Introduction
Early weight gain in broiler chicks is a critical factor in achieving target body weight, influencing overall performance and profitability in poultry farming. The initial days of a broiler's life are crucial, laying the foundation for its future development (Sacranie, 2019). The first seven days of a broiler's life, representing almost 17% of the total growing cycle, set the stage for maximizing physical performance. During this period, the gastrointestinal tract (GIT) develops rapidly, growing four times faster than the body weight in the first two weeks of life, making early nutrition essential for this development and maintaining homeostasis (Jha et al., 2019).
Early chick feeding
Chicks that do not receive feed and water immediately after hatching may experience depressed growth (Boyner, 2023), and flocks that fail to transition to feed and water quickly may suffer higher mortality rates and struggle to catch up (Sacranie, 2019). Conventional commercial hatcheries often do not allow newly hatched chicks to consume feed or water (Boyner, 2023). This feed deprivation, combined with natural variations in hatching time, can lead to some chicks being deprived of feed for up to 72 hours before reaching the rearing site (Boyner et al., 2021). However, research shows that chicks remain relatively inactive for a considerable time after hatching before engaging in eating-related activities. For example, 5% of chicks were recorded eating or standing near the feeder at an average biological age of 25.4 hours, and 50% of the birds had full crops at an average of 30.6 hours (Boyner et al., 2021; Boyner, 2023). Early feeding of chicks provides readily available energy to restore hepatic glycogen stores and maintain a high body temperature, hence leading to the development of strategies, including in-ovo feeding and specially designed post-hatch diets, to mitigate the negative effects of delayed feeding (Jha et al., 2019).
A study by Gawa et al. shows that early post-hatch nutrition has a positive effect on the diameter of breast muscle fibers and the expression of myoG and MRF4 genes and that chicks with early access to feed and water can better exploit their genetic potential. The study further concludes that the average final body weight of chicks with early access to feed and water was 5% higher than in groups hatched under standard conditions (Gaweł et al., 2022). Moreover, research has shown a linear relationship between chicken weight at 6-7 weeks and their weight in the first week (Jha et al., 2019). Therefore, interventions that promote early feed intake and healthy gut development can significantly improve the overall performance of broiler chickens (Sacranie, 2019).
Pre-hatch (in-ovo) feeding
In-ovo feeding (IOF) is an innovative strategy that involves delivering essential nutrients to chick embryos before they hatch, which can significantly impact early development and subsequent growth. This technique has emerged as a promising method to improve the nutritional status of embryos during a critical phase, and these early benefits can continue throughout the entire rearing period (Givisiez et al., 2020).
- IOF can improve embryo metabolism by increasing hepatic and muscular glycogen reserves. For example, in-ovo administration of a nutrient solution containing maltose, sucrose, dextrin, and calcium β-hydroxy-β-methylbutyrate (HMB-calcium) increased both hepatic and muscular glycogen reserves at the end of incubation. Similarly, in-ovo injection of carnitine resulted in increased glycogen stores in the liver and pectoral muscle, improving the glycogen status of hatched chicks (Givisiez et al., 2020).
- IOF can also enhance the development of the gastrointestinal tract. Nutrients provided through IOF are directed towards the functional development of the GIT, enabling better assimilation of exogenous nutrients after hatching. Furthermore, this research by Rubio suggests that the IOF of turkey embryos can speed up digestive and nutrient uptake capacity around the pre-hatch period (Rubio, 2019).
- In terms of immunity, IOF can improve post-hatch resistance against pathogens. Some studies have explored inoculating eggs with probiotics and synbiotics via IOF, which may enhance immunity. However, research on the effects of IOF on immune traits is still ongoing, and results can be inconsistent (Jha et al., 2019; Rubio, 2019; Tona et al., 2022).
- IOF improves growth performance and the attainment of target body weight. By providing embryos with necessary nutrients and stimulating crucial physiological processes, IOF helps set the stage for more efficient growth, as demonstrated by an increase in pectoral muscle yield in broilers at 25 days of age. However, chick response to IOF may depend not exclusively on the injected nutrient, but also on factors that are not completely understood, such as breeder genetics and age, egg size, and incubation conditions (Givisiez et al., 2020).
