PERTANIKA JOURNAL OF SCIENCE AND TECHNOLOGY

Plants, especially on the leaves, have various bioactive compounds capable of becoming natural growth promoters. Plant leaf extracts have been widely studied for their ability as an antibiotic substitute for broiler chickens. This meta-analysis study was aimed to assess the effectiveness of supplementations with leaf extract on the growth performance of broiler chickens, using average daily feed intake (ADFI), average daily gain (ADG), final body weight (FBW), and feed conversion ratio (FCR) as responses observed criteria. The meta-analysis study was based on the articles published from 2006 to recent years as several countries started to ban in-feed antibiotics. Databases (PubMed, Scopus, Directory of Open Access Journals [DOAJ], and ScienceDirect) were searched for peer-reviewed randomised controlled trials (RCTs) published in English. The meta-analysis included 19 research papers that met the criteria. Overall results showed a significant increase (P < 0.001) in ADFI by 0.56 g/day (95% confidence interval [CI] = 0.02 to 1.11), in ADG by 1.57 g/day (95% CI = 0.77 to 2.36), and in FBW by 2.28 (95% CI = 1.40 to 3.16). At the same time, the FCR was reduced (P < 0.001) by -1.25 (95% CI = -1.76 to -0.73) relative to controls taking cognisance of publication bias and heterogeneity. Results in the current meta-analysis study indicated that herbal feed additives were proven to be effective as growth promoters in broiler chickens.

• Al Salman, N. T. S., & Al-Gharawi, J. K. M. (2019). Effect of eucalyptus leaves water extract on some productive traits of broilers. Plant Archives, 19(Supplement 1), 920-923.

• Alabi, O. J., Malik, A. D., Ng’Ambi, J. W., Obaje, P., & Ojo, B. K. (2017). Effect of aqueous Moringa oleifera (Lam) leaf extracts on growth performance and carcass characteristics of Hubbard broiler chicken. Revista Brasileira de Ciência Avícola, 19(2), 273–280. https://doi.org/10.1590/1806-9061-2016-0373

• Alabi, O. J., Ng’ambi, J. W., & Mbajiorgu, E. F. (2020). Aqueous extract of moringa (Moringa oleifera) leaf (AEMOL) on the growth, sensory and histology parameters of broiler chickens. Applied Ecology and Environmental Research, 18(5), 6753–6764. https://doi.org/10.15666/aeer/1805_67536764

• Albarrak, S. M. (2021). Antioxidant and immune responses of broiler chickens supplemented with Rhazya stricta extract in drinking water. Veterinary World, 14(6), 1437-1449. https://doi.org/10.14202/vetworld.2021.1437-1449

• Ali, H., Al-Khalifa, A. R., Aouf, A., Boukhebti, H., & Farouk, A. (2020). Effect of nanoencapsulation on volatile constituents, and antioxidant and anticancer activities of Algerian Origanum glandulosum Desf. essential oil. Scientific Reports, 10, 2812. https://doi.org/10.1038/s41598-020-59686-w

• Aligiannis, N., Kalpoutzakis, E., Mitaku, S., & Chinou, I. B. (2001). Composition and antimicrobial activity of the essential oils of two Origanum species. Journal of Agricultural and Food Chemistry, 49(9), 4168–4170. https://doi.org/10.1021/jf001494m

• Aljumaah, M. R., Suliman, G. M., Abdullatif, A. A., & Abudabos, A. M. (2020). Effects of phytobiotic feed additives on growth traits, blood biochemistry, and meat characteristics of broiler chickens exposed to Salmonella typhimurium. Poultry Science, 99(11), 5744–5751. https://doi.org/10.1016/j.psj.2020.07.033

• Al-khalaifah, H. S., Badawi, M. E., Abd El-Aziz, R. M., Ali, M. A., & Omar, A. E. (2020). Effect of Egyptian leek leaf extract supplementation on productive and economic performance of Broilers. Frontiers in Veterinary Science, 7, 584921. https://doi.org/10.3389/fvets.2020.584921

• Al-Masari, A. I., & Al-Himdany, H. Q. (2022). Effect of adding artichoke leaves extract powder (Cynara scolymus L.) to the diet on the productive performance of broilers. Iraqi Journal of Agricultural Sciences, 53(1), 9–15. https://doi.org/10.36103/ijas.v53i1.1500

• Al-Musawi, T. A. M., Hassan, M. A., Al-Gharawi, J. K. M., & Al-Ziadi, R. A. (2019). Effect of water of extract of parsley (Petroselinum sativum) leaves in some productive traits of broiler. Plant Archives, 19(Supplement 1), 1284-1287.

