Introduction
The Japanese quail (Coturnix japonica) belongs to the family Phasianidae and is renowned for its egg-laying abilities, producing up to 300 eggs annually. Its high productivity, small size, and low feed requirements make it cost-effective for commercial egg production. Quail eggs are nutritionally superior to chicken eggs (Davodzadeh et al., 2017). However, heat stress adversely affects quail well-being, meat quality, production rate, and egg quality, particularly impacting their reproductive performance due to their susceptibility to high temperatures. Effective strategies, including antioxidant additives in their diet, are needed to enhance productivity and mitigate oxidative stress under such conditions (Lukanov, 2018; Habibi et al., 2024).
To combat heat stress, various nutritional interventions have been employed, including supplementation with vitamins (e.g. Vitamins C and E), minerals (e.g. selenium), electrolytes, and herbal extracts, all of which aim to improve antioxidant capacity, immune function, and thermoregulation (Sahin et al., 2009). Among these, antioxidant compounds play a crucial role in neutralizing reactive oxygen species induced by heat stress.
To enhance the reproductive and production characteristics of quails, dietary supplements, like L-carnitine and black seed have been suggested. L-carnitine, an amino acid-like compound, plays a crucial role in cellular energy metabolism and mitochondrial CoA regulation, improving yolk fat metabolism and follicular growth. It potentially increases egg weight through enhanced albumen deposition and eggshell calcification (Peebles et al., 2007). Under heat stress, L-carnitine improves growth, laying performance, and immune function due to its antioxidant properties (Rehman et al., 2017). Similarly, vitamin E, another antioxidant, enhances reproductive performance and protects cells from damage (Raya et al., 2007). Nigella sativa (black seed) is known for its health benefits in humans, but limited research exists on its effects on egg yield and reproductive activity in Japanese quails. Rich in dry matter (50.91-48.94%), fat (34.49-41.6%), and protein (16-26.7%), essential minerals, and vitamins, black seed contains bioactive compounds, like thymoquinone and oleic acid, which have strong antioxidant, anti-inflammatory, and antimicrobial properties (Isik et al., 2019). Studies suggest that incorporating 2% black seed or 0.5% black seed oil into quail diets enhances growth performance and egg production and reduces intestinal bacterial pathogens (Seidavi et al., 2020). Additionally, quails consuming 1 g/kg of black seed extract show higher egg yield and weight, improved feed efficiency, and better egg quality (Denli et al., 2004). Compared to other nutritional strategies, the advantage of black seed supplementation lies in its multi-functional bioactive components, which not only improve antioxidant capacity but also enhance immune response and gut health simultaneously. This multifaceted action may provide more comprehensive protection against heat stress-related damages, thereby improving reproductive performance more effectively than single-component additives.
The purpose of this study was to determine the effects of natural compounds, such as black seed and L-carnitine on egg quality and the morphological properties of the intestine and magnum of laying Japanese quails under both normal and heat stress conditions. Investigating these factors can provide valuable insights into developing effective strategies to manage and optimize egg quality in laying Japanese quails, thereby ensuring a sustainable and profitable poultry industry.
Materials and Methods
Composition of nutrients and essential oil in black seed
The nutrient composition of black seed was determined based on Association of Official Analytical Chemists (AOAC) procedures (AOAC, 2007). Black seed’s nutrient profile included 96% dry matter, 5.34% ash, 8.17% crude fiber, 33.13% fat, 23.54% crude protein, 26.24% neutral detergent fiber (NDF), 17.26% acid detergent fiber (ADF), and 3.60 Kcal/kg dry matter of metabolizable energy. The essential oil content was estimated using gas chromatography (GC) coupled with mass spectrometry (MS) analysis, as shown in Table 1.
