Gut Microbiota and Behavioural Issues in Production, Performance, and Companion Animals: A Systematic Review

Abstract

The literature has identified poor nutrition as the leading factor in the manifestation of many behavioural issues in animals, including aggression, hyperalertness, and stereotypies. Literature focused on all species of interest consistently reported that although there were no significant differences in the richness of specific bacterial taxa in the microbiota of individual subjects with abnormal behaviour (termed alpha diversity), there was variability in species diversity between these subjects compared to controls (termed beta diversity). As seen in humans with mental disorders, animals exhibiting abnormal behaviour often have an enrichment of pro-inflammatory and lactic acid-producing bacteria and a reduction in butyrate-producing bacteria. It is evident from the literature that an association exists between gut microbiota diversity (and by extension, the concurrent production of microbial metabolites) and abnormal behavioural phenotypes across various species, including pigs, dogs, and horses. Similar microbiota population changes are also evident in human mental health patients. However, there are insufficient data to identify this association as a cause or effect. This review provides testable hypotheses for future research to establish causal relationships between gut microbiota and behavioural issues in animals, offering promising potential for the development of novel therapeutic and/or preventative interventions aimed at restoring a healthy gut-brain-immune axis to mitigate behavioural issues and, in turn, improve health, performance, and production in animals.

Zebrafish (Danio rerio) behavioral phenotypes not underscored by different gut microbiota

“…Short-chain fatty acids (SCFAs) produced by a plethora of fermentative gut-associated bacteria in animals (Silva et al, 2020), as well as other microbe-produced neurotransmitters, are known to influence behaviors (Homer et al, 2023). Dopamine, acetylcholine, serotonin, and gamma-aminobutyric acids (GABA) are some examples of neurotransmitters demonstrated to be synthesized both by the neurons and by some gut bacteria (Wong et al, 2015a;Silva et al, 2020;Homer et al, 2023). Members of the phylum Actinomycetota, particularly Bifidobacterium, produce GABA, which influences behaviors.…”

The Impact of Early-Life Cecal Microbiota Transplantation on Social Stress and Injurious Behaviors in Egg-Laying Chickens

“…Numerous psychological (an emotion and/or mental overstimulation) and/or physical (environmental conditions) stressors reduce gut microbiota diversity and/or alter microbiome composition by (1) disrupting the community stability of commensal bacterial populations, often accompanied by reduced beneficial bacteria and increased pathogens (causing a chronic low-grade inflammation); (2) increasing the survival translocation of pathogens and releasing virulence factors; (3) disrupting absorption of nutrients and minerals (metabolic disorders); (4) disrupting microbial neuroendocrine functions (alterations in synthesis of several signaling molecules and neurochemicals including 5-HT in the GIT); (5) disrupting the gut epithelial barrier, thereby increasing intestinal permeability and releasing certain bacteria, bacterial antigens, and metabolites (leaky gut), resulting in both intestinal and systemic immune reactions; and (6) damaging epithelial cells, producing free radicals and reducing antioxidant capacity (oxidative stress) [ 142 , 143 , 144 ]. These changes in the gut microbiota with a chronic low-grade inflammation profoundly influence host health and behavioral homeostasis via the MGB and MGI axes [ 58 , 145 ]. Treatments aimed at restoring normal gut microbiota composition and homeostasis have become effective methods to prevent and/or reduce various stress-induced neuropsychiatric disorders [ 146 , 147 ].…”

“…(5) disrupting the gut epithelial barrier, thereby increasing intestinal permeability and releasing certain bacteria, bacterial antigens, and metabolites (leaky gut), resulting in both intestinal and systemic immune reactions; and (6) damaging epithelial cells, producing free radicals and reducing antioxidant capacity (oxidative stress) [142][143][144]. These changes in the gut microbiota with a chronic low-grade inflammation profoundly influence host health and behavioral homeostasis via the MGB and MGI axes [58,145]. Treatments aimed at restoring normal gut microbiota composition and homeostasis have become effective methods to prevent and/or reduce various stress-induced neuropsychiatric disorders [146,147].…”

“…The gut microbiota plays a critical role in early programming and later activity of the central stress systems, i.e., the hypothalamic–pituitary–adrenal (HPA) and the sympathetic–adrenal–medullary (SAM) axes [ 52 , 53 , 54 ]. Like an endocrine organ, the gut microbiota is sensitive and reactive to various exogenous stimuli, functioning as an environmental sensor linked to the pathogenesis of stress-related illnesses through the bidirectional communication of the MGB axis [ 55 , 56 , 57 , 58 , 59 ] and the microbiota–gut–immune (MGI) axis [ 60 , 61 ] in various animals including chickens [ 62 , 63 , 64 ]. Maintaining gut microbiota balance and health is essential for animals (including chickens) to maintain their optimal physiological and behavioral functions of growth, reproduction, and welfare.…”

Microbes and Mental Illness: Past, Present, and Future

“…Animal models of infections associated with aggression include Borrelia burgdorferi in dogs, Bartonella henselae in dogs, B. henselae in horses, B. burgdorferi postulated in chimpanzee in lay news, rabies virus in multiple animal species, and gut microbiota in dogs, horses, and pigs. [[273][274][275][276][277][278][279][280][281][282][283] …”