Clinical health issues, reproductive hormones, and metabolic hormones associated with gut microbiome structure in African and Asian elephants

Background

The gut microbiome is important to immune health, metabolism, and hormone regulation. Understanding host–microbiome relationships in captive animals may lead to mediating long term health issues common in captive animals. For instance, zoo managed African elephants (Loxodonta africana) and Asian elephants (Elephas maximus) experience low reproductive rates, high body condition, and gastrointestinal (GI) issues. We leveraged an extensive collection of fecal samples and health records from the Elephant Welfare Study conducted across North American zoos in 2012 to examine the link between gut microbiota and clinical health issues, reproductive hormones, and metabolic hormones in captive elephants. We quantified gut microbiomes of 69 African and 48 Asian elephants from across 50 zoos using Illumina sequencing of the 16S rRNA bacterial gene.

Results

Elephant species differed in microbiome structure, with African elephants having lower bacterial richness and dissimilar bacterial composition from Asian elephants. In both species, bacterial composition was strongly influenced by zoo facility. Bacterial richness was lower in African elephants with recent GI issues, and richness was positively correlated with metabolic hormone total triiodothyronine (total T3) in Asian elephants. We found species-specific associations between gut microbiome composition and hormones: Asian elephant gut microbiome composition was linked to total T3 and free thyroxine (free T4), while fecal glucocorticoid metabolites (FGM) were linked to African elephant gut microbiome composition. We identified many relationships between bacterial relative abundances and hormone concentrations, including Prevotella spp., Treponema spp., and Akkermansia spp.

Conclusions

We present a comprehensive assessment of relationships between the gut microbiome, host species, environment, clinical health issues, and the endocrine system in captive elephants. Our results highlight the combined significance of host species-specific regulation and environmental effects on the gut microbiome between two elephant species and across 50 zoo facilities. We provide evidence of clinical health issues, reproductive hormones, and metabolic hormones associated with the gut microbiome structure of captive elephants. Our findings establish the groundwork for future studies to investigate bacterial function or develop tools (e.g., prebiotics, probiotics, dietary manipulations) suitable for conservation and zoo management.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-021-00146-9.

Alternative method for intramuscular fat analysis using common laboratory equipment

A procedure to quantify intramuscular fat was developed using common inexpensive laboratory equipment. Three homogenization methods of lyophilized muscle samples (Ball-mill, Grinder and Mortar) and two extraction methods (Ball-mill or Vortex) were used in turkey meat and pork. Two-hundred mg of lyophilized and homogenized samples were accurately weighed and mixed with 1.5 mL of dichloromethane-methanol (8:2) and shaken either in a Mixer Mill (MM400, Retsch Technology) or in a Vortex. The final mixture was separated by centrifugation. Solvent was evaporated under a nitrogen stream and lipid content was gravimetrically determined. Besides, it was checked that the fatty acid profile was not altered by the protocol used. Moreover, the analysis of 4 replicas from the same sample showed different variation coefficients (16-29%) for the new procedures proposed over a wide range of IMF content. The combination of Grinder and Vortex methodologies can be proposed as a simple and inexpensive alternative to previous ones.