Received: 18/02/2026 Accepted: 20/05/2026 Published: 11/06/2026 1 of 10 https://doi.org/10.52973/rcfcv-e363923 Revista Científica, FCV-LUZ / Vol. XXXVI ABSTRACT 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 Arréridj, 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 (ADG0–90, ADG90–120, ADG0–120) were calculated. Results showed that the mean BW, W90, and W120 were 4.48 ± 0.16 kg, 18.79 ± 0.10 kg, and 21.82 ± 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 ± 1.18 g·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 Arréridj. 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. Key words: Ouled Djellal lambs; growth performance; non-genetic factors; average daily gain; semi-intensive system RESUMEN Se realizó un estudio con el objeto de evaluar la influencia de factores biológicos (sexo y tamaño de camada) y ambientales (región, año y mes de nacimiento) sobre el rendimiento de crecimiento de corderos Ouled Djellal criados en sistemas semi- intensivos en el noreste de Argelia. Se analizaron datos de 2.605 corderos nacidos entre los años 2015 y 2021 en tres wilayas (divisiones administrativas equivalentes a provincias): Constantine, Bordj Bou Arréridj y Oum El Bouaghi, utilizando modelos lineales generalizados. Los pesos corporales se registraron al nacimiento y a los 30, 60, 90 y 120 días de edad , y se calcularon las ganancias medias diarias para los periodos correspondientes (GMD0–90, GMD90–120 y GMD0–120). Los resultados mostraron que los pesos medios al nacimiento, entre los 90 y 120 días fueron de 4,48 ± 0,16 kg, 18,79 ± 0,10 kg y 21,82 ± 0,14 kg, respectivamente. Las ganancias medias diarias GMD0–90, GMD90–120 y GMD0–120 fueron de 159,6 ± 1,08; 107,2 ± 1,64 y 144,7 ± 1,18 g·día -1 , respectivamente. Estos resultados variaron según los factores biológicos y ambientales ( P<0,05). Los machos fueron consistentemente más pesados y presentaron mayores tasas de crecimiento que las hembras (P<0,0001), mientras que, los corderos únicos superaron a los gemelos durante todo el periodo de crecimiento (P<0,0001). Los corderos nacidos en octubre y agosto presentaron los mayores pesos al nacimiento y a los 30 días (P<0,0001 y P<0,05, respectivamente). También se observaron efectos significativos del año y de la región, registrándose los mejores rendimientos en Bordj Bou Arréridj y en 2019. Además, varias interacciones significativas entre estos factores evidenciaron su influencia combinada sobre el rendimiento de los corderos. Estos resultados demuestran que los factores no genéticos desempeñan un papel importante en el crecimiento de los corderos bajo condiciones semiáridas. Ajustar los periodos de parición a condiciones ambientales favorables y adaptar las prácticas de manejo al contexto regional podría mejorar considerablemente la productividad de los sistemas ovinos semi-intensivos en Argelia. Palabras clave: Corderos Ouled Djellal; rendimiento de crecimiento; factores no genéticos; ganancia media diaria; sistema semi-intensivo Influence of biological and environmental factors on growth of Ouled Djellal lambs (Ovis aries) in Northeastern Algeria Influencia de factores biológicos y ambientales en el crecimiento de corderos Ouled Djellal (Ovis aries) en el noreste de Argelia Sihem Belmili 1 * , Saïd Boukhechem 3 , Hithem Bougherara 3 , Abderrahmène Bensegueni 2 , Nassim Moula 1,4 , Mohamed Ezzine Zebiri 5 , Safia Tennah 1 1 Higher National Veterinary School, Research Laboratory Management of Local Animal Resources (GRAL). Algiers, Algeria. 2 University of Constantine 1 Frères Mentouri, Institute of Veterinary Sciences, Constantine, Algeria. 3 University of Constantine 1 Frères Mentouri, Gestion de la Santé et Productions Animales Laboratory, Institute of Veterinary Sciences. Constantine, Algeria. 4 University of Liege, Faculty of Veterinary Medicine, Fundamental and Applied Research for Animals & Health (FARAH). Liege, Belgium. 5 Directorate of Agricultural Services. Bordj Bou Arreridj, Algeria. *Corresponding author: sihem.belmili@umc.edu.dz

Growth performance of Ouled Djellal lambs in Algeria / Belmili et al._____________________________________________________________ 2 of 10 INTRODUCTION Sheep (Ovis aries) production is a key component of Algeria’s agricultural economy, contributing significantly to meat supply and supporting rural livelihoods across the country’s diverse agroecological zones. According to the Ministry of Agriculture most recent official data (2019) [1], the national flock was estimated at around 29 million head, with the Ouled Djellal breed accounting for nearly 60% of the total. This breed is known for its adaptability, hardiness, and high meat potential, forms the basis of red meat production in Algeria. The extensive distribution, particularly in plateaus and semi-arid regions, demonstrates its remarkable capacity to thrive in arid climates [2]. Birth weight, weaning weight, and average daily gain (ADG) are key indicators used to evaluate productivity and management efficiency in sheep production systems. These quantitative traits are influenced by several non-genetic factors, including biological characteristics such as sex and litter size, environmental conditions related to region and time of birth (season and year), as