Kentucky Equine Research (KER) Horse Management Tips
Horses rely on enzymes and microbes to turn forage and concentrates into usable energy, for athletic endeavors, growth, lactation, and other life events.
Understanding Digestion: Animal nutritionists consider themselves specialists in either ruminant or nonruminant nutrition. Ruminant nutritionists follow the significance fermentation plays in the nutritional makeup of animals with multiple stomachs.
Carbohydrate Digestion: Ruminant carbohydrate digestion occurs mainly in the rumen where micro-organisms produce enzymes that convert starch (oats, barley, and corn), cellulose and other non– starch polysaccharides. Starch converts to glucose through the action of bacterial amylases. In contrast, plant fiber is digested in the hindgut of the horse entirely by fermentation, producing Volatile Fatty Acids (VFA).
Adaptations for Microbial Fermentation: For microbial fermentation to be useful, digestive systems must retain digesta and microorganisms over extended periods, while maintaining a suitable fermentation environment. The ability of a horse to use fermentation depends on three factors: volume available for fermentation in the digestive tract, retention time of ingested material, and makeup of microbial population inhabiting the hindgut.
- Volume available for fermentation. Microbial fermentation is related to the proportion of the digestive tract devoted to fermentation. Horses dedicate less of their total digestive capacity to fermentation.
- Retention time. The extent of plant material fermented depends on contact time with the microbes. However, the amount of time material is subjected to fermentation before energy production is compromised is limited. Horses depend on VFA’s, by-products of microbial fermentation, as a source of energy. If digesta is retained too long in the fermentive organs, VFA’s will be degraded by anaerobic microorganisms, depriving horses of energy. Horses’ rate of digestibility equals about 30 hours, digesting about 50% of the dry matter in hay.
- Microbial population makeup. The microflorain the horse hindgut is susceptible to diets other than forage. Starch is a versatile energy source – unless it is overfed. Studies at KER show that hindgut pH drops between four and eight hours after feeding a starch rich meal – making horses susceptible to colic and laminitis. For this reason and others, KER nutritionists recommend feeding small grain meals, generally less than five pounds.
Interspecies Comparisons: Can information from one species improve the way other species are fed? In light of the similarities between microbial fermentation across many species, the answer may be yes.
An example is yeast culture, with research showing it affects microbial fermentation in beneficial ways, affecting the intestinal microbes similarly to the way rumen microflora are affected. The anatomical adaptations each species has developed depend on body size and diet. The volume of the digestive tract devoted to fermentation and the time digesta spends in these organs varies among species. Microflora types inhabiting the digestive tracts of various animals, however, are similar. Thus, it is logical that dietary manipulations for one species may also affect others.
Factors Affecting Nutrient Availability: Feedstuffs horses ingest follow a long, circuitous route from mouth to rectum. Along the way, multiple factors affect the horse’s ability to absorb diet nutrients.
- Processing grains. “Processed food” often produces a negative reaction. For horses, however, processing grains and seeds are beneficial. For example, “Enzymes in the digestive system have trouble penetrating the hard, outer shell of a corn kernel to access the nutrients inside,” said Catherine Whitehouse, M.S., a nutrition advisor with KER. Corn, barley and whole flax seeds are routinely processed – usually through steam flaking, cracking, or rolling.
- Dental health.Horses with poor teeth cannot chew and grind food effectively, making it harder for digestive enzymes to break down and liberate nutrients. Large particles pass through the digestive system without being broken down, wasting potential nutrients. Proper teeth care will minimize dental problems, maximizing chewing ability.
- Diet imbalance. Unbalanced diets disrupt nutrient absorption. “Unlike minerals compete with each other for the same transport molecule to exit the digestive tract. Calcium and phosphorus are an example”, said Whitehouse. Calcium intake should always exceed phosphorus intake. Consuming excess phosphorus from large amounts of wheat bran or unfortified grain blocks absorption of calcium. Calcium and phosphorus ratios for mature horses range from 1.1:1 to 6:1, with the latter acceptable only if consuming sufficient phosphorus. For young horses, the ratio should never exceed 3:1. Zinc and copper compete for their own transporter, and fed in a 4:1 ratio, respectively.
- Parasites. All horses carry internal parasite loads. Severe consequences arise when parasites are not properly monitored and controlled. Parasite larvae develop into adults internally, stealing nutrients and damaging the intestinal lining in the process, resulting in a decreased ability to absorb nutrients. Have a veterinarian analyze fecal samples for parasite loads and establish a parasite control program.
- Rate of passage. Vitamins, minerals, protein, and fat are absorbed in the small intestine. The faster feed and forage travel through the small intestine, the less time it has to be digested and absorbed. Diet content and environment influence rate of passage. “Forage and high-fat meals move slowly through the stomach and small intestine when compared to high-starch meals,” Whitehouse said. Managing modern horses based on human schedules disturbs natural feeding habits. A consistent, well-timed schedule of feeding in a comfortable environment is best to ensure maximum opportunity for nutrient absorption. Horses evolved eating many small, frequent meals.
