30 POSTMORTEM FINDINGS IN CLONED AND TRANSGENIC PIGLETS DEAD BEFORE WEANING

Around 50% of cloned and transgenic piglets are lost during the first month after birth (Reprod. Fertil. Develop. 26, 124), and one reason is malformations of vital organs. The aim of the present study was to describe the distribution of malformations in piglets (until weaning, i.e. age <Day 28) born after transfer to Large White (LW) recipients of cloned embryos. Donor cells were fibroblasts either from LW (non-transgenic) or from Yucatan or Göttingen (made transgenic with 1 of 7 genes related to different human diseases). Handmade cloning was used to produce embryos that, after 5–6 days in vitro culture, were transferred to 202 LW sows 4 days after natural heat. Abortion occurred in 29 sows, and 6.5 ± 0.4 piglets per litter (from 1 to 22) were delivered from 116 sows (46 litters with LW piglets, 40 with Göttingen, 30 with Yucatan). In 78 of these litters (67%), autopsies were performed on 55 ± 4% of piglets stillborn or dead before weaning. Data were analysed by Fisher's Exact test with P < 0.05 as significance level. Malformations were found in 1 to 12 piglets per litter, with a higher malformation rate in transgenic Göttingen and Yucatan piglets (35% and 46% of all born, respectively) than in non-transgenic LW (17%). Many piglets showed 2 (24%) or more (6%) malformations. Some malformations seemed to be related to breed and/or transgene (see Table 1 for most frequent malformations); for example, heart malformations were most frequent in Yucatan litters independent of the transgene, whereas gall bladder and limb malformations were more frequent in Göttingen and in various litters with the same transgene. These results show that pig cloning results in a considerable loss of piglets, and that a majority of these can be related to various malformations. Use of transgenic cells for cloning only adds to this problem. Some malformations are related to the specific breed in use, but the general finding is that the problem is related to the cloning technique as such. However, because approximately half of the cloned piglets still survive, perhaps with unknown minor malformations, use of pigs as a model for human diseases is still realistic. But choice of breed and possible improvements of the transgenic technologies for this kind of work should be considered carefully. Table 1. Malformations in transgenic and nontransgenic cloned piglets dead before weaning