The Science Behind Slow Feed Changes

Most horse owners know that feed changes should be made slowly, and do implement this well. However, I often come across people switching forage sources abruptly. This article is going to delve into the science behind why feed changes should be made slowly and highlight the importance of gradual changes not just for pelleted feeds but also for forage!

The Anatomy

Horses are hindgut fermenters; this means that they have a microbial population in the hindgut that plays a key role in digestion. Just like humans, horses have a stomach and small intestine, where the major differences lie in the hindgut. The hindgut has a few different parts: the cecum, large colon, small colon, and rectum. The cecum is truly what sets the horse apart from other monogastric animals as it is the site of fermentation.

The microbial population ferments the structural carbohydrates primarily from forages in the horse’s diet. This process results in volatile fatty acids (VFAs), which are then used as an energy source by the horse. Abrupt diet changes negatively impact the microbial population by impairing their ability to break down the feedstuff adequately which will result in digestive upset.

So, we know there are microbes in the horse’s hindgut…but how does that relate to feed and feed changes.

Well, there are a variety of different microbes that are present in the hindgut of the horse, and depending on the horse’s diet, a differing proportion of the various microbes will be present. For example, if your horse is consuming an all-forage diet, their microbial population is going to be very different from a horse that is consuming a larger quantity of concentrate feed.

This illustration is from Kauter et al. 2019. In the paper this image is described as depicting a horse that is on a more varied forage-based diet (left) compared to a horse that is managed domestically (right). This illustration highlights that differing management and nutrition does result in different microbial populations.

How Changes Impact Microbes?

Switching feeds or forage sources slowly can seem tedious, but it is crucial to prevent digestive upset. The horse’s microbial population will adapt to the diet they are accustomed to. For example, if you have a horse that is accustomed to a high starch diet, they will have more of the microbes that are meant to break down those nutrients. Whereas, if you have a horse that is on a primarily forage-based diet the microbes that make up the majority of the gut population will be geared towards digesting more fibrous feedstuffs. Therefore, when drastic changes are made e.g., a forage-based diet switched to one that incorporates more starchy feeds the microbes will not be accustomed or tailored to that and will die off. This alteration of the microbial population then contributes to digestive issues.

Now, if we make changes slowly, this allows the horse’s microbial population time to adapt and ensure there are the correct microbes to support the new diet. I strongly encourage horse owners to make all changes slowly – this means even switching from one hay batch to another. Even though they may be the same type of forage, their nutrient profiles will differ. Therefore, best practice is to use gradual changes.

Some specific research examples are:

–          A nutrition program with a highly concentrated grain feed has been shown to increase the lactic acid bacteria (especially Streptococcus spp. And Lactobacillus spp.)

–          A high starch diet has been shown to increase Succinivibrio and decrease Clostridiales and Lachnospiraceae.

–          A high oil and starch diet has been shown to increase Proteobacteria

–          A grass-based diet has been shown to increase Lachnospiraceae Bacillus  

If you are looking to really dive deep into some science, I encourage you to check out this table from (Kauter et al. 2019).

Minimizing Digestive Upset

Now, just because we make changes gradually doesn’t mean that we are eliminating the risk of colic – of course not. But there are ways to decrease that risk. Making stepwise changes over the course of 7-14 days is often recommended when changing nutrition programs.

For example, if you are adding a new feed to your horse’s program start with a small quantity, and as you increase the amount every few days, decrease the product you are taking out by a similar amount. The same can be applied to forage changes. In my balanced diet reports, you will see this tactic detailed in the implementation section.

To conclude, feed changes can be tedious and frustrating but sticking with a gradual plan can really do wonders for your horse’s gut health as you transition programs. So, if you are in the process of transitioning your horse onto summer pasture like I am, maybe this blog post will help to encourage you to keep up with the tedious process. Also, please keep this in mind when your new hay arrives this upcoming summer!

If you have any questions about safe diet transition or how to create a plan that is practical for your horse send me an email!

References:

Al Jassim, R. A., & Andrews, F. M. (2009). The bacterial community of the horse gastrointestinal tract and its relation to fermentative acidosis, laminitis, colic, and stomach ulcers. Veterinary Clinics: Equine Practice, 25(2), 199-215.

Costa, M. C., & Weese, J. S. (2012). The equine intestinal microbiome. Animal Health Research Reviews, 13(1), 121-128.

Dicks, L. M. T., Botha, M., Dicks, E., & Botes, M. (2014). The equine gastro-intestinal tract: an overview of the microbiota, disease and treatment. Livestock science, 160, 69-81.

Dougal, K., de la Fuente, G., Harris, P. A., Girdwood, S. E., Pinloche, E., Geor, R. J., … & Newbold, C. J. (2014). Characterisation of the faecal bacterial community in adult and elderly horses fed a high fibre, high oil or high starch diet using 454 pyrosequencing. PloS one, 9(2), e87424.

Fielding, B. A., & Frayn, K. N. (1998). Lipoprotein lipase and the disposition of dietary fatty acids. British Journal of Nutrition, 80(6), 495-502.

Hesta, M., & Costa, M. (2021). How Can Nutrition Help with Gastrointestinal Tract–Based Issues?. Veterinary Clinics: Equine Practice, 37(1), 63-87.

Kauter, A., Epping, L., Semmler, T., Antao, E. M., Kannapin, D., Stoeckle, S. D., … & Walther, B. (2019). The gut microbiome of horses: current research on equine enteral microbiota and future perspectives. Animal Microbiome, 1(1), 1-15.

Salem, S. E., Maddox, T. W., Berg, A., Antczak, P., Ketley, J. M., Williams, N. J., & Archer, D. C. (2018). Variation in faecal microbiota in a group of horses managed at pasture over a 12-month period. Scientific reports, 8(1), 8510.