Digestive enzymes have been popular due to potential increases in feed efficiency, and by association, reduced environmental impact for more sustainable livestock management. Enzymes help chemical reactions in the body occur, and in the context of nutrition, help break down food into smaller particles which can then be absorbed and used in the body.
While digestive enzymes are a natural part of the horse’s digestion process, supplemental digestive enzymes may offer the potential to improve digestion.
As many digestive issues are associated with starch reaching the hindgut, and some horses may be less efficient at digesting and utilizing feeds, digestive enzymes are an increasingly popular supplement. Unfortunately, an enzyme being present endogenously (ie, the horse produces it themselves) does not guarantee that supplementation will be effective.
Let's do a quick scan of the literature:
Amyloglucosidase supplementation alone does not improve starch digestibility, so the horse may have sufficient endogenous levels (Richards et al, 2004).
Cellulase supplementation alone has varied effects on digestibility in horses, with some studies reporting reduced digestibility with cellulase supplementation (O’Connor-Robinson, Nielsen and Morris, 2007).
Natuzyme, a digestive enzyme mix originally designed for poultry, has been reported to improve fiber digestibility in horses as well, but it is unclear which enzymes in the mix elicited those beneficial effects (Cipriano-Salazar et al, 2019).
Amylase supplementation has been found to improve starch digestion, reducing hindgut acidosis associated with starch overload (Proudman, Darby and Esscalona, 2014; Richards et al, 2004). As horses are naturally adapted to consume low-starch diets, it is possible that horses lack amylase concentrations to handle high-starch diets. Racehorses fed amylase-rich malt extract had improved energy intake, improved race performance, and more stable gut microbiomes (Hunter, 2019).
Allzyme, a feed additive produced by Alltech, contains xylanase and cellulase, and has been found to improve fiber digestibility in some cases, which may help minimize the amount of concentrate fed (Hainze, Muntifering and McCall, 2003). This feed additive has also been shown to improve phosphorus availability (Dunnet, Dunnet and McLachlan, 2009).
Other studies which combined xylanase and cellulase have also reported improved insoluble fiber digestibility, suggesting this combination pairs well when used in horses (Jozefiak et al, 2020).
Variable results indicate more research is required for horses, and as some studies have reported reduced digestibility, enzyme selection is key.
As seen with probiotic supplements, dose and manufacturing are likely important factors which can also impact efficacy. Feed additive manufacturers with a large agricultural scope (such as Alltech) often develop additives with research trials, and their products go through quality control and standardized enzyme activity checks. These are all great characteristics to suggest a quality feed ingredient!
Some types of enzymes have no evidence in horses, and as such, supplementation may just increase feed cost - resources which could instead be spent on vitamin/mineral supplements that use more bioavailable ingredients, or more digestible forage forms.
As with any supplement selection, assessing the whole diet is critical when considering adding a feed ingredient to your horse's nutrition plan!
REFERENCES
Cipriano-Salazar et al, 2018. The Dietary Components and Feeding Management as Options to Offset Digestive Disturbances in Horses. Journal of Equine Veterinary Science 74(2019): 103-110.
Hainze, MTM., Muntifering, RB., McCall, CA. 2003. Fiber digestion in horses fed typical diets with and without exogenous fibrolytic enzymes. Journal of Equine Veterinary Science 23(3): 111-115.
Hunter, 2019. How the Digestion of Nutrients May Improve Horse Trainer Magazine 67: 76-80.
Jozefiak et al, 2020. Exogenous fibrolytic enzymes improve carbohydrate digestion in exercising horses. Journal of Animal and Feed Science 29(2020): 35-45.
O'Connor-Robinson, CI., Neilsen, BD., Morris, R. 2007. Cellulase Supplementation Does Not Improve the Digestibility of a High-Forage Diet in Horses. Journal of Equine Veterinary Science 27(12): 535-538.
Proudman, C., Darby, A., Esscalona, E. 2014. Fecal microbiome of the Thoroughbred racehorse and its response to dietary amylase supplementation. Equine Veterinary Journal 46(2014):35
Richards, N., Choct, M., Hinch, GN., Rowe. 2004. Examination of the use of exogenous alpha-amylase and amyloglucosidase to enhance starch digestion in the small intestine of the horse. Animal Feed Science and Technology 114(2004): 295-305.
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