well as maternal characteristics like ewe age, parity, body condition, and live weight. The independent or combined effects of these factors may mask the expression of genetic potential and complicate selection programs [3, 4, 5, 6]. Previous Algerian studies have evaluated the effects of these factors in Ouled Djellal and other local breeds [2, 7, 8, 9, 10]. Comparable effects of these factors have been reported in Morocco [11], Tunisia [12], Sudan [13], Ethiopia [3], Benin, [4], Pakistan [14], and Mexico [15]. In Algeria, most studies used limited datasets and few explanatory variables, which limits the analysis of interaction effects among factors [2, 7, 8, 9, 10]. To optimize management and increase productivity in semi-arid production systems, it’s crucial to understand the interaction between biological and environmental factors that affect lamb growth. Therefore, this study aimed to evaluate the effects of sex, litter size, region, year, and month of birth on the growth performance of Ouled Djellal lambs raised under semi-intensive systems in northeastern Algeria, as well as to identify significant interactions among these factors. MATERIALS AND METHODS Study area and period The study took place between 2015 and 2021 in three wilayas in northeastern Algeria: Constantine, Bordj Bou Arréridj, and Oum El Bouaghi, which are elevated at a height of 694, 928 and 902 meters above sea level respectively. These regions are characterized by a semi-arid climate with cold winters, hot summers, and an average annual temperature of approximately 15°C. Annual rainfall ranges between 300 and 500 mm, with most precipitation occurring between November and March. The soils are mainly clay-limestone, which supports cereal-pasture systems that are used for both grazing and fodder production [16]. Animals and management practices The study involved 2,605 Ouled Djellal lambs, born between August and December. The animals were raised under semi-intensive systems that are typical of Algerian pilot farms. The feeding system relied primarily on grazing natural and cultivated pastures, with occasional summer supplementation consisting of cereal stubble, oat hay, straw, wheat bran, and commercial concentrates. When there was a lack of food or bad weather, the animals were housed and given stored forages and formulated rations. Mating takes place mostly mainly in autumn, but year- round reproduction is feasible in Algeria, just as in many other Mediterranean countries. To synchronize lambing with optimal forage availability, spring mating (August to January, peaking between September and December) was usually selected. After birth, lambs suckled exclusively for about two months before being gradually introduced to solid foods like wheat bran and straw. Weaning occurred at about 90 days (d) of age. Data collection and growth traits Data were collected from birth to 120 d of age. Body weights were measured at birth (BW), 30, 60, 90, and 120 d of age (W30, W60, W90, W120). ADG were calculated for the following intervals: from birth to 90 d (ADG0–90), from 90 to 120 d (ADG90–120), and from birth to 120 d (ADG0–120). Statistical analysis Statistical analyses were performed using IBM SPSS Statistics (version 25.0). Descriptive statistics were generated for all traits, and general linear models (GLM) were applied to evaluate the influence of non-genetic factors on lamb growth performance. The model included the most important biological and environmental effects that are relevant to semi-intensive systems and their interactions, as shown below: Wijklmn = μ + Si + Lj + Yk + Ml + Pm + (S × L)ij + (S × Y)ik + (S × M)il + (M × Y)lk + (M × L)lj + (M × L × Y)ljk + (M × S × Y)lik + (L × S × Y)jik + eijklmn Where: wijklmn = birth weight (BW), body weights (W), or average daily gain (ADG) of the nth lamb of sex i, of litter size j, in year k, of birth month l, in farm location m; µ = general average; Si = fixed effect of the sex i (2 classes female and male); Lj = fixed effect of the litter size j (2 classes: single and twin); Yk = fixed effect of the year k (7 years: from 2015 to 2021); Ml = fixed effect of the birth month I (3 months: august, September and October); Pm = fixed effect of the farm location m (3 locations: Constantine, Oum El Bouaghi, Bordj Bou Arréridj): eijklmn = residual random effect.

_______________________________________________________________________________________________Revista Cientifica, FCV-LUZ / Vol. XXXVI 3 of 10 The two-way interactions between the factors were studied, and only those which were significant have been kept in the final model. For the three traits, the data distribution in the different classes of fixed effects is given in Table I. The portion of the variation due to the model is provided through the coefficient of determination (R²). RESULTS AND DISCUSSION Growth performance Mean birth weight (BW) was 4.48 ± 0.16 kg, increasing steadily to 21.82 ± 0.14 kg at 120 d (W120). The most rapid growth occurred during the early period of life, when lambs more than doubled their birth weight by 30 d. The highest ADG was recorded during the pre-weaning period (ADG0–90 = 159.6 ± 1.08 g·d -1 ), followed by a marked decline during the post-weaning period 107.2 ± 1.64 