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					      Artificial insemination

     Pig embryo transfer:
     A glimpse into the future
                                                                                                                         Embryo transfer is a collective
                                                                                                                         term for a technology used for
                                                                                                                         replacing embryos from the
                                                                                                                         uterus of one female organism
                                                                                                                         into another. A technique used
                                                                                                                         predominantly in cattle, but
                                                                                                                         also very well applicable to
                                                                                                                         swine – in the future perhaps
                                                                                                                         even more so.

                                                                                                                         By S.L. Terlouw and J.R. Dobrinsky, Minitube
                                                                                                                         International Center for Biotechnology, Mt
                                                                                                                         Horeb, Wisconsin, USA

      Porcine embryo cells, shortly after fertilisation.

                                      his article introduces the basics of    tion including ovulation, fertilisation,   How is ET possible in the pig?
                                      swine embryo transfer, a collective     embryo development, preservation,          Commercial embryo transfer has been
                                      term for a technology that could well   migration, implantation and survival       a practical alternative in cattle breed-
                               be more common in the future of the swine      has been the result of ET related          ing for years. The reproductive tract
                               industry. Once an oocyte or ‘egg’ is ferti-    research.                                  and the size of the animal enable rec-
                               lised by a sperm cell, the resulting zygote       Embryo transfer is now a global         tal palpation of the reproductive tract,
                               is an embryo. The early stages of embry-       industry that reports the transfer of      further enabling the non-surgical rec-
                               onic development have been the focus of        nearly 955,000 commercial (non-            tal-vaginal transcervical deposition of
                               embryo transfer in multiple species for        research) embryos from mammalian           an embryo into the ipsilateral (side of
                               many years.                                    species in 2005, 92% of which are from     ovulation) uterine horn. In the pig, the
                                                                              cattle. The remaining 8% are primarily     smaller size of the animal limits or
                               What is ET?                                    derived from sheep, goats, pigs, and       inhibits the use of non-surgical rectal-
                               Embryo transfer (ET) refers to the area of     horses. It is estimated that nearly        vaginal trans-cervical deposition of
                               reproductive science involved in removing      10,000 in vivo (derived from live ani-     embryos. As well, the pig is a polyto-
                               embryos from the uterus of one female          mals) and over 40,000 in vitro (derived    cous animal with characteristically
                               (the donor) and transferring one or more of    from laboratory research projects) pig     long uterine horns needed to nurture a
                               them into a host or surrogate female (the      embryos are produced each year. The        brood or litter of piglets during gesta-
                               recipient). The first mammalian offspring      major countries reporting this activity    tion. It is the presence of these long
                               resulting from ET was achieved in rabbits      to the International Embryo Transfer       uterine horns and the characteristic
                               almost 119 years ago! The first ET piglets     Society include the United States,         ‘corkscrew’ type cervix of the pig that
                               were born on March 27, 1950 in Ukraine.        Canada, Taiwan, Korea and countries        hinders the non-surgical transcervical
                               Since then, research on porcine reproduc-      in the European Union.                     collection and deposition of embryos.

      14      PIG PROGRESS Volume 26, No. 3 2010                                                                                                 www.PigProgress.net

10PPR003_Pig embryo 14                                                                                                                                    4/14/2010 9:19:11 AM
                                                                                                                                    Artificial insemination

