By Nanna M. Andersen | Published: 03.12.21 | Edited: 02.07.23
A summary of: Aggregation in quads but not pairs of rats exposed to cat odor or bright light By Bowen MT, Keats K, Kendig MD, Cakic V, Callaghan PD, McGregor IS. Behav Processes. 2012 Jul;90(3):331-6. The paper focuses on measuring the anxiety response in Dyads (2 rats) and Quads (4 rats) when exposed to various stimuli, including bright light, cat odor, and conditioning of the cat odor. The experiment followed a timeline as described below:
Complete huddle: Dyads spent more time huddling together compared to Quads, suggesting a potential indication of insecurity. It's important to note that Quads were timed only when all four rats were huddled together and not in pairs or trios. Regarding the specific findings:
Distance traveled: Dyads traveled less compared to Quads on average. Both groups exhibited notably reduced travel distances under bright light compared to the baseline (Base 1). Quads traveled significantly less when exposed to cat odor, and they were also more affected by the conditioning test compared to Dyads. Therefore, it can be concluded that Dyads generally traveled less than Quads, but Quads were more affected by all three tests. Defection: Bright light increased the number of fecal boli (excrement) in Quads, while it decreased in Dyads. Both groups showed an increase in fecal boli when exposed to cat odor and during the conditioning test. Specifically, Quads exhibited more fecal boli under bright light, and both groups displayed an increase during the cat odor test. However, during the conditioning test, Dyads had significantly fewer fecal boli compared to Quads. In summary, the findings suggest that Dyads spend more time huddling together and travel less compared to Quads. Quads tend to huddle significantly more when exposed to cat odor, but overall, they spend less time huddling than Dyads, possibly due to the formation of smaller groups within the Quad. Additionally, Quads traveled less and exhibited increased defecation in response to all three tests (bright light, cat odor, and conditioning) compared to Dyads. These results provide insights into the anxiety responses of Dyads and Quads when exposed to different stimuli. A review of the study: Rat's demand for group size By: Patterson-Kane EP, Hunt M, Harper D. J Appl Anim Welf Sci. 2004;7(4):267-72. The study tested different group sizes (1, 2, 4, 6, and 12) using a small number of females in 90-minute sessions. While the results indicate that rats thrive best in groups of 6, the limited sample size and duration of the sessions do not provide a comprehensive picture of the recommended group size for permanent housing. It is noted that the ideal group size depends on factors such as sex, lineage, housing conditions, handling, and the frequency of group mixing or switching. A summary of: "Stress-like responses to common procedures in individually and group-housed female rats" AND "Stress-like responses to common procedures in male rats housed alone or with other rats" By Sharp J, Zammit T, Azar T, Lawson D. Contemp Top Lab Anim Sci. 2003 Jan;42(1):9-18 and Contemp Top Lab Anim Sci. 2002 Jul;41(4):8-14. The studies focus on stress responses in single-housed and group-housed rats. They measured heart rate (beats per minute, BPM) as rats were exposed to various external stimuli. The baseline heart rate is set at 0, representing the relaxed/resting heart rate. Heightened heart rate can be indicative of anxiety or arousal. The results of the studies are as follows: 1. Cage change:
2. Exposure to paper towel:
3. Exposure to urine and feces odors:
4. Exposure to blood odors:
In general, male quads showed the lowest BPM and the fastest cool-down time, suggesting that quads perform better than pairs and single males. Male pairs had the next lowest BPM and cool-down time. Single females tended to cool down faster than female pairs and quads, and they did not show a significant elevation in BPM compared to the other female groups. However, it is important to note that this does not imply that females can be housed alone. Single males exhibited a significant increase in BPM compared to male pairs and quads, and they also took significantly longer to cool down compared to the other male groups. A summary of: Faecal corticosterone metabolite assessment in socially housed male and female Wistar rats by Cinque C, Zinni M, Zuena AR, Giuli C, Alemà SG, Catalani A, Casolini P, Cozzolino R. Endocr Connect. 