Behavioural issues are often blamed on mood swings and owners seek a solution with Calmers. In fact we have often found that the root cause is down to diet. This paper unlocks the nutritional complexities of starch and sugar in equine diets.
Unlocking the Nutritional Complexity of Carbohydrates in Equine Diets
Horses, being herbivores, have unique dietary requirements that warrant a thorough understanding of the types of carbohydrates they consume and their potential impacts on equine health. In recent years, there has been a significant shift in the way we perceive and manage carbohydrates in horse nutrition. While the consensus now leans toward minimizing starch and sugar intake and emphasizing fibre, the truth lies in navigating the intricate relationship between these components and their corresponding technical terminologies.
Starch and sugars, in isolation, aren’t inherently detrimental. Glucose, a fundamental unit of starch, is a critical energy source, generating adenosine triphosphate (ATP) for muscle contraction, particularly in fast-twitch muscle fibres. Moreover, glucose is one of the select nutrients capable of crossing the blood-brain barrier and plays a role in active nutrient transport in the gut. Consequently, glucose is deemed an essential nutrient.
In a horse’s diet, the most common sugars are sucrose, fructans, and starch, all falling under the category of alpha-carbohydrates. Starch, specifically found in seeds and roots, differs in structure between various sources, which is essential to understand. For instance, grass can have varying sugar content based on factors like the season, cut, and maturity. It may contain fructans, starch, and sucrose in different proportions.
Feeding starch and sugar to horses is an unavoidable reality. As sugars are the end product of photosynthesis, they naturally occur in a horse’s diet. There are times, such as during spring grass consumption or compromised health, when the starch and sugar load can be high.
Understanding Carbohydrates in Your Horse’s Diet
Sugars, at their core, are carbohydrates made up of five or six carbon atoms. While they may seem complex, they come in various forms, including:
Monosaccharides: These are the simplest sugars, such as glucose and fructose.
Disaccharides: One step up, like sucrose.
Oligosaccharides: Slightly more complex, such as fructans.
Polysaccharides: The more complex sugars, including starch.
Fructans are chains of fructose molecules linked together. They’re a type of carbohydrate commonly found in plants. What makes them special is their role in providing “slow-release” energy. Imagine fructans as a steady, long-lasting battery of energy for your horse. Instead of a quick burst, they’re broken down slowly in the digestive system, supplying a consistent stream of fuel. This is crucial for horses who need a constant energy source throughout the day.
Glucose, a fundamental sugar, has two configurations – alpha and beta isomers. These configurations determine how they form chains of sugars. While both alpha and beta glucose are broken down in the body, they are subtly different plays a vital role in how horses process these sugars.
The Unique Equine Digestive System
The horse’s evolutionary development is closely intertwined with its ability to utilise fibre as the primary source of energy. Its hindgut serves as a substantial fermentation chamber where specific microbes can tackle the beta link, generating a spectrum of short-chain acids known as volatile fatty acids (VFAs). These VFAs are subsequently absorbed and metabolized. The hindgut environment is sensitive, and an influx of alpha-linked sugars and starch can disrupt its balance. Higher up in the small intestine, bacteria are equipped to derive energy from starches and sugars, creating competition with the horse itself.
When excessive starch and sugar are introduced to the diet, the horse’s endogenous enzymes and absorption processes become overwhelmed, causing sugars to inundate the hindgut alongside bacteria that thrive on these sugars. This surge in sugar availability alters the environment, leading to changes in microbial populations, a decline in fibre fermenters, and an upswing in toxic end products known as “endotoxins.”
Fermentation of starch by various bacteria within the horse’s hindgut results in the production of lactic acid. This lactic acid is typically processed by other bacteria in the small intestine, but this conversion doesn’t occur within the hindgut. Thus, unabsorbed starch reaching the hindgut contributes to acidification and further environmental disruption.
