During Cornell Equine Hospital and Cornell Cooperative Extension’s monthly seminar series, Nathalie Trottier, PhD, professor of animal sciences in the Cornell College of Agriculture and Life Sciences in Ithaca, New York, took an evolutionary and physiological approach to explain the importance of feed for modern equids.
The evolution of the horse
The horse family Equidae has adapted extremely well to grasslands as they have evolved from browsers to grazers over millions of years. Trottier explained that this is evident in their rich fossil record, which reveals equids’ teeth, feet and more adapted to give them an evolutionary advantage over other herbivores.
As we domesticated the horse over the past 5,500 years, she said, we not only selectively bred them for performance, appearance and temperament, but also added starchy grains and concentrates to their diets instead of regular forage. whole. The outcome? An increased prevalence of gastric ulcers, dental problems, metabolic diseases and digestive disorders.
Physiology of the forage and equine gastrointestinal tract
Trottier analyzed the horse’s digestive anatomy—from the teeth to the large intestine—and how each component is uniquely designed to process feed.
Horses’ teeth erupt slowly and continuously to compensate for the constant grinding (16 to 20 hours a day for some, Trottier said). “Sanding is important because it wears off about 2-3 millimeters a year to counteract the rash,” she said. “Attrition from a herbivorous diet tends to keep pace with eruption rates.”
Allowing horses to consume forage of their choice throughout the day reduces their risk of uneven tooth wear and overgrowth, she said. Feed concentrates, on the other hand, introduce more sugars and starches that are harmful to dental health.
Saliva contains not only water, but also antimicrobial agents, digestive enzymes and electrolytes essential for maintaining pH balance. The most important stimulus to salivation is chewing, Trottier said.
“In dogs, the sight and smell of food is a stimulus, but in horses it is not,” she said. “Chewing is the only thing that stimulates the salivary secretion of the parotid gland.”
When we feed horses grain, however, they secrete less saliva because they chew less. Trottier said the average 1,100-pound horse chews 18-30 minutes per pound of hay, compared to 5 minutes per pound of grain.
Saliva is also essential for dental health as it lowers horses’ risk of developing cavities. “We know that low pH is a leading cause of tooth decay,” Trottier said. “Rich udders mean more starch and less saliva. Then they grow and ferment more bacteria.”
The lower jaw of the horse has evolved to be narrower than the upper jaw. This allows the horse to move its jaws left and right and consume fibrous forage more efficiently. “The larger upper jaw allows for movement to chew and consume grasses,” Trottier said. “Feeding concentrate does not allow horses’ jaws to move as intended, which leads to uneven wear.”
Compared to all other domestic animals, the horse’s stomach is the smallest segment of its gastrointestinal tract. “It’s incredible that this animal has this physiology where the stomach is so small, but it’s able to easily consume 20 kilograms of hay a day,” Trottier said. “The reason is that the horse is a continuous grazer, which licks off a small amount of food at a time as fodder.”
The stomach is divided into glandular and non-glandular regions, the latter lacking mucous secretion and being particularly prone to gastric ulcers. The reduced surface area of the secretory mucosa of the glandular region is an evolutionary adaptation to eating low-protein grasses, she explained.
“The small size of the stomach and capacity of the horse favors continuous movement and gastric passage,” said Trottier. “Pasture grasses have a high moisture content, which increases the gastric transit rate. A high rate of passage accommodates the large amounts of forage that the horse needs on a daily basis. The continuous passage of food is very important to keep the pH balanced in the stomach.”
Feeding forage before grain protects the horse’s stomach from the potentially harmful effects of high-starch concentrates because:
- Increases salivation and pH-buffering bicarbonate ions.
- It reduces the fermentation of grain starch in the hindgut (as well as the large intestine).
- It increases the flow of water through the stomach and thus the rate of passage of the grain bolus. Otherwise, the starch in the grain binds water and reduces the rate of passage, favoring bacterial fermentation.
The capacity of the horse’s large intestine also aligns with the nutritional composition of the forage in their diet. “The slow passage rate here favors higher fermentation efficiency of cellulose and hemicellulose (insoluble fibers in plant cell walls),” Trottier said. “(The large intestine) is designed to ferment slowly fermentable fibers. We can help it thrive by providing enough feed and fiber.”
Take home message
When creating a feeding strategy for your horse, consider how he has evolved and focus on a forage-based diet tailored to his gastrointestinal physiology. By doing so, you can help prevent many dental and digestive problems common in domestic horses.