g·d -1 (ADG90–120). (FIGS. 1 and 2). This decrease reflects the typical slowdown in growth associated with weaning stress and the transition from milk to solid feed. Overall, the growth performance observed in the present study exceeded that reported in most previous Algerian studies. Djellal et al. [2] reported higher birth weights (5.30 kg) in a sample of 30 lambs, while Mohammedi et al. [17] observed lower birth weights (3.3 – 3.9 kg) but comparable weights at 120 d weights (21.95 kg). Nevertheless, both studies reported comparable estimated pre-weaning gains (163.56 g·d -1 , 153.3 g·d -1 , respectively). Zidane et al. [10] and Bendiab & Dekhili. [8] recorded lower mean birth weights (3.04 – 3.8 kg), and 90–d weights (14.5 – 16.3 kg). In contrast, Boubekeur et al. [9] and Baa et al. [7] recorded higher performance in Rambi and D’man lambs (25 kg at 100 d, 211 g·d -1 ; 23.8 kg at 120 d; 176 g·d -1 ), while Yerou et al. [18] reported lower gains (132 – 141 g·d -1 ) in Hamra lambs. Such variability among studies may be explained by differences in feeding practices, ewe nutrition, genetic potential, and environmental conditions. The present study, which is based on a large dataset of 2,605 lambs, provides robust and representative estimates of Ouled Djellal growth performance under semi- intensive production systems in Algeria. Main effects of biological and environmental factors Effect of sex Males and females accounted for 49.25% and 50.75% of the lamb population, respectively. Sex had a highly significant effect on all growth traits (P<0.0001). Males were consistently heavier, ranging from 4.57 ± 0.02 kg vs. 4.39 ± 0.02 kg at birth (a 4.1% difference) to 23.06 ± 0.22 kg vs. 20.47 ± 0.18 kg at 120 d (a 12.7% difference) (TABLE I). They also grew faster, with ADG advantages of 11.6% (0–90 d), 17.2% (90–120 d), and 14.8% (0–120 d) (TABLE II). These findings are consistent with previous Algerian studies [9, 10, 19], which attributed male superiority to testosterone activity, better feed conversion, faster muscle development, and stronger suckling behaviour. However, Djellal et al. [2] and Baa et al. [7] reported no significant pre-weaning differences between the sexes. Consistent with the present results, several other studies have also observed a male advantage in lamb growth. These include studies conducted in Tunisia [20], on D’man lambs; in Morocco on Timahdite , Sardi, Boujaâd, Béni Guil and breeds [11, 21, 22, 23], in Pakistan on Kajli [14], in Benin on Djallonké [4], in India on Avikalin and Sonadi [13, 24], in Ethiopia on Washera [3], in Rajasthan on Bharat Merino sheep [6], in Zimbabwe on Sabi, Dorper and Merino sheep [25], on Icelandic sheep breed [5], and on West African Dwarf sheep [26]. Some authors have suggested that the effect of sex diminishes with age under uniform feeding conditions, whereas others have confirmed a persistent male advantage, depending on breed, management and environmental factors [27, 28, 29]. Overall, sex remains a key determinant of growth performance and should be considered in breeding strategies. Effect of litter size Regarding birth type, 64.6% of lambs were single-born while 35.4% were twins. Litter size had a highly significant effect on growth performance (P<0.0001): singletons were consistently heavier, FIGURE 1. Body weight growth curve of Ouled Djellal lambs from birth to 120 days FIGURE 2. Average daily gain during the pre-weaning, post-weaning, and overall growth periods in Ouled Djellal lambs

Growth performance of Ouled Djellal lambs in Algeria / Belmili et al._____________________________________________________________ 4 of 10 TABLE I Body weights of Ouled Djellal lambs from birth to 120 days: Effects of biological and environmental factors Trait BW W30 W60 W90 W120 N LSM ± SE N LSM ± SE N LSM ± SE N LSM ± SE N LSM ± SE Overall 2605 4.48 ± 0.16 2551 9.80 ± 0.50 2382 14.39 ± 0.77 2240 18.79 ± 0.10 1802 21.82 ± 0.14 Sex Male 1283 4.57 ± 0.02ᵇ 1258 10.17 ± 0.73ᵇ 1206 14.91 ± 0.11ᵇ 1146 19.67 ± 0.15ᵇ 940 23.06 ± 0.22ᵇ Female 1322 4.39 ± 0.02ᵃ 1293 9.44 ± 0.66ᵃ 1176 13.85 ± 0.10ᵃ 1103 17.88 ± 0.13ᵃ 862 20.47 ± 0.18ᵃ P value P<0.0001 P<0.0001 P<0.0001 P<0.0001 P<0.0001 Litter size Singleton 1684 4.67 ± 0.02 b 1643 10.31 ± 0.06 b 1507 15.12 ± 0.10 b 1402 19.70 ± 0.13 b 1112 22.81 ± 0.19 b Twin 921 4.12 ± 0.02 a 908 8.88 ± 0.08 a 875 13.12 ± 0.11 a 847 17.28 ± 0.15 a 690 20.22 ± 0.21 a P value P<0.0001 P<0.0001 P<0.0001 P<0.0001 P<0.0001 Birth month August 468 4.34 ± 0.04 a 466 10.04 ± 0.12 b 463 14.29 ± 0.17 a 450 18.63 ± 0.22 a 426 21.92 ± 0.27 a September 1537 4.43 ± 0.02 a 1530 9.69 ± 0.61 a 1449 14.46 ± 0.10 a 1390 18.84 ± 0.14 a 1112 21.87 ± 0.20 a October 467 4.64 ± 0.04 b 444 9.83 ± 0.12 ab 418 14.20 ± 0.16 a 392 18.66 ± 0.22 a 251 21.17 ± 0.31 a P value P<0.0001 P<0.05 P>0.05 P>0.05 P>0.05 Year of birth 2017 342 4.38 ± 0.05 a 328 8.49 ± 0.98 a 328 11.78 ± 0.59 a 328 16.92 ± 0.24 a 328 18.76 ± 0.32 a 2018 406 4.38 ± 0.04 a 386 9.90 ± 0.11 b 343 15.41 ± 0.17 c 266 19.28 ± 0.25 b – – 2019 437 4.62 ± 0.04 b 427 11.20 ± 0.11 c 359 17.84 ± 0.18 d 344 23.79 ± 0.27 c 312 28.88 ± 0.32 c 2020 615 4.29 ± 0.03 a 605 9.68 ± 0.11 b 582 13.60 ± 0.20 b 568 17.53 ± 0.18 a 559 20.46 ± 0.20 b P value P<0.0001 P<0.0001 P<0.0001 P<0.0001 