Many countries have recognized the ethical concerns of modern society regarding using animals in research and have developed regulatory frameworks to support the humane management and use of laboratory animals (37). According to a UK opinion poll, 65% of the public accepts the use of animals for medical purposes and 68% for scientific purpose (38). However, this acceptance depends on the research situation and the experimental animal species, and it is possible when alternative methods are non-available or unnecessary pain is avoided. Interest in alternative methods to animal testing also increased from 55 to 60% compared to 2 years ago (38). Public opinion in the UK regarding the use of animals in research indicates that 71% accept experimentation under the condition of no alternative methods and minimal animal suffering. Animal welfare is a key concern, with 35% opposing animals’ use in research on ethical grounds, and 54% expressing a desire for more information on efforts to improve animal welfare in research. Legislation reflects these views, emphasizing the need to minimize both animal use and suffering in scientific endeavors (39). European Union (EU) guidelines, which define minimum standards for animal experimentation implemented by 28 EU member states, specify the need to ensure that “procedures that may cause severe pain, suffering, or distress that is long-lasting and cannot be alleviated are not performed.” DIRECTIVE 2010/63/EU is on the protection of animals used for scientific purpose (refer 2). Recital 23 of the Directive states that “From an ethical standpoint, there should be an upper limit of pain, suffering and distress above which animals should not be subjected in scientific procedures. To that end, the performance of procedures that result in severe pain, suffering or distress, which is likely to be long-lasting and cannot be ameliorated, should be prohibited.” The 27 member states of the EU observe the animal welfare standards of DIRECTIVE 2010/63/EU (40). In the case of laboratory animals, pain can sometimes escalate due to experimental protocols or in vivo analyses, as effective measures to eliminate threats to animals cannot always be applied (28). In certain experiments, it may be necessary to induce transient discomfort in animals. For instance, when determining the Approximate Lethal Dose (ALD) or No Observed Adverse Effect Level (NOAEL), there are situations where analgesics cannot be administered, and the administration of substances with specific properties is required to elicit particular reactions. Furthermore, in assessing the safety of medical products, it is unavoidable to induce discomfort. Therefore, strict justifications must be established when inflicting unavoidable suffering on animals (41). Judgment should be made by a specialist with scientific and ethical expertise to achieve this, and well-trained AVs are qualified professionals to provide such assessments. AV should graduate from a veterinary medical college, undergo training and/or gain experience in the care and management of the relevant species. AV must also possess sufficient authority, as provided by the institution, to treat an animal (42, 43). AV is an experienced professional who possesses extensive knowledge in veterinary medicine and understands the biological characteristics of the animal, enabling appropriate clinical treatment (44). Regulations on animal experimentation encompass various aspects, including ethical review bodies and principles, personnel qualifications, facilities, resources, technological procedures, animal care and use, industrial health and safety, transportation, and recommended ethical review processes and standards. Of particular note is the regulation governing AV recruitment (1). AV appointments are mandatory or strongly recommended in countries with high societal demands for animal welfare, such as China, Europe, Israel, South Korea, and United States contrary to India, Indonesia, Japan, Malaysia, Singapore, and Thailand (Table 1) (1, 45, 46).

Article 25 of Directive 2010/63/EU requires that ‘each breeder, supplier and user has a designated veterinarian with expertise in laboratory animal medicine, or a suitably qualified expert where more appropriate, charged with advisory duties in relation to the wellbeing and treatment of the animals’ Under Directive, DV involved in activities related to the functions of ethical committees, facility management, health monitoring, research projects, occupational health and safety, compliance with legislation and the education and training of staff and persons using animals for experimental purposes (47, 48). In the United Kingdom, ‘Named Veterinary Surgeons (NVS)’ offers guidance on the well-being of animals housed in scientific facilities. Under the Animal Scientific Procedures Act, the NVS must uphold the principles of the 3Rs, assuming the responsibility of overseeing and advising on the health, welfare, and treatment of animals (49). The AVs system is not legally required in many Asian countries, including, India, Indonesia, Japan, Malaysia, Singapore, and Thailand (1, 50). In China, Europe, Israel, South Korea, and United States., the Animal Welfare Act was amended, requiring organizations engaged in animal testing to employ AVs (40, 42). However, in countries where societal awareness of animal welfare is limited or where understanding of animal welfare for laboratory animals is lacking, a corresponding deficiency in recognizing the role of AVs may exist. Consequently, this AV awareness deficiency can potentially compromise the welfare of laboratory animals.

