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Abstract. Non-surgical embryo transfer is a promising method for improving efficiency in the pork industry and also for biotechnology applications, such as in vitro embryo production, transgenesis and cloning. Several groups have reported successful piglet production using an artificial insemination catheter or flexible catheter designed for this procedure; however, the efficiency of the technique is still low. The critical points that need to be addressed in order to improve this procedure are (1) the embryo deposition site and (2) volume of transfer medium associated with the embryos; however, the latter has not yet been examined systematically. In the present study, we evaluated the effect of the volume of non-surgical embryo transfer medium on the ability of porcine embryos to survive to term by using a recently produced flexible catheter. The catheter consists of a guide and an injector. Blastocysts 200-230 µm in diameter were collected from donor gilts and transferred to recipient gilts. The time required for the completion of embryo transfer using this catheter was 14.6 ± 3.9 min. The tip of the injector was determined by laparotomy to be located in a uterine horn 20-30 cm anterior from the branching point of the uterus body. We transferred 17.0-17.3 embryos with different volumes of medium (1.6, 3.2 and 10 ml) into each of 5, 4 and 4 recipients, respectively, and pregnancy was confirmed in 4, 3 and 1 of these recipients, respectively. Three recipients in the 1.6 ml group farrowed a total of 19 piglets (4, 5 and 10 piglets, respectively). These results suggest that successful non-surgical embryo transfer is affected by the volume of transfer medium. Key words: Embryo survival, Medium volume, Non-surgical transfer, Pig (J. Reprod. Dev. 54: [30][31][32][33][34] 2008) pioneering study demonstrated that it is possible to transfer porcine embryos non-surgically using a double-walled polythene catheter and obtain successful pregnancy [1]. Thereafter, many researchers succeeded in producing viable piglets after transfer of in vivo-derived embryos using both a commercially available artificial insemination (AI) catheter [2-4] and a specially designed flexible catheter [5][6][7]. This technique offers considerable promise for improving the efficiency of embryo transfer in the pork industry and also for biotechnology applications. However, the technique still has drawbacks because of the low survival rate of transferred embryos and the variable degree of successful transfer.It has been suggested that there are two important parameters related to the success of non-surgical embryo transfer: (1) the embryo deposition site [8] and (2) the volume of transfer medium associated with the embryos [9]. AI catheters require much more medium-10 to 50 ml-when used as a transcervical catheter [3,4]. To allow the transfer of embryos with small amounts of fluid, several types of flexible catheter have been developed. In an experiment by Hazeleger and Kemp [5] and a subsequent study by the same research group [10], embryos were...

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