The information analysed comes from three datasets collected on an experimental farm (‘Le Merle’) where the Booroola gene was first introgressed into the Mérinos d’Arles breed in 1983, and a private farm where Booroola-carrier ewes were bred for production. Reproduction (ovulation rate, litter size, survival rate) and production (body weight, carcass weight, dressing percentage) traits were compared between B+ and ++ animals as well as controls from the Mérinos d’Arles breed. The increase in ovulation rate caused by the Booroola gene had a dramatic effect on litter size at birth, and consequently changed the survival and growth of the lambs. Globally, B+ ewes were able to produce about 50–65% extra lambs, the result being consistent across comparisons. Efforts are now under way by the breeders to exploit the gene at a higher level.