Profound changes in gut microbes seen in ponies suddenly switching between hay and grass

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Abrupt changes to the microbial families in faeces were chronicled in ponies undergoing sudden dietary switches between grass and hay.

Writing in the open-access journal PLOS ONE, researchers reported that a dietary change — either from grass or hay, or hay to grass — can have a profound effect within the first few days of transition.

A rapid swap from hay to grass may present a higher risk of gut problems compared to an abrupt switch from grass to hay, Anna Garber and her colleagues said.

The study team said abrupt dietary changes can occur when managing horses. They may, in turn, trigger compositional changes in gut microbiota, which may result in digestive or metabolic disturbances.

The researchers set out to describe and compare the faecal microbiota of ponies suddenly changed from pasture grazing to a restricted hay-only diet and vice versa.

The experiment, which began in early summer, involved six adult Welsh Section A pony geldings. For a month beforehand, the ponies were grazed on pasture.

The study consisted of two 14-day periods. In the first phase, the ponies were taken off the pasture and fed only hay at a rate of 17.5 grams per kilogram of body weight on a dry matter basis.

In the pasture phase that followed, when the hay was stopped altogether after a fortnight, the ponies were not restricted in the amount of grass they chose to eat.

Faecal samples were collected at the start of each phase, and on days 1 to 3, 7 and 14 after the dietary changes were enacted.

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Molecular-based analysis techniques were used to characterise the microbiome as well as the relative abundance of microbiota present.

“The results of this study suggest that the faecal microbiota of mature ponies is highly diverse, and the relative abundances of individual taxa change in response to abrupt changes in diet,” they said.

The faecal microbiota of ponies maintained on a restricted amount of hay only was similar to that of the ponies fed solely grass in terms of richness and species diversity. However, it differed significantly in terms of the relative abundances at distinct taxonomic levels.

Class Bacilli, order Lactobacillales, family Lactobacillaceae, and genus Lactobacillus were present in increased relative abundance on day 2 after an abrupt dietary change from hay to grass compared to all other experimental days.

“This finding suggests that an abrupt dietary change from hay to grass may represent a higher risk for hindgut pH to drop compared to abrupt change from grass to hay as Lactobacillus is known to be a major lactic acid-producing bacteria.”

The authors continued: “Abrupt changes from grass to hay and vice versa affect the faecal microbial community structure; moreover, the order of dietary change appears to have a profound effect in the first few days following the transition.

“An abrupt dietary change from hay to grass may represent a higher risk for gut disturbances compared to abrupt change from grass to hay.”

The most profound effects on the faecal microbial community structure were in the first few days, they found.

Bacterial phyla dynamics in the faeces of the ponies during the abrupt dietary transitions. Bacterial phyla with a relative abundance greater than 5% are shown. Error bars represent standard error of the mean. Red vertical lines represent abrupt changes in the diet. D represents day; H represents hay; and G represents grass. Image: Garber et al. https://doi.org/10.1371/journal.pone.0237869

Clearly, they said, further studies are required to identify a tool for supporting a more stable gut environment in the horse during quick dietary transitions.

“Determining the role of microbial species in nutrient breakdown and their contribution to metabolism is fundamental to understanding digestive processes and maximising productivity, health and welfare of the horse.”

However, the gene-sequencing technology used in the study allowed the researchers to identify only compositional changes in microbial populations.

“Results from this study can be used to further investigate the role of specific microbes that were affected by the abrupt dietary changes and their contribution to equine microbiota in terms of their immediate response to the change and longer-term adaptation to different diets.”

The study team comprised Garber, with animal nutrition technology company AB Vista; Peter Hastie, David McGuinness and Jo-Anne Murray, all with the University of Glasgow in Scotland; and Pauline Malarange, with EPLEFPA des Combrailles in France.

Garber A, Hastie P, McGuinness D, Malarange P, Murray J-A (2020) Abrupt dietary changes between grass and hay alter faecal microbiota of ponies. PLoS ONE 15(8): e0237869. https://doi.org/10.1371/journal.pone.0237869

The study, published under a Creative Commons License, can be read here

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