As elite athletes, racehorses have extremely high energy demands. This means they need a lot of calories every day to maintain body weight/condition and fuel their hard-working bodies. In addition to copious quantities of high-quality forage (hay), high-energy concentrates (nonstructural carbohydrates or NSC) and oil help fill the void.
“The higher the horse's energy demand, the higher the reliance on NSC, especially in the case of exercise done at speed. Some racehorses eat 10-12 pounds of grain concentrate a day,” explained Dr. Tania Cubitt from Performance Horse Nutrition in Weiser, Idaho.
Feeding high volumes of concentrates, however, may contribute to equine gastric ulcer syndrome (EGUS), colic, colitis (diarrhea), and an unhappy/stressed out horse.
“If we turned our attention away from simply filling the horse's stomach to meet nutritional demands and instead focused on providing meals to the microbiome, we may in fact develop a healthier, happier, nutritionally satisfied horse,” advised Cubitt.
Digestion vs fermentation for energy production
Humans derive most of their energy from digesting/breaking down food in the stomach and small intestine and absorbing the nutrients produced by digestion (sugars, amino acids, small fat globules) in the small intestine.
While horses also rely on digestion and absorption of nutrients from the small intestine, a substantial amount of a horse's energy comes from the bacterial fermentation of structural carbohydrates (cell walls of plants found in forage) in the hindgut. There, in the cecum and large intestine, fermentation produces volatile fatty acids (FVAs) that are absorbed across the wall of the so-called fermentation vat into the bloodstream. The horse's muscles and organs use those VFAs to fuel a large number of vital metabolic processes.
Those billions upon billions of fiber-fermenting bacteria residing in the hindgut together with their genetic material make up the intestinal microbiome. In an ideal world, a horse's intestinal microbiome should be diverse and rich. This means it should contain a wide variety of different types of bacteria, as well as protozoa, yeast, parasites, and even viruses. Examples of some of the most common types of bacteria identified in the intestinal microbiome include Lactobacillus, Enterococcus, Staphylococcus, Bacteroides, Escherichia, and even Clostridium.
Any change in diversity and/or richness—secondary to changing feeds, administering medications, placing the horse under any amount of stress—may result in dysbiosis. This term refers to a profound imbalance in the intestinal microbiota, inducing changes in the normal health and function of the gastrointestinal tract. In turn, dysbiosis can contribute to a variety of disease processes such as:
- Colic;
- Colitis;
- Insulin dysregulation;
- Obesity/keeper status (i.e., hard versus medium versus easy keepers); and
- Behavior and mood disorders.
In addition, laminitis, the excruciating separation of the hoof wall from the underlying sensitive tissues of the hoof, can develop secondary to a variety of repercussions of dysbiosis, putting the horse's life and livelihood in jeopardy.
“Healthy animals have increased microbial diversity,” said Cubitt. “Everything I have read comparing 'healthy/control' to an impaired state shows that the impaired animal's microbiome has less diversity. But whether it is the lack of disease allowing a diverse microbiome or it is the diverse microbiome fighting off disease remains unknown. I believe the latter is correct.”
Based on what we currently know, creating a microbiome mecca will help maintain a diverse, rich array of microbes. And according to Cubitt, managing a horse and making them feel like they have “returned to the wild” is the best medicine for dysbiosis.
“Horses in the wild have a fiber-based diet with access to a large variety of forage. They nibble almost consistently for about 12 to 18 hours a day, move while they are eating, existing in a herd setting,” described Cubitt.
Managing your “wild” racehorse
Clearly, a wild horse and racehorse are diametric opposites. Racehorses have diets laden with cereal grains that are ingested quickly from buckets at chest height and hay nets. They are frustrated at confinement (no matter how beautifully lit and bedded their stall is), and have limited access to conspecifics for mutual grooming and general horseplay.
What can we do to make a racehorse's intestinal microbiome mirror that of a wild horse's?
Cubitt recommended focusing on the forage rather than the concentrates.
“A typical racehorse should be offered as much forage as they will consume, probably well beyond the 2% per body weight per day (about 20 pounds) recommended for the average horse,” she said.
Racehorses should also have access to forage at all times. And ideally, their concentrates, which cannot be eliminated from their diet, should be divided into four separate meals per day.
“When horses are fed large, high-starch meals, the digestive capacity of the small intestine is overwhelmed and excess starch floods the hindgut,” said Cubitt. “By large meals, I mean more than 4 to 5 pounds. Once that starch reaches the hindgut, amylolytic bacteria rapidly ferment the starch.”
Fermentation of starch is a very different process than the fermentation of forage. Starch fermentation produces lactic acid, not the coveted VFAs.
“Lactic acid decreases the pH in the hindgut, creating an acidic environment,” she said. “This type of environment favors the growth of pathogenic bacteria and damages the intestinal lining causing hindgut ulcers, colitis, and potentially leaky gut syndrome.”
Cubitt describes leaky gut as a condition in which the “velcro” between the cells lining the intestinal walls fails. This structural breakdown allows undigested food particles and toxic materials to pass freely into the horse's blood stream, potentially leading to devastating outcomes for the horse.
More Isn't Better
While Cubitt advocates continuous feeding, she also explained that this doesn't mean you need to feed your horses more.
“Slow down their food consumption, instead,” she advised.
- Add chopped forage to their diet;
- Use some sort of slow feeder;
- Offer alfalfa, in any form. Alfalfa provides more calories, increases gastric buffering, and tends to be more palatable in a picky horse;
- Place feed pans closer to the ground
“Feeding from the ground promotes natural drainage from the respiratory tract, increases chewing time, and prevents muscular tension in the neck,” Cubitt relayed.
A healthy microbiome is absolutely critical to the health and performance of a horse. Making a few small but key changes in a racehorse's management, such as those described above, can help return a horse's microbiome to its “wild” ways, resulting in a richer, more diverse microbial community. Using these feeding strategies will also benefit both the gastric and mental health of racehorses.
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