Essential oils from black seed were extracted using the hydrodistillation method, which is a widely accepted procedure for isolating volatile compounds from plant material. The seeds were ground and subjected to hydrodistillation with a Clevenger-type apparatus for approximately 3 hours. The yield of essential oil extracted was approximately 0.5–1.0% (v/w) based on the dry weight of black seed. The extracted essential oils were analyzed using a gas chromatograph (Agilent 7890B GC system) coupled with a mass spectrometer (Agilent 5977A MSD). The GC was equipped with an HP-5MS capillary column (30 m × 0.25 mm internal diameter [i.d.], 0.25 μm film thickness). The oven temperature was programmed to increase from 50 °C to 250 °C at a rate of 5 °C/min. Helium was used as the carrier gas at a flow rate of 1.0 mL/min. The mass spectrometer operated in electron ionization mode at 70 eV, scanning the mass range of m/z 40–450. This technique allowed for the identification and quantification of the main bioactive constituents of black seed essential oil with high precision.
Bird husbandry and experimental groups
A total of 500 laying Japanese quails (C. japonica) were procured from a local hatchery (Amol, Iran). All experimental protocols were reviewed and approved by the Animal Welfare Committee of the Department of Animal Science, University of Tehran, in accordance with institutional guidelines for the care and use of laboratory animals. The birds were randomly allocated to 10 treatment groups, each comprising 5 replicates with 10 quails per replicate. The study employed a completely randomized design with a 2×5 factorial arrangement, including two ambient temperature levels (normal and heat stress) and five experimental treatments: 1) control diet; 2) 1.5% black seed + control diet; 3) 250 ppm L-carnitine+control diet; 4) 1.5% black seed + 250 ppm L-carnitine+control diet; and 5) 200 ppm vitamin E + control diet. These treatments were administered under both normal and heat stress conditions.
The rearing period lasted for 10 weeks. At the beginning of the experiment, when the birds were 58 days old, they were weighed and placed in experimental cages based on their weight (267 g) and egg production (64%). During the first stage, lasting two weeks (from 58 to 72 days old), the laying Japanese quails were acclimated to the experimental diets. In the second stage, spanning five weeks (from 73 to 108 days old), the quails were exposed to both normal temperature and heat stress conditions. Heat stress involved maintaining an ambient temperature of 36 °C for 6 hours daily, from 10 am to 4 pm. In the third stage, the quails underwent a three-week recovery period under normal temperature conditions (from 109 to 130 days old). Throughout the 10-week period, the quails were individually housed in battery wire cages (50×30×50 cm³) with individual feeders and nipple drinkers, ensuring ad libitum access to feed and water. The lighting regimen followed a continuous 16-hour light cycle. Utilizing corn and soybean meal as the primary ingredients, all diets were isocaloric and isonitrogenous, meeting or exceeding NRC (1994) nutritional requirements for laying Japanese quails (Table 2).
Consistent care and control measures were implemented throughout the experiment.
Egg quality traits
To evaluate egg quality traits, two eggs were randomly selected from each replication (10 eggs per treatment) and transported to the laboratory. Eggshell percentage was determined by cracking the eggs, separating the shells, and incubating them at 65 °C for 72 hours. After cooling, shell weight was measured and expressed as a percentage of the total egg weight. Eggshells were divided into three sections (wide, narrow, and middle), and thickness was measured using a precise caliper (Mitutoyo, Tokyo, Japan) with 0.001 mm accuracy. The average of these measurements was recorded as the eggshell thickness. Eggshell strength was assessed using an eggshell strength tester (Okayama, Japan).
Albumen height was measured with a three-legged caliper, and Haugh units were calculated using the Equation 1:
1. HU=100 log (albumen height-1.7×(egg weight0.37)+7.57)
Yolk and albumen percentages were determined by weighing them separately and expressing their weights as percentages of the total egg weight. Yolk color was evaluated using the Roche color scale. The yolk index was calculated by dividing the yolk diameter by the yolk height and multiplying by 100 (Torki et al., 2014). These traits were measured during both the heat stress and recovery periods.
