With the imminent challenge of climate change and its antecedent of global warming, the growing increase in ambient temperature affects all life forms including humans, plants, and animals. This raises a major concern about the extent to which the ongoing variability in climatic conditions would directly and/or indirectly affect the future of animal production (Oke et al., 2021). Heat stress is a significant environmental stressor, especially in the tropics and sub-tropical regions of the world. It occurs under prevailing high temperatures where the animal cannot dissipate its body temperature to the surrounding environment, causing a negative balance between the amount of heat generated and the body’s heat loss (Lara and Rostagno, 2013). Heat stress largely affects poultry production since modern-day birds are highly vulnerable to high temperatures and they have limited heat dissipation capacity (Uyanga et al., 2022a). The feather coverage of birds and their lack of sweat glands makes them prone to high ambient temperatures relative to other monogastric animals (Zaboli et al., 2019). Thus, the incidence of heat stress is associated with severe detrimental effects on the health, welfare, and productivity of poultry species, accruing to significant economic losses (Oke et al., 2021; Madkour et al., 2023). Importantly the effects of heat stress on poultry production are directly associated with food safety issues, thus warranting special attention in order to bridge the protein demand to supply gap.

Studies have shown that heat stress negatively affects growth performance, production indices, behavior, immunity, metabolism, welfare, and physiological responses of poultry (Azad et al., 2010; Soleimani et al., 2011; Farag and Alagawany, 2018). It is characterized by an increase in body temperature, higher respiratory rate, decreased feed intake, lowered body weight, poor feed efficiency, low egg production, decreased reproduction, impaired immunity, impaired metabolism, alterations in intestinal microflora, poor intestinal morphology, increased inflammatory response, increased production of reactive oxygen species, deteriorated meat quality, and in extreme cases, results to death of the animals (Wang et al., 2018; Liu et al., 2020; Alagawany et al., 2021; Nawaz et al., 2021; Uyanga et al., 2021; Madkour et al., 2022). The effects of heat stress have been studied on different poultry species, and the findings reported are multifaceted, and interwoven. To better understand the impacts of heat stress in poultry and the strategies for its alleviation, various studies have been conducted under varied experimental conditions. Several works have extensively reviewed the impacts of heat stress and the approaches for its mitigation in poultry. It can be surmised that these mitigating approaches center on environmental modification, management techniques, nutritional manipulation, genetic manipulation, and perinatal conditioning of the birds (Lin et al., 2006; Saeed et al., 2019; Wasti et al., 2020; Abdel-Moneim et al., 2021; Kumar et al., 2021; Uyanga et al., 2022b; Madkour et al., 2023). Therefore, it is evident that a reasonable number of scientific information has been generated on heat stress in poultry, however, to the best of our knowledge, there currently exists no bibliometric study that has comprehensively examined the available literature to stimulate further research in this area.

Bibliometric analysis has been described as a scientific methodology that utilizes computer-assisted review to examine all the publications on a specific topic or field in order to identify the core research, authors of the subject, and their relationships over a given period (Nicolaisen, 2010; Liu et al., 2022). The conduct of bibliometric analysis provides information on the topic of interest and further gives an overall understanding of the intellectual landscape. Attributes such as the author or citation information, titles, keywords, and abstract data have been developed for network analysis and sociometric analysis (Han et al., 2020; Musa et al., 2020). Bibliometric is increasingly important in managing the increasing number of academic publications which often involve empirical contributions producing voluminous, fragmented, and controversial research outcomes (Aria and Cuccurullo, 2017). Compared to other scientific review techniques, bibliometric provides highly objective and reliable analyses since it employs a “systematic, transparent, and reproducible review process that is based on the statistical measurement of science, scientists, or scientific activity” (Wallin, 2005). Therefore, with the increasing number of research reporting on heat stress in poultry production, it was deemed necessary to provide evidence-based insights via a bibliometric analysis of the research productivity by authors, countries, keywords, funding agencies, and collaboration networks. The findings of this study would help unveil the research progress on heat stress in poultry and its development in recent decades. This would also provide organized information for researchers, poultry industry experts and further advance research in this area.

Therefore, this bibliometric study was conducted to investigate, identify and visualize the network of publications that have shaped the intellectual discourse and research structure on heat stress in poultry from 2000 to 2021. The mapping of the thematically related publications and an examination of the contributions, co-operations, and recent trends as it relates to the heat stress in poultry was also carried out.

