Nutritionist Tania Cubitt, PhD, from Performance Horse Nutrition, relayed this message during the 2021 EquiSummit, held virtually and presented by Kemin, and described how wild horses behave while eating. Importantly, Cubitt said, nondomesticated horses nibble at a large variety of forages for 12 to 18 hours a day. As a herd, horses move constantly while grazing, with their heads down. This head-down position allows natural drainage of the respiratory tract, increases chewing time, and maintains proper tooth alignment.

Showing a picture of a gleaming, dappled horse in a fancy, well-bedded, brightly lit stall, Cubitt noted that although it resembled an equine Taj Mahal, the entire environment induces stress.

Stressed-Out Steeds

“Horses are stressed by pretty much everything we do to them,” Cubitt said. “In this picture the horse is being fed a cereal-grain-based diet that he eats rapidly, the feed bucket is at chest height, and he is frustrated by his confinement.”

Stress easily disturbs the intestinal microbiome—the population of bacteria, fungi, and other microbes found in the hindgut. An unhappy hindgut results in an unhappy horse, especially if one considers the intestinal microbiome as an organ critical to the horse’s health, she said.

The intestinal microbiome has many key roles in the horse’s body: harvesting nutrients and extracting energy from the diet; resisting colonization of pathogens (disease-causing organisms) such as Salmonella or Clostridia; and detoxifying toxic compounds in the host. Stress due to heat, management changes, exercise level, and diet and other external factors such as gastrointestinal disease, hindgut acidosis, laminitis, and colic can all negatively affect the microbiome.

“Domestication alone alters the microbiome by decreasing diversity when what we want is a diverse, wide range of microbes,” said Cubitt.

Microbial Diversity in the Microbiome

Firmicutes and Bacteroidetes are the two most common bacterial phyla found in the microbiome. Firmicutes produce short-chain fatty acids, including butyrate, which provide energy for the horse and are critical to gut health. Bacteroidetes are Gram-negative bacteria that break down carbohydrates.

In addition to domestication, obesity alters the microbiome. Study results show medium keepers have the most diverse microbiomes while hard keepers have the least. Hard keepers’ microbiomes have less lactic acid bacteria that break down carbohydrates and fewer amino-acid-utilizing bacteria that break down topline-building proteins.

Feeding concentrates decreases Lachnospiraceae, a member of the Firmicutes phylum, that produce butyrate—a volatile fatty acid that protects the gut wall by helping prevent leaky gut. But, Cubitt said, some horses need to be fed concentrates to meet their calorie and energy needs. This begs the question, “How do we feed horses to ‘normalize’ the microbiome, making it resemble that of a wild horse?”

“The microbiome serves as a link between nutrition and health,” she said. “So instead of thinking about feeding the horse, try to think about feeding the microbiome and minimizing stress.”

Bolstering the Biome

Said Cubitt, microbiomes thrive when owners embrace these management strategies, which reflect how nondomesticated horses eat:

• Increase the number of meals per day. Four to six meals cause far less stress than only two.
• Decrease the rate of intake by adding chopped forage to mimic grazing behavior.
• Feed hay first or use special feeding pails such as waffle feeders to further slow intake.
• Ensure the diet has adequate forage—about 1.5-2% body weight or 15-20 pounds for a 1,000-pound horse.

“Horses will still eat even if they don’t have adequate forage offered to them. They will eat bedding and feces,” Cubitt warned. “This sort of diet contributes to impaction colics, increases parasite burdens, and may cause bacterial infections and diarrhea.”

Her other suggestions included:

• Keeping a consistent feeding schedule. Horses love their routines, and feeding horses later than normal causes stress, evidenced by a significant increase in pawing and kicking.
• Know any diet change is stressful for a horse and its microbiome. Cubitt emphasized that it takes 21 days for the hindgut population, the Bacteroidetes in particular, to adapt to any change in diet, even from grass to hay or vice versa.

Take-Home Message

To keep a hindgut healthy, mimic wild horse diets and lifestyles, which involves offering plenty of forage and minimizing management-related stress.