This study was carried out to produce monozygotic twin calves by transfer of bisected embryos. Four Korean native cattle donors were superovulated with FSH and flushed to collect embryos on day 6 or 7 of the estrus cycle. Morula and early blastocyst embryos showed 1 or 2 grade were bisected with microblade and each set of demi-embryos without zona pellucida were transferred nonsurgically to 10 recipients respectively. The results obtained were as follows; 1. Twenty four demi-embryos (92.3%) were separated from 13 original embryos and among them 20 demi-embryos (83.3%) had normal appearance without severe damage. 2. Four sets of fresh demi-embryos were transferred to 4 recipients and one recipient was twin pregnant 3. Six sets of frozen-thawed demi-embryos were transferred to 6 recipients. Two recipients were pregnant, one of them twin.

This study was conducted to determine the main effects of the parity and farrowing season on gestation length and newborn pigs on the basis of the data obtained from 234 litters of Landrace breeds raised at an integrated swine farm in Kyunggy province from January 1991 to December 1992. The results obtained are summarized as follows ; 1. The average gestation length was 115.37 days, and 114.64 days of 8th parity and over was shorter than those of other parities. 2. The averages of litter size and litter size alive per sow were 9.91 and 9.50 heads. The litter size horn at 1st parity was smaller than at other parities, and the litter size in spring was larger than in summer, autumn or winter. 3. The averages of birth weight per litter and pig were 13.53 kg and 1.37 kg. The effect of farrowing season for each litter weight(p<0.01) and pig weight(p<0.05) at birth was significantly higher in spring than other seasons. 4. Incidence of malformation and stillbirth at birth was 4. 10%, and it at 8th parity and over showed the highest rate(7.50%).

It is widely recognized that the embryonic or fetal loss after breeding is common in the cattle and that it is an important factor affecting reproductive efficiency. The causes of this loss have been subject of extensive researches and the results indicate that the embryonic mortality may he primary factor responsible for low pregnancy rates in non-embryo transfer bovine populations as well as embryo transfer programs. However, it's causes are still not clearly understood. The embryonic mortality or pregnancy rate has been influenced by various embryonic and maternal effects related to genetic and environmental factors. The timing and extent of embryonic mortality vanes greatly according to authors and estimating methods, because it is difficult to make direct measurements. The major important factors that may influence the embryonic losses or pregnancy rates after embryo transfer can be summeirized. 1.When an embryo is transferred to unmated recipients, the contralateral transfer to corpus luteum results in a lower survival rate than ipsilateral deposition. When the embryos are transferred for the production of twin calves, their survivals and twin pregnancies have quite inconsistent according to the transfer methods either to the unmated-synchronized or already mated recipients and more works are needed to accurrately clarify the previous results. 2.Although embryos can be cultured in vitro some hours without the great declines in pregnancy rates, the rates differ markedly among culture times and media but may be improved by co-transfer systems. 3.Embryo developmental stages and quality grades clearly affect the survival rate following freezing and the pregnancy rate after transfer and the selection of embryos without chromosome abnormalities and of high fertile semen may also be considered to increase the pregnancy rates. 4.Many researches have attempted to relate the plasma progesterone levels to pregnancy rates and others have done either direct progesterone supplementation or luteal stimulation by hCG treatment in order to increase the pregnancy rates. However, these effects on pregnancy rates are inconsistent and also contradictory. 5.The asynchrony between donors or embryos and recipients may he a major cause of embryo death and low pregnancy rate and the sensitivity to uterine asynchyony differs in according to the quality and stages of embryos. 6.The extremes of poor or over nutrition during early pregnancy in the recipients are detrimental to the survival of embryos and the good body condition is required to prevent a reduejion of pregnancy rates. The uterine pathogens in embryonic mortality or fertility have been questioned but the infection of C.pyogenes and Campylobacter fetus is still important pathogens. 7.The heat stress during early pregnancy may reduce conceptus weight and possibly increase the embryonic mortality.

본연구의 목적은 흰쥐의 임신 초기에 있어서 착상의 유발에 PAF의 관련여부를 PAF의 수용체 길항제인 BN-52021d의 작용과 비교하여 결정하기 위함이다. 임신초기 각일에 점증하는 용량의 BN-52021 (체중 200g당 10g 내지 1.25mg)이 근육내로 주사되었을때 10g내지 250g 용량에서는 대조구에 비하여 착상부위의 수 혹은 이것을 가진 흰쥐의 수에 대하여 현저한 영향을 미치지 아니하였으나 1.25mg투여 경우에는 현저히 감소된 효과를 나타

임신랫드에 융모성성선자극호르몬을 투여한 후 모체의 황체와 태아에 미치는 영향을 조사하기 위하여 임신랫드에 융모성성선자극호르몬제제인 Profasai 1000(Serona, Switzland) 50 또는 100IU를 임신 4, 8, 12 또는 16일에 각각 투여한 후 임신20일에 부검하여 태아와 모체에 대한 조사를 한 결과를 요약하면 다음과 같다. 1. 황체는 모든 대조군과 HCG투여군에서 그 수가 거의 비슷한 수준이었고 임신8일의 경우에 그 수가 비교적 감소되었다. 2. 태아의 흡수는 임신 4, 8및 12일의 HCG투여군과 임신 12일의 대조군에서 나타났지만 임신4일의 경우가 발생빈도가 현저하게 높았고 임신 12일의 경우는 매우 낮았다. 3. 태아의 체중은 임신4일에 50IU의 HCG투여군에서만 감소되었다. 4. 태아의 골격검사에서 기형발생과 골화의 이상은 인정되지 않았지만 변이는 인정되었다. 변이는 14번늑골만 인정되었으며, 임신 4, 8 그리고 12일의 HCG투여군과 임신8일과 16일의 대조군에서 다양하게(5.26~8.33%) 나타났다. 5. 임신랫드에 HCG를 투여하면 태아의 흡수가 나타날 수 있지만 골격형성 과정에서 반드시 변이가 발생된다고 생각하지 않는다.