P<0.0001 Region Oum El Bouaghi 251 4.67 ± 0.03 b 251 9.84 ± 0.14 a 251 14.39 ± 0.21 ab 251 17.09 ± 0.25 a 251 19.07 ± 0.29 a Constantine 554 4.62 ± 0.04 b 554 9.52 ± 0.12 a 519 13.85 ± 0.14 a 492 18.60 ± 0.19 b 352 22.51 ± 0.29 b Bordj Bou Arréridj 1800 4.40 ± 0.02 a 1746 9.88 ± 0.59 a 1612 14.56 ± 0.99 b 1506 19.14 ± 0.13 b 1199 22.19 ± 0.19 b P value P<0.0001 P<0.05 P<0.01 P<0.0001 P<0.0001 Body weights (BW, W30, W60, W90, W120) are in kilograms (kg). Values are presented as Least Squares Mean ± Standard Error (LSM ± SE). Sample size (N) decreased over time due to mortality or loss of ear tags, resulting in missing data. Different lowercase letters ( a, b, c, d ) within a row indicate significant differences between group means (Tukey’s HSD, P<0.05). W120 data for 2018 cohort (n = 406) are unavailable due to incomplete data collection TABLE II Average daily gain in pre-weaning, post-weaning and overall period: Effects of biological and environmental factors Trait ADG0–90 ADG90–120 ADG0–120 N LSM ± SE N LSM ± SE N LSM ± SE Overall 2248 159.6 ± 1.08 1796 107.2 ± 1.64 1802 144.7 ± 1.18 Sex Male 1283 168.2 ± 1.61 b 936 115.3 ± 2.39 b 940 154.2 ± 1.76 b Female 1322 150.7 ± 1.40 a 860 98.4 ± 2.19 a 862 134.3 ± 1.48 a P value P<0.0001 P<0.0001 P<0.0001 Litter size Single 1684 167.5 ± 1.40 b 1107 109.5 ± 2.09 a 1112 151.1 ± 1.56 b Twin 921 146.5 ± 1.60 a 689 103.7 ± 2.63 a 690 134.3 ± 1.71 a P value P<0.0001 P>0.05 P<0.0001 Birth month August 468 159.1 ± 2.29 a 425 111.7 ± 3.13 a 426 146.6 ± 2.10 b September 1537 160.0 ± 1.44 a 1109 106.1 ± 2.24 a 1112 145.0 ± 1.63 ab October 467 157.4 ± 2.29 a 249 103.7 ± 3.32 a 251 138.0 ± 2.45 a P value P>0.05 P>0.05 P>0.05 Year of birth 2017 342 139.1 ± 2.58 a 328 61.4 ± 2.58 a 328 119.8 ± 2.58 a 2018 406 166.5 ± 2.50 b – – 2019 437 213.5 ± 2.83 c 310 176.3 ± 2.45 c 312 202.9 ± 2.50 c 2020 615 147.0 ± 1.82 a 555 95.74 ± 1.82 b 559 134.7 ± 1.56 b P value P<0.0001 P<0.0001 P<0.0001 Region Oum El Bouaghi 251 137.9 ± 2.58 a 251 66.2 ± 3.37 a 251 120.0 ± 2.30 a Constantine 491 157.4 ± 2.02 b 352 136.6 ± 4.65 c 352 149.8 ± 2.29 b Bordj Bou Arréridj 1506 163.9 ± 1.39 b 1193 107.2 ± 1.79 b 1199 148.3 ± 1.53 b P value P<0.0001 P<0.0001 P<0.0001 Average daily gain (ADG) is in gram per day (g·d -1 ). Values are presented as Least Squares Mean ± Standard Error (LSM ± SE). Sample size (N) decreased over time due to mortality or loss of ear tags, resulting in missing data. Different lowercase letters ( a, b, c ) within a row indicate significant differences between group means (Tukey’s HSD, p < 0.05). ADG₀₋₁₂₀ and ADG₉₀₋₁₂₀ could not be calculated for 2018 due to missing W120 measurements. ADG₀₋₉₀ values for 2018 are included

_______________________________________________________________________________________________Revista Cientifica, FCV-LUZ / Vol. XXXVI 5 of 10 weighing approximately 12%, weighing more (4.67 ± 0.02 kg vs. 4.12 ± 0.02 kg at birth and 22.81 ± 0.19 kg vs. 20.22 ± 0.21 kg at 120 d (TABLE I). Litter size also influenced ADG (P<0.0001), except during the post-weaning period (TABLE II). This suggests that twin lambs exhibit partial compensatory growth during the post-weaning period. These results confirm the growth penalties associated with twinning especially during pre-weaning period, consistent with findings in Algeria for Ouled Djellal [7, 10] and D’man breeds [8, 9]. Similar patterns have been reported in other regions and breeds, including Timahdite, Béni Guil and Sardi in Morocco [11, 21, 23], Tunisian breeds [20], Kajli in Pakistan [14], Washera and Adilo breeds in Ethiopia [3, 30], Dwarf sheep in West Africa [26], Balouchi in Iran [28], Djallonke in Benin [4], Icelandic sheep breed [5] and the Sabi, Dorper and Merino sheep in Zimbabwe [25, 27]. The recurring growth disadvantage observed in twins likely reflects intrauterine competition for nutrients and reduced milk intake during the early stages of life. These constraints suggest that management practices such as improved maternal nutrition during late gestation, early weaning, and cross-fostering may help mitigate growth limitations and enhance overall flock productivity. Effect of birth month Birth month had a significant effect on BW (P<0.0001) and W30 (P<0.05) (TABLE I). Lambs born in October were the heaviest at birth (4.64 ± 0.04 kg), while those born in August were the heaviest at 30 d (10.04 ± 0.12 kg). This may be attributed to better maternal milk production and pasture availability during these months. No significant differences were observed in later weights or in ADG (TABLE II), suggesting that lambs born later in the season experienced partial compensatory growth due to adaptation to the management practices in the study region, where the animals are kept under permanent housing protected from both cold and summer heat [9]. Although the present analysis focused on birth month rather than season, the patterns align with previous studies on seasonal effects on lamb growth. In Algeria, Bendiab and Dekhili [8] and Boubakeur et al. [9] noted faster growth in autumn-born lambs, while Zidane et al. and Deghnouche et al. [10, 19] observed higher performance in spring-born lambs. Similar results in other regions, where lambs born during periods of abundant forage