      Therefore, scientists and veterinarians     Medical science
      have long relied on surgical mid-ven-       Pig organs are the most compatible
      tral laparotomy for the recovery and        with humans compared to other spe-
      transfer of embryos in the pig.             cies because of similarities in anato-
                                                  my, physiology and size. Ethically,
      Isn’t ET in the pig redundant?              they are less controversial than non-
      Pigs are a litter-bearing species and, in   human primates. In the last decade,
      contrast to a species like cattle where     the number of patients waiting for
      ET is extensively used, pigs are rela-      organ transplant tripled leaving the
      tively young at puberty and have a          US Department of Health and Human
      short gestation length. As a result,        Services organ donation programme
      aggressive mating selection in swine        over 50,000 short. Embryo transfer
      operations that use AI already allows       procedures are a critical step involved
      for rapid genetic improvements, without     in the development and production of
      the need of ET.                             gene-altered pigs suitable for supply-
      Therefore, what motivating factors drive    ing these organs. As well, the pig has
      the industry to continue to attempt         been recognised as a more suitable
      implementing embryo transfer tech-          animal for the basis of medical mod-
      niques? Here are a few:                     els of human disease. In the US, less
                                                  than 8% of studies using rodent or
      Rapid genetic progress                      other traditional models for human
      Only 50% of the genetics can be affect-     disease that head to clinical trials
      ed in one generation through the use of     actually make it to a finished product
      AI, whereas 100%, or entirely new           treating the human condition. The
      genetics, can be introduced with an         pigs’ unique physiology and anatomy
      embryo.                                     make it a more suitable model for
                                                  human disease, and the pig is being
      Expanded markets                            actively used for genetic manipulation
      Pig production continues to grow            for medical model production for dis-
      worldwide, and breeding companies           eases such as atherosclerosis, diabe-       Conventional embryo transfer in sows as it has been practised for a long time,
      that operate internationally will benefit   tes, cystic fibrosis, muscular dystro-      using surgical mid-ventral laparotomy.
      from the cost-effective ability to trans-   phy, cancer, and other dreadful
      port embryos instead of live animals.       diseases.
      This will also allow smaller operations                                                 Oestrus detection
      the opportunity to become more com-         What are the basics?                        A reliable and consistent method of
      petitive by marketing unique genetics       Below is a list of management and           oestrus detection and record keeping
      in the form of stored/shipped embryos.      technical factors that would be involved    must be employed for both donors and
                                                  when integrating ET into a swine oper-      recipients so that the recipients can be
      Reduced health risks                        ation.                                      precisely matched with individual
      Embryo transfer can be used to bridge                                                   donors and their embryos.
      health differences. Pig embryos can be      Oestrous cycle control
      removed from females with diseases          If the process of ET is to be successful,   Artificial insemination
      such as pseudorabies or Porcine             the donors and recipient females must       In most species, ET is typically cou-
      Reproductive and Respiratory                be synchronised (for fresh embryo           pled with an AI programme because
      Syndrome (PRRS), ‘washed’ and trans-        transfer) so that the recipients are in     producers want to take advantage of
      ferred to a recipient to establish dis-     oestrus near the same time as the           mating genetically-superior, donor-
      ease free herds. This unique character-     donors.                                     quality females with genetically-superi-
      istic of ET can also be applied to mini-                                                or males.
      mise or eliminate unknown disease risk      Super-ovulation
      between herds desiring rapid genetic        Even though the pig naturally releases      Embryo recovery & transfer
      progress. This use of ET has been           or ‘ovulates’ 10 to 25 oocytes per          Present technology is rapidly advanc-
      referred to as ‘genetic rescue’.            oestrous cycle, the donor can be hor-       ing, but several surgical, semi-surgical,
                                                  monally stimulated to produce more,         and non-surgical techniques are cur-
      Genetic leverage                            making her even more efficient, since       rently being evaluated to determine the
      Use of other biotechnologies such as        the process of ET involves removing         most effective and practical approach-
      cloning and embryo cryopreservation         those embryos from the donor female.        es in the pig. Currently, surgical recov-
      require ET for production of live off-      However, super-ovulation is not neces-      ery and transfer yield the most consist-
      spring.                                     sary for successful ET.                     ent results.

      www.PigProgress.net                                                                                                        PIG PROGRESS Volume 26, No. 3 2010            15

10PPR003_Pig embryo 15                                                                                                                                             4/14/2010 9:19:12 AM
      Artificial insemination

                                 Donors and recipients
                                 Donor females supply embryos to be
                                 transferred into recipients. Donors can
                                 be maternal or paternal lines but
                                 maternal lines are preferred for recipi-
                                 ents. Donors and recipients can be
                                 either gilts or sows but gilts are much
                                 easier to handle for surgical proce-

                                 Embryo handling and expertise
                                 Acceptable ET results are only
                                 obtained when embryos are properly
                                 managed from recovery to transfer.
                                 Trained personal use sterile techniques
                                 and media designed for embryo growth
                                 to handle embryos from recovery to
                                 transfer in controlled environments.