Intermittent LIGHTING
Intermittent lighting (INL) is a strategy that involves alternating periods of light and darkness. It has shown considerable promise in influencing early chick development, weight gain, health, and overall welfare. Unlike continuous lighting (CL) programs, which provide constant illumination, INL aims to align with chickens' natural behavior, promoting rest and optimizing physiological processes (Zhao et al., 2019).
- Early Growth and Development: Various studies indicate that INL can positively impact growth parameters in broiler chickens (Zhao et al., 2019; Ozkan & Simsek, 2022). For instance, broiler chickens reared under INL (1 L:3 D cycle, repeated six times) had lower mortality rates and reduced plasma T3 levels, which are often associated with stress. Similarly, it has been observed that INL can enhance the antioxidant status of broiler chickens, which is crucial for overall health and growth (Zhao et al., 2019). On a different note, continuous lighting has been linked to increased metabolic and skeletal issues in fast-growing breeds. At the same time, some studies report no significant difference in growth performance between INL and CL. It's important to note that the specific light/dark cycle can significantly affect outcomes (Ozkan & Simsek, 2022).
- Weight Gain and Feed Efficiency: Some studies, like one by Cardeal et al. report similar weight gain in birds raised under both INL and CL programs (Cardeal et al., 2020). Others suggest that specific INL patterns can improve feed efficiency. For example, an intermittent lighting program did not hinder the performance of broiler chickens and promoted the energy economy. The key is finding the optimal balance between light exposure for feeding and dark periods for rest. Intermittent lighting allows birds to rest and digest their feed, potentially leading to better nutrient utilization (Ozkan & Simsek, 2022). This is especially important during the early stages of chick development, where efficient feed conversion into body mass is critical for achieving target weights (Tona et al., 2022; Muir et al., 2024).
- Health and Welfare: One of the primary benefits of INL is its positive effect on broiler welfare (Ozkan & Simsek, 2022). Continuous light exposure can disrupt the natural circadian rhythm of chickens, leading to stress and behavioral problems (James, 2020.; Relić et al., 2022). INL allows for better synchronization of resting behaviors and reduces physical disturbances, potentially promoting better sleep and recovery (Forslind, 2023). Zhao et al. found out that INL can reduce the incidence of stress-related issues such as leg problems and sudden death syndrome (Zhao et al., 2019). Some studies have found that INL can improve the resilience of broilers during sub-clinical necrotic enteritis infection (Olanrewaju et al., 2019), highlighting its role in supporting overall health. However, it's important to monitor other welfare indicators, such as ammonia burns, which can increase with certain intermittent lighting programs (Ozkan & Simsek, 2022).
- Optimising Light Cycles: The specific light and dark cycles in INL programs are crucial for maximizing their benefits (Ozkan & Simsek, 2022). The European Union recommends at least 6 hours of darkness in a 24-hour cycle for broilers from 7 days after arrival at the broiler house until 3 days before slaughter. However, the precise duration and pattern of light and dark periods can vary. Research suggests that both the length and mode of the dark period are significant. Some studies have investigated various INL programs, such as 4x(4L:2D) or 2x(8L:4D), noting differences in water consumption, uniformity, and hormonal parameters (Morvai et al., 2020; Ozkan & Simsek, 2022).
- Practical Applications: For farmers, implementing INL requires careful planning and management. The lighting system needs to be easily adjustable to create specific light and dark periods (Morvai et al., 2020). Monitoring bird behaviour and growth is crucial to ensure the lighting program is effective (Boyner et al., 2021). In addition, light intensity should be considered; while low light intensity can stimulate feed consumption, extremely low intensity can negatively impact welfare (Zhao et al., 2019). Using LED lighting systems, which allow for precise adjustments of both light intensity and wavelength, may be beneficial (Morvai et al., 2020). By focusing on creating lighting programs that match the biological needs of broiler chickens, producers can help ensure that their birds develop properly in the early days, promoting better health, higher welfare standards and helping achieve target body weights (James, 2020).
Temperatures (Pre and Post Hatch)
Temperature management, both pre- and post-hatch, is a critical factor influencing early chick development, weight gain, health, mortality, and yolk sac utilization (Wijnen et al., 2022; Yalcin et al., 2022). Maintaining optimal temperatures during these crucial phases supports proper physiological processes and is essential for achieving target body weights in broilers (Longley, 2019; Yalcin et al., 2022).
