Research progress on animal environment and welfare

Abstract

Animal welfare closely depends on its ability to adapt and thrive in a harmonious relationship with its environment, ensuring both physical and psychological well‐being. Over the years, the welfare of farm animals has gathered global attention and has become increasingly important to the general public and scientific communities. The connection between the environment and animal welfare is primarily established through the provision of suitable and controllable environment for animals. However, it is essential to recognize that the impact of environment extends beyond merely ensuring freedom from discomfort. The environment plays a crucial role in shaping an animal's response to challenges such as disease, stress, and pathogen. While animals may be housed in controlled environments that provide optimal conditions for health, production, and welfare, it is important to acknowledge that specific scenarios can significantly affect and alter the environmental requirements. Even with access to fresh air, certain factors can have a substantial impact on the well‐being of animals. Furthermore, providing appropriate environmental conditions goes beyond meeting basic needs and can greatly contribute to allowing animals to engage in their natural behaviors. It serves as a relevant tool for ensuring and maintaining adequate welfare standards. This review takes a comprehensive approach to environmental welfare by considering the welfare of animals managed in different stocking systems, considering environmental stress, stocking systems, and the provision of environmental enrichment items. By examining these factors, a broader understanding of the relationship between environment and welfare is achieved and recommendations for future research are outlined.

INTRODUCTION

In recent years, under a series of policy shocks, the welfare of farm animals has gained significant importance and received increased attention from both the general public and the scientific community []. Ensuring the well-being of animals is an ethical responsibility known as animal welfare. It encompasses the physical and mental state of animals, considering their health, behavior, and biological functioning. Environmental conditions play a crucial role in animal welfare as providing proper conditions enables animals to exhibit their natural behaviors to the fullest extent []. Consequently, the animal welfare relies on its capacity to adapt and coexist harmoniously with its environment, thereby ensuring the maintenance of both physical and psychological well-being [].

Modern animals have been bred for heightened productivity []. In order to fulfill their genetic potential while upholding welfare standards optimal feeding and housing conditions are imperative. The fundamental objective of an animal facility is to establish and sustain a comfortable environment for animals. Critical environmental factors, including air temperature, relative humidity, and air quality, are vital for ensuring the animal welfare, maximizing productivity, and optimizing feed utilization. By ensuring a comfortable environment, health and welfare can be enhanced significantly in industrial-scale livestock production settings [].

Issues surrounding the welfare of laying hen's welfare have primarily centered around stocking systems, environmental enrichment, and other management strategies []. Inadequate environmental conditions often subject animals to thermal stress, leading to reduced production performance, increased morbidity and mortality rates, and consequential economic losses, all of which concern animal welfare. Comprehending and effectively regulating environmental conditions thus play a crucial role in promoting successful livestock production and welfare. Various practices, such as technological advancements and potential changes in stocking systems, have the potential to enhance the welfare of farm animals []. While environmental control strategies and technical improvements may not be directly aimed at improving the animal welfare, some authors argue such measures can indeed yield positive outcomes in this regard.

Promoting animal health and welfare is essential for achieving optimal productivity and reproductive performance while reducing the environmental footprint per unit of the animal product []. However, to date, no comprehensive review has been conducted to consolidate the knowledge on how the environment impacts animal welfare. This review aims to fill that gap by summarizing studies on animal environment and welfare and by exploring the interplay between the two. The primary objectives of this review are to analyze the published literature to determine the relationship between animal environment, welfare, and health; to evaluate the current impact of technical improvements implemented as mitigation strategies, as well as the effectiveness of environmental control strategies in enhancing animal welfare; and to discuss potential approaches for further improving animal welfare. This review focuses on general environment and have poultry, pigs, and calves as examples to demonstrate the impact of environment on animal welfare.

