EFFECTS OF TRANSFERRED OVA PER RECIPIENT AND DUAL-USE OF DONORS AS RECIPIENTS ON PRODUCTION OF TRANSGENIC SWINE

The purpose of the study was to determine whether the number of transf erred ova per recipient influenced the efficiency of producing transge nic pigs and whether donor gilts were as effective as unmated gilts as recipients of microinjected ova. Eight genes were microinjected into 4,232 ova that were transferred into 169 recipients over a 5-yr period . Although the farrowing rate and litter size was highest for recipien ts receiving 31 to 41 ova per recipient, the percentage of transferred ova developing into piglets was highest for recipients receiving 13 t o 20 ova (P = 0.021 for all recipients and P = 0.011 for pregnant reci pients). Based on these data we conclude transferring more than 20 ova per recipient may incur some loss due to uterine crowding. Gilts used as recipients of microinjected ova immediately after their own ova we re flushed from their oviducts had the same farrowing rate, litter siz e, and ovum development efficiency as unmated gilts that were only use d as recipients. However, donor-recipients that ovulated 21 or more ov a had smaller litters (P = 0.009) and were less efficient in producing pigs (P = 0.024) and transgenic pigs (P = 0.054) from transferred ova than donor-recipients that ovulated 20 or fewer ova. Dual use of dono rs as recipients was an effective method of reducing the number of rec ipients in a transgenic pig project by nearly one-half.