                                 Embryo transport
                                 Embryos must be properly identified
                                 and packaged to be transported to the
                                 recipient location. Transportation can                 Non-surgical embryo transfer is a relatively new technique, developed by scientists at the University of Murcia.
                                 vary from walking, driving or flying
                                 from one location to another. Embryos
                                 can be cultured for up to 72 hours with                embryos will result in the birth of pig-                   other species had limitations, due to
                                 diminishing results.                                   lets. Results are dependent on the rea-                    the smaller size and unique nature of
                                                                                        son for ET. Using ET to rescue geno-                       the female porcine reproductive sys-
                                 Embryo preservation                                    types from health compromised donors                       tem. Research continues to make
                                 Once recovered, embryos may be cul-                    may be less efficient than using ET for                    progress towards making more practi-
                                 tured during transport, especially if ET               genetic transfer in healthy herds (see                     cal use of non-surgical ET in the pig.
                                 is to occur within 24 hours of recovery.               Table 1). Length of time in culture may                    The most promising results have
                                 Alternative methods of embryo preser-                  impact international transfer results.                     come from a catheter developed at the
                                 vation have been developed, including                  The success of pig ET in a wide range                      University of Murcia by Dr Emilio
                                 hypothermic embryo storage for up to                   of applications shows that it is a robust                  Martinez. A 70.8% farrowing rate and
                                 48-72 hours and embryo vitrification                   procedure worthy of consideration. In                      6.9 pigs born was achieved using the
                                 for long-term cryopreservation. While                  our experience, greater risk is taken                      catheter that is now available from
                                 not as routine as embryo culture, these                with donors and embryo quality to                          Minitube. Continued research efforts
                                 technologies will be instrumental for                  accomplish genetic rescue resulting in                     such as these could make non-surgi-
                                 the logistical implementation of a glo-                reduced efficiency. The practical imple-                   cal ET a viable technology, making
                                 bal embryo transfer service in the                     mentation of embryo transfer requires                      the benefits of ET even more cost
                                 future.                                                specialised facilities, equipment and                      effective and practical for pig
                                                                                        skilled surgical teams.                                    producers.
                                 What is the future?                                                                                                 The future of the swine industry is
                                 At present, pregnancy and farrowing                    Non-surgical ET?                                           going to find, however, that embryo
                                 rates up to 85% and embryonic surviv-                  In the last decade, much research has                      transfer procedures will become com-
                                 al rates (within pregnant recipients) of               been devoted to more feasible and                          monplace, it’s just a matter of time.
                                 50-55% are typical. This means that                    repeatable non-surgical techniques in                      Many global market forces and techno-
                                 combined, up to 50% of all transferred                 swine. Borrowing techniques from                           logical breakthroughs are contributing
                                                                                                                                                   to this inevitable fact. It is an exciting
      Table 1. Embryo transfer experience: Comparing genetic transfer to genetic rescue.                                                           time to be involved in this endeavour,
                                                                                                                                                   both, from the standpoint of on-going
       ET group           Embryos/     Transfers    Recipients      Farrow       Born live/       Pigs/Embryo               Pigs/Embryo            integrated research efforts and new
                          Recipient                 farrowed        rate         Recipient        (farrowed recipients)     (all recipients)       possibilities for producers. PP

       Genetic transfer   15.7         63           52              82.5         8.25             0.52                      0.43                   The original paper was published in
       Genetic rescue     15.7         54           30              55.6         8.17             0.52                      0.29                   Ediporc, Spain, March 2009.
                                                                                                                                                   References available on request.

      16      PIG PROGRESS Volume 26, No. 3 2010                                                                                                                                www.PigProgress.net

10PPR003_Pig embryo 16                                                                                                                                                                      4/14/2010 9:19:13 AM

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