RELATIONSHIP BETWEEN ENVIRONMENT AND ANIMAL WELFARE

Enhancing animal welfare has become increasingly important in livestock stocking systems []. Consumer awareness and concerns regarding animal welfare have prompted the introduction of new systems in EU livestock production aimed at improving animal welfare []. For the laying hens, the management system, particularly the housing conditions, plays a crucial role []. Egg producers have made significant investments to upgrade caged-hen facilities and implement colony-caged, barn, and free-range systems to enhance hen welfare and align with consumer expectations []. Furthermore, the European Union is currently implementing standards for broilers targeting the key welfare concern of overcrowding by imposing limits on maximum “stocking density” (bird weight per unit area). However, the impact of these measures on bird welfare remains uncertain due to contradictory evidence []. Dawkins et al [] suggested that stocking density is less important than other environmental factors although very high stocking densities do affect chicken welfare. The five freedoms framework [] and the five domains model [] are commonly used to assesses animal welfare. The five domains model evaluates welfare based on five criteria: nutrition, environment, health, behavior, and mental state. Freedoms from discomfort (providing an appropriate environment, including shelter and a comfortable resting area) and to express normal behavior (providing sufficient space, appropriate facilities, and social companionship) involve environmental considerations. However, the environmental factors that satisfy the other three freedoms—freedom from hunger and thirst, freedom from pain, injury, and disease, and freedom from fear and distress—may not be as readily apparent.

Animal-based indicators offer the most effective means of evaluating animal welfare as they directly capture the actual experience of the animal within its environment. However, using the five freedoms as a framework to describe animal welfare has certain limitations due to its general nature []. It is crucial to continually assess and enhance animal welfare plans. Both management practices and environmental factors have a significant impact on animal welfare. Consequently, evaluating animal welfare can be best achieved by using animal-based measures, while also considering measures related to management and the environment as they can provide insights into factors influencing animal welfare (Figure ) [].

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The main purpose of a livestock building is to establish and sustain an appropriate microclimatic environment for the animals. Among the numerous environmental factors that require regulation in livestock buildings, air quality and its associated parameters are commonly regarded as crucial []. To determine the comfort thresholds of temperature, relative humidity, wind speed, and concentrations of CO₂ and NH₃ for laying hens, relevant references were examined and the findings are summarized in Table  [].

TABLE 1 Laying hens single factor environmental comfort evaluation index.

Environment factor	Comfort	Less comfort	Discomfort
Temperature/°C	18–21	13–18 or 21–26	>30 or <5
Relative humidity/%	60–70	40–60 or 70–72	>72 or <40
Air velocity/(m/s)	0.1–0.2 (W), 0.5–1.5 (S)	0–0.1 or 0.2–0.25 (W); 0.25–0.5 or 1.5–2.5 (S)	>0.25 (W), >2.5 or <0.25 (S)
CO2 concentration (mg/m3)	<1500	1500–4000	>4000
NH3 concentration (mg/m3)	<15	15–20	>25

Several studies have been conducted, which have consistently concluded that inadequate design or operation of livestock buildings can result in cold or heat stress, significant diurnal temperature variations, and uneven airflow distribution. Furthermore, extensive research has been published regarding the impact of heat or cold stress on productivity and immune response []. In their study, Rita et al. [] identified and categorized the primary stressors faced by pigs reared in intensive conditions, distinguishing between those arising from the animal environment and those caused by management practices commonly employed in intensive pig farming (Figure ). The detrimental effects of heat or cold stress on animals encompass reduced growth, diminished productivity, compromised animal quality, and potential safety hazards. However, of utmost concern should be the negative impact of stress on animal welfare.

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The poor air quality poses a threat to the well-being and health of both animals and their caretakers []. Elevated levels of indoor NH₃ (e.g. exceeding 15 mg/m³) and significant quantities of particulate matter contribute to reduced production efficiency as well as inferior welfare and health conditions. These adverse effects include respiratory disorder, reduced feed intake, slower growth rates, diminished egg production or quality, inefficient feed utilization, heightened susceptibility to infectious diseases, and increased mortality rates []. Consequently, there has been an increasing emphasis on creating and maintaining a comfortable environment to enhance the welfare of farm animals [].