• Anggrain, N., Kurtini, T., & Septinova, D. (2014). Perbandingan fase produksi telur kalkun terhadap fertilitas, susut tetas, daya tetas, dan bobot tetas [The comparison of production phase of turkey eggs on fertility, weight loss, hatchability, and hatching weight]. Jurnal Ilmiah Peternakan Terpadu, 2(1), 5-10. https://doi.org/10.23960/jipt.v2i1.523

• Aroche, R., Martínez, Y., Ruan, Z., Guan, G., Waititu, S., Nyachoti, C. M., Más, D., & Lan, S. (2018). Dietary inclusion of a mixed powder of medicinal plant leaves enhances the feed efficiency and immune function in broiler chickens. Journal of Chemistry, 2018, 4073068. https://doi.org/10.1155/2018/4073068

• Azimi, V., Mirakzehi, M. T., & Saleh, H. (2020). Hydroalcoholic extract of Withania somnifera leaf and α-tocopherol acetate in diets containing oxidised oil: Effects on growth performance, immune response, and oxidative status in broiler chickens. Italian Journal of Animal Science, 19(1), 917–928. https://doi.org/10.1080/1828051X.2020.1808537

• Basit, M. A., Arifah, A. K., Loh, T. C., Saleha, A. A., Salleh, A., Kaka, U., & Idris, S. B. (2020). Effects of graded dose dietary supplementation of Piper betle leaf meal and Persicaria odorata leaf meal on growth performance, apparent ileal digestibility, and gut morphology in broilers. Saudi Journal of Biological Sciences, 27(6), 1503–1513. https://doi.org/10.1016/j.sjbs.2020.04.017

• Baskara, A. P., Sharma, S., Sener-Aydemir, A., Koger, S., Ariyadi, B., Dono, N. D., Zuprizal, Z. & Metzler-Zebeli, B. U. (2021). Cinnamon bark oil and coconut oil emulsions modified small intestinal motility and barrier function in laying hens in an ex vivo experiment. British Poultry Science, 62(3), 435-442. https://doi.org/10.1080/00071668.2020.1870662

• Brenes, A., & Roura, E. (2010). Essential oils in poultry nutrition: Main effects and modes of action. Animal Feed Science and Technology, 158(1-2), 1-14. https://doi.org/10.1016/j.anifeedsci.2010.03.007

• Chen, M., Ding, Y., & Tong, Z. (2020). Efficacy and safety of Sophora flavescens (Kushen) based traditional Chinese medicine in the treatment of ulcerative colitis: Clinical evidence and potential mechanisms. Frontiers in Pharmacology, 11, 603476. https://doi.org/10.3389/fphar.2020.603476

• Cheng, L., Zhang, W., Jin, Q., Zhu, Y., Chen, R., Tian, Q., Yan, N., & Guo, L. (2021). The effects of dietary supplementation with lotus leaf extract on the immune response and intestinal microbiota composition of broiler chickens. Poultry Science, 100(3), 100925. https://doi.org/10.1016/j.psj.2020.12.023

• Clavijo, V., & Flórez, M. J. V. (2018). The gastrointestinal microbiome and its association with the control of pathogens in broiler chicken production: A review. Poultry science, 97(3), 1006-1021. https://doi.org/10.3382/ps/pex359

• Delespaul, Q., de Billerbeck, V. G., Roques, C. G., Michel, G., Marquier-Viñuales, C., & Bessière, J.-M. (2000). The antifungal activity of essential oils as determined by different screening methods. Journal of Essential Oil Research, 12(2), 256–266. https://doi.org/10.1080/10412905.2000.9699510

• DerSimonian, R., & Laird, N. (1986). Meta-analysis in clinical trials. Controlled Clinical Trials, 7(3), 177–188. https://doi.org/10.1016/0197-2456(86)90046-2

• Duskaev, G. K., Kvan, O. V., & Rakhmatullin, S. G. (2020). Eucalyptus viminalis leaf extract alters the productivity and blood parameters of healthy broiler chickens. Veterinary World, 13(12), 2673–2680. https://doi.org/10.14202/vetworld.2020.2673-2680

• Elfrida., Tarigan, N. S., & Suwardi, A. B. (2021). Ethnobotanical study of medicinal plants used by community in Jambur Labu Village, East Aceh, Indonesia. Biodiversitas, 22(7), 2893–2900. https://doi.org/10.13057/biodiv/d220741

