Captivity-Induced Depression in Animals

Exploring the similarities between risk factors triggering depression in humans and elevated in-cage "inactive but awake" behavior in laboratory mice

Introduction

Depression is a human mental disorder that can also be inferred in non-human animals. This study explored whether time spent inactive but awake ("IBA") in the home-cage in mice was further triggered by risk factors similar to those increasing vulnerability to depression in humans (early life stress, genetic predispositions, adulthood stress).

Methods

Eighteen DBA/2 J and 18 C57BL/6 J females were tested, of which half underwent as pups a daily maternal separation on post-natal days 2-14 (early-life stress "ELS") (other half left undisturbed). To assess the effect of the procedure, the time the dams from which the 18 subjects were born spent active in the nest (proxy for maternal behavior) was recorded on post-natal days 2, 6, 10 and 14 for 1 h before separation and following reunion (matched times for controls), using live instantaneous scan sampling (total: 96 scans/dam). For each ELS condition, about half of the pups were housed post-weaning (i.e., from 27 days old on average) in either barren (triggering IBA and depression-like symptoms) or larger, highly enriched cages (n = 4-5 per group). Time mice spent IBA post-weaning was observed blind to ELS treatment using live instantaneous scan sampling in two daily 90-min blocks, two days/week, for 6 weeks (total: 192 scans/mouse). Data were analyzed in R using generalized linear mixed models.

Results

The dams were significantly more active in the nest over time (p = 0.016), however with no significant difference between strains (p = 0.18), ELS conditions (p = 0.20) and before/after separation (p = 0.83). As predicted, post-weaning barren cages triggered significantly more time spent IBA in mice than enriched cages (p < 0.0001). However, neither ELS (p = 0.4) nor strain (p = 0.84) significantly influenced time mice spent IBA, with no significant interaction with environmental condition (ELS × environment: p = 0.2861; strain × environment: p = 0.5713).

Discussion

Our results therefore only partly support the hypothesis that greater time spent IBA in mice is triggered by risk factors for human depression. We discuss possible explanations for this and further research directions.

The endangered brain: actively preserving ex-situ animal behaviour and cognition will benefit in-situ conservation

Endangered species have small, unsustainable population sizes that are geographically or genetically restricted. Ex-situ conservation programmes are therefore faced with the challenge of breeding sufficiently sized, genetically diverse populations earmarked for reintroduction that have the behavioural skills to survive and breed in the wild. Yet, maintaining historically beneficial behaviours may be insufficient, as research continues to suggest that certain cognitive-behavioural skills and flexibility are necessary to cope with human-induced rapid environmental change (HIREC). This paper begins by reviewing interdisciplinary studies on the 'captivity effect' in laboratory, farmed, domesticated and feral vertebrates and finds that captivity imposes rapid yet often reversible changes to the brain, cognition and behaviour. However, research on this effect in ex-situ conservation sites is lacking. This paper reveals an apparent mismatch between ex-situ enrichment aims and the cognitive-behavioural skills possessed by animals currently coping with HIREC. After synthesizing literature across neuroscience, behavioural biology, comparative cognition and field conservation, it seems that ex-situ endangered species deemed for reintroduction may have better chances of coping with HIREC if their natural cognition and behavioural repertoires are actively preserved. Evaluating the effects of environmental challenges rather than captivity per se is recommended, in addition to using targeted cognitive enrichment.

Wild and Captive Environments Drive the Convergence of Gut Microbiota and Impact Health in Threatened Equids

To explore how the living environment influences the establishment of gut microbiota in different species, as well as the extent to which changes in the living environment caused by captive breeding affect wildlife’s gut microbiota and health, we used 16S rRNA gene amplicon sequencing and shotgun metagenomic sequencing to compare the gut microbiome of two species of threatened equids, the Przewalski’s Horse and the Asian wild ass, in the wild and captivity. The results revealed that different species of Equidae living in the same environment showed remarkable convergence of gut microflora. At the same time, captive populations exhibited significantly “unhealthy” microbiota, such as low Alpha diversity, high levels of potentially pathogenic bacteria and biomarkers of physical or psychological disease, and enrichment of microbial functions associated with exogenous exposure and susceptibility, implying that the artificial environment created by captivity may adversely impact the health of wildlife to some extent. Our findings demonstrate the importance of the environmental factors for the establishment of gut microbiota and host health and provide new insights into the conservation of wildlife in captivity from the perspective of the microbiome.

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

Simple Summary

Environmental enrichment has been widely studied with laboratory rodents, but there is no consensus regarding what counts as enrichment or what it should achieve. Inconsistent use of the term “enrichment” creates challenges in drawing conclusions about the quality of an environment. We conducted a metareview to better understand the definitions and goals of enrichment, perceived risks or requirements of enrichment, and what forms of enrichment have previously been endorsed for use with rodents housed in laboratories. This may help researchers and animal care staff to better define their chosen approach and intended outcomes when providing environmental enrichment.

