The intestinal microbiota of domestic horses is impoverished when compared to their wild counterparts, researchers report.
“Antibiotic exposure is one of the likely causes considering the observed increase in antimicrobial resistance genes,” Li Ang and his fellow researchers reported in the journal Communications Biology.
Domesticated horses live under different conditions compared with their extinct wild ancestors, the study team wrote. They hypothesized that the microbiota of domesticated horses would be altered because of their housing circumstances, medication use, and feed regimes.
In their study, they assessed the fecal microbiome of 57 domestic and feral horses from different locations on three continents, observing geographical differences.
They found clear differences, with a higher abundance of Eukaryota and viruses, and fewer archaea in the feral animals when compared with domestic horses.
“The abundance of genes coding for microbe-produced enzymes involved in the metabolism of carbohydrates was significantly higher in feral animals regardless of the geographic origin,” they reported.
Differences in the fecal resistomes between both groups of animals were also noted, they said. The fecal resistome comprises all genes in the fecal matter that directly or indirectly contribute to antibiotic resistance.
“The domestic/captive horse microbiomes were enriched in genes conferring resistance to tetracycline, likely reflecting the use of this antibiotic in the management of these animals.”
They also identified differences between the two groups in enzymes involved in carbohydrate metabolism, with the microbiome of domestic horses seemingly enriched in glycosyltransferase genes, whereas feral animals presented higher levels of glycosylhydrolase.
“These results are suggestive of a different plant-carbohydrate metabolism between both groups of animals.
“To test this, the levels of genes related to starch/glycogen metabolism and those of cellulose metabolism were calculated and compared between both groups of animals, with domestic horses having higher levels of genes related to the metabolism of starch and lower levels of those related to that of cellulose than wild-living animals.”
They continued: “Our data showed an impoverishment of the fecal microbiome in domestic horses, with diet, antibiotic exposure and hygiene being likely drivers.”
Common management practices for domestic horses include feeding include high-concentrate diets, low forage quality, meal feeding and confined housing, all of which may affect intestinal function, specifically fermentation in the hindgut.
“The larger metabolic potential regarding enzymes involved in the metabolism of carbohydrates found in feral animals likely reflects the larger complexity of their diets in open spaces compared to confined domestic animals.”
“Taken together, this study has revealed differences in the microbiome of horses from different geographical locations,” they said.
“The data revealed major differences between feral and domesticated animals, thus demonstrating the evolutionary role of domestication-associated antibiotics, feed and environment.”
The results, they said, offer a view of the impact of domestication or captivity on the intestinal microbiome of horses. The findings, they added, may help uncover new targets for regulating the microbiome of horses to enhance their health and well-being.
The study team comprised Ang, Gabriel Vinderola, Akihito Endo, Juha Kantanen, Chen Jingfeng, Ana Binetti, Patricia Burns, Shi Qingmiao, Ding Suying, Yu Zujiang, David Rios-Covian, Anastasia Mantziari, Shea Beasley, Carlos Gomez-Gallego, Miguel Gueimonde and Seppo Salminen, from a range of institutions around the world.
Ang, L., Vinderola, G., Endo, A. et al. Gut Microbiome Characteristics in feral and domesticated horses from different geographic locations. Commun Biol 5, 172 (2022). https://doi.org/10.1038/s42003-022-03116-2