• Erener, G., Ocak, N., Ozturk, E., Cankaya, S., Ozkanca, R., & Altop, A. (2020). Evaluation of olive leaf extract as a growth promoter on the performance, blood biochemical parameters, and caecal microflora of broiler chickens. Revista Brasileira de Zootecnia, 49, e20180300. https://doi.org/10.37496/RBZ4920180300

• Escorcia, M., Sánchez-Godoy, F., Ramos-Vidales, D., Medina-Campos, O. N., & Pedraza- Chaverri, J. (2020). Effect of the age and body weight of the broiler breeders male on the presentation of oxidative stress and its correlation with the quality of testicular parenchyma and physiological antioxidant levels. Veterinary Sciences, 7(2), 69. https://doi.org/10.3390/vetsci7020069

• Fathi, M., Mohammad, H. N., Abdolah, K. A., Saeidian, S., & Haydari, M. (2022). Effects of basil (Ocimum basilicum) leaf extract (BLE) on performance, blood biochemistry, antioxidant status, and oxidative stability of the meat of broiler chickens. Poultry Science Journal, 10(1), 91–97. https://doi.org/10.22069/psj.2022.19725.1753

• Gheisar, M. M., & Kim, I. H. (2018). Phytobiotics in poultry and swine nutrition – A review. Italian Journal of Animal Science, 17(1), 92-99. https://doi.org/10.1080/1828051X.2017.1350120

• Han, G. G., Kim, E. B., Lee, J., Lee, J.-Y., Jin, G., Park, J., Huh, C.-S., Kwon, I.-K., Kil, D. Y., Choi, Y.-J., & Kong, C. (2016). Relationship between the microbiota in different sections of the gastrointestinal tract, and the body weight of broiler chickens. SpringerPlus, 5, 911. https://doi.org/10.1186/s40064-016-2604-8

• Hasemi, S. R., Zulkifli, I., Bejo, M. H., Farida, A., & Somchit, M. N. (2008). Acute toxicity study and phytochemical screening of selected herbal aqueous extract in broiler chicken. International Journal of Pharmacology, 4(5), 352–360. https://doi.org/10.3923/ijp.2008.352.360

• Hedges, L. V. (1981). Distribution theory for glass’s estimator of effect size and related estimators. Journal of Educational Statistics, 6(2), 107–128. https://doi.org/10.3102/10769986006002107

• Huang, Z., Jin, S., & Lv, Z. (2022). Dietary genistein supplementation alters mRNA expression profile and alternative splicing signature in the thymus of chicks with lipopolysaccharide challenge. Poultry Science, 101(2), 101561. https://doi.org/10.1016/j.psj.2021.101561

• Huyghebaert, G., Ducatelle, R., & Van Immerseel, F. (2011). An update on alternatives to antimicrobial growth promoters for broilers. Veterinary Journal, 187(2), 182–188. https://doi.org/10.1016/j.tvjl.2010.03.003

• Ibrahim, D., Eldemery, F., Metwally, A. S., Abd-Allah, E. M., Mohamed, D. T., Ismail, T. A., Hamed, T. A., Al Sadik, G. M., Neamat-Allah, A. N., & Abd El-Hamid, M. I. (2022). Dietary eugenol nanoemulsion potentiated performance of broiler chickens: Orchestration of digestive enzymes, intestinal barrier functions and cytokines related gene expression with a consequence of attenuating the severity of E. coli O78 infection. Frontiers in Veterinary Science, 9, 847580. https://doi.org/10.3389/fvets.2022.847580

• Islam, R., Sultana, N., Bhakta, S., Haque, Z., Hasan, A., Siddique, M. P., & Islam, M. R. (2023). Modulation of growth performance, gut morphometry, and cecal microbiota in broilers by clove (Syzygium aromaticum) and tulsi (Ocimum sanctum) supplementation. Poultry Science, 102(1), 102266. https://doi.org/10.1016/j.psj.2022.102266

• Khan, A., Tahir, M., Alhidary, I., Abdelrahman, M., Swelum, A. A., & Khan, R. U. (2022). Role of dietary Moringa oleifera leaf extract on productive parameters, humoral immunity, and lipid peroxidation in broiler chicks. Animal Biotechnology, 33(6), 1353–1358. https://doi.org/10.1080/10495398.2021.1899936

• Kokkini, S., Karousou, R., & Vokout, D. (1994). Pattern of geographic variation of Origanum vulgare trichomes and essential oil content in Greece. Biochemical Systematics and Ecology, 22(5), 517–528. https://doi.org/10.1016/0305-1978(94)90046-9

