256 COMMERCIAL-SCALE IN VITRO PRODUCTION AND TRANSFER OF JAPANESE BLACK EMBRYOS

In vitro fertilized (IVF) Japanese Black embryos have been preferably transferred to Holstein recipients for beef cattle production in Japan. We have been commercially producing IVF embryos, aiming at increased productivity and hereditary improvement of Japanese Black cattle. However, the use of IVF embryos has been implicated in reduced pregnancy rates as well as in increased risk of abortion and oversized newborns. In this report, we present our cumulative data that summarize the outcome of IVF embryo transfer. The IVF embryos were produced as previously described by Hamano and Kuwayama (1993 Theriogenology 39, 703) using semen collected from five stud bulls. Fertilized oocytes were developed to the blastocyst stage by co-culture with cumulus cells. Developed blastocysts were transported to farms all over Japan in two conditions: (1) non-frozen via air or ground shipping using cell transporters, or (2) cryopreserved in glycerol for direct transfer. Both methods were used at approximately the same rate. We transferred 90% of these embryos to Holstein heifers and 10% to hybrids. Although the average pregnancy rate at the farms was initially low (31%), it has exceeded 40% in recent years. After pregnancy diagnosis, abortion occurred in 9% of these cases. We compared 109 pregnancies from in vivo embryos with 824 from IVF embryos obtained during the same period: the average gestation period was 281.4 and 283.6 days, respectively, the latter being longer by 2.2 days. The average birth weight from IVF was 33.8 kg, 1.3 kg heavier than that of in vivo-derived calves (32.5 kg). In addition, oversized newborns (>50 kg) were absent with in vivo embryos, whereas it occurred in 3.1% of the IVF calves with an average gestation periods of 291.3 days. These gestation period were significantly longer (P < 0.05) than for the normal sized newborn groups. Our study suggests that the IVF technology can be effectively used to increase beef production in Japan and that oversized newborns are associated with delayed parturition. Due to the improved meat productivity obtained with calves derived from these embryos, our sales further increased with 9014, 9334, and 11,932 embryos sold in 2001, 2002 and 2003, respectively.