This study evaluated the influence of biological (sex, litter size) and environmental (region, year, and month of birth) factors growth performance of Ouled Djellal lambs raised under semi-intensive systems in northeastern Algeria. Data from 2,605 lambs born between 2015 and 2021 across three wilayas (administrative divisions equivalent to provinces) Constantine, Bordj Bou Arr & eacute;ridj, and Oum El Bouaghi were analyzed using generalized linear models. Body weights were recorded at birth, 30, 60, 90, and 120 days of age, and average daily gains for the corresponding periods ( AD G(0-90) , ADG(90-120), ADG(0-120)) were calculated. Results showed that the mean BW, W90, and W120 were 4.48 plus/minus 0.16 kg, 18.79 plus/minus 0.1 kg, and 21.82 plus/minus 0.14 kg, respectively. The mean ADG0-90, ADG90-120, and ADG0-120 were 159.6 +/- 1.08, 107.2 +/- 1.64, and 144.7 pm1.18g. day(-1) , respectively. These results varied according to biological and environmental factors (P < 0.05) Males were consistently heavier and grew faster than females (P < 0.0001) , single births outperformed twins throughout the growth period (P < 0.0001) Lambs born in October and August showed the highest Body weights and W30 ( P < 0.0001 , P<0.05) respectively. Year and farm location (wilaya) also had significantly affected growth lambs, with the best performances recorded in 2019 and in Bordj Bou Arr & edot;ridj. Several key interactions among these factors highlighted the combined effect on lamb performance. These findings highlight the crucial role of non-genetic factors in determining lamb growth under semi-arid conditions. Aligning lambing periods with favourable environmental conditions and adapting management practices to regional contexts could considerably enhance productivity in Algeria's semi-intensive sheep systems.