Gut Microbiomes of Endangered Przewalski's Horse Populations in Short- and Long-Term Captivity: Implication for Species Reintroduction Based on the Soft-Release Strategy

Rusa deer microbiota: the importance of preliminary data analysis for meaningful diversity comparisons

The microbiome is an important consideration for the conservation of endangered species. Studies provided evidence of the effect of behavior and habitat change on the microbiota of wild animals and reported various inferences. It indicates the complexity of factors influencing microbiota diversity, including incomplete sampling procedures. Data abnormality may arise due to the procedures warranting preliminary analysis, such as rarefaction, before downstream analysis. This present study demonstrated the effect of data rarefaction and aggregation on the comparison of wild rusa deer's gut microbial diversity. Eighty-five feces samples were collected from 11 deer populations inhabiting three national parks in Java and Bali islands. Using the Illumina Nova-Seq platform, fragments of 16s rRNA gene were sequenced, and raw data of 51,389 reads corresponding to 2 domains, 22 phyla, 45 classes, 83 orders, 182 families, and 460 genera of bacteria were obtained. Data rarefaction was applied at two different library sizes (minimum and fixed) and aggregation (11 populations into 3 research sites) to investigate its effect on the microbial diversity comparison. There are significant differences in alpha diversity between populations, but not research sites, at all library sizes of rarefaction. A similar finding is also found in beta diversity. Moreover, data rarefaction and aggregation result in different values of the diversity metrics. This present study shows that statistical analysis remains a substantial concern in microbiome studies applied to conservation biology. It suggests reporting a more detailed data normalization in microbiome studies as an inherent control of suboptimal sampling, particularly when involving feces.

The faecal microbiome of Exmoor ponies shows step-wise compositional changes with increasing levels of management by humans

BACKGROUND

Horses can suffer from gastrointestinal (GI) disease in domestic environments, often precipitated by human-led changes in management. Understanding the consequences of these changes on equine gut microbiota is key to the prevention of such disease episodes.

OBJECTIVE

Profile the faecal microbiota of adult female Exmoor ponies under three management conditions, representing increasing levels of management by humans, encompassing different diets; whilst controlling for age, breed and sex.

STUDY DESIGN

Cross-sectional descriptive.

METHODS

Faecal samples were collected from three populations of Exmoor ponies kept under contrasting management conditions: 29 adult female ponies in groups with low management (LM) (n = 10), medium management (MM) (n = 10) and high management (HM) (n = 9) levels, based on diet, drug use, handling and exercise. Faecal microbial composition was profiled via high-throughput sequencing of the bacterial 16S rRNA gene, and functional metagenome predictions.

RESULTS

We observed profound step-wise changes in microbiome structure in the transition from LM to MM to HM. A relatively high abundance of Proteobacteria and Tenericutes was associated with the HM group; higher abundance of Methanobacteria was observed in the LM group. The MM group had intermediate levels of these taxa and exhibited high 'within group' variation in alpha diversity. Functional predictions revealed increased amino acid and lipid metabolism in HM; energy metabolism in LM and carbohydrate metabolism and immune/metabolic disease pathways in MM.

MAIN LIMITATIONS

Low group sizes, incomplete knowledge of bacterial genomes in equine gut microbiota and it was not possible to assess the relative impact of diet, drug use, handling and exercise on the microbiome as variables were confounded.

CONCLUSIONS

Human-led management factors had profound step-wise effects on faecal microbial composition. Based on functional metagenome predictions, we hypothesise that dietary differences between groups were the major driver of observed differences.

Gut microbial community structure and function of Przewalski's horses varied across reintroduced sites in China

Host-associated microbiota can significantly impact host fitness. Therefore, naturally occurring variations in microbiota may influence the health and persistence of their hosts. This finding is particularly important in reintroduced animals, as they typically experience habitat changes during translocations. However, little is known about how microbiomes are altered in response to conservation translocation. Here, we accessed the gut microbiome of Przewalski's horse (Equus przewalskii) populations in China from three nature reserves (i.e. Xinjiang Kalamaili Nature Reserve, KNR; Dunhuang Xihu National Nature Reserve, DXNNR; and Anxi Extreme-arid Desert Nature Reserve, AENR) using 16s rRNA gene and metagenome sequencing. The results showed that the microbial composition and function differed significantly across locations, while a subset of core taxa was consistently present in most of the samples. The abundance of genes encoding microbe-produced enzymes involved in the metabolism of carbohydrates, especially for glycoside hydrolases, was significantly higher in open-spaced KNR populations than in more confined AENR individuals. This study offers detailed and significant differential characters related to the microbial community and metabolic pathways in various reintroduced sites of Przewalski's horse, which might provide a basis for future microecological and conservation research on endangered reintroduced animals.