2018 Feb;7(2):250-257. The study examined corticoid levels in fecal matter during light and dark periods to measure stress hormone levels. It was observed that there was a significant increase in corticosterone levels during the dark periods, indicating higher stress levels during those times. Corticosterone levels varied over time, with peaks occurring between 4 and 12 weeks for males and 4 and 16 weeks for females. As time progressed, there was a gradual decrease in corticoid levels in all groups. Although female rats generally excrete higher levels of corticosterone than males, it is important to consider that variations in plasma protein binding and excretion patterns among animals can influence the results of fecal corticoid assays. Higher levels of corticosterone may not necessarily be reflected in fecal measurements. The overall findings of the study indicate that single-housed males exhibited poor grooming and displayed nasal porphyrin by three months, suggesting that the effects of social isolation were amplified as they reached sexual maturation. Single-housed animals also demonstrated more docile behavior when handled compared to pair- or group-housed animals, which may be indicative of learned helplessness resulting from other stressors, such as exposure to inescapable shock. Furthermore, the study observed that paired females and males engaged in more barbering behavior over time compared to group-housed females and males. This behavior is considered an indicator of social stress and supports previous studies suggesting that rats prefer to be housed in small groups. In summary, the study highlights the impact of social isolation on stress levels, grooming behavior, and response to handling in rats. It also suggests that rats tend to experience less social stress when housed in small groups rather than in pairs or as single individuals. A summary of: Long-Term Physiologic and Behavioral Effects of Housing Density and Environmental Resource Provision for Adult Male and Female Sprague Dawley Rats By Pinelli CJ, Leri F, Turner PV. Animals (Basel). 2017 Jun 1;7(6):44. The study aimed to investigate the effects of housing density and environmental resource provision on male and female Sprague Dawley rats. The rats were randomly assigned to be housed singly, in pairs, or in groups of four (quads). The cages provided for singles and pairs measured 44.5 cm × 24.5 cm (1090 cm²), while the group-housed rats were housed in cages measuring 47.5 cm × 38 cm (1805 cm²). Observations and behavioral tests were conducted over a period of 20 weeks, with the rats being observed in their home cages for 30-minute periods at 3, 5, 7, 11, and 16 weeks. Behavior was scored based on 15-second intervals, and the results are as follows: Food or water-directed behavior did not appear to be affected by housing density. However, significant differences in food consumption were observed between males and females, with males consuming more food than females. Moreover, both singly housed males and females exhibited higher food consumption compared to pair- or group-housed rats. Grooming behavior exhibited variations over time, but no significant pattern was observed. Group-housed females tended to groom more than pairs, while single-housed females groomed significantly more than pairs. Other behaviors such as yawning, stretching, and sniffing increased for all animals over time. Female pairs showed a notable increase in these behaviors at week 7, while males displayed a significant decrease in these behaviors at week 16. Cage-directed behaviors decreased significantly over time. These behaviors were particularly high at 3 weeks, indicating that the rats were actively inspecting their new cages. Social behavior did not display significant changes over time. Agonistic behavior, which refers to aggressive or confrontational behavior, differed between the sexes, with males exhibiting more agonistic behavior than females. While males showed a slight increase in agonistic behavior at 7 weeks, no significant pattern was discerned. Inactive behavior increased in single-housed rats, and at 7 weeks, group-housed males showed an increase in inactive behavior. Enrichment-directed behavior was utilized by all groups, with only slight increases observed in group-housed rats. Abnormal behavior occurred infrequently in this study but was exhibited more frequently in males than females. There was a slight increase in abnormal behavior at week 16, with slightly higher occurrences in pairs compared to groups. Movement behavior decreased over time for all groups. In summary, the study found that housing density and environmental resource provision had various effects on the behavior of adult male and female Sprague Dawley rats. Food consumption, grooming behavior, agonistic behavior, inactive behavior, and abnormal behavior were influenced by housing conditions and showed variations over time. Social behavior, enrichment-directed behavior, and movement behavior were less affected by housing density.
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