- Pre-hatch Temperature Effects: The eggshell temperature (EST) directly affects embryonic development during incubation. A constant EST of 37.8°C has been traditionally considered optimal, but research suggests that varying EST during different incubation phases can yield better results. For instance, a higher EST of 38.9°C in the second week of incubation can result in longer chick length, while a lower EST of 36.7°C in the third week can lead to shorter chick length but potentially improved organ development. However, a lower EST in the third week can also lead to lower body weight, average daily gain, and average daily feed intake at slaughter (Wijnen et al., 2022). Maintaining the correct temperature is crucial, as temperatures above 100.5°F can decrease hatchability, body weight, and yolk-free body mass (Lopez et al., 2018). Thermal manipulation during specific periods of incubation can positively affect embryonic weight and tibia length, improve hatching time, and increase chick weight and activity (Iraqi et al., 2024). For example, exposing eggs to a higher temperature of 39.5°C for 4 hours daily from the 12th to the 18th day of incubation can improve post-hatch thermotolerance and body weight. Moreover, suboptimal eggshell temperatures during incubation can negatively impact chick quality and live performance (Iraqi et al., 2024; Tona et al., 2022).
- Post-hatch Temperature Effects: Maintaining the correct temperature is crucial for chick comfort and development once hatched. Newly hatched chicks need a stable environment with specific temperature requirements to optimize their appetite and feeding behavior (Longley, 2019). The optimal body temperature for chicks is between 39.4°C and 40.5°C (Boyner et al., 2021). A chick's body temperature during the post-hatch handling period can affect their body weight, yolk sac utilization, and organ weight. Research shows that higher body temperatures can result in lower body weight at placement due to increased weight loss during handling, as well as reduced weights of organs such as the heart, gizzard, proventriculus, and bursa of Fabricius (Hamissou Maman et al., 2019). In contrast, a low temperature can also negatively impact the chicks' initial development. The initial brooding temperature should be around 30°C for whole-house brooding and 32°C at the edge of the brooder for spot brooding, with floor temperature between 28-30°C and relative humidity between 60-70%. Providing supplementary heat sources is often necessary to maintain the correct temperature (Lopez et al., 2018; Longley, 2019).
- Mortality and Health: Maintaining appropriate temperatures is essential for minimizing mortality and promoting chick health. Chicks that fail to adapt to suboptimal temperatures can experience increased mortality during the first week of life. A stable environment with appropriate temperatures promotes better physiological development and reduces stress, improving the chick’s ability to survive (Yerpes et al., 2020). Additionally, early feeding of chicks has been shown to reduce stress, which leads to lower plasma corticosterone concentration and lower preference temperature (Wijnen et al., 2022).
- Yolk Sac Utilisation: Temperature influences yolk sac utilization in newly hatched chicks. Although chick body temperature during the post-hatch handling period does not affect residual yolk sac weight, ensuring the chicks are not subjected to extreme temperatures in the first hours after hatch can have a beneficial effect on their overall development and subsequent growth (Hamissou Maman et al., 2019). Proper yolk sac utilization is crucial for providing the chicks with necessary nutrients during the first few days of life, which is essential for their growth and development (Tona et al., 2022).
- Achieving Target Body Weight: By carefully controlling both pre- and post-hatch temperatures, poultry producers can help ensure that their broilers have a healthy start, which is essential for achieving target body weights (Lopez et al., 2018; Iraqi et al., 2024). Inadequate temperatures can lead to slower growth, increased stress, and higher mortality, while optimal temperature management contributes to better feed efficiency and overall productivity (Lopez et al., 2018; Wijnen et al., 2022; Iraqi et al., 2024). The goal of temperature management is to create a stable environment that supports optimal growth and development during the critical early stages of life (Longley, 2019; Tona et al., 2022).
By carefully controlling pre- and post-hatch temperatures, farmers and researchers can optimize early chick development, minimize mortality, support yolk sac utilization, and ensure efficient weight gain, ultimately contributing to improved overall flock performance and attainment of target body weight.
Chick quality
Chick quality is an important aspect of poultry production that significantly impacts early development, weight gain, health, and welfare, ultimately influencing the ability to achieve target body weights in broilers. A high-quality chick is optimally developed during incubation, exhibiting high-performance potential and survivability. Several pre-hatch and post-hatch factors, including incubation conditions, hatching systems, and early management practices, affect chick quality (Yerpes et al., 2020; Tona et al., 2022).