• Kumar, R., Kumar, K., Kumar, A., Kumar, S., Singh, P. K., Sinha, R. R. K., & Moni, C. (2021). Nutritional and physiological responses of broiler chicken to the dietary supplementation of Moringa oleifera aqueous leaf extract and ascorbic acid in tropics. Tropical Animal Health and Production, 53, 428. https://doi.org/10.1007/s11250-021-02864-3

• Lambert, R. J. W., Skandamis, P. N., Coote, P. J., & Nychas, G.-J. E. (2001). A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol, and carvacrol. Journal of Applied Microbiology, 91(3), 453–462. https://doi.org/10.1046/j.1365-2672.2001.01428.x

• Liu, M., Zhou, J., Li, Y., Ding, Y., Lian, J., Dong, Q., Qu, Q., Lv, W., & Guo, S. (2023). Effects of dietary polyherbal mixtures on growth performance, antioxidant capacity, immune function, and jejunal health of yellow-feathered broilers. Poultry Science, 102(7), 102714. https://doi.org/10.1016/j.psj.2023.102714

• Liu, S. J., Wang, J., He, T. F., Liu, H. S., & Piao, X. S. (2021). Effects of natural capsicum extract on growth performance, nutrient utilization, antioxidant status, immune function, and meat quality in broilers. Poultry Science, 100(9), 101301. https://doi.org/10.1016/j.psj.2021.101301

• Luo, Q., Tian, Z., Zheng, T., Xu, S., Ma, Y., Zou, S., & Zuo, Z. (2022). Terpenoid composition and antioxidant activity of extracts from four chemotypes of Cinnamomum camphora and their main antioxidant agents. Biofuels, Bioproducts, and Biorefining, 16(2), 510-522. https://doi.org/10.1002/bbb.2320

• Masyita, A., Sari, R. M., Astuti, A. D., Yasir, B., Rumata, N. R., Emran, T. B., Nainu, F., & Simal-Gandara, J. (2022). Terpenes and terpenoids as main bioactive compounds of essential oils, their roles in human health, and potential application as natural food preservatives. Food chemistry: X, 13, 100217. https://doi.org/10.1016/j.fochx.2022.100217

• McGimpsey, J. A., Douglas, M. H., Van Klink, J. W., Beauregard, D. A., & Perry, N. B. (1994). Seasonal variation in essential oil yield and composition from naturalized Thymus vulgaris L. in New Zealand. Flavour and Fragrance Journal, 9(6), 347-352. https://doi.org/10.1002/ffj.2730090613

• Meng, W. S., Zou, Q., Xiao, Y., Ma, W., Zhang, J., Wang, T., & Li, D. (2023). Growth performance and cecal microbiota of broiler chicks as affected by drinking water disinfection and/or herbal extract blend supplementation. Poultry Science, 102(7), 102707. https://doi.org/10.1016/j.psj.2023.102707

• Mohamed, M. A., & Hassan, H. M. A. (2023). Phytogenic substances as safe growth promoters in poultry nutrition. International Journal of Veterinary Science, 12(1), 89–100. https://doi.org/10.47278/journal.ijvs/2022.134

• Nakamura, K., Shishido, M., Shimamoto, S., Ogawa, G., Khandelwal, N., Tatsugawa, K., Fujita, Y., Ohtsuka, A., & Ijiri, D. (2022). Effects of supplementation with dried neem leaf extract on lipid peroxidation and antioxidant enzyme mRNA expression in the pectoralis major muscle of broiler chickens. Journal of Poultry Science, 59(1), 75-80. https://doi.org/10.2141/jpsa.0200120

• Onu, P. N. (2012). Effect of aqueous extract of Telfairia occidentalis leaf on the performance and haematological indices of starter broilers. ISRN Veterinary Science, 2012, 726515. https://doi.org/10.5402/2012/726515

• Page, M. J., McKenzie, J. E., Bossuyt, P. M., Boutron, I., Hoffmann, T. C., Mulrow, C. D., Shamseer, L., Tetzlaff, J. M., Akl, E. A., Brennan, S. E., Chou, R., Glanville, J., Grimshaw, J. M., Hróbjartsson, A., Lalu, M. M., Li, T., Loder, E. W., Mayo-Wilson, E., McDonald, S., … Moher, D. (2021). The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. PLOS Medicine, 18(3), e1003583. https://doi.org/10.1371/JOURNAL.PMED.1003583