In this study, we categorize the role of AVs in enhancing the mental health of researchers into two primary aspects. First, we address the direct promotion of animal welfare by AVs. The goal of enhancing the welfare of laboratory animals is to meet their physiological and behavioral needs appropriately while promoting ethical treatment through adequate housing, nutrition, and social interaction (37, 51, 52). Provision of a minimum living space for each animal species, along with the implementation of appropriate environmental enrichment, is essential. Utilizing social housing whenever possible, instead of single housing, respects the natural tendencies of the animals. Facilitating positive reinforcement training, including cooperative engagement in goal-oriented activities, can enhance management practices and reduce stress (16, 34, 53–55). In a previous study, aggression in pigs decreased following the implementation of social housing and the expansion of floor space in an animal research facility. Additionally, a reduction in plasma cortisol levels, indicative of decreased stress, was reported (56).

Unlike other animals, laboratory animals are confined in limited spaces and often exhibit stereotypic behaviors and distress due to their highly routine daily activities (57). Animal emotions can interact with those of humans when individuals interact with animals daily, potentially elevating human distress levels (58). Individuals responsible for enhancing animal welfare, such as AVs and managers, demonstrated higher empathy and job satisfaction than researchers, whereas Ph.D. students involved in experiments exhibited higher compassion fatigue (22). Furthermore, researchers who implemented environmental enrichment demonstrated a higher professional quality of life (22).

Animal healthcare is a crucial role of AVs in promoting the mental health of researchers during animal experiments. The responsibility of AVs is to monitor the health status of laboratory animals and provide appropriate medical interventions to ensure their well-being (59). Animal pain is primarily expressed through non-verbal means, mainly behavior, and should be evaluated as realistically and objectively as possible. Scientific methods such as grimace scales should accompany behavioral assessments (60, 61). AVs educate researchers on these scales and prescribe appropriate analgesics, leveraging their veterinary knowledge to assess and alleviate pain (59). Non-compliance with post-surgical management and post-surgical analgesia for animals experiencing ongoing pain is a prevalent issue, often promptly rectified through AV involvement. Importantly, procedures should be established within the institution to ensure compliance with post-surgical care.

Regular playtimes for animals, such as dogs and pigs, in playgrounds can serve as environmental enrichment, benefiting the welfare of laboratory animals and the psychological well-being of observing researchers. The provision of engaging activities for animals can contribute to the reduction of stereotypic behaviors and enhance social interactions among them, fostering a positive atmosphere in the experimental environment. Moreover, it can offer researchers the opportunity for direct interaction with animals in a playground setting, promoting mutual. Additionally, routine health check-ups performed on animals, especially larger laboratory animals such as dogs, pigs, and primates, can be perceived as high-quality welfare and provide researchers with psychological reassurance. The maintenance of animals in a healthy state not only enhances the reliability of experimental outcomes but also allows for the minimization of the number of animals used in research. Consequently, meeting ethical responsibilities while reducing the burden on researchers can be achieved.

The Institutional Animal Care and Use Committee (IACUC) plays a dual role in animal experimentation, approving research protocols and supervising post-approval management. AVs can collaborate with the IACUC or serve as members of the IACUC to enhance animal welfare (62, 63). Systems that clandestinely inspect reported harmful animal welfare conditions supplement regular animal welfare checks as part of the Program of Animal Monitoring. Such systems reduce animal distress and stress among researchers, who perceive their workplace as comfortable and psychologically safe.