grew faster [3, 4, 15, 29, 30]. These differences reflect climatic variations, forage availability, and management practices that influence both prenatal and postnatal growth. Effect of year of birth The year of birth had a significant effect on all growth traits (P<0.0001) (TABLES I and II). This analysis included only records from Bordj Bou Arréridj, the only site with complete annual data, and therefore reflects conditions specific to that region. Lambs born in 2019 showed the best performance, whereas those born in 2017 performed the poorest. At 120 d, lambs from 2019 were 47% heavier than those from 2017 (22.2 kg vs. 12.1 kg). A similar pattern was observed for growth rates: ADG0–90 was about 50% higher in 2019 than in 2017 (176.3 vs. 117.2 g·d -1 ), while ADG90–120 in 2019 (176.3 g·d -1 ) was nearly three times that recorded in 2017 (61.4 g·d -1 ). Favourable rainfall in 2019 likely improved ewe nutrition, body condition, and milk production. In contrast, 2017 and 2020 were characterized by drought and forage scarcity. Overall, these differences highlight the strong influence of annual climatic variation, pasture availability, and feeding conditions. Similar year effects have been reported in Morocco [21, 23], Mexico [15], India [13, 24], Benin [4], Ethiopian [3], Zimbabwe [25], Iran [28], and Pakistan [14]. In these studies, annual variations in growth were mainly attributed to differences in forage availability and climatic conditions. Effect of farm location (Wilaya) Farm location had a significant effect on all growth traits (TABLES I and II). Lambs born in Oum El Bouaghi (4.67 ± 0.03 kg) and Constantine (4.62 ± 0.04 kg) were the heaviest at birth, which may reflect better maternal nutrition. After 60 d, lambs from Bordj Bou Arréridj consistently outperformed those from the other locations, reaching 19.14 ± 0.13 kg at 90 d and 22.19 ± 0.19 kg at 120 d, suggesting more favourable feeding management practices in that region. Constantine showed higher ADG (136.6 ± 4.65 g·d -1 ), followed by Bordj Bou Arréridj. The performance differences between regions may be directly linked to management and feeding practices rather than geography, given that all regions share a similar semi-arid climate. These results suggest that nutrition and health management should be adjusted to regional conditions. Comparable findings have been reported in Algerian flocks [17] and Ethiopian Washera and Adilo lambs [3, 30]. Effects of factor interactions As biological and environmental factors tend to act together rather than separately, the combined effects of these factors were examined in more detail using interaction analyses. Only significant interactions are presented. Interaction between Sex and litter size The interaction between sex and litter size had a significant effect on all growth traits (P<0.0001) (TABLES III and IV). Male singletons were the heaviest at birth (4.46 ± 0.04 kg) and at 120 d (23.76 ± 0.27 kg) and they also exhibited the highest growth rates (173.5 g·d -1 from 0 to 90 d and 116.8 g·d -1 from 90 to 120 d). In contrast, female twins recorded the lowest values. Overall, singletons outperformed twins and males outperformed females, confirming the combined effect of both factors on early growth. These results reflect well-known biological mechanisms. Singletons experience less intrauterine competition and greater postnatal milk intake, enhancing nutrient availability and early growth. Meanwhile, males exhibited higher growth potential due to androgen-driven muscle development, greater growth hormone activity, and improved feed efficiency. Comparable findings have been reported in Sardi [21], Icelandic sheep [5], and Washera sheep [3], and Sabi, Dorper and Merino sheep [25]. These results suggest that the observed interaction

Growth performance of Ouled Djellal lambs in Algeria / Belmili et al._____________________________________________________________ 6 of 10 TABLE III Effect of biological and environmental factor interactions on lambs weights from birth to 120 days interaction BW W30 W60 W90 W120 N LSM±SE N LSM±SE N LSM±SE N LSM±SE N LSM±SE Sex * Litter size Male singleton 890 4.46 ± 0.04 c 872 10.48 ± 0.09 d 831 15.41 ± 0.14 d 779 20.29 ± 0.19 c 641 23.76 ± 0.27 c Male twin 393 3.92 ± 0.06 b 386 9.47 ± 0.13 b 375 13.81 ± 0.18 b 367 18.37 ± 0.25 b 299 21.54 ± 0.37 b Female singleton 794 4.42 ± 0.04 c 771 10.11 ± 0.08 c 676 14.77 ± 0.14 c 623 18.97 ± 0.18 b 471 21.51 ± 0.27 b Female twin 528 3.51 ± 0.05 a 522 8.43 ± 0.09 a 500 12.6 ± 0.13 a 480 16.45 ± 0.18 a 391 19.21 ± 0.24 a P value P<0.0001 P<0.0001 P<0.0001 P<0.0001 P<0.0001 Sex * Year of birth Male 2017 207 4.23 ± 0.08 bcd 203 8.97 ± 0.13 b 203 12.61 ± 0.22 b 203 18.1 ± 0.32 c 203 20.29 ± 0.42 bc Male 2018 193 4.34 ± 0.09 cd 185 10.31 ± 0.16 c 162 15.93 ± 0.27 d 124 19.92 ± 0.38 d – Male 2019 209 4.57 ± 0.08 d 204 11.51 ± 0.16 d 198 18.44 ± 0.27 f 191 24.86 ± 0.38 f 180 30.28 ± 0.43 e Male 2020 274 3.99 ± 0.08 abc 266 10.58 ± 0.18 c 256 14.36 ± 0.21 c 252 18.7 ± 0.29 cd 250 21.70 ± 0.34 c Female 2017 135 3.88 ± 0.11 ab 125 7.71 ± 0.13 a 125 10.43 ± 0.22 a 125 15 ± 0.32 a 125 16.27 ± 0.42 a Female 2018 213 3.79 ± 0.09 a 201 9.53 ± 0.14 b 181 14.95 ± 0.24 cd 142 18.71 ± 0.32 cd – Female 2019 228 4.23 ± 0.08 bcd 223 10.93 ± 0.15 cd 161 17.1 ± 0.29 e 153 22.44 ± 0.36 e 132 26.98 ± 0.42 d Female 2020 341 3.85 ± 0.07 a 339 8.97 ± 0.11 b 326 13 ± 0.16 b 316 16.6 ± 0.21 b 309 19.47 ± 0.23 b P value P<0.0001 P<0.0001 P<0.0001 P<0.0001 P<0.0001 Sex * Birth month Male August 204 4.07 ± 0.09 ab 204 10.93 ± 0.22 d 204 14.80 ± 0.26 bc 204 19.59 ± 0.35 b 196 23.34 ± 0.43 c Male September 776 4.28 ± 0.04 bc 772 9.96 ± 0.09 bc 763 14.98 ± 0.15 c 728 19.76 ± 0.20 b 603 23.15 ± 0.29 c Male October 303 4.47 ± 0.07 c 282 10.2 ± 0.17 c 239 14.81 ± 0.23 bc 214 19.46 ± 0.31 b 141 22.27 ± 0.46 bc Female August 273 3.92 ± 0.07 a 271 9.39 ± 0.13 a 268 13.99 ± 0.22 ab 255 18.01 ± 0.28 a 238 20.90 ± 0.33 ab Female September 761 4.01 ± 0.04 a 758 9.41 ± 0.09 ab 686 13.87 ± 0.14 a 662 17.82 ± 0.17 a 509 20.35 ± 0.26 a Female October 288 4.33 ± 0.08 bc 264 9.56 ± 0.17 ab 222 13.61 ± 0.21 a 186 17.88 ± 0.29 a 115 20.10 ± 0.37 a P value P<0.0001 P<0.0001 P<0.0001 P<0.0001 P<0.0001 Birth month * Year of birth August 2018 19 4.23 ± 0.28 ab 19 11.06 ± 0.58 c 19 17.60 ± 1.01 ef 19 21.99 ± 1.10 c – – August 2019 31 4.14 ± 0.22 ab 31 10.87 ± 0.43 c 31 17.43 ± 0.85 de 28 24.40 ± 0.91 cd 27 29.58 ± 1.01 d August 2020 344 3.86 ± 0.07 a 342 10.06 ± 0.16 bc 339 13.93 ± 0.19 bc 329 18.04 ± 0.26 a 324 20.97 ± 0.29 b September 2017 297 4.07 ± 0.07 ab 297 8.33 ± 0.10 a 297 11.48 ± 0.18 a 297 16.48 ± 0.25 a 297 18.18 ± 0.33 a September 2018 302 3.91 ± 0.07 a 302 9.73 ± 0.11 bc 299 15.33 ± 0.19 cd 247 19.07 ± 0.25 ab – – September 2019 376 4.39 ± 0.06 ab 370 11.12 ± 0.12 c 303 17.72 ± 0.21 ef 300 23.63 ± 0.30 cd 283 28.84 ± 0.34 d September 2020 160 3.79 ± 0.10 a 159 9.25 ± 0.17 ab 148 13.06 ± 0.23 ab 144 16.57 ± 0.29 a 144 19.50 ± 0.34 ab October 2017 41 4.26 ± 0.18 ab 27 10.24 ± 0.24 bc 27 15.10 ± 0.37 bc 27 21.81 ± 0.51 bc 27 25.22 ± 0.66 c October 2018 85 4.50 ± 0.13 ab 65 10.38 ± 0.29 bc 25 14.76 ± 0.82 bc – – – – October 2019 30 4.74 ± 0.24 b 26 12.82 ± 0.48 d 25 19.78 ± 0.67 f 16 25.62 ± 1.05 d – – October 2020 111 4.24 ± 0.11 ab 104 9.06 ± 0.20 ab 95 13.25 ± 0.30 abc 95 17.22 ± 0.38 a 91 20.18 ± 0.38 ab P value P<0.0001 P<0.0001 P<0.0001 P<0.0001 P<0.0001 Birth month * Litter size Singleton August 237 4.46 ± 0.08 cd 237 10.93 ± 0.18 d 235 15.39 ± 0.25 b 229 20.21 ± 0.32 b 214 23.49 ± 0.38 c Singleton September 1057 4.34 ± 0.04 c 1053 10.07 ± 0.07 c 991 15.07 ± 0.12 b 940 19.59 ± 0.17 b 745 22.74 ± 0.25 c Singleton October 390 4.69 ± 0.06 d 353 10.61 ± 0.14 cd 281 15.10 ± 0.21 b 233 19.68 ± 0.29 b 153 22.18 ± 0.41 bc Twin August 240 3.52 ± 0.07 a 238 9.19 ± 0.14 b 237 13.3 ± 0.20 a 230 17.23 ± 0.29 a 220 20.55 ± 0.36 ab Twin September 480 3.71 ± 0.05 ab 477 8.84 ± 0.11 ab 458 13.12 ± 0.16 a 450 17.27 ± 0.22 a 367 20.09 ± 0.32 a Twin October 201 3.85 ± 0.09 b 193 8.58 ± 0.18 a 180 12.87 ± 0.22 a 167 17.39 ± 0.3 a 103 19.97 ± 0.43 a P value P<0.0001 P<0.0001 P<0.0001 P<0.0001 P<0.0001 Birth month * Litter size * Year P value P>0.05 P>0.05 P>0.05 P>0.05 P>0.05 Birth Month * Sex * Year P value P>0.05 P<0.001 P<0.01 P<0.01 P<0.05 Litter size * Sex * Year P value P>0.05 P>0.05 P>0.05 P>0.05 P>0.05 Body weights (BW, W30, W60, W90, W120) are in kilograms (kg). Values are presented as Least Squares Mean ± Standard Error (LSM ± SE). Sample size (N) decreased over time due to mortality or loss of ear tags, resulting in missing data. Different lowercase letters ( a, b, c, d, e, f ) within a row indicate significant differences between group means (Tukey’s HSD, P<0.05). W120 data for 2018 cohort (n = 406) are unavailable due to incomplete data collection

_______________________________________________________________________________________________Revista Cientifica, FCV-LUZ / Vol. XXXVI 7 of 10 TABLE IV Effect of biological and environmental factor interactions on average daily gains in pre-weaning, post-weaning and overall period Interaction ADG0–90 ADG90–120 ADG0–120 N LSM ± SE N LSM ± SE N LSM ± SE Sex * Litter size Male singleton 779 173.5 ± 1.99 c 637 116.8 ± 2.82 b 641 158.9 ± 2.16 c Male twin 367 157.0 ± 2.67 b 299 112.2 ± 4.45 b 299 144.1 ± 2.97 b Female singleton 623 160.2 ± 1.91 b 470 99.5 ± 3.06 a 471 140.5 ± 2.15 b Female twin 479 138.5 ± 1.87 a 390 97.2 ± 3.11 a 391 126.8 ± 1.92 a P value P<0.0001 P<0.0001 P<0.0001 Sex * Year of birth Male 2017 203 150.8 ± 3.34 bc 203 73.1 ± 3.34 b 203 131.4 ± 3.34 b Male 2018 124 171.9 ± 3.80 d – – Male 2019 191 224.0 ± 4.01 f 179 183.7 ± 3.35 e 180 213.5 ± 3.41 e Male 2020 252 158.8 ± 2.97 cd 247 100.3 ± 3.41 c 250 144.1 ± 2.65 c Female 2017 125 120.2 ± 3.43 a 125 42.4 ± 3.43 a 125 100.7 ± 3.43 a Female 2018 142 161.8 ± 3.29 cd – – Female 2019 153 200.4 ± 3.67 e 131 166.3 ± 3.38 d 132 188.3 ± 3.24 d Female 2020 316 137.7 ± 2.13 b 308 92.5 ± 1.80 c 309 127.1 ± 1.72 b P value P<0.0001 P<0.0001 P<0.0001 Sex * Birth month Male August 204 168.4 ± 3.59 b 196 129.9 ± 4.91 b 196 157.6 ± 3.37 c Male September 728 168.9 ± 2.13 b 601 113.3 ± 3.11 ab 603 154.8 ± 2.37 c Male October 214 165.6 ± 3.24 b 139 103.6 ± 5.27 a 141 146.7 ± 3.64 bc Female August 254 153.1 ± 2.92 a 237 97.3 ± 3.74 a 238 138.7 ± 2.56 ab Female September 662 150.1 ± 1.82 a 508 97.4 ± 3.17 a 509 133.3 ± 2.08 ab Female October 186 149.2 ± 3.12 a 115 105.2 ± 3.52 a 115 129.6 ± 3.00 a P value P<0.0001 P<0.0001 