Over the last decades, with the increasing awareness and global actions towards climate change and global warming, research on heat stress in farm animals especially poultry has gained attention, as evidenced by the annual increment in the number of publications. The number of publications and citation counts achieved each year is an indicator of the research interest and progress made by researchers in that specific area (Musa et al., 2020; Xu et al., 2022). Several researchers, countries, institutions, and industry partners have collaborated on studies to address “heat stress in poultry”, thus necessitating this bibliometric analysis to understand the milestones achieved, research gaps uncovered, and the trends for future research. Over the past two decades, the annual publications on heat stress in poultry showed a significant increase, and so far, the highest number of articles was achieved in 2021. The annual number of publications increased relatively slowly from 2000 until 2011, with fewer than 15 articles per year. The increase observed from 2012 could possibly occur due to increasing awareness of the impacts of heat stress on poultry (Lin et al., 2006; Yahav, 2009) and its association with oxidative stress (Altan et al., 2003; Mujahid et al., 2005), as seen from the records of top globally cited documents. More so, the dietary manipulation of heat stress in poultry using prebiotics and probiotics (Lan et al., 2004; Sohail et al., 2010), polyphenols (Pena et al., 2008; Aengwanich and Suttajit, 2010), amino acids (Zarate et al., 2003; Dai et al., 2011), as well as, minerals and vitamins (Sahin et al., 2002; Niu et al., 2009; Mohiti-Asli et al., 2010; Vakili et al., 2010; Moeini et al., 2011) etc., were gradually gaining research attention. The last 5 years have witnessed production exceeding 40 documents annually, accounting for 61.9% of the total documents. The increase in the number of publications was positively associated with the rise in the average annual citation in a monotonic relationship. Also, it is expected that with an increase in the number of citable years, the average citation will continue to increase. Therefore, consistent efforts to foster research and collaboration are necessary to drive annual publications, growth rate, and article citations on heat stress and poultry.

Importantly, China ranked foremost in its contribution to research on heat stress in poultry in terms of publications, top contributing authors, funding agencies, institutional affiliations, and corresponding authorship. The network analysis also revealed that China significantly cooperated with other countries including United States, Egypt, Turkey, Germany, and Australia. In terms of co-authorship, citations, and bibliographic coupling, China had the greatest connections, networks, and TLS with other countries. This may be closely attributed to the significant financial investments by the Chinese government to support research on heat stress in poultry. The study revealed that out of the top 10 funding agencies, five were sponsors from China including the National Natural Science Foundation of China, National Key Research and Development Program of China, and Natural Science Foundation of Jiangsu Province. Evidently, the most productive institutions were also from China, with the most significant being the Nanjing Agricultural University. The institutional networks for co-authorship and citation analysis further revealed that Nanjing Agricultural University played a significant role in establishing strong research cooperation and collaboration with other institutions both within and outside China.

With respect to the authors, Kazim Sahin from Firat University, Turkey, Nurhan Sahin from Firat University, Turkey, and Feng Gao from Nanjing Agricultural University, China contributed the highest to global research on heat stress in poultry. Studies by Kazim Sahin and Nurhan Sahin were majorly centered on vitamin and mineral metabolism, quail production, phytochemicals, oxidative stress, and heat stress alleviation (Sahin et al., 2012; Sahin et al., 2013; Sahin et al., 2017; Orhan et al., 2021). Both authors were closely affiliated and collaborated on most of their research. On the other hand, Feng Gao focused on studies related to muscle metabolism, taurine supplementation, heat stress-induced oxidative damage, and the effects of chronic heat stress on broilers (Lu et al., 2017; Ma et al., 2018; Lu et al., 2019; Ma et al., 2021). Furthermore, the co-authorship analysis revealed that several of the authors, even those with a higher number of publications were excluded from the network. In line with this, the international co-authorship of authors was found to be 24.36%, thus suggesting that the inter-collaborative efforts of authors in this research field were relatively low. In addition, research works from Gao, Feng; Bao, Endong; Tang, Shu; Lamont, Susan J; and Alagawany Mahmoud were highly cited by other authors, while the works from Sahin, K., Yahav, S., Attia, Y.A., Quinteiro, W.M., and Lin, H. were among the top co-cited papers, suggesting that they contributed to the high impact papers sought after in the field. Consequently, documents from these authors were also found among the top globally cited research in this field (Sahin and Kucuk, 2003; Lin et al., 2006; Yahav, 2009; Attia et al., 2021). The bibliographic coupling of authors characterizes the phenomenon where two authors cite similar document (s) in the articles that they have published (Ma, 2012; Zhang and Yuan, 2022). Findings from both the citation and bibliographic coupling analysis showed that Bao, Endong and Tang, Shu who were affiliated with Nanjing Agricultural University, China had a strong connection in their bibliographic network, suggesting that these authors have close similarities in their research outputs. Altogether, key scholars who have contributed quantitatively or qualitatively to promoting research on heat stress in poultry were identified, indicating their substantial contributions to the field.

