A rise in the levels of Streptococcal bacteria seen in the hindgut of some Welsh ponies has been linked to barley feeding, with the end result being a decrease in bacterial gut diversity.
Changes in the make-up of the bacteria that populate the hindgut of horses bring a greater risk of gut-related problems such as colic.
Increases of Streptococcal species have been linked to the development of oligofructose-induced laminitis. It has also been linked to ruminal acidosis, which can cause major digestive problems among cattle and sheep.
Researchers who carried out the British study found significant variations between individual ponies in terms of their Streptococcus response to barley feeding.
Streptococcus promoted its own growth following the introduction of barley to the diet, Philippa Morrison and her fellow researchers reported in the open-access journal PLOS ONE.
It may indicate that those “responders” in the current study were unable to maintain a favourable environment for the growth of lactate-utilising bacterial populations, which in turn allowed the overgrowth of Streptococcus.
“Although animals in the current study remained healthy throughout, it could be suggested that the large variation in Streptococcus response reflects variation in individual susceptibility to gastrointestinal disturbances and other metabolic disorders,” the study team reported.
Further work is needed, they say, to provide more insights into the reasoning behind the individual variation to dietary responses.
“The ability to identify those ‘high risk’ animals who may display an elevated Streptococcus response prior to the introduction of dietary starch would be advantageous in aiding dietary management strategies,” they wrote.
The researchers say that although horses are adapted to consuming fibre-based diets, high-energy feed, often containing a lot of starch, are increasingly used.
For their two-year study, they assessed the impact of age on the faecal bacteriome of ponies transitioning from a hay-based diet to a high-starch diet. They used 23 Welsh Section A pony mares, some of whom served as controls.
Data on the bacteria present was collected by analysing faecal samples.
They found that age had a minimal effect on the bacteriome response to diet.
However, the dietary transition increased Candidatus Saccharibacteria and Firmicutes phyla abundance and reduced Fibrobactres abundance.
Streptococcus abundance increased, but not consistently across individual animals. Bacterial diversity reduced during dietary transition among the Streptococcus “responders”.
Faecal pH and concentrations of volatile fatty acids were altered by the change in diet but, again, considerable variation between the ponies was seen.
The findings, they say, emphasise the individual nature of dietary responses, which may reflect functional differences in the bacterial populations present in the hindgut.
They suggest that future studies should try to advance the understanding of bacterial function during dietary changes.
The study team comprised Morrison, Charles Newbold, Eleanor Jones, Hilary Worgan, Dai Grove-White, Alexandra Dugdale, Clare Barfoot, Patricia Harris and Caroline Argo, variously affiliated with Scotland’s Rural College, Aberystwyth University in Wales, the University of Liverpool, ChesterGates Veterinary Specialists in England, Mars Horsecare and the Waltham Petcare Science Institute.
Morrison PK, Newbold CJ, Jones E, Worgan HJ, Grove-White DH, Dugdale AH, et al. (2020) Effect of age and the individual on the gastrointestinal bacteriome of ponies fed a high-starch diet. PLoS ONE 15(5): e0232689. https://doi.org/10.1371/journal.pone.0232689