Avoid Abrupt Changes in Equine Diets

We have heard the phrase “abrupt change in diet” repeatedly from nutrition experts over the years, but what exactly does this mean? How can horse owners avoid these changes, and why do we need to?

An abrupt change describes any drastic deviation to a diet, such as suddenly adding or increasing a concentrate or switching from a forage-based diet to a complete feed, according to Kathleen Crandell, Ph.D., a Kentucky Equine Research nutritionist. “Even alternating between different types of hay or between hay and pasture can be considered an abrupt diet change, depending on the horse.”

The gastrointestinal tract must adapt to any change in the diet. The microorganisms that live within the hindgut, called the microbiota, play an important role in the fermentation of forages, and thus are active in the health and vitality of the entire tract.

Consistency of diet keeps the microbiota content. When an abrupt diet change occurs, the population of bacteria, fungi, and protozoa suddenly shifts in type, number, and robustness, and feeds may not be efficiently or properly digested and fermented. Further, alterations in the microbiota and fermentative capacity can provoke deleterious effects, such as the development of subclinical acidosis in the hindgut, colic, laminitis, diarrhea, weight loss, and behavioral issues.

Keeping the microbiota stable is imperative for optimal health and feed utilization (i.e., deriving as much energy from the feed as possible). This explains why effective digestive tract supplements such as EquiShure continue to be popular. EquiShure stabilizes the pH of the cecum and colon, thus supporting the health of the microbiota.

“If the acidity level of the hindgut remains fairly constant, then the negative effects of abrupt dietary changes can be mitigated,” Crandell noted. “Even when pH can be controlled through a hindgut buffer, other factors such as the types of feeds or energy substrates, such as starch, reaching the microbiota for fermentation can cause some bacteria to bloom and others to diminish.”

In a recent study, changing between hay and fresh grass and vice versa resulted in appreciable alterations in the microbiota, particularly within the first few days of the change.^* The researchers reported a notable increase in the Lactobacillus bacterial population, which produces lactic acid, a substance that can drop the pH in the hindgut. The increased Lactobacillus population was more pronounced when the diet changed abruptly from hay to grass pasture.

“Even in situations that seem relatively innocuous such as changing hays, be sure to make diet changes over the course of a week or two. When possible, offer a hindgut buffer during any diet change to help protect the microbiota,” Crandell advised.

Other tips from Crandell included the following:

• Buying new hay before you run out of the old supply and mixing the two together to transition from one to the next;
• Providing continual access to pasture, even if for only a few hours a day rather than only a few hours once or twice a week;
• Allowing horses to become acclimatized to pasture by slowly increasing the number of hours on pasture per day. If needed, use a grazing muzzle to keep the horse from consuming too much fresh pasture initially and causing shifts in the microbiome; and
• Offering regular hay in addition to pasture to maintain some consistency among the substrates reaching the microbiota.

 ^*Garber, A., P. Hastie, D. McGuinness, P. Malarange, and J. Murray. 2020. Abrupt dietary changes between grass and hay alter faecal microbiota of ponies. PLoS One 15(8):e0237869.