Water plays a fundamental role in various metabolic processes and is crucial for ensuring animal welfare. Inadequate drinking water conditions not only harm the welfare and health of animals but also increase the incidence of intestinal diseases, leading to substantial economic losses in large-scale livestock production []. The effect of drinking water quality and temperature on animal health and welfare is outlined in Table . Surprisingly, water temperature, despite being one of the primary factors influencing animal performance, often receives insufficient attention from producers. For instance, dairy calves tend to consume warmer water without influencing their feed intake, body weight gain, or health parameters []. When considering animal welfare, it is essential to address the comfort and upkeep of housed or sheltered animals. Overcrowding situations should be avoided to minimize stress on animals and reduce the risk of disease transmission (Figure ).

TABLE 2 The effect of drinking water quality and temperature on animal health conditions and welfare.

Livestock breed	Water treatment	Water quality	Results
Item	ROW	TW	UWW
Heifer calves []	ROW, municipal TW and, UWW	Calcium, mg/L	5.33a	40.00b	230.00c	The preference level of heifer calves is ROW > TW > UWW. Water quality affected water intake by heifer calves. The amount of TDS and hardness of the water source influence taste preferences and drinking behavior of growing heifer calves
Magnesium, mg/L	1.07a	36.20b	94.30c
Phosphorus, mg/L	0.07a	0.36b	94.30c
Potassium, mg/L	0.23a	3.34b	8.22c
Iron, mg/L	0.04a	0.17b	0.25b
Sodium, mg/L	2.50a	19.10b	73.90c
Manganese, mg/L	0.002a	0.01a	0.23b
Chloride, mg/L	5.20a	24.20b	6.67a
Sulfate, mg/L	1.36a	195.00b	622.00c
Total dissolved solids, mg/L	339.00a	462.00b	1432.00c
Escherichia coli, CFU/mL	ND	ND	1200.00
		Item	Cold water	Warm water
Range cattle []	Water temperature: Cold water (8.2°C) and warm water (31.1°C)	Calcium, mg/L	1.1–1.4	1.1–1.4	Cows drinking warmed water showed no improvement in body weight increase, body condition score change, or calf birth weight. Energy expenses for grazing cows are inversely correlated with the amount of water they consume at temperatures below body temperature
Chloride, mg/L	19.0–22.0	19.0–22.0
Fluoride, mg/L	2.3–2.7	2.3–2.7
Iron, mg/L	0.01–0.03	0.01–0.03
Magnesium, mg/L	0.3–0.5	0.3–0.5
Nitrate, mg/L	0–0.3	0–0.3
Manganese, mg/L	0	0
pH	8.6–9.3	8.6–9.3
Sodium, mg/L	357–367	357–367
Sulfate, mg/L	38–42	38–42
Total dissolved solids, mg/L	907–1013	907–1013
Water temperature	8.2 ± 0.4°C	31.1 ± 1.3°C
		E. coli concentrations	Low	High
Dairy cattle []	Different levels of manure contamination (mg refrigerated manure/g water): 0 mg/g water (clean), 0.05 mg/g water (low), or 1.0 mg/g water (high)	The first day	<1 to <10 cfu/100 mL	717 cfu/100 mL	When given a free choice, cows showed a clear preference for the clean drinking water
The fifth day	<1 to 5 cfu/100 mL	1153 cfu/100 mL
		Item	Normal drinking water	Treated-drinking water
Broiler []	Drank normal drinking water and drank sodium dichlorocyanurate (50 mg/L) treated-drinking water	Colony number, CFU	68,000	2.5	Chlorinated drinking water reduced the abundance of Dysgonomonas and Providencia in the cecum and is therefore beneficial to improve broiler chicks' body weight gain and feed efficiency
Coliform bacteria, CFU	1042.25	4
Mold, CFU	30	0
		Item	Acetic acid	Neutral pH	Sodium bicarbonate
Young broiler []	The pH of water acetic acid (0.4%), neutral pH, and sodium bicarbonate (1%)	Temperature, °C	26.37	26.33	26.27	An alkaline pH and high values of salinity, electrical conductivity, and dissolved solids in drinking water provoked high mortality, ascites, low productive efficiency, abnormal growth of the heart and liver, and low activity of the immune organs
pH	4.01c	7.03b	8.60a
Electrical conductivity, S/cm	166.73b	86.00c	4850.00a
TDS, ppm	117.67b	61.20c	3443.33a
Salinity, ppm	0.08b	0.04b	2.427a
Turbidity, NTU	0.00	0.00	0.00
Residual chlorine, mg/L	0.00	0.20	0.00
Broiler []	Water temperature 35.0 and 23.9°C	/	Higher body weight gain and feed consumption were attained with water at a temperature of 23.9°C as compared with 35.0°C

