Global poultry production faces conflicting challenges; most efforts have focused on increasing poultry productivity to address animal protein deficiency in the human diet(Mir et al., 2017). Poultry meat at an affordable price for the average consumer can generally be achieved through intensive production under conventional rearing systems (e.g., deep litter or multilayer cage). In many Western markets, particularly in the EU and the USA, a category of consumers pays close attention to poultry rearing conditions and is willing to pay a premium for products they perceive as safer, more authentic, and produced under higher welfare standards(Mulder & Zomer, 2017);(Jin et al., 2019);(Marchewka et al., 2023). In line with these preferences, broiler meat consumption patterns have increasingly shifted toward products from environmentally sustainable, welfare-oriented production systems, although the magnitude of this shift varies across regions and market segments(Amato & Castellini, 2022);(Campbell et al., 2025). Consequently, free-range and organic chicken meat have gained popularity, as they are commonly regarded as healthier and associated with improved animal welfare and management practices compared with conventional confined systems(Rehman et al., 2017);(Hautefeuille et al., 2026).

Growing consumer awareness of broiler welfare, along with varying willingness to pay, has driven the development of diverse husbandry systems that balance animal welfare, environmental sustainability, and product affordability(Papageorgiou et al., 2025). At the same time, farm animal welfare has become a major concern for policymakers, consumers, and stakeholders throughout the food supply chain(Sánchez-Casanova et al., 2020). Furthermore, research has highlighted that free-range management is a fundamental component of organic farming, as it aligns closely with the natural behaviors and biological needs of animals(Pettersson et al., 2016);(Jin et al., 2019).

Broiler production is increasingly shifting toward higher-welfare systems that incorporate slower-growing strains, lower stocking densities, and enhanced environmental enrichment. In this context, semi-intensive production systems (e.g., free-range, pasture, or organic) with outdoor access are associated with higher animal welfare standards, resulting in improved sensory quality and greater product security(Tong et al., 2015);(Jong et al., 2022). Recently, consumer preferences have shifted, driven by tremendous advances in human living standards, toward products from hens raised in free-range settings with pasture access(Zheng et al., 2021). Conversely, the intensification of broiler chicken farming has been widely associated with compromised broiler welfare. Under intensive conditions, broilers are frequently subjected to high stocking densities, suboptimal ventilation, and musculoskeletal and cardiovascular disorders arising from accelerated growth rates(Nielsen et al., 2023);(Papageorgiou et al., 2025).

An outdoor rearing system requires a moderate climate and abundant vegetation to promote broiler pasture, which is available in tropical and subtropical regions where most developing countries are located. Although these developing countries are more concerned about animal protein shortages than meat quality, they can expand this type of production for export, given the limited local consumption of such expensive natural products, which could be highly profitable(Sánchez-Casanova et al., 2020). Some studies have shown that free-range production systems enable birds to display natural behaviors by providing greater space and environmental enrichment, thereby improving living conditions, reducing stress levels, and enhancing health and performance(Martínez-Pérez et al., 2023);(Safwat et al., 2026). There is some research comparing broilers raised in free-range systems with those kept indoors that shows inconsistent results, largely influenced by differences in breed, environmental conditions, and management practices.(Tellis et al., 2024);(Campbell et al., 2025);(Hautefeuille et al., 2026). Although several studies have investigated free-range systems, most have focused on slower-growing genotypes or temperate environments, with limited integration of behavioral, productive, physiological, and metabolic responses. Consequently, the adaptability and performance of fast-growing commercial broiler strains, such as Cobb500, widely used in intensive production systems, under free-range management in tropical environments, remain poorly understood. Therefore, the present study aimed to provide a comprehensive evaluation of free-range rearing in a tropical production system using a fast-growing commercial genotype, focusing on behavior, growth performance, nutrient digestibility, serum lipid profile, and carcass characteristics of Cobb500 broilers compared with a conventional indoor system. It was hypothesized that free-range rearing would improve bird welfare and physiological status without compromising growth performance.

Free-range birds engaged in a wider variety of activities, particularly foraging, locomotion, and dust bathing. These behaviors are associated with improved welfare because they align with chickens’ natural behavior(Baxter et al., 2019). Indoor housing, by contrast, restricted opportunities for such behaviors, leading to more feeding and resting. In both systems, foraging and locomotion tended to decline slightly with age, while resting increased. In this respect, broiler chickens maintain a tightly regulated overall energy budget, with resting metabolic demands accounting for an increasingly larger proportion of total energy expenditure as birds mature. This shift limits the energy available for other functions, particularly physical activity, and likely contributes to the progressive decline in locomotor capacity with age(Tickle et al., 2018);(Bonnefous et al., 2024). Consistent with previous behavioral studies, the proportion of time spent in active movement decreases markedly during development, declining from approximately 12% in two-week-old chicks to less than 5% in birds at market weight(Eijk et al., 2022);(Whittle et al., 2025). In parallel, walking speed decreases with increasing body mass, following a pattern similar to that observed for activity levels, with a steep reduction until a critical body weight is reached, after which further changes are minimal. Notably, both mean and peak walking speeds decline substantially as body mass increases, a response that may be attributed to higher body weight and reduced agility in older broilers(Tickle et al., 2018);(Sánchez-Casanova et al., 2020).