Abstract

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.

The effects of cow dominance on the use of a mechanical brush

An animal's social position within a group can influence its ability to perform important behaviours like eating and resting, but little is known about how social position affects the ability to express what are arguably less important but still rewarding behaviors, such as grooming. We set out to assess if dominance measured at the feeder is associated with increased use of a mechanical brush. Over a 2-year period, 161 dry cows were enrolled in a dynamically changing group of 20 individuals with access to a mechanical brush. We determined dominance using agonistic behaviors at the feeder and retrospectively analyzed brush use for the 12 most, and 12 least dominant individuals during the week before calving. Cows that were more dominant at the feeder used the brush more, especially during peak feeding times. Agonistic interactions at the brush did not differ between dominants and subordinates and were not related to brushing duration. These findings indicate that social position, calculated using competition for feed, affects mechanical brush access such that subordinates use the brush less than dominant cows independent of competition or time of day.

Postpartum Stressors Cause a Reduction in Mechanical Brush Use in Dairy Cows

Dairy cows are often subjected to multiple post-partum stressors but how these stressors impact cows' affective states remain poorly understood. Negative affective states are often associated with reduced expression of low-resilience behaviors, so we explored whether cows would reduce their use of a brush after calving. Before calving, cows were offered the opportunity to use a mechanical brush once a week for 10 min. In Experiment 1, we explored whether cows reduced their use of a mechanical brush after parturition (compared to prepartum values) when subjected to the myriad of stressors typically experienced by cows at this time. In Experiment 2, we assessed the effect of cow-calf separation. Results from Experiment 1 showed that cows displayed a reduced brush use following parturition compared to the week before calving. In Experiment 2, we showed that cows given more time to bond with their calf, and who were separated more recently from their calf, showed a more pronounced reduction in brush use. Cows provided part-time contact with their calf for 29 days also reduced their brush use when they were permanently separated from their calf on day 30 after calving. These results suggest that cows experienced anhedonia and point to new directions for research on dairy cow affective states.

A Perspective on Strategic Enrichment for Brain Development: Is This the Key to Animal Happiness?

Livestock animals are sentient beings with cognitive and emotional capacities and their brain development, similar to humans and other animal species, is affected by their surrounding environmental conditions. Current intensive production systems, through the restrictions of safely managing large numbers of animals, may not facilitate optimal neurological development which can contribute to negative affective states, abnormal behaviors, and reduce experiences of positive welfare states. Enrichment provision is likely necessary to enable animals to reach toward their neurological potential, optimizing their cognitive capacity and emotional intelligence, improving their ability to cope with stressors as well as experience positive affect. However, greater understanding of the neurological impacts of specific types of enrichment strategies is needed to ensure enrichment programs are effectively improving the individual's welfare. Enrichment programs during animal development that target key neurological pathways that may be most utilized by the individual within specific types of housing or management situations is proposed to result in the greatest positive impacts on animal welfare. Research within livestock animals is needed in this regard to ensure future deployment of enrichment for livestock animals is widespread and effective in enhancing their neurological capacities.

Putative neural consequences of captivity for elephants and cetaceans

The present review assesses the potential neural impact of impoverished, captive environments on large-brained mammals, with a focus on elephants and cetaceans. These species share several characteristics, including being large, wide-ranging, long-lived, cognitively sophisticated, highly social, and large-brained mammals. Although the impact of the captive environment on physical and behavioral health has been well-documented, relatively little attention has been paid to the brain itself. Here, we explore the potential neural consequences of living in captive environments, with a focus on three levels: (1) The effects of environmental impoverishment/enrichment on the brain, emphasizing the negative neural consequences of the captive/impoverished environment; (2) the neural consequences of stress on the brain, with an emphasis on corticolimbic structures; and (3) the neural underpinnings of stereotypies, often observed in captive animals, underscoring dysregulation of the basal ganglia and associated circuitry. To this end, we provide a substantive hypothesis about the negative impact of captivity on the brains of large mammals (e.g., cetaceans and elephants) and how these neural consequences are related to documented evidence for compromised physical and psychological well-being.

Negative expectations and vulnerability to stressors in animals

Humans express stable differences in pessimism that render some individuals more vulnerable to stressors and mood disorders. We explored whether non-human animals express stable individual differences in expectations (assessed via judgment bias tests) and whether these differences relate to susceptibility to stressors. Judgment bias tests do not distinguish pessimism from sensitivity to reinforcers; negative expectations are likely driven by a combination of these two elements. The available evidence suggests that animals express stable individual differences in expectations such that some persistently perceive ambiguous situations in a more negative way. A lack of research prevents drawing firm conclusions on how negative expectations affect responses to stressors, but current evidence suggests a link between negative expectations and the adoption of avoidance coping strategies, stronger responses to uncontrollable stressors and risk of mood-related disorders. We explore implications for animals living in captivity and for research using animals as models for human disorders.