19 LIFETIME MORTALITY OF CLONED PIGLETS

Abstract

Perinatal mortality of cloned animals is a well-recognised problem, but it is not clear if and how the problems continue throughout the life of cloned animals. Here we report occurrence and causes of lifetime mortality of cloned piglets from their perinatal period and onwards. From 2006 until 2013, 178 Large White (LW) sows received Day 5–6 handmade cloned morulae or blastocysts where donor cells were from LW, Yucatan, or Göttingen, and were either transgenic or not. Pregnancy rate on Day 30 was 73%, but 19% terminated before term, resulting in 104/178 deliveries. For each litter, each piglet was characterised as either alive or stillborn (i.e. dead without signs of autolysis or dying during the first minutes after birth). Data were analysed by Fisher's Exact test with a significance level of P < 0.05. In the 104 litters, stillborn piglets were found in 54 (from 1 to 7 stillborn piglets in a litter), and the highest number of stillborns was found in Göttingen piglets (P < 0.05; see Table 1). Alive piglets were followed and their mortality registered, and they either died spontaneously (arthritis, pericarditis, enteritis, septicemia, lethal malformations) or were killed if they had other malformations, no weight gain, anorexia, bristly hair coat or signs of compromised well-being. Piglet mortality was highest in the perinatal period but remained high until weaning at Day 28 (see Table 1), so almost half of the alive piglets died during the first month; this preweaning mortality was highest in Yucatan piglets (P < 0.05), which also had the highest cumulative mortality. Further analyses are needed to describe differences observed between donor cell breeds. After weaning, where the pigs were kept under standard conditions, the mortality was at the normal level for the farm. Few died of infections with no breed differences, so most were killed over the subsequent months and years for various experimental purposes. The oldest pig lived until 6 years of age. During their life, no differences compared with noncloned pigs were observed in behaviour, growth, occurrence of diseases, or viability. This study confirms the well-known high perinatal mortality of cloned piglets and shows also high mortality until weaning. However, after weaning, mortality was not different from that of noncloned piglets.

Table 1.  Lifetime mortality rates in cloned piglets of different breeds and at different time periods after birth