P<0.0001 Birth month * Year of birth August 2018 19 194.2 ±10.8 cde – – – – August 2019 28 222.3 ± 9.31 ef 27 175.2 ± 10.61 c 27 210.1 ± 7.81 d August 2020 329 153.0 ± 2.61 ab 323 94.0 ± 2.65 b 324 139.1 ± 2.26 b September 2017 297 134.4 ± 2.64 a 297 56.7 ± 2.64 a 297 115.0 ± 2.64 a September 2018 247 164.4 ± 2.52 bc – – – – September 2019 300 211.7 ± 3.07 def 281 176.9 ± 2.49 c 283 202.2 ± 2.65 d September 2020 144 137.2 ± 2.85 ab 143 98.6 ± 2.68 b 144 127.3 ± 2.53 ab October 2017 27 191.5 ± 5.11 cd 27 113.7 ± 5.11 b 27 172.0 ± 5.11 c October 2019 16 230.9 ± 10.43 f – – – – October 2020 95 141.3 ± 4.00 ab 89 97.3 ± 4.28 b 91 130.5 ± 3.06 ab P value P<0.0001 P<0.0001 P<0.0001 Birth month * Litter size Singleton August 229 172.7 ± 3.28 b 214 116.6 ± 4.54 a 214 156.9 ± 3.01 c Singleton September 940 166.6 ± 1.78 b 742 108.0 ± 2.69 a 745 150.9 ± 2.05 bc Singleton October 233 166.0 ± 3.05 b 151 106.2 ± 4.47 a 153 144.3 ± 3.34 abc Twin August 229 147.2 ± 3.01 a 219 107.6 ± 4.27 a 220 137.8 ± 2.85 ab Twin September 450 146.0 ± 2.28 a 367 101.9 ± 4.01 a 367 133.0 ± 2.55 a Twin October 167 146.8 ± 3.29 a 103 101.6 ± 4.79 a 103 131.2 ± 3.49 a P value P<0.0001 P>0.05 P<0.0001 Birth month * Litter size * Year P value P>0.05 P<0.05 P>0.05 Birth Month * Sex * Year P value P<0.01 P>0.05 P<0.05 Litter size * Sex * Year P value P>0.05 P<0.05 P>0.05 Average daily gain (ADG) is in gram per day (g·d -1 ). Values are presented as Least Squares Mean ± Standard Error (LSM ± SE). Sample size (N) decreased over time due to mortality or loss of ear tags, resulting in missing data. Different lowercase letters ( a, b, c, d, e, f ) within a row indicate significant differences between group means (Tukey’s HSD, P<0.05). ADG₀₋₁₂₀ and ADG₉₀₋₁₂₀ could not be calculated for 2018 due to missing W120 measurements. ADG₀₋₉₀ values for 2018 are included

Growth performance of Ouled Djellal lambs in Algeria / Belmili et al._____________________________________________________________ 8 of 10 largely reflects the additive effects of reduced foetal competition and the inherent growth advantage of males. Interaction between sex and birth month The interaction between sex and birth month significantly affected all growth traits (P<0.0001; TABLES III and IV). Males born in October had the highest birth weights, while females born in August had the lowest. At 60 and 120 d, males born in August and September reached the greatest body weights, while females born in September and October showed the lowest. Overall, males exhibited higher ADG than females across all months, with the largest sex differences observed in August and September. Male lambs born in August demonstrated the best performance (129.94 ± 4.91 g·d -1 from 90 to120 d; 157.59 ± 3.37 g·d -1 overall), whereas female lambs born in September and October recorded the lowest gains (133.3 ± 2.08 g·d -1 and 138.7 ± 2.56 g·d -1 , respectively). These results suggest that environmental and nutritional stress during late summer and early autumn lambing amplifies sex differences, with males growing faster and adapting better than females. Zidane et al. [10] reported similar results which highlights the role of environmental conditions in modulating sexual dimorphism in lamb growth. Whereas Chopra et al. [6] found no significant effect for this interaction. Interaction between sex and year of birth Sex and year of birth interaction had a significant influence on all growth traits (P<0.0001; TABLES III and IV). Males born in 2019 showed the best performance, with an average birth weight of 4.57 ± 0.08 kg, an average weight of 30.28 ± 0.43 kg at 120 d, and an overall ADG of 213.52 ± 3.41 g·d -1 . In contrast, females born in 2017 performed the poorest. Across all years, males outperformed females, although the magnitude of this difference depended on environmental conditions. The performance gap widened in years with favourable rainfall and forage availability, such as 2019, reflecting better ewe nutrition and milk production. Conversely, under drought conditions (in 2017 and 2020), growth rates declined and sex differences narrowed. Similar interactions between sex and year have been reported in Morocco [11, 21], Zimbabwe [25]. These studies all show that favourable years amplify sex differences in growth performance. These findings confirm that male growth potential is more fully expressed under optimal climatic and nutritional conditions. Chopra et al. [6] found no significant effect for this interaction. Interaction between birth month and litter size As shown in TABLES III and IV, the interaction between birth month and litter size had a significant effect on all growth traits (P<0.0001). Singleton lambs consistently outperformed twins across all months. The heaviest lambs were singletons born in October (4.69 ± 0.06 kg), while those born in August had the highest weights at 30 and 120 d (10.93 ± 0.18 kg and 23.49 ± 0.38 kg, respectively) and exhibited the fastest growth rate (172.7 ± 3.28 g·d -1 from birth to 90 d; 156.9 ± 3.01 g·d -1 overall). In contrast, twins born in August had the lowest birth weights (3.52 ± 0.07 kg), and those born in September and October remained lighter at later stages (17.2–17.4 kg at 90 d and approximately 20.0 kg at 120 