- Pre-hatch Factors: The quality of a day-old chick is influenced by several pre-hatch factors, including breeder flock age, egg characteristics, and incubation conditions (Yerpes et al., 2020; Tona et al., 2022). Older breeder flocks tend to produce eggs with a larger yolk, which can provide higher nutrient availability for the developing embryo (Nangsuay et al., 2021). However, the age of the breeder does not improve incubation results or chick quality (Machado et al., 2020). Egg storage conditions and duration before incubation also play a crucial role (Tona et al., 2022). A study by Yalcin et al. Showed that incubation conditions such as temperature, humidity, gas exchange, and turning directly affect embryonic development (Yalcin et al., 2022). For instance, suboptimal eggshell temperatures during incubation can decrease chick quality and live performance (Wijnen et al., 2022). Variations in temperature during incubation are not unusual, as the mother hen may leave the nest for food and water or rise to turn the eggs. This environmental stimulus during the embryonic period may be useful to prepare the embryo for post-hatching life (Yalcin et al., 2022).
- Incubation and Hatching Systems: The design of incubation and hatching systems directly impacts chick quality (Lingens et al., 2021; Tona et al., 2022). Traditional commercial hatcheries often do not allow newly hatched chicks to consume feed or water, potentially leading to feed deprivation for early hatchlings due to variations in hatching time. This can harm the chicks' early development, as they remain inactive for a considerable time before engaging in eating-related activities (Boyner et al., 2021; Boyner, 2023). Hatcheries with immediate access to feed and water in the hatcher can improve weight gain and muscle development (Gaweł et al., 2022). Different hatching systems also impact chick development and growth, with some systems resulting in higher body weight for chicks during the first weeks of life (Souza da Silva et al., 2021). On-farm hatching systems that provide early access to feed and water can help to mitigate the negative effects of delayed access to nutrients and result in improved growth performance (Boyner et al., 2021; Boyner, 2023). Providing colored photoperiodic light stimulation during incubation can positively affect early post-hatch growth, immune response, and production performance (Li, 2023).
- Chick Quality Parameters: Several physical parameters are used to assess chick quality. These include chick activity, body weight (between 40-44g), a healed navel, and dry down (Yerpes et al., 2020). Chick length uniformity can also be used to measure chick quality (Souza da Silva et al., 2021). Research has shown that chick quality scores, which evaluate physical characteristics, are used as indicators of post-hatch performance and can be more reliable for predicting early growth (Souza da Silva et al., 2021; Wijnen et al., 2022). Other important factor to consider are the development of the gastrointestinal tract, which is essential for nutrient absorption (Givisiez et al., 2020). The yolk-free body mass (YFBM) at hatch is an important parameter and can be affected by both breeder age and incubation conditions (Nangsuay et al., 2021). In addition, the relative weights of organs such as the small intestine and bursa fabricii can indicate differences in chick development (Boyner et al., 2021).
- Impact on Early Development and Weight Gain: High-quality chicks exhibit better early development and weight gain. Chicks hatched with access to feed and water from the beginning show better performance and muscle growth, highlighting the positive impact of early nutrition (Gaweł et al., 2022). Delayed access to feed and water can reduce weight gain and feed intake early in life, but birds can compensate during the later growth phase (Boyner, 2023). Furthermore, chicks hatching later in the hatching window can have better performance results than those hatching earlier (Machado et al., 2020). Using in-ovo feeding strategies, which provide nutrients to the chick embryo before hatch, can also improve body weight at hatch (Tona et al., 2022).
- Health and Welfare: Chick quality is directly related to health and welfare. High-quality chicks are more resilient, experience less stress, and have higher survival rates during the first week of life. In contrast, poor chick quality can lead to increased mortality, especially during the critical first week of life. Factors that negatively influence chick morpho-physiology during this stage will have an impact on welfare and, if animals fail to adapt, could lead to increased mortality in the first week (Yerpes et al., 2020). Chicks with early access to feed show lower stress levels (Jha et al., 2019). Additionally, proper chick handling and environmental management post-hatch is essential for ensuring chick well-being and minimizing mortality (Lingens et al., 2021; Tona et al., 2022).