Intestinal and magnum morphological assay and ovary weight
Following the completion of the heat stress and recovery periods, five birds were randomly selected from each treatment group. These birds were weighed and euthanized. After opening the abdominal cavity, the ovaries were collected and individually weighed. The weight of the ovaries was expressed as a percentage relative to the body weight (%). For histomorphometry experiments, five tissue samples were randomly selected from each treatment and transferred to the laboratory. The ventral cavity, including the oviduct and intestines, was carefully dissected. Three-centimeter sections from the small intestine (jejunum) were obtained at the end of both the heat stress and recovery periods.
Tissue sections from the magnum (part of the oviduct) were collected at the end of the recovery period. These tissue samples were first washed with a phosphate buffer solution and then fixed in a 10% formalin solution. The fixed tissue samples were then transported to a laboratory for histological analysis. Hematoxylin-eosin (H&E) staining was used to stain the tissue sections. Paraffin embedding was performed to prepare the tissue slides, and a microtome was used to obtain thin sections from the paraffin blocks. Various morphological characteristics were measured using a light microscope (Olympus CX31) connected to a computer. These measurements included villus height and width, crypt depth in the intestinal tissue, height and thickness of folds, epithelium height, depth and diameter of glands, as well as the thickness of the internal and outer muscle layers in the magnum tissue (Uni et al., 2001).
Statistical analysis
The data collected from the experiment were analyzed using a 2×5 factorial design within a completely randomized design (CRD). The main factors were ambient temperature (normal and heat stress) and the experimental treatments (control, black seed, L-carnitine, black seed + L-carnitine, and vitamin E). There were a total of 10 treatments, each replicated 5 times. The statistical analysis was performed using a general linear model (GLM) in SAS software (SAS, 2003), according to the following model:
Yij = μ + Ai + Bj + (A + B)ij + eij
Where, Yij is the dependent variable; μ is the population mean, Ai is the effect of ambient temperature, Bj is the effect of experimental treatments, (A × B)ij is the two-way interaction of treatment, and eij is the random error. The significance of differences between the means was assessed using Tukey’s test, with a significance level set at 5%.
Results
Egg quality traits
This study found a significant interaction between ambient temperature and experimental treatments that influenced egg quality traits in laying Japanese quails during heat stress (Table 3), but not during the recovery period (Table 4).
At the end of the heat stress period, the albumin percentage was higher in birds on the control diet under heat stress and those on a vitamin E diet under normal conditions compared to birds receiving a black seed + L-carnitine diet under heat stress (P<0.05). Additionally, albumin height and Haugh unit values were significantly higher in birds on the control diet and those consuming black seed under heat stress compared to those receiving L-carnitine (P<0.05). The yolk percentage was higher in birds receiving black seed + L-carnitine during heat stress than in birds on black seed alone under heat stress and those on vitamin E under normal conditions (P<0.05). Shell strength was greatest in birds on a vitamin E diet under normal conditions and lowest in those on the control diet under heat stress (P<0.05). No significant effects of temperature or treatments were observed on yolk color, shell percentage, or eggshell thickness. The yolk index increased under heat stress but was unaffected by experimental treatments (P<0.05) (Table 3).
During the recovery period, there were no significant effects of ambient temperature or experimental treatments on albumen height, albumen percentage, Haugh unit, yolk color, yolk index, yolk percentage, or eggshell percentage and thickness. However, eggshell strength decreased under heat stress (P<0.05). Birds receiving vitamin E and those on a black seed + L-carnitine diet demonstrated higher eggshell strength compared to the control group (P<0.05). A trend was observed for a lower eggshell percentage in birds raised under heat stress (P=0.06) (Table 4).
