22. "Large offspring syndrome" or "fetal oversize" is a phenomenon found occasionally in calves and lambs which are born following embryo manipulations such as in vitro fertilisation (IVF) and nuclear transfer. During IVF and related technologies the embryo is kept for a short time in a synthetic medium before being transferred into its new mother. It is thought that the culture process can alter normal development and lead to over-large offspring. In the experiment that produced Dolly, none of the lambs was significantly larger than normal. It is too early to know whether the incidence of assisted parturitions will be increased by the use of the nuclear transfer procedure. We recognised that work is currently underway, funded by MAFF, with the aim of devising embryo production methods which avoid "large offspring syndrome". The first aim is to identify factors which might induce this syndrome and then to identify markers which correlate with oversize and which can be used for diagnosis.
23. FAWC believes that advice from an appropriately knowledgeable and experienced veterinary surgeon is essential both in the supervision of the procedures involved in nuclear transfer and in ensuring that suitable recipient dams are selected. Invasive techniques of this nature should not be undertaken lightly and the production of offspring of a size or shape which will cause problems at birth, or which require elective caesarean section, is unacceptable.
24. In the regulations governing embryo transfer (ET) in cattle, a veterinary surgeon is required to examine clinically the recipient and to certify that "he knows of no reason existing at the time of his examination which would cause him to believe that the animal would not be able to carry to term a normal calf of the breed and type specified and to calve naturally". Similar certification should be required by law to govern nuclear transfer.
25. In nuclear transfer, the recipient dam must be of an appropriate size in relation to the size of offspring to be produced. Regulations should be introduced requiring the suitability of the dam to be certified by a veterinary surgeon in a manner similar to that required in embryo transfer.
26. A greater understanding is required of the underlying causes of oversized offspring, especially of the effects of in vitro culture on fetal size.