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Non-surgical embryo transfer in pigs
There is enormous potential for the use of embryo transfer (ET) in pigs because it allows the movement and introduction of new genetic material into a herd with minimal risk of disease transmission, reduced transportation costs and no effect on animal welfare. Despite these advantages, the commercial use of ET in pigs is very limited due to the lack of effective non-surgical ET procedures. Although the first pregnancy in pigs through non-surgical ET was reported 45 years ago (Polge and Day, 1968; Vet Rec 82:712), non-surgical ET was considered as an impossible technique for many years because of the complex anatomy of the swine genital tract. However, in the 1990s, several non-surgical techniques to deposit embryos directly into the uterine body were developed, although most of them were not successful, achieving farrowing rates of 5–41% and litter sizes of 5–7.5 piglets. To overcome some physiological and practical limitations of non-surgical uterine body ET, in 2000, in collaboration with the laboratory of Dr. BN Day at the Animal Science Research Center, University of Missouri-Columbia, we developed a simple, safe and quick procedure for the non-surgical transfer of embryos deep into a uterine horn (NsDU-ET) of gilts and sows with acceptable farrowing rates (71.4%) and litter sizes (6.9 piglets). With the recent improvement of the procedure, the results have been greatly increased when using fresh morulae and blastocysts cultured for 0–6 h or fresh morulae cultured for 24 h (80–90% farrowing rate and 9.0–9.5 piglets born). Although a period of 24 h of culture permits the international transport of embryos, cryopreservation of embryos is obviously preferred. Currently, a high percentage (80–95%) of untreated morulae and blastocysts survive the vitrification procedure and high farrowing rates (75%) and litter sizes (10 piglets) are obtained when these embryos are surgically transferred into the recipients. However, when embryo vitrification and NsDU-ET are combined, the farrowing rates are decreased (50%), although the litter sizes are maintained. The excellent reproductive performance of recipients following non-surgical transfer of fresh embryos and the promising results obtained with vitrified embryos represent a fundamental advance for the widespread commercial use of ET by the pig industry in the near future. Supported by MINECO-FEDER (AGL2012-38621), Madrid, Spain and Fundación Séneca (GERM 04543/07), Murcia, Spain.
Keywords: porcine; blastocyst; transfer