The absence of significant differences in growth performance between the conventional indoor and free-range systems suggests that broilers reared outdoors maintained comparable productive efficiency despite increased locomotor activity. This may be explained by a compensatory mechanism in which the higher energy expenditure associated with movement is offset by improved welfare status, reduced chronic stress, and better physiological adaptation. Previous studies have similarly reported no significant differences in growth performance traits between rearing systems(Jin et al., 2019);(Zheng et al., 2021);(Safwat et al., 2026), indicating that environmental and management conditions may moderate system-related effects. Conversely, some studies have reported either improved or reduced performance under free-range conditions, which may be attributed to differences in environmental variability, including temperature fluctuations, as well as bird-related factors such as genotype and activity level(Haruna et al., 2018);(Bonnefous et al., 2024).

Furthermore, fast-growing broilers often exhibit low sustained activity in free-range environments, spending much of their time resting or near shelters, thereby minimizing additional energy expenditure(Horna et al., 2023). Consequently, genetic efficiency, restricted outdoor activity, and compensatory feed intake together may help explain why growth performance often does not differ significantly between free-range and conventional systems. It should be noted that, to reduce the impact of temperature variation, birds in both treatment groups were kept indoors overnight in the present study. Moreover, the commercial broiler breed (used in our study) did not exhibit excessive free-range activity, like local chicken breeds, and this activity decreased as birds aged(Sánchez-Casanova et al., 2022).

The improvement in apparent DM and EE digestibility observed in broilers reared under the free-range system could be attributed to the stimulatory effect of free-range activity on digestive enzyme secretion. This may be associated with greater physical activity and the possible ingestion of fibrous material or grit from the available outdoor area. However, this was not directly measured in the present study. Such factors could increase digesta retention time, thereby improving nutrient digestibility and absorption by increasing the digesta exposure period to digestive enzymes and absorptive cells(Wang et al., 2015);(Kheravii et al., 2017). The positive effect of free-range treatment on the digestibility of DM and EE may partially explain how these birds could maintain their growth performance as the indoor birds without increasing FI, despite the excessive energetic demand during free-range activities, which suggests higher efficiency of feed utilization for broilers in a free-range rearing system.

Generally, blood biochemical parameters provide good insight into the physiological and metabolic state of the bird(Jin et al., 2019). Determination of these parameters can be used to evaluate stress induced by environmental, housing, managerial, or nutritional conditions in farm animals(Dong et al., 2017);(Tellis et al., 2024). The concentration of lipid parameters in blood serum (including triglyceride, cholesterol, HDL, LDL, and VLDL) is strongly related to lipid metabolism and fat deposition(Ma et al., 2014). In this study, the reduced serum triglyceride concentration in the free-range group might be attributed to the excessive physical activity of birds in the range area, leading to decreased fat deposition in adipose tissue. Consistent with this finding, Jin et al. (2019)(Jin et al., 2019) observed a significant decrease in fat deposition in Wannan Yellow chickens as the duration of free-range rearing increased. The observed reduction in serum LDL and VLDL concentrations (the harmful cholesterol fractions) could reflect a better health status of broilers reared under this alternative system. In this regard, previous studies have revealed that the free-range rearing system not only improves the comfort and welfare of birds but also enhances their physiological and health status(Jin et al., 2019);(Martínez-Pérez et al., 2023).

The lack of significant differences in carcass traits between rearing systems indicates that overall tissue accretion was not substantially affected, likely because net energy availability for growth was similar under both conditions(Tong et al., 2015). This outcome may be explained by a compensatory energy allocation mechanism, whereby increased energy expenditure from locomotor activity in free-range birds is offset by physiological adaptations that sustain muscle deposition. In contrast, the reduced abdominal fat observed in free-range birds can be attributed to altered energy partitioning, with more metabolizable energy directed toward maintenance and activity rather than lipogenesis(Li et al., 2016);(Mutibvu et al., 2019);(Safwat et al., 2026). Increased physical activity enhances lipid mobilization and oxidation, thereby limiting fat accumulation while preserving lean tissue growth(Jin et al., 2019). Furthermore, improved protein deposition efficiency in free-range birds may be linked to enhanced metabolic efficiency and reduced chronic stress, promoting anabolic processes over fat storage(Połtowicz & Doktor, 2011);(Evaris et al., 2021). These metabolic responses align with the observed serum lipid profile, indicating reduced lipogenesis and improved nutrient utilization. However, variations reported in the literature, including improved carcass yield under outdoor access(Schreiter et al., 2025), likely reflect differences in genotype, management, and environmental conditions.

Under the conditions of the present study, free-range rearing did not negatively affect the growth performance of Cobb-500 broilers compared with the conventional indoor system. However, it reduced abdominal fat deposition and improved selected lipid-related serum markers, indicating a favorable shift in body fat metabolism. These findings suggest that free-range production enhances nutrient utilization and carcass composition. Therefore, within the limits of this experiment, free-range rearing can be considered a viable and sustainable production system for welfare-oriented broiler production in tropical environments.