d), with the slowest growth (146 ± 2.28 g·d -1 from birth to 90 d; 131.2 ± 3.49 g·d -1 overall). These results suggest that singletons born in August experienced the fastest growth rates, reflecting reduced intrauterine competition and greater milk availability. In contrast, twins, particularly those born in September and October, exhibited slower growth rates until weaning. This suggests that late-summer nutritional constraints in late summer intensify the disadvantage of twins, whereas singletons benefit more from a favourable early-season milk supply. These findings align with those reported by Zidane et al. [10]; confirming that twin lambs are more sensitive to seasonal feed limitations in semi-arid environments. Interaction between birth month and year of birth The interaction between birth month and year of birth had a significant effect on all growth traits (P<0.0001) (TABLES III and IV). Lambs born in October 2019 demonstrated the best performance, with the highest birth weight (4.74 ± 0.24 kg), W90 (25.62 ± 1.05 kg), and the fastest pre-weaning growth rate (230.9 ± 10.43 g·d -1 ). At 120 d, lambs born in August and September 2019 remained the heaviest (29.58 ± 1.01 kg and 28.84 ± 0.34 kg, respectively), and had the highest overall ADG (210.1 ± 7.81 g·day -1 and 202.2 ± 2.65 g·d -1 , respectively). In contrast, lambs born in September 2017 demonstrated the poorest performance throughout the growth period, reaching 18.18 ± 0.33 kg at 120 d and growth of 115.0 ± 2.64 g·d -1 . Similarly, lambs born in August and September 2020 also grew below average (20.97 ± 0.29 kg; 139.1 ± 2.26 g·d -1 and 19.50 ± 0.34 kg; 127.3 ± 2.53 g·d -1 , respectively). Overall, lambs born in 2019 clearly outperformed those from other years, reflecting highly favourable environmental and nutritional conditions. Conversely, lambs born in 2017 and 2020 when there was a drought and feed scarcity, showed reduced growth. confirming that interannual and seasonal climatic variability strongly influence lamb performance. Similar patterns have been reported by Chopra et al. [6] where the combined effects of birth period and year determine growth trajectories. Analysis of three-way interactions revealed variable limited but significant effects on lamb growth (TABLES III and IV). For body weights from birth to 120 d, the interaction between birth month, litter size and year of birth and the interaction between litter size, sex and year of birth were not significant (P>0.05). However, the interaction between birth month, sex and year significantly affected weights at 30 d (P<0.001), 60, 90 d (P<0.01) and 120 d (P<0.05). Regarding growth rate, the interactions between birth month, litter size and year and the interaction between litter size, sex and year were significant only during the post-weaning period (P<0.05). In contrast, the interaction between birth month, sex and year significantly influenced growth in the pre-weaning period (P<0.01) and overall ADG (P<0.05). Similar studies on three way interactions were conducted elsewhere: Chopra et al. [6] found no significant effect for the interaction season, sex and year while Assan and Makuza [25] noted a significant effect of the interaction between sex, litter size and year on birth weight and weaning weight.

_______________________________________________________________________________________________Revista Cientifica, FCV-LUZ / Vol. XXXVI 9 of 10 Interestingly, while three-way interactions were generally less consistent than two-way effects, some combinations of sex and birth month across different years still appeared to influence growth, especially during the early stages of growth. CONCLUSIONS This study confirms that the pre-weaning growth in Ouled Djellal lambs raised in northeastern Algeria is strongly influenced by both biological and environmental factors. Sex and litter size were the main biological determinants, with males and single-born lambs consistently outperforming females and twins. Among environmental factors, birth month, year, and region significantly affected growth performance, while the superior performance observed in 2019 highlighted the major influence of climatic conditions and feed availability. The results emphasize the importance of improving nutritional management during late gestation and early lactation, particularly for twin-bearing ewes. They also suggest that aligning lambing periods with favourable forage availability and adapting feeding strategies to annual climatic variation may improve lamb growth under semi-arid conditions. Overall, improving growth performance in these production systems requires an integrated approach combining appropriate nutrition, adapted management practices, and consideration of non-genetic factors in breeding and production strategies. Conflict of interest The authors declare no conflict of interest. ACKNOWLEDGEMENT The authors acknowledge the institutional support and the farms that assisted in animal management and data collection. BIBIOGRAPHIC REFERENCES [1] Ministry of Agriculture (MADR). Statistique agricole: Superficies et productions [Internet]. Direction of agricultural statistics and information systems. 2021. 87 p. 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