실험실 쥐의 건강과 복지의 지표로 둥지 건물
Summary
We demonstrate the utility of nest building behavior in laboratory mice as an indicator of welfare. Nest scoring is a sensitive technique that is altered by temperature, illness, and aggression. The time to integrate into nest test (TINT) is a simple cage-side assessment that can detect postoperative pain.
Abstract
The minimization and alleviation of suffering has moral and scientific implications. In order to mitigate this negative experience one must be able to identify when an animal is actually in distress. Pain, illness, or distress cannot be managed if unrecognized. Evaluation of pain or illness typically involves the measurement of physiologic and behavioral indicators which are either invasive or not suitable for large scale assessment. The observation of nesting behavior shows promise as the basis of a species appropriate cage-side assessment tool for recognizing distress in mice. Here we demonstrate the utility of nest building behavior in laboratory mice as an ethologically relevant indicator of welfare. The methods presented can be successfully used to identify thermal stressors, aggressive cages, sickness, and pain. Observation of nest building behavior in mouse colonies provides a refinement to health and well-being assessment on a day to day basis.
Introduction
Measurement of animal welfare is a difficult and often subjective assessment. When animals are used for scientific purposes, there is an obligation to provide the best care possible and minimize discomfort1. Species-specific objective methods are needed to measure overall well-being for scientific and husbandry purposes. Current methods of welfare assessment in laboratory mice are either time consuming, require expensive equipment, or must be analyzed later to determine if an alteration has occurred2-3. These techniques are useful in a scientific setting, but difficult to incorporate in day to day husbandry. A simple, mouse-oriented method that can quickly and easily identify mice in pain or distress would be a step toward the immediate identification and alleviation of those stressors.
Nests are used by wild mice to shelter from predators, retreat from harsh environmental conditions, and protect young4. Behaviors associated with nest building are therefore highly linked to the survival of wild mice5. Laboratory mice, even though removed from wild conditions for many generations, are highly motivated to build a nest when given proper materials6,7. Any changes to these highly motivated behaviors, or the nest itself, should indicate a substantial alteration in the environment or the animals themselves.
The goal of this method is to exploit highly motivated nesting behaviors in the laboratory mouse to quickly identify pain, illness, or other stressors that may affect or reduce the animal's overall welfare. This binary cage-side assessment technique is advantageous over other existing methods because little training is needed, testing materials are found in the average mouse colony, and the test can be completed with little to no manipulation of the animals. Additionally, the provision of fresh and or different nesting material on a frequent basis may provide a positive interaction between mice and caretakers since nesting material has been found to be rewarding to mice8.
Protocol
Representative Results
Discussion
Based on these results, nest building is altered depending on the degree of thermal stress, the amount of aggression present within the cage, when animals experience a general malaise, and gathering behavior is not seen in postsurgical and potentially painful mice. Since any and all of these factors will reduce a mouse's welfare, we believe that nest building can be utilized to identify cages or animals where interventions need to be made to improve their overall well-being. We believe that nest scoring may be a method best utilized for scientific purposes because the scale is more refined and can detect smaller differences than the binary TINT. However, we believe that the TINT is a more practical tool that is best applied during daily husbandry or postsurgical identification of painful animals.
Unlike social predatory species, where displays of illness or injury may be beneficial, displaying signals of weakness in prey species may be the difference between survival or death. Rabbits, for example, have been observed to respond to pain or distress by remaining motionless, especially in the presence of a human, making behavioral indicators of distress seemingly useless16. Ongoing pain behaviors in mice are also difficult to identify and use to quantify pain17. This is especially difficult in nocturnal laboratory species where, at a glance, distressed and inactive mice can easily be confused with sleeping ones.
Resources, such as food or materials which allow for nest building, are strongly tied to the survival and fitness of wild mice5,18,19. In studies, nesting material is a resource laboratory mice are strongly motivated to obtain7,8. Enviro-Dri has been shown to be an ethologically relevant enrichment for mice which allows them to alleviate thermal stress by building more insulating nests7,10,13. The long fiber length, which requires little to no processing, allows even poor nest builders to build better nests6,7. This material is also suitable for nude mice20, which are often susceptible to eye lesions. While Enviro-Dri is superior for nest building, other material (i.e. Nestlets) functions better for the TINT. The presence or absence of the test square from the designated area is less subjective than attempting to determine if a portion of Enviro-Dri strips was removed.
Both nest scoring and TINT can easily be utilized in singly housed animals however issues may arise if 1 animal out of the group may be experiencing pain or distress. The data presented in this manuscript illustrate that thermal stress and cage aggression can be identified in group housed mice. Further work looking into social cohesion and interactions between healthy and unhealthy animals is currently being investigated. Therefore we caution utilizing these methods in group housed animals to detect illness or pain in a subset of the group.
Variation in building and gathering material between types of laboratory mice is well documented7,21-23 and should be considered before using this technique for all types of mice. Specifically, C3H mice do not gather or build as complex nests as other inbred strains21,22. Therefore, normal nest conformation and TINT outcomes in unmanipulated mice should be observed prior to utilizing this technique in any strain or stock. It is possible that different cage types may influence building outcome. For instance, increased convective heat loss experienced in individually ventilated cages may increase overall nest scores due to additional thermal stress.
The utility of the examination of nesting behavior has only begun to be explored. The literature indicates that nests change due to the hormonal status of the dam24,25 and therefore could also be a tool for identifying periparturient females without disturbing them. Although it has not yet been directly tested, researchers studying models of human disease might also use evaluation of nesting behavior as a humane end point or to identify disease onset, ultimately alleviating overall suffering. Alteration in this essential and complex behavioral sequence might also be a more valid, mouse-oriented, task for models of mental health disorders or even drug testing.
Divulgaciones
The authors have nothing to disclose.
Acknowledgements
The research presented here was supported by Charles River and Tufts Cummings School of Veterinary Medicine. The authors are most grateful to Megan Rock and Miranda Gallo for their work with TINT testing.
Materials
| Enviro-Dri | Shepherd Specialty Papers | Crinkled paper nesting material | ||
| Nestlet | Ancare | Compressed cotton nesting material | ||
Referencias
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