Cultivation in vitlo of bovine embryos in a medium supplemented with bovine serum which was collected from 23 superovulated cows 7 to 8 days after estrus.
Bovine embryos at the stages of morula and blastocyst were cultured at 38 C for 72 h in a stoppered test tube containing 1 ml medium supplemented with 20% bovine serum.
When embryos were cultured in a modified PBS with serum collected on day 7-8 from cows which produced good embryos, 49/57 embryos (86%) were developed to the blastocyst or hatched blastocyst and 83% of the embryos were finally hatched after 72 h of cultivation. On the other hand, when serum, collected from donor cows which produced poor embryos, were supplemented to the medium, none of the 24 embryos was developed.
Effect of bovine serum collected from donor cows on day 7-8 on the developement in vitro of bovine embryo was compared with that of foetus calf serum (FCS). When 20% bovine serum was supplemented to the medium, all 17 frozen-thawed embryos were developed to the blastocyst or hatched blastocyst and the proportion of hatched blastocysts was finally 70%. In contrast, when 20% FCS was supplemented to the medium, 7 of 12 frozenthawed embryos 58% were developed to the blastocystor hatched blastocyst and the final proportion of the hatched blastocysts (22%)was also lower than the rate obtained in the medium including bovine serum.

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Eighteen Holstein heifers were subjected to repetitive superovulation by the injections of follicle stimulating hormone and prostaglandin F_2α analogue. Embryos were obtained non-surgically 7 days after artificial insemination.
1. From 16 heifers, 65 embryos were collected in the first trial and from 10 heifers 23 embryos in the second trial.
2. The mean ratios of the corpora lutea to the embryos were not different significantly be-tween the first (9.3/7.9) and the second (5.6/3.1) trials. The average number of developed embryos by the first trial (3.6) and the second trial (1.3) was dissociated from each other significantly.
3. Injections of prostaglandin F2a analogue, 10 or 11 days after the embryo collection, prevented pregnancy and somewhat shortened the period to the onset of the next estrus.

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Effects of photoperiods on prolactin (PRL) secretion were investigated by keeping female Saanen goats under artificial long days (16L8D) or short days (8L16D). Exposure to experimental photoperiods was started in December 1980 (day 0) and continued for about a year. Plasma PRL of the long-day group was elevated to the levels much higher than those of the short-day group. Effects of photoperiods on the diurnal fluctuation of plasma PRL were also evident on selected days when blood samples were taken at short intervals (day 24 and 118): being enhanced under long days and damped under short days. In July and August 1981, a marked elevation of PRL levels was noted in both groups, probably due to high ambient tem-perature which might have masked the effects of short-days. In the long-day group, goats were anovulatory when PRL levels were high (day 78-148), however, by day 200 they re-sumed estrous cyclicity spontaneously in association with the decrease in plasma PRL, sug-gesting that there might be an intrinsic mechanism which gradually increases the critical day lengths.

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Two trials were conducted to evaluate effects of injection time of pregnant mare'sserum gonadotropin (PMSG), gonadotropin releasing hormone (GnRH) and individual rams on fertility in seasonally anestrous Suffolk ewes. Trials 1 and 2 were carried out at 2-weeks apart during April to May. Hormonal treatments were; I) 60 mg 6-methyl-17-acetoxy-progesterone (MAP) vaginal sponge for 9 days insertion, 600 IU PMSG at the time of sponge removal and a 100 μg GnRH injection at estrus detection, II) MAP sponge for 9 days and 600 IU PMSG 2 days before sponge removal, and III) II)+ the GnRH injection. In Trials 1 and 2, 50 and 60 ewes were used, respectively. For natural mating, 5 mature Suffolk rams were used to compare the reproductive efficiency. In Trial 1, proportions of estrous ewes within 4 days after treatment and lambing rates were not significantly different among the groups (92.9% and 53.8%, 85.7% and 58.3%, 92.3% and 58.3% for groups I, II and III, respectively). However, there were significant differences in both proportions of estrous ewes (P< 0.05) and lambing rates (P<0.05) among the rams used. In Trial 2, group II showed a significantly higher lambing rate (57.1%) than group I (15.8%), although the proportion of estrous ewes in group II was significantly low (P<0.05). Lambing rates in Trial 2 significantly decreased as compared with Trial 1, but not for the proportion of estrous ewes and prolificacy. It appears that the repeated uses of the same 5 rams at 2-weeks apart lowered fertility in Trial 2. The present study indicates that a GnRH injection may be unnecessary if the injection of PMSG was given 2 days before sponge removal. The PMSG injection 2 days before the progestogen withdrawal and the use of rams with high libido and semen quality could induce improvement of fertility in hormonally treated ewes during the non-breeding season.

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High levels of egg fertilization have been reported in ewes after insemination into the uterus using a laparoscope. The experiment was carried out to compare lambing rates of four different techniques for artificial insemination with frozen-thawed ram semen.
Ejaculates cellected by artificial vagina from four rams were diluted to 1:4 with a tris-based extender and frozen by the pellet method. The frozen pellets were stored for at least three weeks in liquid nitrogen until use for inseminations. A ram with marking harness and apron was joined to to 17 ewes. Heat detection was carried out every 6 hours and estrous ewes were inseminated 12 hours later with 0.3 ml% frozen-thawed ram semen containing 250-340 x 10⁶ spermatozoa either by cervical, deep-cervica. non-surgical intrauterine or intrauterine inseminations using a laparoscope. After insemination, ewes were brought back to the flock and non-return ewes were recorded.
Lambing rates obtained were as follows: 33.3% by cervical insemination, 0% by deep-cervical insemination, 66.7% by non-surgical intrauterine insemination and 80.0% by intrauterine insemination using a laparoscope. Owing to small sample size, there was no significant difference in lambing rate among the insemination techniques (x²=5.78, df=3), but a single intrauterine insemination using a laparoscope gave the best lambing rate.

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An improved one-step straw method for bovine frozen-thawed embryos was described. The main objective was to remove the glycerol from the straw after thawing.
After glycerol equilibration, the 0.25 ml straws were filled with four compartments, each separated by small air bubbles. In each straw two embryos were placed in the second upper compartment containing PBS and 10% glycerol as cryoprotectant. Other three compartments contained 0.3 mole sucrose solution (292 mOsm) supplemented with 20% bovine serum. After thawing at 37 to 38 C the straw was shaken once or twice, so that the embryos might migrate from the glycerol to the sucrose layer. Ten minutes after shaking, the glycerol layer moved to the upper part of the straw was re-moved by cutting about 1.5 cm from the tip. The straw containing the embryos was inserted into the plastic sheath for transfer and immediately transferred to 2 recipients (R-3 and 4). The other 2 recipients (R-1 and 2) were transferred the embryos taken out from the frozen-thawed straw.
All the four recipients became pregnant.

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[in Japanese]

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[in Japanese]

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