If you’ve ever wondered what is a low-starch diet for horses, and more importantly, should my horse be on one, then you’re not alone. However, it isn’t ideal for all horses. Ultimately, it will depend on their caloric requirements, the work they’re in and existing health conditions..
Forages should of course be the basis of any diet and are 75-90% carbohydrates. Carbohydrates include sugars, starches, and some fibre. These carbohydrates found in pasture and hay fall into two broad categories: nonstructural and structural. So horses actually rely on carbohydrates as the largest portion of their diet. Especially soluble and insoluble fibres that make up forage.
Carbs, sugars and starches in forage.
Non-structural carbohydrates (NSCs) in forages are simple sugars and fructans and can be readily digested or fermented by horses. They are produced in plants during warmer weather, and are higher in more immature forages. Pasture is usually lowest in NSCs in the early morning unless overnight temperatures are cold. However, these carbohydrates can affect some disease processes, so you need to monitor how much your horse eats.
Carbs, sugars, and starches in your horse’s hard feed
Grain based hard feeds contain carbohydrates, including simple sugars and starch. Grains such as barley, maize and oats are high in NSCs, mostly starches. Starches are long chains of attached sugar molecules. These sugars get broken apart during the digestive process and the simple sugars (glucose) readily absorbed. Most horses can digest and absorb sugars and starches in the small intestine through a process called hydrolysis. From there, glucose in the bloodstream triggers the pancreas to release insulin. Then the glucose molecules move into cells for storage as glycogen. This is the fuel for the working muscles.
If there’s more starch in a single meal than the horse can digest, starch will enter the caecum, (the first part of the hindgut after the small intestine). Any undigested starch here is rapidly fermented creating lactic acid. This lowers hindgut pH, killing the good bacteria that live there. The endotoxins released from microbial death can then contribute to both colic and laminitis.
So, just how much starch is in a low-starch diet for horses?
A “low-starch” feed usually contains less than 15% starch, but some feed companies might classify low-starch as any feed below 20%. Compare this to a traditional hard feed with grains such as barley, maize and oats as its base. These types of feed might be as much as 40-60% starch. A “mid-level” starch content is usually between 20 and 25%. Whilst many horses are fed high starch feeds seemingly without problems, the key consideration that still remains for any horse is how much starch is fed in any one meal.
Ultimately, there is no single definition of a “low- starch” diet as both sugar and starch concentrations are important. Therefore, it’s better that feeds are referred to as ‘low-sugar and starch’ or ‘low nonstructural-carbohydrates (NSC). NSC is a laboratory measure containing starch plus all water-soluble carbs (sugars and fructans). The recommendation for horses with metabolic issues therefore is not actually low-starch but low-Non-Structural Carbohydrates. So, if f low starch/low NSC is a primary concern for your horse and it’s not quoted on your bag of feed, then contact the feed manufacturer directly to find out.
Starch Content of Common Feed Ingredients
|Feed Ingredient||Starch %|
|Legume hay (besides lucerne)||1.56|
|Mixed, Mostly Grass, Pasture||2.00|
|Beet Pulp, Dried, No Molasses||0.99|
|Maize, Whole Grain||69.44|
Data collected from Equi-Analytical Laboratories
When should your horse have a low-starch diet?
For some horses with certain health conditions, vets and nutritionists might recommend a low-starch diet to help maintain blood glucose at a steady level. These are conditions that cause horses to become more sensitive to sugars and starches. This then means that owners will need to reduce these levels in both forages and concentrates. Individual horses have variable responses related to a variety of factors, including age, body condition, fitness, metabolic status, and disease status.
Obesity and equine metabolic syndrome (EMS)
These metabolic conditions are of major concern and there needs to be an overall reduction in calories consumed, not just from starches. Some breeds, especially pony breeds are “metabolically thrifty”, so they’re able to readily convert glucose into fat for storage. They will benefit from a lower-quality forage and no hard feed. This is where a quality feed balancer supplement such as one from the Fibregenix range, is ideal. It will provide vitamins, minerals, protein, fatty acids and other essential nutrients to bridge nutritional gaps in forage.
Insulin dysregulation (ID)
Insulin dysregulation is considered a component of EMS. In affected horses or ponies, insulin is not effective at transporting glucose from the bloodstream into cells, so both remain elevated. This can increase susceptibility to laminitis. Horses with this condition are extremely sensitive to starches. Ideally, they should be on as low a starch and, specifically, soluble-carbohydrate diet as possible.
Pituitary pars intermedia dysfunction (PPID, formerly Equine Cushing’s)
This endocrine disease mostly affects horses or ponies over the age of 15. Some, but not all, PPID horses will require a lower-starch diet. PPID horses that are also insulin-dysregulated are the ones which will benefit. However, some PPID horses are thin, non-insulin-dysregulated, and they need calories. In such cases a more traditional NSC level is fine.