Litter management
Litter management is a crucial aspect of broiler production that significantly impacts early chick development, weight gain, health, and welfare, and thus plays a key role in achieving target body weights. Proper litter management provides a suitable environment for chicks, affecting their leg health, overall well-being, and exposure to harmful substances like ammonia. The selection and management of litter directly influence the microclimate in the poultry house and can be a determining factor in the success of early growth (Cohuo-Colli et al., 2018).
- Litter Material and Requirements: The choice of litter material is vital for creating an optimal environment for broiler chicks (Kuleile et al., 2019). Ideal litter materials should be absorbent, insulating, and non-toxic and should also support good foot health. Commonly used litter materials include wood shavings and rice hulls. The depth of the litter material is also important; a greater depth of litter can significantly affect ammonia emissions, while varying depths of litter, such as sand and wood shavings, have been shown to have differing effects on broiler performance (Cohuo-Colli et al., 2018; Shaoun, 2023). Proper litter should be dry and friable, allowing chicks to move freely and exhibit natural behaviors (Forslind, 2023). Litter that becomes too wet or compacted can increase the risk of health problems, such as footpad dermatitis, which can compromise welfare and performance (Muir et al., 2024). The litter material should also be free of contaminants that could introduce pathogens (Shaoun, 2023).
- Impact on Chick Leg Health: Litter quality is intrinsically linked to the leg health of broiler chicks (S. Khan et al., 2011; Muir et al., 2024). Poor litter conditions, including high moisture content and caking, can lead to footpad lesions and lameness (James, 2020). These conditions cause pain and discomfort and impede the chicks' ability to access feed and water, hindering weight gain. Good litter management, on the other hand, promotes normal gait and allows the chicks to maintain good leg health, contributing to better overall well-being (Forslind, 2023). Maintaining adequate litter depth and dryness is essential for preventing leg problems and ensuring that chicks have a comfortable and safe surface to rest on (K. Khan et al., 2023).
- Overall Health and Welfare: Effective litter management is essential for maintaining overall chick health and welfare (Shaoun, 2023). The litter acts as a primary surface for the chicks, significantly impacting their exposure to pathogens and environmental stressors. Too moist litter can promote the proliferation of harmful bacteria and fungi, increasing the risk of diseases like pneumonia and coccidiosis (Lingens et al., 2021; Shaoun, 2023). Proper management, which includes regular monitoring and maintenance, can help to prevent such outbreaks. The presence of dry and clean litter allows chicks to exhibit natural behaviors, such as foraging and dust bathing, which are important for their welfare (Morvai et al., 2020; Forslind, 2023). Providing a comfortable environment also reduces stress, which in turn promotes better growth and feed conversion. Higher stocking densities, coupled with poor litter conditions, can negatively affect bird welfare.
- Ammonia Emission and Air Quality: Litter management is a major factor in controlling ammonia emissions in broiler houses (Cohuo-Colli et al., 2018). The breakdown of poultry excreta in the litter produces ammonia, a gas harmful to chicks when present in high concentrations. High ammonia levels can cause respiratory issues, eye irritation, and reduced growth rates (Cohuo-Colli et al., 2018; James, 2020). The type and depth of litter, as well as the moisture content, directly impact ammonia production. Proper ventilation and frequent litter changes are important to reduce ammonia buildup and maintain good air quality. Using organic minerals and Yucca schidigera extract, along with increased litter density, can significantly reduce ammonia emissions (Cohuo-Colli et al., 2018). Effective litter management practices, such as regular stirring and the addition of litter amendments, are critical for minimizing ammonia production and creating a healthy environment for the birds (Muir et al., 2024). Furthermore, maintaining appropriate temperature and humidity levels within the poultry house aids in controlling ammonia emissions.
Conclusion
Achieving target broiler body weight requires a holistic approach focusing on early development and consistent management. Early feeding and water access are vital, with hatcher feeding enhancing muscle growth. Maintaining optimal post-hatch body temperature and incubation conditions - specifically thermal manipulation - positively affects post-hatch adaptation and growth. Lighting management, including intensity, duration, and color, influences feed efficiency. Effective litter management is crucial for chick health, with absorbent, dry, and non-toxic materials preventing leg issues and controlling ammonia emissions. A combination of optimized early feeding, environmental controls, and careful management practices is essential to support healthy growth and achieve target body weights in broilers.