The Digestion of Carbohydrates
The challenge arises from the fermentation of these essential nutrients, which occurs in the wrong location within the horse’s digestive system, disrupting the hindgut’s normal equilibrium. This predicament is primarily a consequence of how we feed horses.
Horses are natural grazers, continuously nibbling on grass. As they chew and swallow, the initial digestion begins in the stomach, preparing starches and sugars for subsequent processing in the small intestine. This portion of the horse’s gastrointestinal tract provides an environment conducive to the horse’s own enzymes to break down starch into shorter-chain sugars, further hydrolysed into sugars and disaccharides small enough for absorption across the gut lining. The horse’s stomach is relatively small compared to its body size, with continuous acid secretion. Consequently, feed moves swiftly into the small intestine, where enzyme secretion remains relatively low, resulting in limited starch and sugar absorption.
This setup poses minimal challenges for wild horses consuming tundra grass and scrub with inherently low sugar levels. However, domesticated horses face a different reality, where high-starch diets can overload their digestive capacity. The horse’s system can only handle a certain threshold of starch, as opposed to sugar, which may not necessitate enzymatic breakdown. Additionally, there’s a time factor at play. The swift passage of feed through the small intestine leaves insufficient time for complete absorption.
The type of starch also matters. Starch, an energy storage system, exhibits structural variations between cereals, oilseeds, and roots and tubers, further varying within these groups. For instance, analysing starch granules under a microscope reveals distinctions among cereal starches. Oat starch, for instance, has an uneven and pitted surface, which facilitates amylase (the starch-breaking enzyme) attachment and penetration. In contrast, maize starch granules present almost impermeable barriers. Oat starch boasts a digestibility value of about 90%, while maize and barley are around 30%. These values can be enhanced through cooking, which involves steam to open up granules for improved enzyme access.
Despite efforts to optimize digestibility, there will always be a trickle of starch making its way into the hindgut. In small quantities, this is generally manageable. The problem escalates when substantial amounts enter the hindgut, triggering a cascade of adverse effects.
The Perils of High Sugar and High Starch Diets
High sugar and high starch diets can lead to severe health issues in horses, including Cushing’s Disease, Exertional Rhabdomyolysis, Insulin Resistance, and Polysaccharide Storage Myopathy. A common thread across these conditions is a malfunction in glucose processing for energy production, mainly related to the initial breakdown of glucose or the supply of glucose stored in the body as glycogen. Energy metabolism occurs in two phases, with the first dedicated exclusively to glucose and other sugars. In this scenario, switching to alternative nutrients like fat, protein, and “slow-release nutrients” can help conserve glucose energy.
Two additional factors must be considered. Overfeeding of starch and sugars can result in nutritional laminitis. The lactic acid generated in the hindgut weakens the gut wall, enabling the absorption of endotoxins contributing to hoof inflammation.
Furthermore, cereals, the primary starch source in equine nutrition, can exacerbate stomach acidity. Cereals fail to absorb stomach acids and can serve as fuel for acid-generating bacteria, which, in some cases, have been found to penetrate the mucosal stomach layer, contributing to ulcers.
Balancing the Equine Diet
In these situations, it’s prudent to replace some of these high-sugar sources with low-starch alternatives. A common guideline recommends that an active, healthy horse should ingest no more than 1 gram of starch per kilogram of body weight per meal. Consequently, incorporating low-starch products, such as No Starch Fibregest, alongside regular feeds or as replacements for high-sugar products, helps ensure that daily intake remains manageable.
In essence, the challenge in equine nutrition revolves around striking a delicate balance between supplying the essential nutrients found in starch and sugar and avoiding the detrimental consequences of overfeeding these carbohydrates. A comprehensive understanding of carbohydrate types, their digestibility, and the horse’s digestive anatomy is essential in achieving this balance. Equine caregivers must embrace a nuanced approach to diet management to safeguard the overall health and well-being of their equine companions, ensuring they thrive in a managed nutritional environment.