Intestinal morphological assay and ovary weight
The interaction between ambient temperature and experimental treatments did not significantly affect the intestinal morphology of laying Japanese quails during heat stress and recovery periods. However, exposure to high ambient temperatures resulted in a reduction in villus width (P<0.05). Other morphological characteristics, including villus length, crypt depth, and the ratio of villous length to crypt depth, remained unaffected by ambient temperature. During heat stress, quails receiving a black seed diet tended to have increased villus length (P=0.06), and those provided with black seed and L-carnitine exhibited greater villus width compared to the control diet and the vitamin E group (P<0.05). In the recovery period, no significant impact on villus length and width was observed from any treatments. Birds that received black seed and the black seed + L-carnitine treatment had greater crypt depth than the control group during both periods (P<0.05). The the ratio of villous length to crypt depth was higher in birds on the control diet, black seed, and L-carnitine during the heat stress period. In contrast, higher ratios were observed in the control and vitamin E groups during recovery compared to the black seed + L-carnitine group (P<0.05) (Table 5).
Furthermore, the interaction between ambient temperature and experimental treatments significantly affected the relative ovary weight of the quails during both heat stress and recovery periods. During heat stress, quails on the control diet displayed higher relative ovary weights compared to all other treatments, except for the black seed + L-carnitine group (P<0.05). This trend continued into the recovery period, where the control diet group showed the highest relative ovary weight at high temperatures (P<0.05). The absence of dietary supplements in the control group may have led to a physiological response aimed at maintaining reproductive function during heat stress (Table 5).
Magnum morphological assay
The effects of ambient temperature and experimental treatments on the microscopic structure of magnum tissue in laying Japanese quails are illustrated in Figure 1 and detailed in Table 6.
The interaction between temperature and treatments significantly influenced the histological properties of the oviduct magnum. Quails supplemented with vitamin E at high temperatures and those receiving black seed or black seed + L-carnitine at normal temperatures exhibited higher magnum fold heights compared to the groups that received black seed, L-carnitine, or black seed + L-carnitine at high temperatures (P<0.05). Quails on the control diet at high temperatures displayed the thinnest folds, except when compared to those receiving the black seed treatment at high temperatures (P<0.05). At normal temperatures, vitamin E supplementation resulted in increased epithelial height, outperforming other treatments except for black seed + L-carnitine under both temperature conditions (P<0.05). L-carnitine supplementation at high temperatures produced the thickest internal muscular layer (P<0.05). The group receiving black seed + L-carnitine at high temperatures also showed increased outer muscular layer thickness compared to the control, black seed, L-carnitine at high temperatures, and black seed + L-carnitine at normal temperatures (P<0.05). Moreover, vitamin E at high temperatures, along with control, black seed, L-carnitine, and black seed + L-carnitine at normal temperatures, enhanced magnum gland depth compared to L-carnitine at high temperatures (P<0.05). However, vitamin E supplementation reduced the magnum gland diameter relative to L-carnitine and black seed + L-carnitine (P<0.05).
Discussion
Egg quality traits
This study examined how ambient temperature and dietary treatments affected egg quality in laying Japanese quails during heat stress. The results showed significant improvements in albumin and Haugh unit values for control and vitamin E diets compared to the black seed + L-carnitine diet. Eggshell strength peaked in the vitamin E group. The findings of this study align with previous research by Mehaisen et al., (2019) which indicated that heat stress reduces eggshell strength in laying Japanese quails by impacting electrolyte regulation and altering blood acid-base balance, resulting in blood alkalosis and dehydration. Such imbalances adversely affect eggshell quality, enzyme activity, and protein synthesis. In this study, birds supplemented with dietary additives exhibited enhanced eggshell strength compared to the control group. Specifically, vitamin E was found to significantly improve eggshell strength and weight due to its antioxidant properties and improved bioavailability of calcium supplements (Nemati et al., 2020). Moreover, black seed extract at a concentration of 1 g/kg was shown to increase albumin height and support eggshell gland integrity, particularly under heat stress (Denli et al., 2004). L-carnitine was found to aid energy metabolism, enhancing fatty acid oxidation and calcium metabolism—both critical for eggshell formation (Łukaszewicz et al., 2007; Nemati et al., 2020). Thus, implementing tailored dietary strategies that include vitamin E, black seed, and L-carnitine may improve eggshell strength, egg quality, and production efficiency in environments experiencing high temperatures.