• Parobali, T., Adjei-Mensah, B., Songuine, T., Yarkoa, T., Karou, S. D., & Eklu-Gadegbeku, K. (2024). Influence of Citrus sinensis seed powder on growth performance, morphological, and histological development of the small intestine of broiler chickens. Journal of Applied Poultry Research, 33(2), 100395. https://doi.org/10.1016/j.japr.2023.100395

• Platzer, M., Kiese, S., Tybussek, T., Herfellner, T., Schneider, F., Schweiggert-Weisz, U., & Eisner, P. (2022). Radical scavenging mechanisms of phenolic compounds: A quantitative structure-property relationship (QSPR) study. Frontiers in Nutrition, 9, 882458. https://doi.org/10.3389/fnut.2022.882458

• Prakatur, I., Miskulin, M., Pavic, M., Marjanovic, K., Blazicevic, V., Miskulin, I., & Domacinovic, M. (2019). Intestinal morphology in broiler chickens supplemented with propolis and bee pollen. Animals, 9(6), 301. https://doi.org/10.3390/ani9060301

• Qureshi, S., Banday, M., Adil, S., Shakeel, I., & Munshi, Z. H. (2015). Effect of dandelion leaves and fenugreek seeds with or without enzyme addition on performance and blood biochemistry of broiler chicken, and evaluation of their in vitro antibacterial activity. Indian Journal of Animal Sciences, 85(11), 1248–1254.

• Racanicci, A. M. C., Menten, J. F. M., Alencar, S. M., Buissa, R. S., & Skibsted, L. H. (2011). Mate (Ilex paraguariensis) as dietary additive for broilers: Performance and oxidative stability of meat. European Food Research and Technology, 232, 655–661. https://doi.org/10.1007/s00217-011-1432-x

• Ranga Niroshan Appuhamy, J. A. D., Strathe, A. B., Jayasundara, S., Wagner-Riddle, C., Dijkstra, J., France, J., & Kebreab, E. (2013). Anti-methanogenic effects of monensin in dairy and beef cattle: A meta-analysis. Journal of Dairy Science, 96(8), 5161–5173. https://doi.org/10.3168/jds.2012-5923

• Rashid, Z., Mirani, Z. A., Zehra, S., Gilani, S. M. H., Ashraf, A., Azhar, A., Al-Ghanim, K. A., Al-Misned, F., Al-Mulahim, N., Mahboob, S., & Galani, S. (2020). Enhanced modulation of gut microbial dynamics affecting body weight in birds triggered by natural growth promoters administered in conventional feed. Saudi Journal of Biological Sciences, 27(10), 2747-2755. https://doi.org/10.1016/j.sjbs.2020.06.027

• Rasouli, B., Movahhedkhah, S., Seidavi, A., Haq, Q. M. I., Kadim, I., Laudadio, V., Mazzei, D., & Tufarelli, V. (2020). Effect of sage (Salvia officinalis L.) aqueous leaf extract on performance, blood constituents, immunity response, and ileal microflora of broiler chickens. Agroforestry Systems, 94, 1179–1187. https://doi.org/10.1007/s10457-019-00401-8

• Sahu, J., Koley, K. M., & Sahu, B. D. (2017). Attribution of antibacterial and antioxidant activity of Cassia tora extract toward its growth promoting effect in broiler birds. Veterinary World, 10(2), 221–226. https://doi.org/10.14202/vetworld.2017.221-226

• Salgueiro, A. R., Vila, R., Cristina Figue, A., Barroso, G., Canigueral, S., Casanova, J., da Cunha, A. P., & Adzet, T (1997). Variability of essential oils of Thymus caespititis from Portugal. Phytochemistry, 45(2), 307–311. https://doi.org/10.1016/S0031-9422(96)00872-2

• Sani, G. L., Mohammadi, M., Jalali Sendi, J., Abolghasemi, S. A., & Roostaie Ali Mehr, M. (2013). Extract and leaf powder effect of Artemisia annua on performance, cellular, and humoral immunity in broilers. Iranian Journal of Veterinary Research, 14(1), 15-20.

