The influence of weaning age on the efficiency of an accelerated mating frequency with sheep.  One hundred late pregnant South African Mutton Merino ewes were divided into two comparable groups (an early and a late-weaning group) of 50 animals each and SUbjected to a system of three lambing periods in 2 years. The lambs of the early and the late-weaned groups were weaned at 8 and 19 weeks (at slaughtering) respectively after the beginning of every lambing period. In order to investigate the effect of weaning age the ewes in both groups were subjected to the same feeding level according to production stage. The lambs in both groups also received a similar ration from approximately 3 weeks of age up to slaughter. Late weaning resulted in a highly significant (P < 0,01) lower livemass of the ewes at mating and at slaughtering of the lambs. Similarly, the reproduction ability of the ewes was suppressed by late weaning. On the other hand, an early weaning system resulted in a highly significant (P< 0,01) lower growth rate and carcass mass as well as a significant (P< 0,05) lower grading of the carcasses. The net result was a small biological advantage in favour of the late weaning  system.