Intestinal morphological assay and ovary weight
The results demonstrated that additive supplements significantly influence the intestinal structure, epithelial integrity, and villus morphology in laying Japanese quails. Heat-stressed quails often experience decreased intestinal epithelial integrity (Yu et al., 2010), and specific antioxidants can help mitigate the detrimental effects of heat stress on growth and overall physiology (Sahin et al., 2008). The findings are consistent with previous research by Aziza et al., (2019) which showed that the inclusion of black seed oil in Japanese quail diets resulted in longer villi compared to the positive control group, enhancing intestinal morphology and feed utilization efficiency. Moreover, L-carnitine supplementation has been associated with increased length, width, surface area, and depth of villous crypts, attributed to improvements in growth performance and feed digestion (Abu-Alya et al., 2021). Interestingly, the combination of L-carnitine and black seed led to the lowest ratio of villous length to crypt depth, suggesting possible disturbances in intestinal morphology. This outcome could be due to the energy-diverting effects of L-carnitine, which enhances lipid metabolism and energy production but may also detract from maintaining intestinal structure (Rouhanipour et al., 2021). The combination of these supplements may further complicate nutrient absorption dynamics and gut microbiota composition, potentially triggering stress responses and hormonal changes that adversely affect intestinal health (Habibian et al., 2015).
Regarding relative ovary weight, the study highlights the physiological adaptations of quails under heat stress conditions. The increased relative ovarian weight in the control group may represent a compensatory response to heat stress, as heat stress negatively impacts reproductive systems, resulting in reduced egg production, egg quality, and ovarian development. Supplementation with black seed, vitamin E, and L-carnitine may have enabled birds to manage heat stress more effectively, reducing the necessity to allocate resources for ovarian maintenance, leading to lower relative ovarian weights compared to the control group (Attia et al., 2010). The presence of essential fatty acids, antioxidants, and bioactive compounds in black seed (Abd El-Hack et al., 2018), together with L-carnitine’s role in supporting energy metabolism and antioxidant protection (Rehman et al., 2017), suggests that these supplements can enhance reproductive performance and general health during stress conditions.
Magnum morphological assay
Heat stress is known to adversely impact the reproductive function of quails by disrupting hormone secretion rates and affecting gonadal sensitivity to hormones. High environmental temperatures negatively influence the production of various hormones, including estrogen, parathyroid hormone, thyroid hormone, gonadotropin, and calcitonin (Ayo et al., 2011). In this study, L-carnitine supplementation—particularly at a dosage of 100 mg/kg—was found to increase the thickness of the magnum’s internal muscle layer in quails, corroborating findings from Rouhanipour et al. and Agarwal and Said, who noted L-carnitine’s positive effects on magnum morphology. L-carnitine enhances fatty acid oxidation, facilitating the synthesis of estrogen and progesterone by regenerating the reducing equivalents necessary for cholesterol side-chain cleavage—a critical process for ovarian growth and follicular maturation (Agarwal & Said, 2004). Additionally, L-carnitine possesses antioxidant properties (Xu et al., 2003), and improved magnum morphology resulting from L-carnitine supplementation may lead to increased egg protein synthesis throughout the oviduct, thereby enhancing albumen quality. L-carnitine may also expedite yolk lipid storage, promoting follicular development and increasing metabolic activity in both the shell gland and magnum. Consequently, this process facilitates the accumulation of albumen and calcium in the eggshell, contributing to increased eggshell thickness and egg weight (Kazemi-Fard et al., 2015). While research specifically targeting the effects of black seed on reproductive health is limited, some studies have indicated its antioxidant and anti-inflammatory benefits. For instance, Saleh et al. (2019) evaluated the impact of cumin seed oil on reproductive morphology in laying hens and found no adverse effects. Further investigation, including clinical trials, is necessary to better understand the beneficial effects and modes of action of black seed on reproductive health.
