A three- year study was conducted at the Kokstad Research Station to investigate the effect of three lambing seasons, year, sex and birth status on the growth performance of Merino ewe and lambs. Data was collected over 3 years (2017-2019) using a total of 226 lambs born in autumn (AL 86), spring (SL 71), or year-round (YR 69) lambing seasons. Lambs born in spring were 1.0 kg heavier (P<0.001) than those born in AL and YR (0.6 kg) at birth (0 days). Lambs born in SL (3.4 kg) and AL (2.9 kg) were heavier (P<0.001) than those born in YR at weaning weight (90 days). Moreover, lambs born in AL (4.1 kg) and YR (3 kg) were heavier (P<0.001) than those born in SL at post-weaning (180 days). Male lambs were 0.4, 1.3 and 1.2 kg heavier (P<0.05) than female lambs at birth (0 days), 90 and 180 days, respectively. Lambs born as singles were 0.6, 1.6 and 2.3 kg heavier (P<0.001) than those born as twins at birth (0 days), 90, and 180 days. The year of lambing had a significant (P<0.001) effect on birth, weaning and post-weaning live weights. Lambs born in 2018 had a higher birth weight of 0.7 kg than 2017 and 2019, respectively. Lambs born in 2017 were 6.0, 4.0, 9.8 and 5.1 kg heavier than those born in 2019 and 2018 at 90 and 180 days respectively. Lambs born in the AL had a higher (P<0.001) weaning average daily gain (ADG) of 58.5 and 47.4 g/day than the lambs born in the SL and YR treatments. In contrast, lambs born in YR had a higher post-weaning ADG (27.9 and 66.3 g/day) than lambs born in AL and SL (P<0.001). The male and single lambs gained 5.8 and 12.8 g/day more than lambs born female and twins at 90 days. The effect of sex and birth status of lambs was not significant on post-weaning ADG (P>0.05). Lambs born in 2017 gained more pre-weaning 67.5 and 58.5 g/day and post weaning 47.5 and 30.2 g/day than those born in years 2019 and 2018.Magawana M_2021 Vol 14 (1)Magawana M_2021 Vol 14 (1)