The phenotypic costs of captivity

The breeding of threatened species in captivity for release is a central tool in conservation biology. Given gloomy predictions for biodiversity trends in the Anthropocene, captive breeding will play an increasingly important role in preventing future extinctions. Relative to the wild, captive environments drastically alter selection pressures on animals. Phenotypic change in captive animals in response to these altered selection pressures can incur fitness costs post-release, jeopardising their potential contribution to population recovery. We explore the ways in which captive environments can hinder the expression of wild phenotypes. We also stress that the phenotypes of captive-bred animals differ from their wild counterparts in multiple ways that remain poorly understood. We propose five new research questions relating to the impact of captive phenotypes on reintroduction biology. With better use of monitoring and experimental reintroductions, a more robust evidence base should help inform adaptive management and minimise the phenotypic costs of captivity, improving the success of animal reintroductions.

Effect of ellagic acid on body weight, nutrient digestibility, fecal microbiota, and urolithin A metabolism in Thoroughbred horses

This study aimed to investigate the effects of ellagic acid (EA) supplementation on body weight (BW), nutrient digestibility, fecal microbiota, blood biochemical indices, and urolithin A metabolism in 1-yr-old Thoroughbred horses. A group of 18 1-yr-old Thoroughbred horses, with an average weight of 339.00 ± 30.11 kg, were randomly allocated into three groups of six horses each (three males and three females). The control group (n = 6) received only the basal diet, whereas test groups I (n = 6) and II (n = 6) were fed the basal diet supplemented with 15 mg/kg BW/d and 30 mg/kg BW/d of EA, respectively, for 40-d. The results showed that test group I and II horses had a significant increase in total weight gain by 49.47% and 62.74%, respectively, compared to the control group. The digestibility of various components in the diets of the test group horses was improved, including dry matter, organic matter, gross energy, neutral detergent fiber, acid detergent fiber, and calcium. Additionally, the digestibility of crude protein and phosphorus (P) in test group II horses increased significantly by 10.96% and 33.56% (P < 0.05), respectively. Moreover, EA supplementation significantly increased the fecal abundance of Firmicutes, Bacteroidetes (P < 0.05), Fibrobacterota, p-251-o5, Desemzia incerta (P < 0.05), and Fibrobacter sp. (P < 0.05), while reducing the abundance of Proteobacteria, Pseudomonadaceae, Pseudomonas, and Cupriavidus pauculus (P < 0.05 or P < 0.01). Fecal samples from test group II showed 89.47%, 100%, and 86.15% increases in the concentrations of acetic acid, valeric acid, and total volatile fatty acids, respectively. In addition, the plasma levels of total protein, and globulin increased significantly in test groups I (7.88% and 11.35%, respectively) and II (13.44% and 16.07%, respectively) compared to those in the control group (P < 0.05). The concentration of urolithin A in fecal and urine samples was positively correlated with increasing doses of EA. These findings suggest that supplemental feeding of EA improved nutrient digestibility, blood biochemical indices, and fecal microbiota in 1-yr-old Thoroughbred horses, promoting growth and development.

The putative maintaining mechanism of gut bacterial ecosystem in giant pandas and its potential application in conservation

Animals living in captivity and the wild show differences in the internal structure of their gut microbiomes. Here, we performed a meta-analysis of the microbial data of about 494 fecal samples obtained from giant pandas (captive and wild giant pandas). Our results show that the modular structures and topological features of the captive giant panda gut microbiome differ from those of the wild populations. The co-occurrence network of wild giant pandas also contained more nodes and edges, indicating a higher complexity and stability compared to that of captive giant pandas. Keystone species analysis revealed the differences between geographically different wild populations, indicating the potential effect of geography on the internal modular structure. When combining all the giant panda samples for module analysis, we found that the abundant taxa (e.g., belonged to Flavobacterium, Herbaspirillum, and Escherichia-Shigella) usually acted as module hubs to stabilize the modular structure, while the rare taxa usually acted as connectors of different modules. We conclude that abundant and rare taxa play different roles in the gut bacterial ecosystem. The conservation of some key bacterial species is essential for promoting the development of the gut microbiome in pandas. The living environment of the giant pandas can influence the internal structure, topological features, and strength of interrelationships in the gut microbiome. This study provides new insights into the conservation and management of giant panda populations.