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IMPROVING ANIMAL ENVIRONMENT AND MANAGEMENT PRACTICES

The review focused on developing strategies to address environmental stress conditions, mitigate large variations in air temperature, establish uniform air distribution for cooling, study the effects of air pollution emissions, and explore methodologies and technologies for scientific research and pollution control. Among those factors, the ventilation system stands out as a vital means of controlling the environment, specifically regulating temperature, humidity, litter moisture, and ammonia concentration, which are critical for production and mortality rates []. Additionally, it has a profound impact on animal behavior and welfare []. Tunnel ventilation together with pad cooling has been widely used in climate with hot summer and moderate humidity level. However, numerous studies have highlighted limitations associated with animal houses equipped with tunnel ventilation and a wet-pad evaporative cooling system, including challenges, such as cold or heat stress, significant diurnal temperature fluctuations, and uneven airflow distribution []. As a result, alternative cooling methods have been explored to mitigate heat stress. These methods include intermittent partial surface sprinkling, misting, fogging, and alternative ventilation systems [].

Researchers have developed multiple control strategies for livestock buildings, including on/off control [], proportion integration differentiation control [], statistical models [], fuzzy control [], and intelligent network models []. However, despite the application of these modern technologies, the desired performance is not always achieved []. These control strategies often fail to address issues, such as device latency, or provide accurate real-time control over indoor thermal environments [].

To overcome these limitations, the prediction of the indoor environmental conditions has emerged as an effective approach. By forecasting indoor temperature and humidity variations, predictive models can help avoid control delays and facilitate optimal control strategies []. Meanwhile, various mitigation strategies, including , chemical, managerial, physical, and physiological practices, have been analyzed, compared, and discussed to control NH₃ levels, emissions, and dust removal []. However, it is important to note that research is needed to gather more data and enhance our understanding of existing data. There is still much work to be conducted in both fundamental and applied research areas to advance knowledge and improve overall control strategies.

Water supplied to the poultry farm in Australia is from various sources, such as surface water from dams, lakes, and rivers, as well as underground water or treated town water. The quality of these water sources can vary significantly []. It is thus crucial to assess water quality, and if concentrations of nitrites, chloride, other minerals, and bacterial contamination exceed the values specified in drinking water quality guidelines, appropriate treatment measures should be implemented [].

Disinfection plays a vital role in the comprehensive disease prevention in livestock farming. Slightly acidic electrolyzed water (SAEW) is an effective, safe, and environmental friendly chemical disinfectant that exhibits rapid bactericidal properties and has a broad spectrum of activity. It demonstrates good efficacy against bacteria, fungi, and viral microorganisms, effectively eliminating microorganisms from object surfaces and surrounding air. SAEW disinfection technology can solve the challenges associated with frequent disinfection and diseases prevention, as well as the increasing bacterial resistance to drugs and excessive use of medications. Therefore, it has been widely used in livestock farming (Table ).

TABLE 3 Slightly acidic electrolyzed water disinfection technology applications.