Bibliometric analysis of document sources (including journals, books, etc.) is important in providing updated insights and trends for a particular research area, as well as in guiding scholars to select suitable journals for their research communication (Cheng et al., 2022; Liu et al., 2022). Journals including Poultry Science, British Poultry Science, Journal of Thermal Biology, Animal, and Brazilian Journal of Poultry Science were the most prolific sources of articles on heat stress in poultry and they also accrued higher citation index. Journal co-citation analysis and bibliographic coupling further emphasized that Poultry Science had the largest network and was strongly connected with other journals such as Journal of Thermal Biology, World’s Poultry Science Journal, Animals, and British Poultry Science. These may be related to the publication of high-impact findings in these journals, thus suggesting that the hot topics and future trends emanating from research on heat stress in poultry are likely to be reported in these journals. Evidently, Poultry Science journal produced most of the top globally cited articles, revealing that this journal is a relevant, consistent, and authoritative source for high-caliber research and information related to poultry production.

The article, titled “Effect of heat stress on oxidative stress, lipid peroxidation and some stress parameters in broiler” by Altan O. et al. (2003) was identified as the most globally cited document on heat stress in poultry. Key findings of this study were that heat stress increased fearfulness, induced oxidative stress, and initiated significant physiological responses in broilers (Altan et al., 2003). Two review articles also contributed significantly to the global research progress on heat stress in poultry. They were “Strategies for preventing heat stress in poultry” by Lin H et al. (2006) and “Association between heat stress and oxidative stress in poultry; mitochondrial dysfunction and dietary interventions with phytochemicals” by Akbarian A. et al. (2016). Given the widespread concerns on how to mitigate the adverse impacts of heat stress in poultry production, Lin et al. (2006) was among the early reports to surmise various methods, which included, genetic, nutritional, feeding, and environmental strategies that can be adopted to cope with heat stress in poultry. In addition, following the discovery that oxidative stress was closely associated with heat stress in poultry, Akbarian et al. (2016) provided a detailed discussion that explained the mechanisms through which heat stress induces oxidative stress, and also presented the use of antioxidant phytochemicals as a nutritional strategy for the alleviation of mitochondrial dysfunction in heat-stressed birds. From the citation networks, documents including Altan et al. (2003), Bartlett (2003), Lin et al. (2006), Akbarian et al. (2016), and Sohail et al. (2010) had the greatest linkages and also contributed substantially to the advancement of research on heat stress in poultry. Several documents were commonly cited by scholars in this research area, especially the works of Lara and Rostagno (2013) which reported on the “Impact of heat stress on poultry production” and Quinteiro-Filho et al. (2010) which reported that “Heat stress impairs performance parameters, induces intestinal injury, and decreases macrophage activity in broiler chickens”.

Keywords are considered important terms and phrases from a research paper that rightly expresses the content covered, help generate new information and frontiers of knowledge, and assist in the retrieval of relevant content. Commonly, author-generated keywords (that is, Author keywords) are provided during article submission to describe the main contents/concepts addressed in their research. Also, the Keyword Plus is generated by Web of Science from the words and phrases that occur in the titles of cited references (Tripathi et al., 2018). Therefore the use of both author keywords and Keyword Plus explicitly expresses the knowledge structure, the article’s content, and the interactions of various research in a given subject area (Zhang et al., 2016). In this study, the top five keywords with the highest WordCloud frequency were “chickens”, “growth performance”, “supplementation”, “performance”, and “oxidative stress”. Word Cloud provides a visual representation of texts that are frequently occurring, such that the bigger and bolder a word appears, the higher its frequency of occurrence. Interestingly, the keyword “oxidative stress” had a higher occurrence than “heat stress” revealing a shift in research interest, which suggest that more researchers were gradually getting involved with studies that addressed oxidative stress in poultry. In addition, the thematic evolution of Keyword plus identified that research on oxidative stress had gained momentum over the years. Importantly, the thematic growth on oxidative stress had evolved to integrate other terms related to performance, supplementation, gene expression, and growth performance. This was also consistent with the overlay visualization which showed that heat stress co-occurred with various new topics such as “meat quality”, “antioxidants”, “microflora”, “intestinal barrier”, “expression”, and “rna-seq”.

