Can diet influence strongyle FEC results in horses?

Worms, the microbiome and diet – how are these related? A 2024 study by Laroche, N., Grimm, P., Julliand, S., & Sorci, G. 2024 investigated this question, with this post a summary.  

As hindgut fermenters, horses are reliant on the bacteria and other microbes that reside within their intestines, as these microbes are responsible for the breakdown of cellulose (fibre) and other plant material into compounds horses can use for energy. These bacteria are known as the microbiome, and as research into gut microbiomes of all species increases, it is becoming clear that feeding the microbiome correctly will massively improve an animal’s health.

To add to the complexity, most animals (including humans for most of our history) also have a nemabiome (population of worms) that have to fit into the gut ecosystem. Within a horse’s gut there is a four-way relationship between the horse’s immune system, the microbiome, the nemabiome, and diet, which all together is likely to be the biggest influence for horse health.

Graphic taken from Laroche et al (2024), showing how diet influences the microbiota, worm population and host immunity, while the microbiota, worms and host immunity can all influence each other.

In the study, the effect of a high fibre versus high starch diet was investigated. Horses that were used in this study were originally fed a high fibre diet consisting of hay and grass, and were naturally infected with strongyles. Over the study period, horses were fed either an unchanged high fibre diet (0% starch, 61% fibre) or a high starch diet of grass, hay, hay pellets and barley (20.5% starch, 44% fibre).

It was found that over a three-week period, the number of strongyle eggs shed by the horses on the high starch diet increased significantly, while there was no change in the FEC results of the horses that were kept on the high fibre diet. At the end of the three-week period, the horses fed the high starch diet were swapped back to their original high fibre diet, and their EPG values decreased back to original levels after three weeks. From this, the authors suggested that the level of starch and/or fibre in a horse’s diet can have an impact on the fecundity (egg laying) of the strongyle worms, with a higher starch diet resulting in more eggs shed.

Other factors that were monitored in this study included immunomarkers, red blood cell levels and microbiome diversity. It was found that for either diet, changes to the immune system (e.g. cytokine levels, white blood cell counts) did not change. There was a trend found however, where horses with higher EPG values also had a lower haemocrit (red blood cell) level. It was not clear why this occurred, but it is thought that worms may take more blood when producing higher numbers of eggs.

There was also no significant change to the gut microbiome of horses across the diets. However, horses fed high fibre diet had a higher percentage of bacteria responsible for the breakdown of cellulose (fibre), while horses fed high starch diet had a higher percentage of bacteria in their gut that digests starch and sugar (e.g. lactic acid bacteria). Whether the slight changes in the microbiome effected the egg shedding of the strongyles was not able to be determined, however other research that has investigated microbiome and worm burdens suggests it may be a possibility.

Overall, this study showed that there is a strong link between diet, immune system, microbiome and strongyle egg shedding. Exactly how this relationship works is not yet fully known or understood, however the authors of the study state that the “first step in the strategy to control helminth [worm ed.] infection should be to provide animals with diets that preserve a healthy intestinal ecosystem… We therefore suggest that a safer strategy to control helminth infection [compared to using dewormers ed.] would be to improve host tolerance to the infection.”

While this study showed a clear link between high fibre diets and low EPG values, it is only one part of the puzzle when developing a horse’s diet plan, and parasite management regime. However, it does show a simple improvement to diet that could be made to help decrease strongyle egg shedding.   

Reference: Laroche, N., Grimm, P., Julliand, S., & Sorci, G. (2024). Diet modulates strongyle infection and microbiota in the large intestine of horses. Plos one, 19(4), e0301920.

Link to paper: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0301920