• Shen, M., Xie, Z., Jia, M., Li, A., Han, H., Wang, T., & Zhang, L. (2019). Effect of bamboo leaf extract on antioxidant status and cholesterol metabolism in broiler chickens. Animals, 9(9), 699. https://doi.org/10.3390/ani9090699

• Song, B., He, J., Pan, X., Kong, L., Xiao, C., Keerqin, C., & Song, Z. (2023). Dietary Macleaya cordata extract supplementation improves the growth performance and gut health of broiler chickens with necrotic enteritis. Journal of Animal Science and Biotechnology, 14, 113. https://doi.org/10.1186/s40104-023-00916-2

• Sun, H. Y., Kim, Y. M., & Kim, I. H. (2020). Evaluation of Achyranthes japonica Nakai extract on growth performance, nutrient utilization, cecal microbiota, excreta noxious gas emission, and meat quality in broilers fed corn–wheat–soybean meal diet. Poultry Science, 99(11), 5728–5735. https://doi.org/10.1016/j.psj.2020.07.023

• Teteh, A., Lawson, E., Tona, K., Decuypere, E., & Gbeassor, M. (2013). Moringa oleifera leave: Hydro-alcoholic extract and effects on growth performance of broilers. International Journal of Poultry Science, 12(7), 401–405. https://doi.org/10.3923/ijps.2013.401.405

• Wallace, B. C., Lajeunesse, M. J., Dietz, G., Dahabreh, I. J., Trikalinos, T. A., Schmid, C. H., & Gurevitch, J. (2017). OpenMEE: Intuitive, open-source software for meta-analysis in ecology and evolutionary biology. British Ecological Society, 8(8), 941–947. https://doi.org/10.1111/2041-210X.12708

• Wang, M. L., Suo, X., Gu, J. H., Zhang, W. W., Fang, Q., & Wang, X. (2008). Influence of grape seed proanthocyanidin extract in broiler chickens: Effect on chicken coccidiosis and antioxidant status. Poultry Science, 87(11), 2273–2280. https://doi.org/10.3382/ps.2008-00077

• Wang, S., Zhang, L., Li, J., Cong, J., Gao, F., & Zhou, G. (2017). Effects of dietary marigold extract supplementation on growth performance, pigmentation, antioxidant capacity and meat quality in broiler chickens. Asian-Australasian Journal of Animal Sciences, 30(1), 71-77. https://doi.org/10.5713/ajas.16.0075

• Windisch, W., Schedle, K., Plitzner, C., & Kroismayr, A. (2008). Use of phytogenic products as feed additives for swine and poultry. Journal of Animal Science, 86(suppl_14), E140–E148. https://doi.org/10.2527/jas.2007-0459

• Xie, P., Deng, Y., Huang, L., & Zhang, C. (2022). Effect of olive leaf (Olea europaea L.) extract addition to broiler diets on the growth performance, breast meat quality, antioxidant capacity, and caecal bacterial populations. Italian Journal of Animal Science, 21(1), 1246–1258. https://doi.org/10.1080/1828051X.2022.2105265

• Xu, P., Wang, J., Chen, P., Ding, H., Wang, X., Li, S., Fan, X., Zhou, Z., Shi, D., Li, Z., Cao, S., & Xiao, Y. (2024). Effects of pomegranate (Punica granatum L.) peel on the growth performance and intestinal microbiota of broilers challenged with Escherichia coli. Poultry Science, 103(2), 103304. https://doi.org/10.1016/j.psj.2023.103304

• Yan, J., Hu, R., Li, B., Tan, J., Wang, Y., Tang, Z., Liu, M., Fu, C., He, J., & Wu, X. (2022). Effect of Eucommia ulmoides leaf extract on growth performance, carcass traits, parameters of oxidative stress, and lipid metabolism in broiler chickens. Frontiers in Veterinary Science, 9, 945981. https://doi.org/10.3389/fvets.2022.945981

• Yang, C., Kabir Chowdhury, M. A., Hou, Y., & Gong, J. (2015). Phytogenic compounds as alternatives to in-feed antibiotics: Potentials and challenges in application. Pathogens, 4(1), 137-156. https://doi.org/10.3390/pathogens4010137

• Zhang, S., Zhu, C., Xie, H., Wang, L., & Hu, J. (2022). Effect of Gan Cao (Glycyrrhiza uralensis Fisch) polysaccharide on growth performance, immune function, and gut microflora of broiler chickens. Poultry Science, 101(10), 102068. https://doi.org/10.1016/j.psj.2022.102068

• Zhao, J. S., Deng, W., & Liu, H. W. (2019). Effects of chlorogenic acid-enriched extract from Eucommia ulmoides leaf on performance, meat quality, oxidative stability, and fatty acid profile of meat in heat-stressed broilers. Poultry Science, 98(7), 3040–3049. https://doi.org/10.3382/ps/pez081