Secondly, AVs can contribute to improving the mental health of researchers through direct means. One of the most critical aspects in this regard is euthanasia. Euthanasia of laboratory animals involves the deliberate act of causing death to minimize unnecessary pain and stress to animals (64, 65). Unlike companion animals, the euthanasia timing for laboratory animals can be determined from the planning stages of the experiment or anticipated if the animal’s suffering outweighs additional data collection (66). Euthanasia procedures must be conducted carefully to ensure minimal pain and stress, and one of the critical criteria for euthanasia is its psychological impact on researchers (67). Individuals who have witnessed the death of animals, not limited to laboratory animals, may be exposed to excessive stress, substantially impacting their mental health. Many researchers are chronically exposed to “moral stress,” as their typical duties ultimately involve euthanizing animals or engaging in practices that cause pain, suffering, disease, and other harmful conditions required for research (30, 32, 33). According to a study, researchers who have experienced animal stress and pain tend to exhibit higher levels of compassion fatigue, and there is also a reported association between the use of physical euthanasia methods and researcher burnout (22). Individuals working in the field of laboratory animal welfare, such as animal facility staff, demonstrated higher levels of Professional Quality of Life and compassion satisfaction compared to researchers (27). AVs play a mediating role in the management of research and animal interventions, highlighting the need for emotional relief programs for AVs themselves. The AV should ensure that ethical procedures and regulations are adhered to by researchers when performing euthanasia to mitigate their stress. Researchers using physical methods such as cervical dislocation for euthanasia have reported higher burnout levels (22). Therefore, proposing humane methods, such as CO₂ displacement within 30–70%, to minimize animal distress during euthanasia is essential. Additionally, constructing CO₂ chambers using non-transparent materials can alleviate visual stress. Furthermore, euthanasia itself and the anticipatory grief that can occur before euthanasia induce extreme stress among researchers. Therefore, AVs should ensure that researchers adhere to ethical procedures and rules when performing euthanasia, thereby reducing the various stresses they may experience, including the care-killing paradox.

Notably, while euthanasia is one of the critical considerations in animal experimentation, it is not an inevitable outcome, and scientific, ethical, and legal frameworks should be carefully contemplated (68). One such means is rehoming. Programs have recently become more active in rehoming animals such as rodents, rabbits, and beagles after completing experiments (69, 70). ‘Rehoming’ is defined as a change in residence for an animal previously used or designated for scientific purposes, where the animal resides for the remainder of its life in a setting appropriate for its requirements without undergoing any additional scientific procedures (69, 71, 72). Directive 2010/63/EU issued by the European Parliament and Council on September 22, 2010, stipulates that upon completing a scientific procedure, the optimal course of action regarding an animal formerly used or designated for scientific purposes should be determined considering animal well-being and potential environmental hazards (40). Rehoming provides researchers with an opportunity to provide animals with a better quality of life without euthanizing them, allowing them to move beyond the distress associated with euthanasia. Rehoming provides a higher level of welfare to laboratory animals and can also boost the morale and well-being of those caring for the animals (73). However, successful rehoming is not guaranteed for all animals. According to one study, 6.2% of rehomed beagles experienced failed adaptation and were returned to research facilities (74). Rehoming efforts should be undertaken following thorough veterinary examinations and socialization training by AVs to enhance the likelihood of successful reintegration into new environments. Since AVs must provide animal welfare and treatment consultation, they should be involved in adoption decisions (59). Therefore, AVs can enhance their health through the veterinary management of laboratory animals, increasing the likelihood that more animals can be rehomed elsewhere. In a previous study, 16 beagles were rehomed, and the owner responses 4 years later indicated that the majority of the beagles initially experienced separation anxiety, but subsequently, no behavioral issues were reported, and the beagles adapted well to their new homes (75). AVs should recognize the value of extending the lives of sentient beings as a principle that ought to be promoted for the benefit of animals. Moreover, by providing such opportunities to animals, they contribute to fostering a more virtuous and compassionate institution and staff (76).

So far, we primarily focused on the direction from animals to humans. However, recognizing that animal-human interaction is bidirectional is essential. Building resilience, referring to the ability to cope with stress and adversity and recover effectively, enhances the well-being of both humans and animals (64). We propose extending the responsibility of AVs to include workplace well-being to enhance researchers’ psychological well-being. Recognizing the inevitable stress factors resulting from animal experimentation and developing programs that promote positive workplace cultures through initiatives such as peer counseling and social support is essential. In developed countries, efforts have already been made to develop programs that consider not only animal use but also the emotions of researchers to foster a healthy research environment (77). The program should encompass efforts by researchers to recognize and mitigate stress-inducing factors and psychological and physical risks (78). Additionally, in the context of workplace well-being, fostering open communication among researchers and affirming the scientific value of their work is imperative. This affirmation serves as a reminder that their endeavors improve human health, addressing the negative perceptions of animal experimentation within the public sphere. In a previous study, a survey was conducted with 1,000 employees to identify those experiencing compassion fatigue, and external consultants were engaged for counseling. A well-being program was developed by consolidating various ideas, one of which involved providing employees with dedicated time to distribute special treats for animals. Additionally, to enhance the bond with animals, an animal-dedicated garden was established. Over time, this compassion fatigue program evolved, gaining traction and interest among many employees, ultimately exerting a positive influence on the overall culture of the animal research institution (77).