Polysaccharide storage myopathy (PSSM)
Horses with this muscle disorder often have a normal glucose/ insulin metabolic process. They’re unable to use the form of glucose stored in their cells as energy and are also susceptible to tying-up (exertional rhabdomyolysis). This is the breakdown or destruction of skeletal muscle cells associated with exercise.
Laminitis prone horses and ponies should also have diets low in soluble carbohydrates and starch. Elevated levels of starch reaching the hindgut can lead to hindgut acidosis, killing off the good microbes. This releases endotoxins, which can negatively affect enzymes involved in maintaining the integrity of the laminae in the hoof leading to laminitis. Susceptible horses should not be allowed to graze immature or lush, rapidly growing pasture routinely found in spring and early autumn.
Gastric ulcers (EGUS)
Signs of this condition include poor performance, poor attitude, and mild colic. Horses prone to ulcers and hindgut acidosis benefit from a low-starch/high fibre diet. This is because chewing and consuming fibrous carbohydrates produces more saliva which in turn helps reduce acidity in the stomach.
Anxious or hyperactive horses may also benefit from less starch in their diets. Multiple studies (Bulmer et al., 2019; Destrez et al., 2015) have focussed on the diet’s effect on behaviour. But more recently, they’ve focussed on the “why” behind this. The latest studies have revealed that glucose is a sugar that easily crosses the blood-brain barrier. Elevated glucose levels are associated with increased dopamine production. And this can lead to elevated awareness or hyperexcitability.
Should you change your horse to a low-starch diet?
If your horse doesn’t have any of the aforementioned conditions, then he probably doesn’t need a low-starch diet. In fact, performance horses benefit from a diet with readily available carbohydrates needed to replace the stored glycogen in skeletal muscle. Especially those that do anaerobic exercise (short bursts of high-intensity training) during work. When muscle glycogen is low, the muscle adapts by slowing contraction rate and power to conserve fuel (glycogen). This is obviously not desirable in a competition horse. Traditional hard feeds with grains such as barley, maize and oats as its base might be as much as 40-60% starch. A “mid-level” starch content is usually between 20 and 25%. Whilst many horses are fed high starch feeds seemingly without problems, the key consideration that still remains for any horse is how much starch is fed in any one meal.
Similarly, hard keepers might not be good candidates for low-starch feeds either, unless you increase the fat content in the diet. These horses need more readily available calories than the fibrous ingredients often used in low- starch feeds.
The table below shows ideal targets to follow when considering how much starch your horse should have.
|% starch in your hard feed||IDEAL TARGET|
|To avoid starch overload,rapid fermention in the h/gut||50-65% for sweet feeds, 45-75% for straight grains||<2g/kg BW/meal|
|To avoid risk of gastric ulcer syndrome
|For metabolic disorders such as IR, Cushings, laminitis etc
Making Changes To a Horse’s Diet Safely
Any changes MUST be slow and gradual so as not to upset the hindgut microflora. Gut microbes must have time to adjust to a new diet, so it’s generally accepted to make the complete transition over about two weeks.
For horses needing a low-starch concentrate, transition them the same way you would to any new diet. Start with a meal that is ¼ of the new feed and ¾ old feed and stay at this level for four days. Move up to ½ and ½ for another four days. Then switch to ¾ new feed and ¼ old feed for another four days. By the end of this period, you should be able to feed a full meal of the new feed. If you are concerned about NSC levels in forage, then limit pasture access when they’re elevated (e.g. during spring grass growth). Soak hay before feeding. Just remember to discard the soak water, so the horse doesn’t drink it.
What if a sudden change can’t be avoided?
Sometimes, the transition to a low-starch diet has to happen suddenly. For instance, after a metabolic event (e.g., laminitis) where the horse is moved from lush pasture to being yarded. Or begins to wear a grazing muzzle. In these cases, you don’t have days or weeks to make the change. So watch your horse carefully for signs of digestive disturbance such as diaorrhea. If signs develop (and if possible), back off the transition rate and make the conversion more slowly.
What if you have more than one horse and only one requires a low-starch diet? You might be tempted to think you could feed all the horses the same feed. However, whilst it may make feeding more convenient, you still have to consider each individual horse’s needs and feed accordingly.
Feeding for individual needs
What if you have more than one horse and only one requires a low-starch diet? Tempted to feed all the horses the same feed? Whilst it may make feeding more convenient, you still have to consider each individual horse’s needs.
5 Take-home messages
- A low-starch diet might be a suitable option for your horse, but it depends on his health status.
- Horses in good body condition, fit for their discipline, with high caloric demands can cope on a more traditional feed containing higher starch levels. Even so, care must still be taken with how much starch is fed in any one meal.
- Before making any changes, talk to your vet or an equine nutritionist.
- Find out how much starch is in your horse’s feed when the term “low starch” is used. This will ensure you are making decisions based on the best information available.
- Always make any changes to the diet gradually so as not to upset the digestive microbes.
Reviewed and amended April 2021