References
- Boyner, M. (2023). A flying start: Adapted hatching and post-hatch feeding in broiler chickens: Vol. 2023:38. Swedish University of Agricultural Sciences.
- Boyner, M., Ivarsson, E., Franko, M. A., Rezaei, M., & Wall, H. (2021). Effect of hatching time on time to first feed intake, organ development, enzymatic activity and growth in broiler chicks hatched on-farm. Animal, 15(2), 100083.
- Cardeal, P. C., Rocha, J. S. R., Pompeu, M. A., Pereira, L. F. P., Saldanha, M. M., Baião, N. C., Araújo, I. C. S. D., & Lara, L. J. C. (2020). Effects of placement time on performance and gastrointestinal tract growth of male broiler chickens. Revista Brasileira de Zootecnia, 49, e20190242.
- Cohuo-Colli, J. M., Salinas-Ruíz, J., Hernández-Cázares, A. S., Hidalgo-Contreras, J. V., Brito-Damián, V. H., & Velasco-Velasco, J. (2018). Effect of litter density and foot health program on ammonia emissions in broiler chickens. Journal of Applied Poultry Research, 27(2), 198–205.
- Forslind, S. (2023). Never wake a sleeping broiler: An undisturbed natural resting pattern in broilers: Vol. 2023:17. Swedish University of Agricultural Sciences.
- Gaweł, A., Madej, J. P., Kozak, B., & Bobrek, K. (2022). Early post-hatch nutrition influences performance and muscle growth in broiler chickens. Animals, 12(23), 3281.
- Givisiez, P. E. N., Moreira Filho, A. L. B., Santos, M. R. B., Oliveira, H. B., Ferket, P. R., Oliveira, C. J. B., & Malheiros, R. D. (2020). Chicken embryo development: Metabolic and morphological basis for in ovo feeding technology. Poultry Science, 99(12), 6774–6782.
- Hamissou Maman, A., Özlü, S., Uçar, A., & Elibol, O. (2019). Effect of chick body temperature during post-hatch handling on broiler live performance1. Poultry Science, 98(1), 244–250.
- Iraqi, E., Hady, A. A., Elsayed, N., Khalil, H., El-Saadany, A., & El-Sabrout, K. (2024). Effect of thermal manipulation on embryonic development, hatching process, and chick quality under heat-stress conditions. Poultry Science, 103(1), 103257.
- James, C. (2020). THE IMPACT OF ULTRAVIOLET WAVELENGTHS ON BROILER CHICKEN PERFORMANCE, HEALTH AND WELFARE.
- Jha, R., Singh, A. K., Yadav, S., Berrocoso, J. F. D., & Mishra, B. (2019). Early Nutrition Programming (in ovo and Post-hatch Feeding) as a Strategy to Modulate Gut Health of Poultry. Frontiers in Veterinary Science, 6.
- Khan, K., Kaya, M., Fidan, E. D., & Kilimci, F. S. (2023). Impact of litter on femur and tibial morphology, bone biomechanics, and leg health parameters in broiler chickens. Animal Bioscience, 36(9), 1393–1402.
- Khan, S., Rehman, A., & Jehanzeb, A. (2011). Effects of dietary minerals on postmolt performance of laying hens. Veterinary World, 389.
- Kuleile, N., Metsing, I., Tjala, C., Jobo, T., & Phororo, M. (2019). THE EFFECTS OF DIFFERENT LITTER MATERIAL ON BROILER PERFORMANCE AND FEET HEALTH.
- Li, X. (2023). SHINING A LIGHT TO CHICKEN EMBRYOS: A NEW PERSPECTIVE ON HATCHERY MANAGEMENT.
- Lingens, J. B., Abd El-Wahab, A., Ahmed, M. F. E., Schubert, D. C., Sürie, C., & Visscher, C. (2021). Effects of early nutrition of hatched chicks on welfare and growth performance: A pilot study. Animals, 11(10), 2888.
- Longley, E. (2019). Health, efficiency and sustainability: Making the first seven days count.
- Lopez, J. C., Kitto, L., & Hulet, R. M. (2018). Effect of eggshell temperature on survival rate, development at hatch, and 7-day growth. Journal of Applied Poultry Research, 27(2), 249–252.