Keeping Tabs on Carbs in Equine Diets:
Can’t live with them, can’t live without them. Fitness and diet experts warn of carbohydrates tendency to expand waistlines. But how do carbohydrates affect the equine diet? Do horse owners count carbs in their horses’ diets?
A carbohydrate is a compound composed of carbon, hydrogen, and oxygen. Nutritionally, carbohydrates consist of nonstructural and structural types. Nonstructural (soluble) carbohydrates occur as disaccharides (two simple sugars chemically bound together) or as polysaccharides (long chains of simple sugars chemically coupled).
Starch constitutes the most important polysaccharide in equine nutrition. Digestive enzymes convert disaccharides and polysaccharides into usable energy sources. An exception to the rule of enzymes digesting disaccharides is Fructans, polymers of fructose bound together that are broken only by microbial digestion in the hindgut. Dangerous fructans can make up a significant proportion of the sugars in pasture during certain phases of plant growth and under some weather conditions.
The amount of nonstructural carbohydrate consumed depends on the amount of concentrate eaten. Horses on forage-only diets, such as lightly ridden pleasure horses or barren broodmares, would ingest few nonstructural carbohydrates. Horses consuming large amounts of textured or pelleted feed would ingest substantially more nonstructural carbohydrates.
Structural (or insoluble) carbohydrates resist the actions of digestive enzymes. Bacterial fermentation in the cecum and colon are used to break down cellulose and hemicellulose carbohydrates, thereby generating needed energy.
Monosaccharides are the only carbohydrates that can be absorbed through the intestinal wall into the bloodstream. Therefore, all complex carbohydrates (disaccharides and polysaccharides) must be dissolved into monosaccharides before the horse can obtain energy from them. Disaccharides such as maltose, lactose, and sucrose are split into two monosaccharide units by their respective enzymes maltase, lactase, and sucrase. These disaccharides are digested in the small intestine.
Starch, the polysaccharide of primary importance in equine nutrition, is processed differently. The enzyme amylase, produced by the pancreas and delivered to the small intestine, reduces starch to its basic monosaccharide components. Amylase production in horses is limited, producing 8-10% as much as an adult pig. Because of this low amylase production, starch often escapes digestion in the small intestine and heads to the voluminous large intestine, which is comprised of two key areas, the cecum and the colon.
Maximizing Starch Digestibility.
Researchers have studied methods to maximize digestibility of starch before it enters the cecum. The term “prececal digestion” denotes nutrient absorption occurring in the small intestine. Five factors influence prececal starch digestibility in horses: source of starch, processing of starch, amount of starch intake, source and timing of forage feeding, and individual differences among horses.
- Source of starch: Differences exist among starch molecules in grains commonly fed to horses. Oats contain the most digestible starch, while corn and barley starch is less digestible.
- Processing of starch: With the starch in oats already digestible, added processing does little to enhance digestion. Processing of other grains, however, increases their digestibility. KER measured the prececal starch digestibility of corn processed by steam flaking, grinding, or cracking. Digestibility was determined by evaluating glycemic response to each grain. Higher digestibility was assumed as the level of glucose in the blood increased. Steam flaking offered the greatest advantage in digestibility, thus reducing the likelihood of starch leaving the small intestine undigested. Barley that undergoes heat or steam processing makes its starch content more easily digested. Dry rolling or crushing barley does little to improve the digestibility of starch in the small intestine.
- Starch intake: The amount of starch consumed affects prececal starch digestibility. California researchers measured the pH of the large intestine after feeding ponies oat or corn starch at three levels. The pH of the large intestine remained unfazed by oat starch regardless of the amount offered. Results for corn revealed a decrease in large intestinal pH, indicating that starch did not use amylase assisted digestion in the small intestine. The amount of corn starch creating this result was comparable to feeding an 1100-pound horse 4.5 to 6.5 pounds of corn in a single meal.
- Source and timing of forage feeding: Studies showed forage type, such as hay, and feeding time, relative to oats, corn, and barley, affects prececal starch digestibility and utilization. Several horses were fed five pounds of a mix of oats, corn, vitamin/mineral pellet, and molasses. This was supplemented with 5 pounds of hay. Starch digestion was greatest in horses fed only sweet feed, with a large difference between this treatment and the treatments where grain was fed with hay.
- Why the difference? Consuming hay stimulates salivation and increases the production of digestive secretions. To replenish fluids lost in digestive processes, horses were offered water, consuming the most two to three hours after being fed hay. Drinking diluted the intestinal contents and increased the speed at which ingesta passed through the intestinal tract. As a result, prececal starch digestibility was reduced.
- Individual differences among horses: Though studies are designed to provide accurate, repeatable results, horses sometimes foil those efforts. No two horses are alike, so differences in the ability to digest starch among horses may be due to variances in rate of starch intake, or passage through the gastrointestinal tract, or the amount of digestive enzymes produced.
Why the Fuss over Prececal Starch Digestion?
