To increase the frequency of lambing, ewes must be mated during seasonal anestrus and while lactating. The present study investigated the effect of lactation and season on the fertility of Katahdin ewes rebred while lactating. Fall-lambing ewes (n = 57, 2 mo postpartum, experiment 1) and spring-lambing ewes (n = 40, 3 mo postpartun, experiment 2) were randomly assigned within birth type to be weaned approximately 3 weeks before breeding or to continue to suckle their lambs for an additional 3 mo. In experiment 1, all ewes were treated with a controlled internal drug releasing (CIDR-g; 0.3 g progesterone) device for 5 d and introduced to rams. In experiment 2, half of the ewes in each lactation status group were treated with an estrus induction protocol consisting of a pre-treatment with a CIDR device for 5 d and an injection with 3 mL P.G. 600 (240IU eCG and 120 IU hCG) at insert removal or received no further treatment. In experiment 1, the mean estrous response, conception rate, pregnancy rate to the first and second service period, proportion of ewes lambing and prolificacy was 64.9, 89.2, 57.9, 91.2, 67.3 and 129% respectively and was not affected by lactation status. In experiment 2, estrous response tended to be higher in suckling compared with weaned ewes (50 vs 11.1%, P = 0.08) but lactation status did not affect any of the other variables measured. Ewes receiving the estrous induction protocol had a higher (P < 0.01) estrous response, conception rate, pregnancy rate to the first and second service period, proportion of ewe lambing to the first service period and overall and lambing rate (84.2 vs 33.3%; 81.3 vs 0; 80 vs 0; 94 vs 23.8; 61.1 vs 0; 72.2 vs 30 and 111.1 vs 40%, respectively). Lambs suckling their dams gained more weight and grew faster (19.6 vs 14.1 kg; 13.1 ± 0.68 vs 11.3 ± 0.85 kg and 183 ± 0.6 vs 131 ± 0.6 g/d; 128.2 ± 0.7 vs 110.4 ± 0.8 g/d, (P < 0.001 and P < 0.1 for experiments 1 and 2, respectively). In conclusion, weaning depressed growth of lambs and did not improve the ability of Katahdin ewes to rebreed in the postpartum period. However, treatment with an estrous induction protocol is necessary for early rebreeding of Katahdin ewes during seasonal anestrus.