Conclusion
This study evaluated the effects of black seed and L-carnitine on egg quality, as well as intestinal and magnum morphology of laying Japanese quails under both normal and heat stress conditions. The findings indicated that dietary supplementation with black seed and vitamin E significantly enhances egg quality, particularly in terms of Haugh unit values and eggshell strength, especially during heat stress. Additionally, these supplements improve intestinal health and ovarian weight through enhanced metabolic efficiency and antioxidant protection. While the combination of black seed and L-carnitine shows potential in improving certain morphological aspects, its effects vary with temperature conditions. Overall, implementing these dietary strategies can optimize quail performance and welfare under different environmental stressors, emphasizing the critical role of tailored nutrition in poultry management. The study highlights the need for further research to explore additional nutritional interventions and management practices to further optimize performance in laying quail production systems.
Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Animal Welfare Committee of the Department of Animal Science, University of Tehran, Tehran, Iran (Code: IR.AUSMT.REC.1400.16).
Funding
This study was extracted from the PhD dissertation of Atefe Habibi, approved by the Department of Animal Science, Faculty of Agricultural Technology (Aburaihan), University of Tehran, Pakdasht, Iran. This research was financially supported by the University of Tehran, Faculty of Agricultural Technology (Aburaihan), Pakdasht, Iran.
Authors' contributions
Conceptualization and statistical analysis: Shokoufe Ghazanfari; Methodology, data curation, and formal analysis: Atefe Habibi, Shokoufe Ghazanfari, and Abdullah Mohammadi-Sang Cheshmeh; Investigation: Atefe Habibi and Abdullah Mohammadi-Sang Cheshmeh; Sample collection, analysis, and writing the original draft: Atefe Habibi; Supervision, review and editing: Shokoufe Ghazanfari, Abdullah Mohammadi-Sang Cheshmeh, and Mohammad Amir Karimi Torshizi; Final approval: All authors.
Conflict of interest
The authors declared no conflict of interest.
Acknowledgments
The authors would like to thank the Faculty of Agricultural Technology (Aburaihan), University of Tehran, for providing the research facilities and administrative support.
References
Abd El-Hack, M. E., Mahgoub, S. A., Hussein, M. M. A., & Saadeldin, I. M. (2018). Improving growth performance and health status of meat-type quail by supplementing the diet with black cumin cold-pressed oil as a natural alternative for antibiotics. Environmental Science and Pollution Research International, 25(2), 1157–1167. [DOI:10.1007/s11356-017-0514-0] [PMID]
Abu-Alya, I. S., Alharbi, Y. M., Abdel-Rahman, H. A., & Zahran, I. S. (2021). Effect of l-carnitine and/or calf thymus gland extract supplementation on immunity, antioxidant, duodenal histomorphometric, growth, and economic performance of Japanese quail (Coturnix coturnix japonica). Veterinary Sciences, 8(11), 251. [DOI:10.3390/vetsci8110251] [PMID]
Agarwal, A., & Said, T. M. (2004). Carnitines and male infertility. Reproductive Biomedicine Online, 8(4), 376-384. [DOI:10.1016/S1472-6483(10)60920-0] [PMID]
AOAC. (2007). Official methods of analysis of AOAC international. Gaithersburg (MD): AOAC Int.
