher survival rate was obtained in the A class embryos (95% and 100% respectively) than that of the B class embryos (66.7% and 50.0% respectively) dilluted with 0.3 mole and 0.6 mole sucrose solutions.
Exp 3. The mean conception rates were 58.6% for Holstein recipients and 33.3% for Japanease black recipients.

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The experiments were carried out to clarify the effects of PGF_2α on the contractility of bull testis, epididymis and vas deferens in vitro. The preparations were placed in a Magnus tube containing Tyrode's solution (33 C). Contractile responses were recorded isotonically on a kymograph. The parenchyma and mediastinum of the testis showed no response to PGF_2a, but the head (above 10^-6 g/ ml), body (above 10^-6 g/ml) and tail (above 10^-7 g/ml) of the epididymis and the vas deferens (2×10^-5 g/ml) contracted in response to PGF_2α. Tonic contraction was common in each sample. Rhythmical contraction was observed in some preparation from the tail of the epididymis and of the vas deferens and phasic contraction was mainly in the vas deferens. The height of contraction of the tail of the epididymis and the vas deferens had a tendency to be greater than that of the head and body of the epididymis.

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A total of 304 mouse expanded blastocysts were cultured in a CO₂ incubator at 37 C to obtain the optimum conditions, namely, the kind of medium, the concentration of colchicine and duration of culture for chromosomal analysis. Criteria used to determine the optimum culture conditions were the number of nuclei, metaphase plates and size of chromosomes. In the culture by BMOC-3, it was significant that the largest number of metaphases was observed compared with the culture by MEM+ 20%FCS and PBS+20%FCS (P<0.05). In the culture of 0.4-1.6μg/ml colchicine in the BMOC-3, more metaphases were obtained than that of 0.025-0.05μg/ml colchicine. The number of metaphases increased with the extension of culture period up to 12 h, but the number of nuclei decreased con-versely because of the degeneration of cells. The contraction of chromosomes was observed in the culture of over 6 h with colchicine. From the results, it was concluded that the 2-hour culture by BMOC-3 containing 0.4μg/ml colchicine is the optimum condition for chromosomal preparation in this study.
Under this condition, a total of 155 expanded blastocysts from 3 weeks young females of ddY strain were examined. They had an average of 66.0 nuclei and 5.7 metaphases per embryo. The 145 blastocysts out of 155 blastocysts showed explicitly countable metaphases, and normal diploidy was found in 118 blastocysts (81.8%). Out of 529 metaphases from 145 blastocysts, only 272 metaphases (51.4%) showed a normal diploidy, while 156 metaphases (29.5%) showed hypodiploidy. It seems that a slight loss of chromosomes from metaphase plate is inevitable in the chromosomal analysis of em-bryos.

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PGF_2α and progesterone (P) levels were determined by RIA to examine the transfer of _PGF2α from the uterus to the ovary by "counter current mechanism". Plasma samples were collected simulta-neously from 5 vessels (the uterine branch of the ovarian vein, the ovarian vein close to the caudal vena cava, the abdominal aorta close to the ovarian artery, the ovarian branch of the ovarian artery and the jugular vein) in 3 Shiba-goats (small Japanese native goats of non-seasonal breeder) injected with intrauterine 1 mg PGF_2α.
After the injection, PGF_2α was taken into the ovarian vein within short time and it's concentra-tion showed marked decrease when it reached to the abdominal aorta after the general circulation (Figs. 2, 5 & 8). PGFs levels in the plasma of the ovarian branch of the ovarian artery peaked at 60 min after the injection. Though PGFs levels in the plasma of the abdominal aorta adjacent to the ovarian artery were higher than those in the ovarian branch of the ovarian artery till 20-30 min after the PGF_2α, injection, there-after the relation between these PGFs levels was reversed. Thence-forth, PGFs levels in the plasma of the ovarian artery seemed to be related to the stage of ovarian cycle (Figs. 3, 6 & 8).
The results of the present studies demonstrated that the transfer of PGF_2α from the uterus to the ovary was performed directly by "counter current mechanism" between the ovarian vein and the ovari-an artery in the Shiba-goat.
P levels in the plasma of the ovarian vein elevated rapidly soon after PGF_2α injection in 2 goats (Day 16 and Day 18). P levels in the plasma of the ovarian branch of ovarian artery were higher than those in the abdominal aorta as well as PGFs levels in the same plasma samples from the 2 goats (Figs. 7 & 8). In the remaining 1 goat with no corpus luteum, P levels in the plasma samples col-lected from 5 vessels were low (Fig. 4).
It was supposed that P should be also transfered directly from the ovarian vein to the ovarian artery in the Shiba-goat.

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Wistar-Imamichi female rats were treated with 10, 20, or 40 IU of PMSG. The females were placed with a male in order to determine the effect of copulation on PMSG-in-duced ovulation. At 76 to 78 h after PMSG injection, they were killed and the number of ova were counted. The percentage of rats ovulating and the number of ova shed in the non-cop-ulated group decreased markedly with increasing dose of PMSG, but in the copulated ones, the percentage of rats that ovulated decreased only slightly and the number of ova shed increased with increasing dose of PMSG. The ovulatory responses of the copulated group were signifi-cantly different from that of the non-copulated, except the proportion of rats ovulating after treatment with 10 IU of PMSG. When females were placed with a male for 1 to 11/2h, the stimuli with single copulation and mounting had a little or no effect on PMSG-induced ovula-tion. Exposure to a male without copulation overnight had no effect. The percentage of ova fertilized in rats placed with a male overnight decreased significantly with increasing dose of PMSG. These results suggest that the favourable effect of copulation on PMSG-induced ovul-ation in adult rats may caused by the stimulus of multiple intromission.

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Effects of photoperiod on estrous cyclicity in goats were investigated. Two strains of goats with different seasonality in reproductive activity; seasonally breeding Saanen goat (n=13) and nonseasonal Shiba goat (n=11) were exposed to artificial long days (16h light and 8h dark, 16L8D) or short days (8L16D). Changes in plasma progesterone concentrations were monitored to assess the estrous cyclicity during the experimental period (Dec. 1980-Nov. 1981). Saanen goats which were chronically exposed to short days continued to cycle beyond their anestrous season as long as short days were maintained. On the other hand, exposure to suppressed ovulatory cycles with two months of latent period not only in Saanen but also in Shiba goats. By transferring the goats from long to short days the goats resumed cycling with a latent period of about 70 days. Prolonged exposure to long days for more than seven months, however, resulted in a spontaneous resumption of estrous cyclicity; the goats were supposed to become refractory to the inhibitory effect of long days. Results of the present study have clearly demonstrated a relation between reproduction and photoperiod in female goats. The different seasonality in Saanen and Shiba goats would be attributable to the difference in critical daylength necessary for gonadal regression between the two.

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