Enhanced efficiency in the production of offspring from 4- to 8-week-old lambs.

The rate of production of offspring from lambs following the transfer of embryos produced by in vitro maturation and fertilisation has been disappointing. This study was conducted on the rationale that gonadotropin treatment protocols used in the past failed to maximise oocyte quality. Consequently, three experiments were conducted in Merino lambs to examine: (1) the method of FSH administration (single versus multiple treatments), (2) the time of oocyte collection (48, 60 or 72 h after the first FSH treatment), (3) progesterone treatment and (4) eCG treatment and its timing on oocyte yield, cleavage rate and blastocyst formation rate. No factor significantly influenced oocyte yield, but all significantly influenced the rates of cleavage and/or blastocyst formation in one or more experiments. The preferred protocol consisted of the administration of 4x40 mg of FSH, no progesterone treatment and with 500 IU of eCG given at the time of the last FSH treatment. The optimal time of oocyte collection was 48 h after the first FSH treatment. A field evaluation, involving lambs from five generations, resulted in the production of 9.0-13.9 lambs per donor lamb; this protocol generated more lambs per donor lamb than protocols previously reported.