Attia, Y. A., Abdalah, A. A., Zeweil, H. S., Bovera, F., Tag El-Din, A. A., & Araft, M. A. (2010). Effect of inorganic or organic selenium supplementation on productive performance, egg quality and some physiological traits of dual-purpose breeding hens. Czech Journal of Animal Science, 55, 505-519. [DOI:10.17221/1702-CJAS]
Ayo, J. O., Obidi, J. A., & Rekwot, P. I. (2011). Effects of heat stress on the well-being, fertility, and hatchability of chickens in the northern Guinea savannah zone of Nigeria: A review. ISRN Veterinary Science, 2011, 838606. [DOI:10.5402/2011/838606] [PMID]
Aziza, A. E., Abdelhamid, F. M., Risha, E. F., Elsayed, M. M., & Awadin, W. F. (2019). Influence of Nigella sativa and rosemary oils on growth performance, biochemical, antioxidant and immunological parameters, and pathological changes in Japanese quail challenged with Escherichia coli. Journal of Animal and Feed Science, 28(4):354-366. [DOI:10.22358/jafs/114239/2019]
Davodzadeh, M., Vakili, S. T., Mirzadeh, K., & Aghaei, A. (2017). [Effect of different levels of dietary vitamin A on reproductive and productive parameters in Japanese quail (Persian)]. Iranian Journal of Animal Science, 48(2), 251-259. [DOI:10.22059/ijas.2017.235166.653534]
Denli, M., Okan, F., & Uluocak, A. N. (2004). Effect of dietary black seed (Nigella sativa L.) extract supplementation on laying performance and egg quality of quail (Coturnix coturnix japonica). Journal of Applied Animal Research, 26(2), 73-76. [DOI:10.1080/09712119.2004.9706511]
Habibi, A., Ghazanfari, S., Karimi Torshizi, M. A., & Mohammadi-Sangcheshmeh, A. (2024). [The effects of adding black seed, L-carnitine, and vitamin E on production performance, carcass characteristics blood biochemical, and immune parameters of Japanese laying quail under heat stress (Persian)]. Iranian Journal of Animal Science Research, 16(1),101-124. [DOI:10.22067/ijasr.2024.85782.1185]
Habibian, M., Sadeghi, G., Ghazi, S., & Moeini, M. M. (2015). Selenium as a feed supplement for heat-stressed poultry: A review. Biological Trace Element Research, 165(2), 183-193. [DOI:10.1007/s12011-015-0275-x] [PMID]
Isik, S., Erdem, S., & Kartal, M. (2019). Investigation of the fatty acid profile of commercial black cumin seed oils and seed oil capsules: Application to real samples. Journal of Chemical Metrology, 13(2), 53-60. [DOI:10.25135/jcm.26.19.08.1385]
Kazemi-Fard, M., Yousefi, S., Dirandeh, E., & Rezaei, M. (2015). Effect of different levels of L-carnitine on the productive performance, egg quality, blood parameters and egg yolk cholesterol in laying hens. Poultry Science Journal, 3(2), 105-111. [Link]
Lukanov, H. (2019). Domestic quail (Coturnix japonica domestica): Is there such a farm animal? World’s Poultry Science Journal, 75(4), 547-558. [DOI:10.1017/S0043933919000631]
Łukaszewicz, E., Kowalczyk, A., Korzeniowska, M., & Jerysz, A. (2007). Effect of feed supplementation with organic selenium and vitamin E on physical characteristics of Japanese quail (Coturnix japonica) eggs. Polish Journal of Food and Nutrition Sciences, 57(4B), 377-381. [Link]
Mehaisen, G. M. K., Desoky, A. A., Sakr, O. G., Sallam, W., & Abass, A. O. (2019). Propolis alleviates the negative effects of heat stress on egg production, egg quality, physiological and immunological aspects of laying Japanese quail. Plos One, 14(4), e0214839. [DOI:10.1371/journal.pone.0214839] [PMID]