Application scenario	Disinfection object	Disinfection method	Effect	Reference
Disinfection of personnel and vehicles in the field	Personnel	Available chlorine concentration (ACC) of 100 mg/L, spray disinfection time ≤1 min	The bactericidal rate of exposed body and clothing surface ≥90%	[]
Vehicle	ACC 80–100 mg/L, spray disinfection time 3 min	The sterilization rates of the outer surface of the car and the surface of the tire are 90.5% and 91.3%, respectively	[]
Air purification in livestock and poultry houses	Poultry house air	ACC 100 mg/L, spray disinfection for 30 min	The bactericidal rate is 68.3%, better than that of chemical disinfectants and inhibits dust generation	[]
Pig house air	ACC >90 mg/L, spray time 20 min	The air microbial bactericidal rate is 83%	[]
Dairy cow house air	ACC 60 mg/L, close doors and windows for 20 min after spraying	The air microbial bactericidal rate reached 61% and can also disinfect the cattle body at the same time	[]
Exhaust air outlet air	Disinfect with ACC of 100 mg/L	The purification efficiency of bacterial aerosols in the dust removal room is about 40%	[]
Disinfection of facility equipment surfaces	Ground surface	Disinfect with ACC of 60 mg/L	The bactericidal rate for total bacteria and mold reached over 63%	[]
Wall surface	Disinfect with ACC of 80 mg/L	The bactericidal rate for total bacteria is 92%
Feeder surface	ACC 60 mg/L, 80 mg/L, and 100 mg/L, respectively	60 mg/L can achieve good results
Egg collection belt	Disinfect with ACC of 100 mg/L	A higher concentration of slightly acidicelectrolyzed water can achieve the ideal bactericidal effect
Milking pipeline	ACC 60 mg/L, cleaning time is 10 min, temperature is around 37.8°C	Adenosine triphosphate (ATP) on stainless steel surfaces can be completely removed	[]
Transport chicken cage	ACC 70 mg/L, cleaning time is 15 s, disinfection time is 40 s	Can reach a maximum killing value of 3.12 lg cfu·cm−2	[]
Hatching equipment	ACC >60 mg/L, rinse disinfection	Achieve good bactericidal effect and better than povidone iodine and benzalkonium bromide	[]
Wet curtain circulating water	Wet curtain circulating water ACC reaches 1.33 mg/L	Can significantly reduce the total number of bacterial colonies on the wet curtain circulating water, wet curtain surface, and wet curtain inlet air microbial concentration	[]
Drinking water disinfection	The chicken farm drinking water system	Keep the ACC in water at 0.3 mg/L	Effectively reduce drinking water bacterial concentration and inhibit biofilm formation on water pipe walls	[]
The pig farm drinking water system	Add slightly acidic electrolyzed water with a concentration of 29.8 mg/L	Total coliforms decreased to zero and total bacteria decreased to 9.5/mL	[]
The cattle farm drinking water system	ACC 1 mg/L and treat cow drinking water for 10 min	Can completely kill bacteria in drinking water	[]
Epidemic prevention and treatment	Virus	ACC 80 mg/L	Reduce the avian influenza virus by ≥5.2 logarithmic values and the African swine fever virus by ≥4.6 logarithmic values	[]
Prevention and control of dairy cow mastitis	ACC is 60 mg/L +3% glycerin and sterilization time is 15 s	The bactericidal rate of the main pathogens causing dairy cow mastitis exceeds 88%	[]
Poultry seed egg disinfection	Hatching eggs	ACC is 150 mg/L, spray for 90 s, and keep closed for 90 s	The bactericidal rate on the seed egg surface can reach 86.2%	[]

WELFARE STOCKING SYSTEMS AND ENVIRONMENTAL ENRICHMENT ITEMS

With the growing focus on animal welfare and the increasing sustainability demands of the industry, there has been a development of standards and regulations aimed at safeguarding livestock health and welfare in large-scale farming. Simultaneously, research on welfare farming systems has been carried out globally, involving countries across the world []. Consequently, internationally recognized benchmarks for optimal welfare states offer valuable guidance and a framework for evaluating and assessing animal welfare situations. These standards serve as essential references for determining and evaluating animal welfare in various farming systems.

