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Title: EMBRYO DEVELOPMENT AND ESTABLISHMENT OF PREGNANCY AFTER EMBRYO TRANSFER IN THE PIG: COPING WITH LIMITATIONS IN THE AVAILABILITY OF VIABLE EMBRYOS

Author
item KING, T - ROSLIN INST, EDINBURGH,UK
item Dobrinsky, John
item ZHU, JIE - ROSLIN INST, EDINBURGH,UK
item ARCHIBALD, A - ROSLIN INST, EDINBURGH,UK
item BOSMA, WILLEM - ROSLIN INST,EDINBURGH,UK
item HARKNESS, L - ROSLIN INST, EDINBURGH,UK
item RITCHIE, W - ROSLIN INST,EDINBURGH,UK
item TRAVERS, A - ROSLIN INST,EDINBURGH,UK
item MCCORQUODALE, C - ROSLIN INST,EDINBURGH,UK
item DAY, B - UNIV OF MISSOURI

Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2001
Publication Date: 4/20/2002
Citation: N/A

Interpretive Summary: The pig is a polytocous animal that requires at least four viable embryos in utero to maintain a pregnancy past twelve days of gestation. We evaluated strategies and developed a novel approach for maintaining pregnancy after transfer of limited numbers of viable embryos (ET), such as in nuclear transfer when few viable cloned embryos are available. Micromanipulation had no effect on blastocyst production, while developmen in vivo improved blastocyst quality. Zona pellucida compromised embryos resulted in live piglets after ET. Supplemental hormonal treatments resulted in <25% pregnancy after ET, when <9% of transferred embryos survived. Also, 50% of mated recipients successfully carried 25% of transferred embryos. Lastly, parthenogenetic embryos transferred into recipients yielded 62% pregnancy rates, and no pregnancy continued beyond day 55 of gestation. Following co-transfer of 3 fertilized embryos with 55- -60 parthenogenetic embryos into each of 6 recipients, 2 live piglets were born. Our results showed that parthenogenetic embryos support desired embryo development through maternal recognition of pregnancy and are capable of supporting select embryo development to term. This novel approach technology will aid researchers in maintaining pregnancy after transfer of few valuable embryos that could not maintain pregnancy on their own in the pig after transfer.

Technical Abstract: Embryo transfer and pregnancy maintenance strategies in the pig were evaluated with reference to situations where limited numbers of viable embryos or micromanipulated embryos are available, such as pig cloning. Development of embryos whose zona pellucida had been compromised was compared with those whose zona pellucida was left intact. Micromanipulation nhad no effect on blastocyst production rates following development in vivo or in vitro, while in vivo development improved blastocyst cell numbers. Transfer of zona pellucida compromised embryos resulted in live piglets. Several hormone treatments to maintain pregnancy were tested in a model in which 3 embryos were transferred into unmated recipient gilts, compared with transfer of 3 embryos into mated recipients. None of the hormonal treatments resulted in pregnancy rates higher than 25% at term and no more than 9% of transferred embryos survived. This compared with 50% of the mated recipients successfully carrying 25% of transferred embryos. Lastly, the developmental potential of parthenogenetic embryos was assessed with 62% of transferred embryos resulting in pregnancies, none of which continued beyond day 55 of gestation. Following co-transfer of 3 fertilized embryos with 55-60 parthenogenetic embryos into each of 6 recipients, 2 live piglets were delivered. Our results suggest that transfer of zona pellucida-compromised embryos can yield litters of normal piglets. The hormonal pregnancy maintenance strategies tested were poor at supporting small numbers of embryos to term. However, co-transfer with parthenogenetic embryos was shown for the first time to be a novel alternative capable of supporting fertilized embryo development to term.