A simple procedure for the production of identical sheep twins.

Eggs were collected surgically on day 6, 7 or 8 from 18 Jacob ewes mated to a Welsh mountain ram. Thirty one (86 per cent) of the 36 eggs ovulated were recovered and of these 27 (87 per cent) had developed normally. All ovulated eggs were collected from 14 of the ewes. One (or more) normally developing morula or blastocyst was collected from 16 of the ewes. While the ewes remained under general anaesthesia each embryo was divided into two 'half' embryos with a thin glass needle. One monozygotic pair of 'half' embryos was retransferred to the embryo donor. The two ewes from which no normal embryos had been recovered were used as recipients for surplus bisected embryos from two other donors. Two of the 18 ewes returned to oestrus. The remaining 16 went to term producing, in all, eight pairs of identical twins, one pair of non-identical twins and seven single lambs.