The present study was a 2*2 factorial design.
Purebred single embryos were transferred within and reciprocally between Suffolk (S: large breed; pre-mating without fasting mean (±SD) liveweight:74.3±9.2 kg) and Cheviot (C: small breed; pre-mating without fasting mean (±SD) liveweight: 57.9±7.3 kg) ewes, to establish four groups ofpregnancies: SinS (large genotype embryo in large uterus), SinC (largegenotype embryo in small uterus), CinS (small genotype embryo in largeuterus) and CinC (small genotype embryo in small uterus). The transfer of larger genotype Suffolk embryo into a Cheviot ewe resulted in a potentially restricted uterine environment for the development of Suffolk embryo. Similarly, the transfer of smaller genotype Cheviot embryo into a Suffolk dam generated a potentially capacious uterine environment for the development of Cheviot embryo. Animals were fed on mixed ryegrass (Lolium sp.) and white clover (Trifolium repens) pastures and had ad libitum access to drinking water. Approval to manipulate animals was obtained from Massey University Animal Ethics Committee.