Forage

What do they eat?

While horses can and do eat a variety of foods, grass is their primary source for nutrients (7, 8). Certain types of grasses are more appetizing than other types. When grass is limited, horses may eat other plants like the greenery of shrubs, fruits, and veggies. Horses generally prefer sweeter foods over savory, which makes high-sugar grasses like alfalfa so appetizing.

Microbiome and the Gut-Brain Axis

By now, you may have learned about the role of gut bacteria in digestion. Gut bacteria exists in all animals and aids in breaking down food for the animal to absorb nutrients. A healthy gut will always have bacteria. However, imbalances of bacteria in the gut, or too much of bad bacteria can cause harm (10, 11). With the rise of dietary issues in humans, quite a bit of research has looked into the connection between gut health and other functions of the body, most notably the brain. Equine scientists have done their own research into the connection between the horse gut and brain, and it is very comparable to other species. 

An unhealthy gut can greatly affect a horse, causing skin inflammation and more. Skin irritation/inflammation can cause a lot of discomfort, which might make the horse act out. Have you ever brushed a horse with ulcers, and he turned to bite you? This could be a reaction to the gut pain it is feeling and anticipating, but sensitivity all over could also indicate skin irritation. All of these factors play into how the horse is feeling and, thus, how it will behave, just like how we might feel down when we have a stomachache and do not want to be touched. Therefore, the microbiome needs to be maintained carefully to avoid these negative consequences, and pain responses should not be punished, only checked out by the vet.

Forage Vs. Grain

If horses mostly eat grass in the wild, why do we feed them grain in domestic settings? Grain is used very commonly internationally, but it is not an adequate alternative to forage like grass and hay. Horses need forage for optimal digestion and absorption as discussed above, but they also need the forage to chew enough for gut health. Part of maintaining a good digestive system is maintaining good dental health. Horses have hypsodont teeth, meaning their teeth grow throughout their lives (12). Because of this, horses need to chew long enough to grind down their teeth. Forage will often achieve this, but grain requires significantly less chewing time, which not only decreases how much the teeth grind down, but also saliva production, which aids in breakdown of food and buffering the stomach from stomach acid (13). On top of decreasing oral health, high-starch diets (which is what grain is) can change the composition of gut bacteria, causing the imbalances above (14).

The best practice is to give the horse 24/7 access to forage (hay/grass) as the base of the diet, and supplementing additional foods as needed on top of that. Working with a vet and nutritionist will be instrumental in developing a horse's diet.

Sources:

1. Hampson, B. A., de Laat, M. A., Mills, P. C., & Pollitt, C. C. (2010). Distances travelled by feral horses in 'outback' Australia. Equine veterinary journal. Supplement, (38), 582–586. https://doi.org/10.1111/j.2042-3306.2010.00203.x 

2. Duncan, P. (1980). Time-Budgets of Camargue Horses Ii. Time-Budgets of Adult Horses and Weaned Sub-Adults. Behaviour, 72(1-2), 26-48. https://doi.org/10.1163/156853980X00023 

3. Boyd, L. E., Carbonaro, D. A., & Houpt, K. A. (2003, October 2). The 24-hour time budget of Przewalski Horses. Applied Animal Behaviour Science. https://www.sciencedirect.com/science/article/pii/0168159188900986 

4. Ermers, C., McGilchrist, N., Fenner, K., Wilson, B., & McGreevy, P. (2023). The fibre requirements of horses and the consequences and causes of failure to meet them. Animals, 13(8), 1414. https://doi.org/10.3390/ani13081414  

5. Clayton, H. M., Flood, P. F., Rosenstein, D. S., & Mandeville, D. (2015). Clinical anatomy of the horse. Mosby Elsevier.

6. Auwerda, Peggy. (n.d.). Digestive anatomy and physiology of the horse. Equine Science. https://www.extension.iastate.edu/equine/blog/dr-peggy-m-auwerda/digestive-anatomy-and-physiology-horse 

7. Salter, R. E., & Hudson, R. J. (1979). Feeding ecology of feral horses in western Alberta. Journal of Range Management, 32(3), 221. https://doi.org/10.2307/3897127 

8. McInnis, M. L., & Vavra, M. (1987). Dietary relationships among feral horses, cattle, and pronghorn in southeastern Oregon. Journal of Range Management, 40(1), 60. https://doi.org/10.2307/3899363. Sourced from (9).

9. Harvey, A. M., Ramp, D., & Mellor, D. J. (2022). Review of the foundational knowledge required for assessing horse welfare. Animals, 12(23), 3385. https://doi.org/10.3390/ani12233385. Sourced from (9).

10. Mach, N., Ruet, A., Clark, A., Bars-Cortina, D., Ramayo-Caldas, Y., Crisci, E., Pennarun, S., Dhorne-Pollet, S., Foury, A., Moisan, M.-P., & Lansade, L. (2020, May 20). Priming for welfare: Gut Microbiota is associated with equitation conditions and behavior in horse athletes. Nature News. Retrieved January 29, 2023, from https://www.nature.com/articles/s41598-020-65444-9 

11. Jezioro, V., & Auwerda, P. (n.d.). Stomach ulcers in horses. Equine Science. https://www.extension.iastate.edu/equine/blog/dr-peggy-m-auwerda/stomach-ulcers-horses  

12. Pieper, B. (2018, April 21). Horse's teeth need dental care. Veterinary Medicine at Illinois. Retrieved February 12, 2023, from https://vetmed.illinois.edu/pet-health-columns/horse-teeth/ 

13. Elia, J. B., Erb, H. N., & Houpt, K. A. (2010, September 24). Motivation for hay: Effects of a pelleted diet on behavior and physiology of horses. Physiology & Behavior. https://www.sciencedirect.com/science/article/pii/S0031938410003380 

14. Raspa, F., Vervuert, I., Capucchio, M. T., Colombino, E., Bergero, D., Forte, C., Greppi, M., Cavallarin, L., Giribaldi, M., Antoniazzi, S., Cavallini, D., Valvassori, E., & Valle, E. (2022). A high-starch vs. high-fibre diet: Effects on the gut environment of the different intestinal compartments of the horse digestive tract. BMC Veterinary Research, 18(1). https://doi.org/10.1186/s12917-022-03289-2