Assessment of Adaptation Status of Reintroduced Equus Przewalskii Based on Comparative Analysis of Fecal Bacteria with Those of Captive E. Przewalskii, Domestic Horse and Mongolian Wild Ass

Intestinal microbiota play an important role in the survival of the host. However, no study to date has elucidated the adjustment of intestinal microbiota of the host during rewilding. Thus, this study aims to describe the intestinal bacterial community of reintroduced Przewalski’s horse (RPH) after being released into their original habitat for approximately 20 years in comparison with that of captive Przewalski’s horse (CPH), sympatric domestic horse (DH) and Mongolian wild ass (MWA) by sequencing the 16S rRNA gene. The results showed that the prevalent bacterial communities were different among CPHs, RPHs, DHs and MWAs at the family level. NMDS and ANOSIM analysis showed that the pattern of bacterial community composition in captive equines was distinct from that in the wild groups. It is shown that some bacteria had significant differences among different taxa (p < 0.001), such as Firmicutes, Bacteroidetes, Armatimonadetes, Clostrida, Bacteroidia, Clostridiales, Bacteroidales, Rikenellaceae and Bacteroidales_UCG-001. These bacteria were associated with the transition from in captive to in the wild (CPH and RPH), which reflected the change of environmental conditions. Meanwhile, Proteobacteria, Clostridia, Bacilli, Negativicutes, Gammaproteobacteria, Clostridiales, Bacillales, Selenomonadales, Pseudomonadales and Planococcaceae were the changed groups among RPHs, MWAs and DHs, which are related to feeding habits and diseases. Our results clearly showed the differences between intestinal microbiota in reintroduced animals and wild animals and led us to understand the survival state of reintroduced animals in the wild.

Oral and fecal microbiome of confiscated Bengal slow lorises in response to confinement duration

Slow lorises are small arboreal and nocturnal primates. Due to the illegal trade, a large number of slow lorises were confiscated into wildlife sanctuaries or rescue centers. The re-release has been considered a preferable approach for alleviating the captive pressure, but inappropriate and long-term confinement make it difficult to achieve this goal. In this study, we investigated and compared the fecal and oral microbiome of Bengal slow lorises (Nycticebus bengalensis) under long-term captivity (LC) and short-term captivity (SC) groups based on 16s rRNA high-throughput gene sequencing. The oral microbiome displayed higher Chao1 richness but lower Shannon and Simpson indices than the fecal microbiome. The Bengal slow lorises under long-term captivity had abundant pathogenic genera in both gut and oral microbiomes, such as Desulfovibrio, Actinomyces, Capnocytophaga, Neisseria, and Fusobacterium, while some specific bacterial taxa associated with intestinal balance were more enriched in the SC group. Due to the plant gum scarcity in the diet, both groups had a low abundance of Bifidobacterium. Function profile prediction indicated that the LC group was enriched with genetic information processing and metabolism pathways due to the stable food intake. The increased membrane transport and xenobiotic metabolism and degradation functions in the SC group could be explained by the function of the host microbiome in facilitating adaptation to changing environments and diets. The results demonstrated that the oral microbiome had the potential to be used as a regular surveillance tool. Also, current captive management should be improved to ensure reintroduction success.

