Szczepan W. Baran Veterinary Bioscience Institute
Karen Froberg-Fejko Bio-Serv
Jaime Lecker Bio-Serv
Elizabeth J. Johnson Putney Inc
David Disselhorst Laboratory Animal Resources Center, The University of Texas at San Antonio
Daniel Terreros Department of Biomedical Sciences, Paul Foster School of Medicine
Marcel Perret-Gentil Laboratory Animal Resources Center, The University of Texas at San Antonio
Environmental enrichment is a key component of rodent animal welfare since it influences the animal’s overall well being, provides opportunities for activity, and encourages rodent appropriate behaviors110. Many aspects of rodent enrichment have received a significant amount of attention during the last few years, which has lead to great advances in developing a beneficial enrichment program1,4,7. AAALAC International encourages the implementation of rodent enrichment and many institutions require justification by scientists stating why animals should not receive environmental enrichment.
One widely accepted reason for eliminating enrichment is surgery. Some Institutional Animal Care and Use Committees (IACUCs) state that withholding environmental enrichment, such as group or pair housing, during the post-surgical period does not require justification by the investigator because single housing is considered within the standard of normal post-operative care. In other words, it will create a safer recovery environment if this form of enrichment is withheld.
Environmental enrichment is intended to decrease stress levels and provide opportunities for rodents to express species-typical behaviors. Therefore, it is possible that depriving an animal experiencing the added stress of isolation, coupled with the catabolic state the animal may already be in because of surgery, may turn an already physiologically abnormal animal more abnormal still. This obviously could lead to confounding data results as well as animal welfare issues.
We have observed that even a change in the animal bedding alters blood pressure measurements11. We conducted an experiment in which we used lean Zucker rats implanted in the abdominal aorta with Data Sciences International PA-C20 tele-metric units interfaced to corresponding radio telemetry receptors, which were stored digitally and displayed on a computer screen. Data were analyzed with the ART 3.1 Analysis software6 using technology we previously used in mice10.
The rats were normally housed on 1/4” bed-o’cobs™ (The Andersons, Inc, Maumee, Ohio) bedding. Once the animals were implanted and their abdominal wound was healed, we replaced the bedding with Enviro-dri™ (Shepherd Specialty Papers, Milford, NJ) for 2.5 days and observed their blood pressure with interesting results. Enviro-dri is a cellulose material consisting of paper strips. We observed that when placed on Enviro-dri, which allows for “tunneling” behavior, the animals initially became more active as they explored their new environment. This activity diminished some as they probably became acclimated to their new environment after the first day. As expected, with this increase in activity we detected increases in heart rate. Interestingly, when the animals returned to the less enriching environment, we did not observe the same “exploratory” behavior with increased activity. The systolic and diastolic pressures, however, were significantly higher in the non-tunneling bed-o-cobs bedding than when Enviro-dri was used. When the animals were returned to the original, less enriching bedding material, we observed that their blood pressure elevated gradually. In this pilot study, we concluded that Enviro-dri is a better substrate for chronic blood pressure experiments when compared to bed-o’cobs.
Surgical procedures and environmental factors produce significant stress in laboratory animals that, as in the study described above, can affect their biomarkers and thus can confound experimental results. It is crucial therefore to place even more emphasis on environmental enrichment techniques to reduce stress and improve recovery.
Providing environmental enrichment to rats post-operatively or post-injury has been demonstrated to improve the ability of the animal to heal and recover2,5,13. A barren environment is stressful to animals and isolation of social animals can lead to delayed recovery and return to normal physiology. Buchhold et al found enrichment to have a beneficial effect on rat recovery in a stroke model, including a reduction in infarct size, in the number of proliferating astrocytes, and in the volume of the glial scar3. Additionally, enrichment provided in the form of nesting materials improved wound healing in rats recovering in isolation12.
One of the most effective forms of enrichment is to pair or group house compatible cohorts together. A common practice post-surgically is to remove a rodent from its group housing and isolate it to recover in a new cage. The most common reasoning is the concern that cage mates will remove sutures and/or injure the surgical site. While theoretically possible, in our experience this is an extremely rare occurrence, leading us to question this practice. If suture “picking” by a cage mate is still a concern, then refining surgical technique by using a subcuticular skin closure instead of closure with external sutures or clips may address this concern.
Subcuticular suture technique can be especially challenging with mice due to the thinness of the skin’s layers, but with expert training and practice, it can be performed. Levine’s study, which supports cohort pair or group housing, found that rats housed individually during physical injury healing had impaired healing compared to rats group housed, emphasizing the negative effect of isolation on wound repair9. When recovering rodents are in wired bottom cages, acclimatization should be performed prior to the surgical procedure to minimize the effects and compilation of stress from anesthesia, surgery and removal of environmental enrichment such as bedding. If post surgical single housing is the only option, we at least concur with the guide when it states, “It is desirable that social animals be housed in groups; however, when they must be housed alone, other forms of enrichment should be provided to compensate.8”
Often, after gastrointestinal surgery, food is removed, as well as edible enrichment, in order to prevent post-surgical complications. This can be problematic for recovery, since a post-surgical animal that’s already in a catabolic state is in greater need of proper nutrition for post-operative survival and recovery. Post-operative rodent diets in soft pelleted, gelled and liquid forms are available and can typically be provided sooner than traditional hard pelleted diets. These diets can stimulate appetite and provide balanced nutrition to facilitate a quicker recovery and return to metabolic homeostasis.
Therefore, reconsidering the traditional practice of housing rodents individually in a barren environment post-surgery, and implementing pair housing with a compatible companion and enrichment has the potential to improve post-surgical recovery. Identifying specific environmental and nutritional enrichment, which facilitate a quicker recovery in rodents, will provide further rationale for including them in rodent post-surgical protocols. Further studies are warranted to address this topic; however it is clear that changing a rodent’s environment and removing enrichment (including single housing) post-surgically is stressful to the animal, which can lead to delayed recovery and overall well-being.
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2 Berrocal Y, Pearse DD, Singh A, et al. 2007. Social and environmental enrichment improves sensory and motor recovery after severe contusive spinal cord injury in the rat. J Neurotrauma. 24(11):1761-1772.
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5 Hoffman AN, Malena RR, Westergom BP, et al. 2008. Environmental enrichment-mediated functional improvement after experimental traumatic brain injury is contingent on task-specific neurobehavioral experience. Neurosci Lett. 431(3):226-230.
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8 Institute of Laboratory Animal Resources (U.S.). Guide for the care and use of laboratory animals. 7th ed., Washington, D.C.: National Academy Press; 1996.
9 Levine JB, Leeder AD, Parekkadan B, et al. 2008. Isolation rearing impairs wound healing and is associated with increased locomotion and decreased immediate early gene expression in the medial prefrontal cortex of juvenile rats. Neuroscience. 151(2):589-603.
10 Sparling JE, Mahoney M, Baker S, Bielajew C. 2009. The effects of gestational and postpartum environmental enrichment on the mother rat: A preliminary investigation. Behav Brain Res.
11 Terreros D. Effect of bedding type on Blood Pressure Lean Zucker Rat. El Paso 2010.
12 Vitalo A, Fricchione J, Casali M, et al. 2009. Nest making and oxytocin comparably promote wound healing in isolation reared rats. PLoS One. 4(5):e5523.
13 Whishaw IQ, Zaborowski JA, Kolb B. 1984. Postsurgical enrichment aids adult hemidecorticate rats on a spatial navigation task. Behav Neural Biol. 42(2):183-190.