Probiotics Wanted: Dead Or Alive?

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May 2017

Probiotics wanted: Dead or alive?


New study finds bacterial supplements for horses may be effective even if lifeless.

To maximise the performance of sports horses, it is important that their energy demands are met. To do this, their diets are commonly supplemented with cereal grains that provide an important source of calories. But this simple addition is not without its problems.

The inclusion of high starch feed ingredients can result in various clinical disorders, such as colic (gut pain) and laminitis, particularly when fed in large quantities. This is, in part, thought to be due to a sudden change in the bacterial population within the gut and associated with a marked decrease in the pH. Horses are primarily hindgut fermenters. This means they maximise the digestion of their food by microbial fermentation in their specialised hindgut (large intestine and caecum). The products of this fermentation can then be absorbed and used by the animal. Sudden changes to this microbial population and their fermentation products can impact the health of the horse. Optimal feeding management should, therefore, aim to prevent disturbances to these essential processes.

Why feed a probiotic?

Feeding a probiotic supplement may help stabilise the gut population. The term ‘probiotic’ is commonly used to describe live micro-organisms which have health benefits to the host animal when fed in sufficient amounts. However, little is known about the benefit of feeding different types of potential probiotics to horses, so a research team from the University of Kentucky and United States Department of Agriculture, Agricultural Research Service, in partnership with WALTHAM, decided to investigate further.

Faeces were collected from horses with no gastrointestinal issues in order to extract gut bacteria. These were then incubated with or without one of three potential probiotic bacterial strains together with one of three different grains (ground corn, wheat or oats). The change in the bacterial population was measured after 24 hours.

When the gut bacteria were incubated with the different grains without the probiotic, a sudden drop in pH and a significant change in the microbial population occurred, especially with corn or wheat. The addition of the different probiotic bacteria (Lactobacillus acidophilus, Lactobacillus buchneri, Lactobacillus reuteri) showed some beneficial effects. All three bacterial strains limited the decrease in pH seen with the corn and wheat fermentation and resulted in significant changes in the ratios of   some key functional groups of bacteria. Only L. acidophilus and L. reuteri had the same effect with the oats. The researchers also found no additional benefit from using an equal mix of all 3 bacterial strains compared to a single bacterial strain.


Dead, but not forgotten

However, there was an unexpected twist; when the research team killed the probiotic bacteria and repeated the study, the dead bacteria had the same effect as when they were alive. They still limited the change in pH and promoted changes in the ratios of key functional bacterial groups.

'This is a fascinating, and unexpected, finding' explained Prof Pat Harris

“This is a fascinating, and unexpected, finding” explained Prof Pat Harris, Head of the Equine Studies Group at WALTHAM. “At the moment, we don’t know why the dead bacteria have the same effect, but it provides an exciting observation for future studies to explore.”

There are obviously limitations in using a laboratory based technique instead of directly sampling horses fed probiotics. However, studies conducted in the laboratory, like this, can be used to direct more targeted animal based evaluations in the future.  Such studies offer some insight and/or raise questions as to what may occur in the horse.


Read more about choosing feed supplements for horses, click here

Reference:  Harlow BE, Lawrence LM, Harris PA, Aiken GE, Flythe MD (2017) Exogenous lactobacilli mitigate microbial changes associated with grain fermentation (corn, oats, and wheat) by equine fecal microflora ex vivo. PLoS ONE 12(3): e0174059. https://doi.org/10.1371/journal.pone.0174059

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