Comparative Analysis of Microbiome Metagenomics in Reintroduced Wild Horses and Resident Asiatic Wild Asses in the Gobi Desert Steppe

The gut microbiome offers important ecological benefits to the host; however, our understanding of the functional microbiome in relation to wildlife adaptation, especially for translocated endangered species, is lagging. In this study, we adopted a comparative metagenomics approach to test whether the microbiome diverges for translocated and resident species with different adaptive potentials. The composition and function of the microbiome of sympatric Przewalski’s horses and Asiatic wild asses in desert steppe were compared for the first time using the metagenomic shotgun sequencing approach. We identified a significant difference in microbiome composition regarding the microbes present and their relative abundances, while the diversity of microbe species was similar. Furthermore, the functional profile seemed to converge between the two hosts, with genes related to core metabolism function tending to be more abundant in wild asses. Our results indicate that sympatric wild equids differ in their microbial composition while harboring a stable microbial functional core, which may enable them to survive in challenging habitats. A higher abundance of beneficial taxa, such as Akkermansia, and genes related to metabolism pathways and enzymes, such as lignin degradation, may contribute to more diverse diet choices and larger home ranges of wild asses.

Metagenomics reveals contrasting energy utilization efficiencies of captive and wild camels (Camelus ferus)

Captive conditions can affect the symbiotic microbiome of animals. In this study, we compared the structural and functional differences of the gastrointestinal microbiomes of wild Bactrian camels (Camelus ferus) between wild and captive populations, as well as their different host energy utilization performances through metagenomics. The results showed that wild-living camels harbored more microbial taxa related to the production of volatile fatty acids, fewer methanogens, and fewer genes encoding enzymes involved in methanogenesis, leading to higher energy utilization efficiency compared to that of captive-living camels. These findings suggest that the wild-living camel fecal microbiome demonstrates a series of adaptive characteristics that enable the host to adjust to a relatively barren field environment. Our study provides novel insights into the mechanisms of wildlife adaptations to habitats from the perspective of the microbiome.

Metagenomic Analysis of Fecal Archaea, Bacteria, Eukaryota, and Virus in Przewalski's Horses Following Anthelmintic Treatment

Intestinal microbiota is involved in immune response and metabolism of the host. The frequent use of anthelmintic compounds for parasite expulsion causes disturbance to the equine intestinal microbiota. However, most studies were on the effects of such treatment on the intestinal bacterial microbes; none is on the entire microbial community including archaea and eukaryotic and viral community in equine animals. This study is the first to explore the differences of the microbial community composition and structure in Przewalski's horses prior to and following anthelmintic treatment, and to determine the corresponding changes of their functional attributes based on metagenomic sequencing. Results showed that in archaea, the methanogen of Euryarchaeota was the dominant phylum. Under this phylum, anthelmintic treatment increased the Methanobrevibacter genus and decreased the Methanocorpusculum genus and two other dominant archaea species, Methanocorpusculum labreanum and Methanocorpusculum bavaricum. In bacteria, Firmicutes and Bacteroidetes were the dominant phyla. Anthelmintic treatment increased the genera of Clostridium and Eubacterium and decreased those of Bacteroides and Prevotella and dominant bacteria species. These altered genera were associated with immunity and digestion. In eukaryota, anthelmintic treatment also changed the genera related to digestion and substantially decreased the relative abundances of identified species. In virus, anthelmintic treatment increased the genus of unclassified_d__Viruses and decreased those of unclassified_f__Siphoviridae and unclassified_f__Myoviridae. Most of the identified viral species were classified into phage, which were more sensitive to anthelmintic treatment than other viruses. Furthermore, anthelmintic treatment was found to increase the number of pathogens related to some clinical diseases in horses. The COG and KEGG function analysis showed that the intestinal microbiota of Przewalski's horse mainly participated in the carbohydrate and amino acid metabolism. The anthelmintic treatment did not change their overall function; however, it displaced the population of the functional microbes involved in each function or pathway. These results provide a complete view on the changes caused by anthelmintic treatment in the intestinal microbiota of the Przewalski's horses.