In response to public concerns and perceptions regarding animal welfare, the European Union implemented a ban on battery cage systems used in chicken egg production in 2012 (i.e., European Union Council Directive 1999/74/EC). As a result, the cage system was predominantly replaced with an alternative system, such as new enriched colony cages or free-range production []. The alternative systems provided chickens increased exercise space and welfare amenities, such as nest boxes, perches, and sand baths. These systems significantly differed from the cage system in terms of group size, exercise space, and environmental complexity (Table ).

TABLE 4 Significant differences in designing the cage system and alternative system.

Index	Cage system	Alternative system
Group size	Small	Large
Freedom of movement	Limited	Yes
Space allowance per group	Small	Large
Complexity of the environment	Medium	Complex
Litter	No	Large amount
Perches	No	High
Access to different tiers	No	Yes (aviaries)

The implementation of alternative systems has allowed for enrichment of natural behaviors in chickens, enhanced physical functions, including bone health and immune responses, improved production indicators, such as egg quality and the production rate, and facilitated the overall development of a healthy and sustainable poultry farming industry []. In broiler production, there is also a growing demand for birds reared in more extensive stocking systems. This involves developing enhanced stocking systems, adopting lower stocking densities, and utilizing slower-growing breeds [].

The key aspects of beef cattle welfare, including housing conditions, feeding areas, walking and resting areas, space allowance, flooring, social and maternal behavior, dominance, grouping, and regrouping of animals during housing, have been identified by organizations, such as EFSA [], the European Commission (2001), and the EU Welfare Quality® project (2009) []. In the case of pigs, they are protected by a specific EU directive (Council Directive 2008/120/EC) that sets standards for aspects, such as flooring, living space, and access to materials for rooting []. For large-scale pig farming, implementing moderate regulations on rearing density and enhancing environmental enrichment within pens are crucial for improving animal welfare. Setting appropriate stocking densities can help address issues, such as reduced growth and feed conversion rates, increased mortality, frequent aggressive behavior, and reduced pork quality []. Additionally, increasing environmental enrichment through the addition of welfare facilities, such as bedding, sticks, and rubber, can have positive effects. This includes reducing physiological indicators, such as serum IgG concentration, improving production indicators like pork yield and quality, and mitigating abnormal behaviors such as stereotyping [].

DISCUSSION AND FUTURE CHALLENGES

In recent years, advancements in sensor technology, video monitoring technology, information and communication technology, big data, and artificial intelligence have led to the widespread integration of modern information technology in farming. Computer vision techniques, such as convolutional neural networks and random forests, are employed for image recognition using pretrained models. These techniques facilitate individual livestock identification, body size estimation, body temperature monitoring, and behavior recognition []. Biometric identifiers like voice recognition and face recognition are used to identify individual livestock, allowing for tracking of growth changes, health status, behavior monitoring, and other data analysis requirements []. Regional monitoring and real-time recognition of individual livestock are achieved through the use of electronic labels and radio frequency technology. This enables instantaneous identification of livestock. Moreover, wearable biosensing devices and wireless sensors are utilized to collect various physiological information of livestock, such as temperature and heart rate, and to identify individual behavioral activity status. This enables more accurate animal identification and management []. Collectively, these technological advancements have revolutionized livestock farming by providing farmers with advanced tools for precise monitoring, identification, and management of animals, ultimately enhancing animal welfare in the livestock industry.

Intelligent farming technology holds significant potential improving production efficiency, ensuring animal welfare, and reducing environmental pollution in the livestock industry. However, it also faces several challenges and obstacles in the future. One of the key challenges is the current high price of intelligent equipment and the associated operation and maintenance costs, which might discourage some livestock farmers from adopting these technologies. Additionally, there is a wide range of intelligent equipment available for livestock, but the lack of relevant technical standards and certification systems poses difficulties in regulation and quality control. This situation introduces certain risks to the farming industry.

Another challenge lies in the rapid growth of data generated in the livestock industry. Collecting, storing, analyzing, and processing this data to transform it into actionable insights and decision support systems is a significant undertaking. Furthermore, ensuring data security is a critical aspect that needs to be emphasized to maintain the integrity and privacy of data.

