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Why Digestive Aids are Like Bits

Updated: Mar 22

*Is it possible to find the perfect bit or the perfect digestive aid for our horse(s)? Microbiome research on humans, mice and cattle is leading us closer to finding the right fit.

A 4* Star level eventer and I were swapping stories one afternoon as we drove down for jump night with friends. Her upper level gelding was incredibly difficult to keep weight on. He was picky, uninterested in food, stressful, and unhappy. Not only was he very picky, but he needed a tremendous amount of calories to perform at that level, so the pair was struggling. She had tried multitudes of digestive aids to no avail. Later in our discussion I asked her what that she might recommend for my young five-year-old that likes to evade the bit. Her answer was priceless- "I think bits are like digestive aids. You can try dozens of them and never find exactly what you are looking for."

"I think bits are like digestive aids. You can try dozens of them and never find exactly what you are looking for." - An Intuitive Eventer

If you've been around horses for more than 5 minutes, you know that each one is unique. A horse's acceptance of the bit may be due to shape and contours of the mouth, sensitivity of the tongue or bars, and the horse's temperament not to mention the complex interactions of the rider's position and aids. In the horse's microbiome, we call the same complexity of internal and external factors "host specificity". Host specificity refers to the very unique ecosystem of microbiota that can live within a host (your horse in this case). We now know that the microbiome of your horse is like it's own universe of star stuff- influenced from birth by what that horse eats, how it's managed, and its own genome. Just as every horse's mouth is unique, so is there digestive system, but infinitely more so, because inside the horse's hindgut are trillions of organisms from all branches of evolutionary tree. If individual horse specificity is important to the success of a bit or a digestive aid, how do we begin to choose? Where are the algorithms when you need one!?!

No where is this host specificity better illustrated than in the story of the transfaunated cow! What is transfaunation you might ask? It is an extremely interesting method of scientific inquiry where researchers transfer the entire contents of one cows rumen directly into the rumen of another through cannulation! Surprisingly, this is relatively easy to do in cows and relatively common in the pursuit of milk production efficiency of dairy cows and performance metrics of beef cattle! It's a gold mine of information. In cattle we can produce a literal WINDOW into a wild microbial ecosystem that has been a black hole to us in the past. By contrast in horses, we can measure what goes in and we can measure what comes out, but we have very little means to measure anything inside it in real time! The instrumental methods we use to answer the big questions about the horse's microbiome are still very blunt at best, but we can infer a few things from the cannulation of these cattle.

So, here's the really crazy story! Do you know what happens during and after transfaunation in cattle? Well, scientific literature agrees that, most of the time, the micriobiome will return to the individual host's pre-exchange state within one to two weeks! According to Cox et al. (2021) this "underscored the strong host-specificity of the adult rumen bacterial communities which apparently was able to re-establish even after extreme perturbation." An earlier transfaunation experiment came to the same conclusion. We need to better understand individual host factors such as gene expression in order to better manipulate the microbiome long-term (Zhou et al., 2018). Long-term is the key phrase here. Transfaunation of these cattle did have strong short-term effects, so we know that performance does and can change. These studies really underscore for me how little we really understand about microbiomes in general. We might not have as much control over the ecosystem as supplement companies would like us to believe, but recent research enthusiasm around the microbiome of many species is taking positive steps in that direction and that is very exciting. There are so many more interesting microbiome stories that I'd love to share with you about human fecal transplants, germ-free mice, and cannulation in horses, but I'll leave that to another day.


What scientists (specifically microbiologists) are telling us is that the individualism of the horse's microbiome is made from trillions of archae, bacteria, fungi and protozoa and their interactions with the host's (your horse) diet, genome, and immune system. What is surprising is that we can actually manipulate that universe at all! We know that different feed ingredients and management strategies will change the ecology of the horse's digestive system enough to experience positive external changes. We know that digestive aids can indeed influence the digestibility of nutrients, the strength of the immune system, and the overall performance of horses. The trick is to find the right one!

What this tells us about digestive aids is that experimentation, just like bitting, is necessary when selecting the right one for your horse. There are digestive aids that affect the foregut and some that affect the hindgut. Some are living digestive aids and others are non-living digestive aids. Digestive aids can be plant based, animal based or mineral based, and there's a new one on the market everyday! But do not despair. If you have not yet read "How to Trial a New Supplement" and the three things that I recommend you do- start there. You can then check out my pet project RATE MY HORSE SUPPLEMENT to see how I've rated several digestive aids on the market today. Finally, you can schedule a 3 Month Guided Nutrition Practice to help step you through the trials of digestive aid hunting!


Cox, M.S., Deblois, C.L., and G. Suen. 2021. Assessing the Response of Ruminal Bacterial and Fungal Microbiota to Whole-Rumen Contents Exchange in Dairy Cows. Frontiers in Microbiology. 12:1386. Retrieved October 8, 2021 from

E.J. DePeters and L.W. 2014. George. Rumen transfaunation. Immunology Letters. 162(2): 69-76. ISSN 0165-2478

Zhou, M., Peng, YJ., Chen, Y. et al. 2018. Assessment of microbiome changes after rumen transfaunation: implications on improving feed efficiency in beef cattle. Microbiome 6:62.

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