- Machado, J. P., Mesquita, M. A., Café, M. B., Assis, S. D., Veríssimo, S., Santos, R. R., Leandro, N. S. M., & Araújo, I. C. S. (2020). Effects of breeder age on embryonic development, hatching results, chick quality, and growing performance of the slow-growing genotype. Poultry Science, 99(12), 6697–6704.
- Morvai, P., Žitňák, M., & Lendelová, J. (2020). Design of Artificial Lighting in Broiler Housing. Acta Technologica Agriculturae, 23(4), 190–194.
- Muir, W. I., Akter, Y., Kho, S. K. Y., Bruerton, K., & Groves, P. J. (2024). The Impact of Lighting Regimen and Feeding Program during Rearing on Hy-Line Brown Pullets at the End of Rearing and during Early Lay. Animals : An Open Access Journal from MDPI, 14(19), 2850.
- Nangsuay, A., Molenaar, R., Meijerhof, R., van den Anker, I., Heetkamp, M. J. W., Kemp, B., & van den Brand, H. (2021). Effects of oxygen concentration during incubation and broiler breeder age on embryonic heat production, chicken development, and 7-day performance. Animal, 15(9), 100323.
- Olanrewaju, H. A., Collier, S. D., Purswell, J. L., & Branton, S. L. (2019). Effects of light-sources and photoperiod on hemato-physiological indices of broilers grown to heavy weights. Poultry Science, 98(3), 1075–1082.
- Ozkan, M., & Simsek, U. G. (2022). The effect of light/dark cycles on performance and welfare in broiler. Annals of Animal Science, 22(2), 795–802.
- Relić, R., Škrbi̇Ć, Z., Boži̇Čkovi̇Ć, I., Luki̇Ć, M., Petri̇Čevi̇Ć, V., Deli̇Ć, N., Bondži̇Ć, A., & Vi̇Torovi̇Ć, D. (2022). Effects of dietary melatonin on broiler chicken exposed to continuous lighting during the first two weeks of life. Ankara Üniversitesi Veteriner Fakültesi Dergisi, 69(4), 361–366.
- Rubio, L. A. (2019). Possibilities of early life programming in broiler chickens via intestinal microbiota modulation. Poultry Science, 98(2), 695–706.
- Sacranie, A. (2019). Broiler performance: The importance of the first seven days. Challenge, 16(14), 12.
- Shaoun, H. M. (2023). Effect of different litter materials on broiler production and occurrence of pneumonia.
- Souza da Silva, C., Molenaar, R., Giersberg, M. F., Rodenburg, T. B., van Riel, J. W., De Baere, K., Van Dosselaer, I., Kemp, B., van den Brand, H., & de Jong, I. C. (2021). Day-old chicken quality and performance of broiler chickens from 3 different hatching systems. Poultry Science, 100(3), 100953.
- Tona, K., Voemesse, K., N’nanlé, O., Oke, O. E., Kouame, Y. a. E., Bilalissi, A., Meteyake, H., & Oso, O. M. (2022). Chicken Incubation Conditions: Role in Embryo Development, Physiology and Adaptation to the Post-Hatch Environment. Frontiers in Physiology, 13.
- Wijnen, H. J., Molenaar, R., Kemp, B., van Roovert-Reijrink, I. A. M., van den Brand, H., & van der Pol, C. W. (2022). Effects of late incubation temperature and moment of first post-hatch feed access on neonatal broiler development, temperature preference, and stress response. Poultry Science, 101(10), 102088.
- Yalcin, S., Özkan, S., & Shah, T. (2022). Incubation temperature and lighting: Effect on embryonic development, post-hatch growth, and adaptive response. Frontiers in Physiology, 13, 899977.
- Yerpes, M., Llonch, P., & Manteca, X. (2020). Factors Associated with Cumulative First-Week Mortality in Broiler Chicks. Animals, 10(2), Article 2.
- Zhao, R. X., Cai, C. H., Wang, P., Zheng, L., Wang, J. S., Li, K. X., Liu, W., Guo, X. Y., Zhan, X. A., & Wang, K. Y. (2019). Effect of night light regimen on growth performance, antioxidant status and health of broiler chickens from 1 to 21 days of age. Asian-Australasian Journal of Animal Sciences, 32(6), 904–911.