The composition of gut bacteria in horses is highly dynamic and responds distinctly to seasonal dietary factors and changing weather, researchers have found.
These changes were monitored in seven healthy horses kept on pasture over 12 months, across all four seasons, with minimal changes in management.
Changes in the management of horses, such as the addition of a new feed, have long been linked to an increased risk of colic, but the researchers say that considering a potential change in gut bacteria as the sole trigger is clearly too simplistic.
University of Liverpool researcher Shebl Salem and his colleagues reported that whilst a clear pattern of change in the faecal microbiota of the study horses was evident over the 12 months, this did not result in any clinical abnormalities, including colic, developing in any of the animals.
“This work demonstrates that the faecal microbiota is highly dynamic and responds distinctly to dietary factors and ambient environmental conditions in normal horses,” the study team wrote in the journal Scientific Reports.
“These findings suggest that any proposed relationship between change in management and altered risk of colic that solely considers shifts in gut microbiota composition is too simplistic.”
“The faecal microbiota of the study horses was found to be in a continuous process of adaptation and change in association with alterations in grass, supplementary forage and ambient weather conditions.”
For the study, faecal samples were collected every 14 days from the horses for 52 weeks and the faecal microbiota was characterised by next-generation sequencing of genes.
All horses used in the study were assessed as healthy beforehand and lived in pasture for the length of the research, with free access to grass and water. During the months of the year when grass quality was insufficient for adequate nutrition, they were given access to haylage. The animals varied in age and breed.
The researchers found that the faecal microbiota was dominated by members of the phylum Firmicutes and Bacteroidetes.
The seasons, supplementary forage, and ambient weather conditions – rainfall and temperature – were linked to the changes seen in the faecal microbiota.
The findings, they said, provided important baseline information on variation in the faecal microbiota of normal horses over 12 months without development of colic.
The authors noted that many studies had investigated risk factors for colic and had identified several modifiable and non-modifiable factors.
Consistently reported factors that increase the risk relate to changes such as feeding a new batch of forage, a change in forage type, a change in type and amount of grain-based feed, decreased access to pasture, and increased time spent stabled.
It has been proposed that such changes may alter the colonic microflora, inducing changes in colonic pH and volatile fatty acid production, predisposing horses to colic.
Colic, they noted, has been shown to have a seasonal pattern which differs between different populations of horses and between different types of colic.
However, it was unknown whether stability over time was a primary feature of gut microbial populations in horses, particularly under constant management conditions.
Their research had addressed this question, they said, providing important baseline data.
“This information is essential prior to exploring differences between the faecal microbiota in normal horses under conditions of minimal management and those managed more intensively (e.g. concentrate feed and stabling) or with horses that have developed or are at high risk of colic.”
The faecal microbiota of the study horses was found to be in a continuous process of adaptation and change in association with alterations in grass, supplementary forage and weather.
“Dynamic adaptation of the gut microbiota has been observed in people and similar seasonal shifts in gut microbiota composition in response to seasonal dietary variation have also been reported for other animal species.
“Based on these results, it is plausible that intestinal dysfunction/colic could develop either because of lack of adaptation of gut microbiota in some horses or due to major shifts/disruption in gut microbiota composition as a response to marked, sudden management changes.”
They said it was not possible in the study to determine how quickly the gut microbiota may adapt to a change in diet because of the duration of time between the sampling occasions and the gradual change in diet (for example, the natural gradual decrease in the amount of grass available to the horses under investigation).
The results suggested fluctuations in the composition of the horse gut microbiota associated with weather and dietary forage variations is normal, they said, even though only a small number of normal horses were studied.
The influence of weather was interesting, they said.
“This effect could be either due to direct correlation between weather conditions and feed types available for the horses, or because of the effect of weather on the composition of environmental bacteria (soil and grass/haylage microbiota).”
The most prominent change in the study was the increased relative abundance of members of the phylum Fibrobacters and Spirochaetes when haylage was introduced into the horses’ diet.
This increase appeared to be associated with a decrease in the relative abundance of members of the phylum Firmicutes.
One of the seven horses used in the study was lost early in the research. The animal was euthanised due to an injury.
The full research team comprised Salem, Thomas Maddox, Philipp Antczak, Nicola Williams and Debra Archer, all from the University of Liverpool; and Adam Berg and Julian Ketley, both from the University of Leicester.
Variation in faecal microbiota in a group of horses managed at pasture over a 12-month period
Shebl E. Salem, Thomas W. Maddox, Adam Berg, Philipp Antczak, Julian M. Ketley, Nicola J. Williams & Debra C. Archer.
Scientific Reportsvolume 8, Article number: 8510 (2018) https://doi.org/10.1038/s41598-018-26930-3