Nemati, Z., Ahmadian, H., Besharati, M., Lesson, S., Alirezalu, K., & Domínguez, R., et al. (2020). Assessment of dietary selenium and vitamin e on laying performance and quality parameters of fresh and stored eggs in Japanese quails. Foods (Basel, Switzerland), 9(9), 1324. [DOI:10.3390/foods9091324] [PMID]
Peebles, E. D., Kidd, M. T., McDaniel, C. D., Tanksley, J. P., Parker, H. M., & Corzo, A., et al. (2007). Effects of breeder hen age and dietary L-carnitine on progeny embryogenesis. British Poultry Science, 48(3), 299-307. [DOI:10.1080/00071660701261278] [PMID]
Raya, A. H., Dorra, T. M., Rabie, M. H., El Sherif, K., & Kalaba, Z. M. (2007). The use of dietary vitamin E and potassium chloride to alleviate the effects of heat stress on the performance of laying hens. Journal of Animal and Poultry Production, 32(12), 9897-9915. [DOI:10.21608/jappmu.2007.221160]
Rehman, Z., Naz, S., Khan, R. U., & Tahir, M. (2017). An update on potential applications of L-carnitine in poultry. World’s Poultry Science Journal, 73(4), 823-830. [DOI:10.1017/S0043933917000733]
Rouhanipour, H., Sharifi, D., & Irajian, G. H. (2021). The effect of L-carnitine and omega-3 fatty acids in the diet on morphology of liver, intestine and oviduct of laying hens. Research on Animal Production, 12(31), 31-42. [DOI:10.52547/rap.12.31.31]
Sahin, N., Orhan, C., Tuzcu, M., Sahin, K., & Kucuk, O. (2008). The effects of tomato powder supplementation on performance and lipid peroxidation in quail. Poultry Science, 87(2), 276-283. [DOI:10.3382/ps.2007-00207] [PMID]
Sahin, N., Tuzcu, M., Orhan, C., Onderci, M., Eroksuz, Y., & Sahin, K. (2009). The effects of vitamin C and E supplementation on heat shock protein 70 response of ovary and brain in heat-stressed quail. British Poultry Science, 50(2), 259-65. [DOI:10.1080/00071660902758981] [PMID]
Saleh, A. A., Kirrella, A. A., Dawood, M. A., & Ebeid, T. A. (2019). Effect of dietary inclusion of cumin seed oil on the performance, egg quality, immune response, and ovarian development in laying hens under high ambient temperature. Journal of Animal Physiology and Animal Nutrition, 103(6), 1810-1817. [DOI:10.1111/jpn.13206] [PMID]
SAS. (2003). SAS/STAT User's Guide, Release 8.02 ed. Cary, NC, US: SAS Institute Inc.
Seidavi, A. R., Laudadio, V., Khazaei, R., Puvača, N., Selvaggi, M., & Tufarelli, V. (2020). Feeding of black cumin (Nigella sativa L.) and its effects on poultry production and health. World’s Poultry Science Journal, 76(2), 346-357. [DOI:10.1080/00439339.2020.1750328]
Torki, M., Zangeneh, S., & Habibian, M. (2014). Performance, egg quality traits, and serum metabolite concentrations of laying hens affected by dietary supplemental chromium picolinate and vitamin C under a heat-stress condition. Biological Trace Element Research, 157(2), 120–129. [DOI:10.1007/s12011-013-9872-8] [PMID]
Uni, Z., Gal-Garber, O., Geyra, A., Sklan, D., & Yahav, S. (2001). Changes in growth and function of chick small intestine epithelium due to early thermal conditioning. Poultry Science, 80(4), 438-445. [DOI:10.1093/ps/80.4.438] [PMID]
Xu, Z. R., Wang, M. Q., Mao, H. X., Zhan, X. A., & Hu, C. H. (2003). Effects of L-carnitine on growth performance, carcass composition, and metabolism of lipids in male broilers. Poultry Science, 82(3), 408-413. [DOI:10.1093/ps/82.3.408] [PMID]
Yu, J., Yin, P., Liu, F., Cheng, G., Guo, K., & Lu, A., et al. (2010). Effect of heat stress on the porcine small intestine: a morphological and gene expression study. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 156(1), 119-128. [DOI:10.1016/j.cbpa.2010.01.008] [PMID]
