Pebble to the Metal: A Boulder Approach to Enrichment for Danio rerio.

Zebrafish are an established and widely used animal model, yet there is limited understanding of their welfare needs. Despite an increasing number of studies on zebrafish enrichment, in-tank environmental enrichment remains unpopular among researchers. This is due to perceived concerns over health/hygiene when it comes to introducing enrichment into the tank, although actual evidence for this is sparse. To accommodate this belief, regardless of veracity, we tested the potential benefits of enrichments presented outside the tank. Thus, we investigated the preferences and physiological stress of zebrafish with pictures of pebbles placed underneath the tank. We hypothesized that zebrafish would show a preference for enriched environments and have lower stress levels than barren housed zebrafish. In our first experiment, we housed zebrafish in a standard rack system and recorded their preference for visual access to a pebble picture, with two positive controls: visual access to conspecifics, and group housing. Using a crossover repeated-measures factorial design, we tested if the preference for visual access to pebbles was as strong as the preference for social contact. Zebrafish showed a strong preference for visual access to pebbles, equivalent to that for conspecifics. Then, in a second experiment, tank water cortisol was measured to assess chronic stress levels of zebrafish housed with or without a pebble picture under their tank, with group housing as a positive control. Cortisol levels were significantly reduced in zebrafish housed with pebble pictures, as were cortisol levels in group housed zebrafish. In fact, single housed zebrafish with pebble pictures showed the same cortisol levels as group housed zebrafish without pebble pictures. Thus, the use of an under-tank pebble picture was as beneficial as being group housed, effectively compensating for the stress of single housing. Pebble picture enrichment had an additive effect with group housing, where group housed zebrafish with pebble pictures had the lowest cortisol levels of any treatment group.

Mouse isoflurane anesthesia using the drop method.

Anesthesia with isoflurane prior to carbon dioxide euthanasia is recommended as a refinement, but vaporizer access can be limited. An alternative to vaporizers is the 'drop' method, introducing a fixed volume of isoflurane into the induction chamber. Previous work suggests that isoflurane administered at a concentration of 5% via the drop method is effective but aversive to mice; lower concentrations have not been tested. We assessed mouse behavior and insensibility with induction using the drop method for isoflurane concentrations below 5%. Male Crl:CD-1 (ICR) mice (n = 27) were randomly allocated to one of three isoflurane concentrations: 1.7%, 2.7%, and 3.7%. During induction, measures of insensibility and stress-related behaviors were recorded. All mice reached a surgical plane of anesthesia, and mice exposed to higher concentrations did so more quickly; as concentrations increased from 1.7 to 2.7 and 3.7%, the time to recumbency (Least squares means ± SE: 120.5 s ± 8.1, 97.9 s ± 8.1, and 82.8 s ± 8.1, respectively), loss of righting reflex (149.1 s ± 8.5, 127.7 s ± 8.5, and 100.7 s ± 8.5, respectively), and loss of pedal withdrawal reflex (214.5 s ± 8.3, 172.2 s ± 8.3, and 146.4 s ± 8.3, respectively) all declined. Rearing was the most frequently performed stress-related behavior, and was most pronounced immediately following isoflurane administration for all treatments. Our results indicate that the drop method can be used to effectively anesthetize mice with isoflurane concentrations as low as 1.7%; future work should assess mouse aversion.

Environmental Enrichment for Rats and Mice Housed in Laboratories: A Metareview.

Environmental enrichment has been widely studied in rodents, but there is no consensus on what enrichment should look like or what it should achieve. Inconsistent use of the term "enrichment" creates challenges in drawing conclusions about the quality of an environment, which may slow housing improvements for laboratory animals. Many review articles have addressed environmental enrichment for laboratory rats and mice (Rattus norvegicus and Mus musculus). We conducted a metareview of 29 review articles to assess how enrichment has been defined and what are commonly described as its goals or requirements. Recommendations from each article were summarised to illustrate the conditions generally considered suitable for laboratory rodents. While there is no consensus on alternative terminology, many articles acknowledged that the blanket use of the terms "enriched" and "enrichment" should be avoided. Environmental enrichment was most often conceptualised as a method to increase natural behaviour and improve animal welfare. Authors also commonly outlined perceived risks and requirements of environmental enrichment. We discuss these perceptions, make suggestions for future research, and advocate for the adoption of more specific and value-neutral terminology.

Using approach latency and anticipatory behaviour to assess whether voluntary playpen access is rewarding to laboratory mice.

Laboratory mice are typically housed in "shoebox" cages that limit the expression of natural behaviours. Temporary access to more complex environments (playpens) may improve their welfare. We aimed to assess if access to playpens is rewarding for conventionally-housed mice and to document mouse behaviour during playpen access. Female C57BL/6J, BALB/cJ, and DBA/2J mice were provided temporary access to a large enriched playpen three times per week; control mice remained in their home cages. We measured latency to enter playpens and anticipatory behaviour to determine if access was rewarding, and recorded mouse behaviour during playpen sessions. Over time, playpen mice entered the playpen more quickly; latency declined from 168 ± 22 to 13 ± 2 s over the 14-d trial. As expected, playpen mice showed an increase in anticipatory behaviour before playpen access (mean ± SE = 19.7 ± 2.6 behavioural transitions), while control mice showed no change in anticipatory behaviour relative to baseline values (2.4 ± 1.6 transitions). Mice in the playpen performed more ambulatory behaviours than control mice who remained in home cages (21.5 ± 0.7 vs 6.9 ± 1.1 observations of 25 total observations). We conclude that conventionally-housed mice find voluntary playpen access rewarding, and suggest this as a useful option for providing laboratory mice with access to more complex environments.

A break from the pups: The effects of loft access on the welfare of lactating laboratory rats.

Rats (Rattus norvegicus) bred for research are typically confined with their litters until weaning, but will spend time away from pups when given the opportunity. We aimed to assess how dam welfare is affected by the ability to escape from their pups. Rat dams (n = 16) were housed in cages either with or without an elevated loft. We measured time dams spent in lofts, time spent nursing, and affective states using elevated plus maze and anticipatory behavior testing. We predicted that 1) dams housed with lofts would use them increasingly as pups aged, 2) dams without a loft would spend more time passively nursing (i.e. initiated by pups rather than the dam) and more total time nursing as pups aged, and 3) dams housed with lofts would show evidence of a more positive affective state. Dams housed with lofts spent more time in the loft with increasing pup age; dams spent on average (mean ± SE) 27 ± 5% of their time in the loft when pups were 1 wk old, increasing to 52 ± 5% of their time at 3 wks. When pups were 3 wks old, dams with lofts spent less time passively nursing (10 ± 2% of total time, compared to 27 ± 4% for dams without a loft) and less time nursing overall (36 ± 4% of time versus 59 ± 2% for dams without a loft). Rats without loft access showed increased anticipatory behavior potentially indicative of negative affective state (24.5±1.8 behaviors per minute in wk 3 compared to 18.8±1.0 in wk 1). These findings indicate that rat dams in laboratories choose to spend time away from their pups when provided the opportunity, particularly later in lactation; an inability to do so is associated with increased passive nursing and negative affect.