Do Horses Select Feed based on Macronutrient Needs?

Do Horses Select Feed based on Macronutrient Needs?

Researchers know horses can adjust their rate of feed intake based on food source availability, but they recently set out to determine if horses can select for or against certain nutrients or nutrient compositions.

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Grazing comes naturally for horses, but there's more to it than just chewing pasture. Researchers know horses can adjust their rate of feed intake based on food source availability, but they recently set out to determine if horses can select for or against certain nutrients or nutrient compositions.

Sarah E. Redgate, PhD, now a senior equine lecturer at Nottingham Trent University in England, worked with colleagues from the University of Lincoln and the WALTHAM Equine Studies Group (both also in England) to evaluate if horses' voluntary feed intake, selection patterns, and behavior could be influenced by dietary composition.

The team employed seven geldings, ranging in age from 6 to 20 years, in good health and dental status. During the study, the horses resided in individual stalls with drylot turnout and received daily exercised in a mechanical horse walker. The researchers fed the horses three diets containing a chopped timothy hay base to ensure digestive health and natural feeding behavior; each diet contained similar levels of digestible energy but were individually rich in either protein, hydrolysable carbohydrates (carbs that can be broken down with water), or fat. In addition, study horses received free-choice haylage, soaked beet pulp, and chopped forage daily, and a vitamin/mineral supplement twice daily to meet their nutritional requirements.

Then the researchers collected data via a technique not previously used in horses. They initially allowed horses access to all three diets—each at 2-2½% of the horse's body weight—in a "self-selection" phase. Next, they fed the horses every diet alone for two three-day periods each during a "monadic" phase, which the researchers said was crucial to the study design as it ensured the horses learned to associate each diet with its individual nutritional characteristics. Finally, the horses underwent another self-selection phase with free-choice feed access. This allowed the researchers to gauge whether horses had changed their diet selection after consuming each one individually, the team said.

Key findings included:

  • The team observed similar voluntary intake of the three diets in the first self-selection phase after four hours of access; and
  • After the monadic phases, the horses showed a preference for the protein-rich diet, followed by the hydrolysable carbohydrate- and fat-rich diets, respectively.

Then, the team used the voluntary intake data to calculate the horses' nutrient consumption in the two self-selection phases. The researchers determined that horses' intake of the three macronutrients increased in the second self-selection phase, which could easily be explained by the fact that horses had free-choice access to the feed in that test. However, the team noted, the horses consumed more protein and hydrolysable carbohydrates during the second self-selection phase than in the first, while their fat intake remained similar between the two phases. This could indicate the horses were selecting for a certain level of fat in their diet, the team explained.

Finally, the team evaluated videos of the horses' feeding behavior recorded during each self-selection phase; specifically, they analyzed the horses' foraging behavior (the animal's head either in the bucket or raised and chewing), the time it took each horse to approach the bucket after feed presentation, and each horse's total number of visits to the feed. They found that the length of time it took horses to approach the buckets and time spent foraging was similar between monadic and self-selection phases; however, the total number of visits to the buckets decreased after prior experience with the diets. This is a novel finding, the team said, as it suggests that dietary experience modified the horses' feeding behavior, as the animals spent less time switching between diets and more time foraging on the feed they preferred.

What Does it Mean?

The researchers concluded that horses were able to change their voluntary intake and feeding behavior only after they had been given the time to experience each diet. Although the diets were only moderately rich in each nutrient to reduce digestive disturbances, horses did increase their intake of the protein- and hydrolysable carbohydrate-rich diets over the phases, suggesting they could have been targeting these nutrients. They noted that further research is needed to determine if horses can choose nutrients based on post-ingestive effects, such as satiation (a positive reinforcement) or digestive disturbances (a negative reinforcement).

So will this research impact how we feed our horses? The researchers hope it will in the future. The WALTHAM Equine Studies Group, which funded this research, places a major emphasis on better understanding horses' nutrient requirements, said Patricia Harris, MA, VetMB, PhD, Dipl. ECVCN, MRCVS, the group's director of science.

“Although this latest research suggests that there may be a macronutrient profile that horses will target when given the opportunity, further work will be required to confirm this and whether meeting such a target would have any benefit to horse health," she concluded.

The study, "Dietary experience modifies horses’ feeding behavior and selection patterns of 3 macronutrient rich diets," was published in the Journal of Animal Sciences

About the Author

Kristen M. Janicki, MS, PAS

Kristen M. Janicki, a lifelong horsewoman, was born and raised in the suburbs of Chicago. She received her Bachelor of Science degree in Animal Sciences from the attend the University of Illinois at Urbana-Champaign and later attended graduate school at the University of Kentucky, studying under Dr. Laurie Lawrence in the area of Equine Nutrition. Kristen began her current position as a performance horse nutritionist for Mars Horsecare, US, Inc., and Buckeye Nutrition, in 2010. Her job entails evaluating and improving the performance of the sport horse through proper nutrition.

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