The co-occurrence network of all keywords unveiled that current research on heat stress in poultry mainly focused on studies of growth performance, environment and production (red nodes), studies on intestinal morphology, and microbiota (green nodes), studies on the molecular mechanisms of heat stress (blue nodes), studies on immune response and metabolites, studies on meat quality and carcass characteristics (purple nodes), and studies on oxidative stress (aqua nodes). With the recent development in research, it is interesting to note that several terms have emerged in relation to heat stress such as “essential oils”, “resveratrol”, “betaine”, “curcumin”, “probiotic mix”, “flavonoids”, and “plant extracts”. These are important agents provided as supplements to poultry in a bid to alleviate the detrimental effects of heat stress. Several studies have demonstrated their protective and beneficial effects on the growth performance, behavior and welfare, immune system, antioxidant capacity, egg production, nutritional metabolism, intestinal health, thermotolerance, and other physiological variables of heat-stressed birds (Nawab et al., 2020; Sariozkan et al., 2020; Jiang et al., 2021; Liu et al., 2021; Mohammadi, 2021; Wen et al., 2021; Yang et al., 2021).

The thematic map analysis of keywords allows for the organization of keyword groupings according to their density and centrality into a single circle for mapping as a two-dimensional image (Ejaz et al., 2022). From the Keyword plus, it was identified that motor topics including “growth performance”, “supplementation”, “ascorbic acid research”, and “meat quality”, have been well-researched with respect to heat stress in poultry (Mahmoud et al., 2004; Abidin and Khatoon, 2013; Kumar et al., 2021; Piray and Foroutanifar, 2021). However, some topics that were weakly developed from both the emerging and declining themes (microflora, intestinal morphology, and probiotic mixture) and the basic themes (lipid-peroxidation, egg production, and ambient temperature) could be of research interest for further studies on heat stress in poultry. In examining the Author keywords, some underdeveloped and marginally important topics grouped into the emerging and declining themes were “hsp70”, “rna-seq”, “co-enzyme q10”, and “transcriptome”. To address this, studies have reported that co-enzyme q10 protects the chicken primary myocardial cells against damage and apoptosis during in vivo heat stress by upregulating hsp70 expression and HSF1 binding activity (Xu et al., 2017a; Xu et al., 2017b; Xu et al., 2019b), and that co-enzyme q10 induced autophagy and suppressed the PI3K/AKT/mTOR signaling as a protective mechanism against heat stress (Xu et al., 2019a). Alongside this, several studies have employed the whole transcriptomics approach, as well as other RNA sequencing technology to investigate the effects of heat stress in poultry (Saelao et al., 2018; Te Pas et al., 2019; Kim et al., 2021; Liang et al., 2021). With the advent of this tool, the molecular mechanisms that occur in distinct cells or tissues of various poultry species during heat stress exposure can be profiled, quantified, and comprehensively understood, thus presenting useful information to advance research in this field. The transcriptomics approach has been utilized to investigate the effects of heat stress on various tissues including the liver (Jastrebski et al., 2017; Wang et al., 2020), bursa (Monson et al., 2018; Chanthavixay et al., 2020), thymus (Monson et al., 2019), cardiac and skeletal muscle (Srikanth et al., 2019), hypothalamus (Sun et al., 2015), and heart (Zhang et al., 2017; Zhang et al., 2019). In addition, some topics which are relevant but weakly developed were identified in the basic theme, such as “corticosterone”, “acute heat stress”’ “chronic heat stress”, “oxidative stress”, “feed restriction, “meat quality”, and “gene expression”. Importantly, these topics may be considered highly relevant and of great potential in stimulating future research and scientific development on heat stress in poultry.

To the best of our knowledge, the present study is the first to examine the global research status and emerging trends on heat stress in poultry species using the bibliometric approach. Noteworthy, research progress in this field is gradually developing with greater growth potential. Presently, the need for extensive global cooperation between authors, institutions, and countries cannot be overemphasized. Current research on heat stress in poultry could be identified as focusing on production performance, physiological responses, oxidative stress, and dietary supplements. However, it is deduced that future research trends will focus more on topics such as; “antioxidants”, “meat quality”, “microflora”, “intestinal barrier”, “rna-seq”, “animal welfare”, “gene expression”, “probiotics”, “feed restriction”, and “inflammatory pathways”. Therefore, this comprehensive analysis of the current status and emerging topics on heat stress in poultry would serve as a useful reference for researchers, policymakers, and other stakeholders in the poultry industry.

It is important to point out that despite the novelty of this work and the important findings established from this study, there are a few limitations associated with it. 1.

The documents retrieved for this study were solely based on the WoSCC database, as such not inclusive of other database collections such as Scopus, Pubmed, Dimension etcetera, which may have more information to deliver. However, it is agreed that Web of Science is the most suitable database and the most recommended for bibliometric studies in a specific field (Cheng et al., 2022; Shan et al., 2022).