Wild horse survival rate linked to methane-producing gut bacteria

Sable Island horses on the island's beach. (Photo courtesy of Mason Stothart and the University of Calgary Faculty of Veterinary Medicine)

A recent observational study has revealed a link between methanogenic patterns in the gut microbiome of Sable Island horses and their survival.¹ These horses have been monitored every summer since 2007 and have no natural predators, making their main challenge competition for food.² The study is the first of its kind to offer substantial evidence on the remarkable role microbiomes play in the survival of animals in the wild, with its findings having broad implications for the health of animals and the environment, according to a news release.²

“While microbiomes are widely hypothesized to influence the fitness of wild animals, evidence for this remains extremely scarce” Jocelyn Poissant, PhD, associate professor at University of Calgary Faculty of Veterinary Medicine (UCVM), planner and initiator of the study more than a decade ago, said in the release.²

The study, a genetic analysis of gut microbiome diversity, represents the largest ever conducted for a population of wild animals, according to the release.² "Mounting evidence suggests that gut microbiomes can influence animal health, but much of this research has been conducted under highly controlled laboratory conditions or in humans,” Mason Stothart, BSc, MSc, PhD, postdoctoral research associate at the University of Oxford in the United Kingdom, and lead of the study, said in the release.²

Conducted by UCVM in Calgary, Alberta, the study aimed to quantify the connections between variations in the gut microbiome and survival rates within a feral horse population experiencing natural food limitations on Sable Island, Canada. To do this, researchers used long-term, individual-based life history and shallow shotgun metagenomic sequencing data of 2,394 fecal samples from 794 Sable Island horses collected between 2013 and 2019. They tested their predictions using data on short-chain fatty acids derived from the metagenomic data.¹

Poissant conducting field work at Sable Island. (Photo courtesy of Jocelyn Poissant and the University of Calgary Faculty of Veterinary Medicine)

The study provided evidence that variation in the gut microbiome is linked with horses’ ability to survive in the wild, finding an association between the survival of these horses and certain types of bacteria in the gut that produce, increase, or support the production of methane. The researchers postulated that pathogenesis and methanogenesis could be fundamental causal mechanisms underlying these patterns in feral horses, and potentially in wild herbivores more broadly.¹

“What we've discovered is that variation in microbial communities in the gut can be consequential for host health, even in the wild,” expressed Stothart in the release.²

According to the study, methanogenesis helps prevent the buildup of hydrogen gas (H2) in the gut, which is important given high levels of hydrogen can block important metabolic processes. However, the production of methane through methanogenesis requires a lot of energy. For herbivorous mammals, like horses, methane emissions can result in an energy loss ranging from 2% to 15% of the total energy they consume.¹ The research showed that while methanogenesis helps prevent harmful hydrogen buildup in the gut, it comes at the cost of significant energy loss, which can affect the survival of wild horses like those on Sable Island, especially during times of low food availability in winter.¹

Further implications

According to UCVM, the study found that wild herbivores could potentially live longer if they have efficient digestion aided by gut microbes who not only help in digestion, but also reduce the energy loss associated with methane emissions, making the study’s findings significant not just for Sable Island horses but potentially for other large-bodied, at-risk, wild species like elephants, rhinoceroses, tapirs, and Przewalski's horses.²

The discovery might also offer insight into mitigating methane emissions in animal agriculture. “We know from research on livestock that methane emissions are both an environmental and economic problem. Environmental, because methane is a potent greenhouse gas. Economic, because methane emissions from animals cause a loss of energy that could otherwise be used by the host, and therefore a reduction in animal feed efficiency,” explained Stothart in the release.²

“It appears that the same patterns of energetic loss to methane emissions that we observe in animal agriculture could be important for free-living wildlife. Our results lead us to suggest that the key to surprisingly low methane emissions among horses may derive from unique features in their gut microbiome, which could potentially serve as the basis for microbiological tools to reduce methane emissions in animal agriculture,” he continued.

UCVM’s research also holds relevance to human health: certain gut bacteria traits associated with methane emissions and mortality prediction in horses have been identified as being indicators of a lean body mass index (BMI) in humans, according to the release.²

References

1. Stothart MR, McLoughlin PD, Medill SA, Greuel RJ, et al. Methanogenic patterns in the gut microbiome are associated with survival in a population of feral horses. Nature Communications. 2024;15(1). https://doi.org/10.1038/s41467-024-49963-x
2. Knopp N. What the wild horse microbiome can teach us about health and longevity. News release. July 22, 2024. Accessed July 23, 2024. https://www.ucalgary.ca/news/what-wild-horse-microbiome-can-teach-us-about-health-and-longevity