Assessing these challenges will require collaborative efforts from policymakers, technology developers, and industry stakeholders. Establishing standard frameworks, certification systems, and regulations will assist in ensuring the reliability and quality of intelligent farming technologies. Additionally, investments in research and development are imperative to enhance the affordability and accessibility of these technologies for livestock farmers. Besides, developing robust data management and security protocols will be crucial for leveraging the full potential of the data generated in the livestock industry. By overcoming these challenges, intelligent farming technologies can potentially revolutionize the livestock industry, resulting in improved efficiency, enhanced animal welfare, and reduced environmental impact.

SAEW has been widely used in facility breeding fields and has shown positive application results in various aspects of livestock and poultry farms. However, there is limited research on using SAEW for wastewater treatment in livestock and poultry farms. Large-scale farms generate substantial amount of wastewater daily, containing pollutants, such as residual antibiotics and numerous pathogens. If left untreated, this wastewater can cause significant pollution to surface water or groundwater. SAEW exhibits strong interactions with organic matter, making it a promising candidate for wastewater treatment in livestock and poultry farms. However, effectively applying this disinfection technology in facility breeding requires adequate technical equipment support. Therefore, the development of mechanical equipment that facilitates the application of SAEW, particularly intelligent equipment such as disinfection robots, is essential based on existing research on SAEW spray disinfection.

Livestock welfare is a pressing issue that demands attention and action, aligning with the values of the general consumer and the growing global awareness. The facilities and equipment developed so far have improved various aspects of welfare compared to traditional farming models. However, it is important to address safety concerns associated with these advancements []. The introduction of welfare facilities also necessitates a careful consideration of livestock health, striking a balance between behavioral welfare and overall livestock health conditions. Moreover, further trials are needed to evaluate how increased activity and behavioral welfare resulting from the implementation of additional facilities affect livestock health and the underlying physiological mechanisms involved. Therefore, further research and optimization of welfare farming facilities are still needed.

Many of the demonstrated technologies have only been applied in a limited scale. The current research and demonstrations mainly build upon previous efforts, aiming to enhance and refine existing methods. Future developments in livestock management and monitoring are expected to focus on intelligent platforms that enable efficient and intelligent management practices. Additionally, there is a growing emphasis on the development of smart devices for caged layer identification of dead birds, breeding modes that prioritize animal welfare, and technical equipment tailored for laying hens. It is clear that future efforts are needed in both fundamental and applied research areas to advance these technologies. Creating and maintaining an appropriate microclimatic environment for animals are essential to improve animal welfare in the context of industrial-scale livestock production.

CONCLUSION

It emphasizes the importance of environment management in order to improve animal raising conditions. The review identifies and determines the parameters that arise from the interaction between the animal environment and welfare. It is evident that animal welfare is greatly affected by environmental conditions, and providing proper environmental conditions is essential for enabling animals to engage in their natural behaviors. By establishing a theoretical foundation for welfare-environmental control in large-scale poultry farming, this review seeks to facilitate the high-quality transformation necessary for the sustainable development of the modern poultry stocking industry. Furthermore, it emphasizes the need for additional research in this field to further advance our knowledge and practices in environment management for livestock welfare.

AUTHOR CONTRIBUTIONS

Baoming Li: Conceptualization (lead); funding acquisition (lead); project administration (lead); resources (lead). Yang Wang: Data curation (equal); formal analysis (equal); methodology (equal); supervision (equal); writing – original draft (lead); writing – review & editing (equal). Li Rong: Validation (equal); writing – review & editing (equal). Weichao Zheng: Investigation (equal); methodology (equal).

ACKNOWLEDGMENTS

This research was supported by the National Natural Science Foundation of China (32272925), the China Agricultural Research System (CARS-40), and the 2115 Talent Development Program of China Agricultural University.

CONFLICT OF INTEREST STATEMENT

The authors declared that there is no conflict of interest.

DATA AVAILABILITY STATEMENT

No data was used for the research described in the article.

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