Effects of Gasterophilus pecorum infestation on the intestinal microbiota of the rewilded Przewalski's horses in China

Horse botflies have been a threat to the Przewalski’s horses in the Kalamaili Nature Reserve in Xinjiang of China since their reintroduction to the original range. As larvae of these parasites could infest the intestine of a horse for months, they could interact with and alter the structure and composition of its intestinal microbiota, affecting adversely its health. Nonetheless, there are no such studies on the rewilded Przewalski’s horses yet. For the first time, this study characterizes the composition of the intestinal microbiota of 7 rewilded Przewalski’s horses infected severely by Gasterophilus pecorum following and prior to their anthelmintic treatment. Bioinformatics analyses of the sequence data obtained by amplicon high throughput sequencing of bacterial 16S rRNA genes showed that G. pecorum infestation significantly increased the richness of the intestinal microbial community but not its diversity. Firmicutes and Bacteroidetes were found the dominant phyla as in other animals, and the parasitic infestation decreased the F/B ratio largely by over 50%. Large reduction in relative abundances of the two genera Streptococcus and Lactobacillus observed with G. pecorum infestation suggested possible changes in colic and digestion related conditions of the infected horses. Variations on the relative abundance of the genus groups known to be pathogenic or symbiotic showed that adverse impact of the G. pecorum infestation could be associated with reduction of the symbiotic genera Lactobacillus and Bifidobacterium that are probiotics and able to promote immunity against parasitic infection.

Effects of Pasture Grass, Silage, and Hay Diet on Equine Fecal Microbiota

Simple Summary

The intestinal microbial community in horses is very complex and interacts closely with diets. Apart from traditional forage diets, such as hay and pasture grass, silage is used to feed horses in China and other areas of the world for economic reasons or convenience of storage. Additionally, silage is also used for its convenience of harvesting and its nutrient components, including lactic acid and volatile fatty acids. In this study, we detected the characteristic composition of a fecal microbial community in horses that were fed silage with the use of a relatively new sequencing technique; we compared this result with that from horses that were fed hay and pasture grass. This study revealed some characteristic findings on the fecal microbial composition in horses that were given each of type of diet and showed significant differences between the groups. Our results provided novel data about the fecal microbial composition in horses on the silage diet. We hope that these could help balance the intestinal microbiota in horses that are mainly fed silage in combination with other types of forages in order to maintain intestinal health.

Abstract

Diet is an important factor affecting intestinal microbiota in horses. Fecal microbiota is commonly used as a substitute for studying hindgut microbiota when investigating the relationship between intestinal microbial changes and host health. So far, no study has compared the difference between the fecal microbiota found in horses that are fed pasture grass, silage, and hay. The present study aims to characterize the fecal microbiota in horses that were exclusively on one of the three forage diets, and to analyze the potential impact of these forages, especially silage, on horse intestinal health. There were 36 horses randomly assigned to each of the three groups; each group was fed only one type of forage for 8 weeks. High throughput sequencing was applied to analyze the bacterial taxa in fecal samples collected from the horses at the end of the feeding trial. The Lachnospiraceae family was statistically more abundant in horses fed with hay, while it was the least abundant in horses fed with silage. The Streptococcaceae spp., considered a core microbial component in equine intestinal microbiota, were present in significantly lower quantities in feces from horses that were fed pasture grass as compared to those from horses fed hay or silage. The novel data may help promote the balancing of horse intestinal microbiota and the maintenance of intestinal health in horses.

Effect of Gender Bias on Equine Fecal Microbiota

Many studies on human intestinal microbiota indicate that gender difference is one of the key factors influencing microbial community composition. To date, the degree of influence that gender has on equid intestinal microbiota has not been reported. Thus, microbiota was analyzed in feces of seven female Przewalski's horses (FRPHs) and seven male Przewalski's horses (MRPHs) in this study, determining which microbiota characteristics respond to gender biases. The microbial community composition and structure were explored by 16S rRNA sequencing, followed by diversity analysis and difference analysis. Female Przewalski's horses showed higher Shannon diversity than MRPHs, no difference in Simpson diversity, and displayed difference in beta diversity. Although gender had little effect on the overall microbiota, it significantly changed the dominant microbial community in each classification level. Male Przewalski's horses contained significantly higher amounts of microorganisms related with diseases, including spirochetes (phylum), deltaproteobacteria (class), fibrobacteria (class), spirochaetia (class), desulfovibrionales (order), fibrobacterales (order), spirochaetales (order), and spirochaetaceae (family). Female Przewalski's horses showed less than MRPHs in the top 10 genera. To our knowledge, this study is the first to document the gender-related intestinal microbiota profile in equines and discovered notable differences between the gender, which suggests that gender should be considered as a biological variable in future microbiota studies.