Incidences of spontaneous mortalities and congenital abnormalities...

Incidences of Spontaneous Mortalities and Congenital Abnormalities in a New Zealand White Rabbit Breeding Colony

Verchère Beau Charlotte 1, Duparay Julien 2, Allouche Myriam 1, Blondel Audrey 1, Marsden Edward 1

1 Charles River Lyon, 329 Impasse du Domaine Rozier, 69210 Saint Germain-Nuelles, France

2 Charles River France, 2109 Route de Châtillon, 01400 Romans, France

Background data, especially the incidence of spontaneous congenital abnormalities, are essential for interpreting results from developmental and reproductive toxicology studies. Fetal abnormalities are commonly noted in embryo-fetal development (EFD) studies, but post-natal findings are less common due to fewer littering studies in rabbits. The aim of this investigation was to provide additional post-natal information by collecting data and specimens directly from the rabbit supplier’s facility. 121 lactating New Zealand White rabbits (Crl: KBL(NZW)) were monitored from four separate zones in the breeding facility. The number of live and dead pups was counted daily up to weaning (± post-natal day (PND) 35). Any pups found dead or euthanized for ethical reasons were retained and stored frozen, pending examination for external and visceral abnormalities by an accredited fetal morphologist. In total, 1143 delivered pups were recorded from 121 females with a subsequent 20% mortality rate before weaning (stillborn, dead or euthanized), including 2 females with total litter death post-partum. After exclusion for autolysis and/or cannibalization, examination was possible for 198 pups. Fetal and litter incidences of external and/or visceral malformations were 0.9% and 11.3%, respectively. Amongst the external malformations, cleft palate and omphalocele were noted. Visceral malformations included heart defects, i.e. ventricular septum defect (VSD), generally associated with great blood vessel abnormalities, retroesophageal right subclavian artery and malpositioned kidneys and testes. Of note, two pups with a VSD (associated or not with other heart defects and dilated right anterior vena cava) survived for up to PND35. Other less severe visceral variations were also recorded. These data could facilitate interpretation of post-natal endpoints from rabbit studies together with the historical control data from EFD studies, since there was no major difference in the observed malformations.

Keywords: Background data, Congenital abnormalities, New Zealand White rabbit