If starch is not digested in the small intestine, it travels to the large intestine, where billions of microorganisms aid in the fermentation of roughages. When starch slides undigested into the large intestine, a portion of the bacterial population feeds frenziedly on it. A byproduct of microbial starch fermentation is lactic acid, which irritates the intestinal lining and alters the pH of the large intestine. This causes a massive die-off of other bacteria, releasing endotoxins into the bloodstream, endotoxins known to induce laminitis and colic.
Search for Low-Starch Feeds:
Low-starch feeds, translated into high fat and high-fiber, are a solution for diets too rich in complex carbohydrates. To reduce the starch content of feeds, manufacturers limit the amount of cereal grains used in the formulations, replacing them with other ingredients. Nutritionists substitute starch with ingredients laden with fat and fiber, which are abundant in calories. Common fat sources in low-starch feeds are vegetable oil, soybean oil, and rice bran. Fat has a decided edge in the amount of dietary energy it delivers, packing 2.25 times the calories contained in a similar measure of carbohydrates.
Common, low-starch fiber-rich ingredients are beet pulp, the residue remaining after extracting sugar from sugar beets, and soybean hulls, produced during the processing of whole soybeans.
What Horses Benefit?
Each aspect of a foals development must be carefully planned, especially, a sound feeding program. Following a low-starch program makes good sense; studies conducted at KER suggest that feeds producing a large glycemic response contribute to skeletal disorders, such as osteochondritis dissecans (OCD), in young horses. OCD disrupts the maturation of cartilage, the connective tissue providing joints their resilient, concussion-absorbing properties. Researchers at KER found that spikes in insulin, occurring when young horses consume starch-riddled diets, contribute to OCD development.
When the glucose-insulin apparatus works correctly, horses properly store glycogen for energy. Occasionally, insulin receptors that remove glucose from the blood become less sensitive, permitting glucose to remain in the blood. Finding elevated levels of glucose, the pancreas produces insulin resulting in a buildup of insulin in the bloodstream creating hyperinsulinemia.
With hyperinsulinemia, the body is unable to use glucose as an energy source, using its fat and muscle stores to fuel body functions. The result is lost weight and muscle mass. If the condition continues unchecked, the body may quit producing insulin altogether. Adult horses are seldom troubled by hyperinsulinemia; however, aged horses suffering from Cushing’s syndrome often have hyperinsulinemia.
PSSM and RER:
Polysaccharide Storage Myopathy (PSSM) and Recurrent Exertional Rhabdomyolysis (RER) are two forms of tying-up that are intensified by high-starch diets. When switched to low-starch rations, most horses are relieved of muscle problems. Researchers believe reduction of tying-up episodes due to RER may be linked to behavioral changes – for as dietary starch levels diminish, excitability, thought to provoke RER related tying-up, subsides.
Insulin-resistant horses are prone to laminitis, though a reason for the phenomenon cannot be pinpointed. Horses that have suffered one bout of laminitis are more susceptible to successive bouts; therefore, a low-starch diet is prudent for laminitic horses. Low-starch feeds are not designed as a cure, but as an adjunct to veterinary supervision.
Domestication Alters Intestinal Microbiome
The horse’s intestinal microbiome supports immunity, protects bacterial overgrowths, produces energy through fermentation of short-chain fatty acids and synthesizes vitamins, among other roles.
Established early in life, the intestinal microbiome of a foal changes its composition as the horse matures. “Weaning, exercise, disease conditions, diet, and even the natural ageing process alter the intestinal microbiome and occasionally, negatively affect the health of the horse or foal,” explained Kathleen Crandell, Ph.D., a nutritionist for KER.
One study reported that domestication has altered the microbiome, creating changes to both lifestyle and diet. To explore this theory, fecal samples were collected from populations of Przewalski’s horses – the only non-domesticated horses alive today – and from domestic horses residing on grasslands. Analyzing microbiomes in these samples found they were distinctly different and more diverse in Przewalski’s horses than in domesticated horses.
The importance of an abundant and diverse microbiome cannot be disputed. Consistent management, avoiding abrupt changes in diet and providing ample forage is a cornerstone of maintaining a healthy gut.
Impact of Abrupt Diet Changes
Due to the risk of laminitis, do not make abrupt feed changes. The rapid ingestion of unfamiliar concentrates or other feeds high in starch can induce the painful, life-threatening disease, characterized by the separation of the hoof wall from the coffin bone. “Aside from the laminitis potential, suddenly adding feeds rich in dietary starch may cause changes in the intestinal microbiome,” explained Kathleen Crandell, Ph.D., a nutritionist with KER.
“Dietary alterations can adversely affect digestive health, causing diarrhea and colic, among other intestinal issues.” Crandell said. In an ideal world, horses would not be faced with diet changes; however, situations sometimes call for dietary supplementation. As an example, “Performance horses requiring additional calories or other nutrients are often offered concentrates high in water-soluble carbohydrates with no adaptation period,” offered Crandell.
About Kentucky Equine Research
For 30 years Kentucky Equine Research has developed innovative solutions to the health and nutritional challenges inherent in equine management. The results of studies conducted at its research farm, as well as advancements in equine nutrition from institutions around the world, are applied and thoroughly tested in the creation of KER products.