Slow and Fast Horse Feeds

Slow and Fast Horse Feeds 

Dr Tim Kempton B.Rur. Sc, Ph.D. (Nutrition)

Horse nutrition is not complicated. Horses have nutrient needs that can be calculated. What  makes horse nutrition complicated is the process of  selecting feeds to balance the nutrient intake with nutrient requirement, and to provide the feeds in a form that suits the digestive system of the horse. It is the lack of understanding about the relationship between the digestive system of the horse and the form of the feed, and how this affects the horse, that causes the confusion.

It is well established in humans that we are what we eat. Obesity is now one of the major disorders in the western world in both humans and horses. So what can we learn? What are the similarities?  Can we join the dots?

Some facts

  1. Pastures often do not provide enough nutrients for horses
  2. Most pastures are for cattle, not horses.
  3. Horses are fed supplements of concentrates and hay.
  4. Some concentrates are ?fast foods?
  5. Many horses are overfed on fast foods and underworked
  6. Horses are designed as ?slow feeders? and not for pulse or shock feeding.
  7. Obesity is a worldwide issue
  8. NSC in horse feed = GI in human food
  9. NSC= non structural carbohydrate (sugar and starch)
  10. Insulin resistance = type II diabetes is now identified in horses
  11. Many metabolic disorders in horses are associated with high NSC feeds.

Digestion in horses

Digestion in horses is not the same as in cattle and sheep.  Cattle and sheep have large forestomachs and are called ruminant?s because they can ruminate, ie they store food in their rumen, and regurgitate and rechew their food to gain more nutrients.  By comparison, horses have a small stomach, and have to graze little and often to maintain nutrient intake.  Horses graze at least 18 hours per day, ie they are ?slow feeders?.

Unfortunately with modern day horses, they mostly graze pastures designed for cattle, and are held in small paddocks or yards, which means that often pasture alone is not sufficient to deliver the required nutrient intake, especially for active horses in work. To meet the total nutrient demand, the horse often must be supplemented with other feeds including hay and processed feeds, usually containing grain.  Our lifestyle and work hours determine that most horses are only fed morning and night. This can deliver pulse or shock loads of nutrients into a digestive system that is designed for a continuous supply. Pulse/shock feeding is exacerbated when the feeds contain levels of some digestible nutrients (particularly sugar and starch) that exceed the digestive capacity of the horses intestines. These concentrate feeds can be considered as ?fast foods?. Pulse feeding fast foods is one of the major factors contributing to the metabolic disorders in horses today.

Slow feeding

Slow feeding horses makes sense. It provides a semi continuous supply of nutrients to a digestive system designed to digest nutrients on a natural, continuous basis. This can be achieved with roughages and pastures, but is difficult to achieve when feeding high energy concentrates. Our lifestyle makes that difficult because we don?t have time to feed concentrates little and often throughout the day.

Feeding concentrates

Horse nutrition is based on mathematics. The nutrient requirement of horses can be calculated, and the nutrient composition of feeds can be measured, and described in feed tables. The amount of feed required is a simple calculation.  The difficulty is in knowing the effects of feeding concentrated  feeds as pulse feeds rather than ?slow feeds?, and overfeeding concentrate feeds.

What is a fast food.

Studies over recent years have identified the sugar and starch content of feed as being one indicator of the ?fast food? status of a feed.  All feeds contain sugar and starch, which are the major energy supplies to the horse. The sugar and starch content is called NSC (non structural carbohydrate) which is the same as GI (glycaemic index)in human nutrition.

The NSC content in a range of Australian horse feeds is shown below (Richards, N. Proc. Aust. Equine Sc. Symp., Vol 2, 2008)

This figure shows that commercially  available horse feeds contain a range of NSC concentrations. Grain can contain 70% NSC.  High NSC feeds can be fed to horses in active work.

For metabolically sensitive horses, the suggested ?safe? NSC requirement is 10-12% (Richards, N. Proc. Aust. Equine Sc. Symp., Vol 2, 2008).   It is proposed that feeding more than 12% NSC, and not increasing work load is a possible reason for the metabolic disorders associated with overfeeding and under working, because the horse is unable to burn off the additional energy from the NSC.

NSC and metabolic disorders.

The possible effects of overfeeding NSC feeds, in combination with pulse/shock load feeding rather than slow feeding can be outlined as follows.

  1. Stomach.

The horses stomach is divided into two sections. The second half has a thick cell wall lining. The front half has a thin cell wall lining.  With slow feeding, the feed enters the first part of the stomach, and the horse releases acids into the stomach continuously to help digest the food.  With pulse/shock feeding (feeding only twice per day) and feeding high NSC feeds, the horse releases higher levels of acid into the first stomach. The pH declines and can cause damage to the thin cell wall lining, causing ulcers.  Select low NSC feeds to reduce acid release into the first stomach, and feed little and often to avoid pulse/shock loading.

  1. Small intestines

The small intestine is designed to digest and absorb  proteins, carbohydrates, oils, minerals and vitamins. The intestines has a maximum digestive capacity (g/hour), and this capacity can be overloaded by feeding too much at any one time.  The intestines contains a large population of benign micoroganisms, which live in symbiosis with the horse, ie they live together where the horse provides the home and the food supply, and the microbes digest the feed and provide nutrients to the horse. Dysbiosis occurs when the relationship between the host and the microbes is disturbed, such as when the feed supply to the microbes increases, and there is rapid growth of the benign organisms, which can colonise the cell wall lining in the intestines causing ?leaky gut?. LEAKY GUT SYNDROME allows leakage of molecules such as glucose into the blood stream, together with microbial toxins and other compounds. Is this far fetched? Leaky gut syndrome is known in humans. It is implicated in Candida albicans in humans. It is possible that ?leaky gut? occurs in horses fed high NSC feeds, and causes increased blood glucose. What happens to the increased circulating level of glucose? If the horse does not use the glucose for energy (ie for exercise) the glucose has to go somewhere.

The horse releases insulin to enable the passage of glucose into the muscle cells, ie the cells are SENSITIVE to INSULIN. If there is too much glucose, the horse continues to produce insulin, but the cells lose INSULIN SENSITIVITY and cease transporting glucose into the muscle cells. The cells become INSULIN RESISTANT, which is the same as Type II diabetes in humans. Blood  sugar levels rise, and insulin levels rise.  The blood sugar must go somewhere, and some can be stored in the fat cells causing OBESITY. Increased insulin causes increased CORTISOL, which in turn is implicated in LAMINITIS, CUSHINGS and EQUINE METABOLIC SYNDROME (EMS). In some breeds, the glucose can be converted into an unusual polysaccharide and stored in the muscles, causing TYING UP.  It is well known that low NSC feeds should be fed to horses susceptible to TYING UP (Valberg, S. Am J Vet Res. 1999 Apr;60(4):458-62).

Some glucose can also combine with proteins forming a proteoglycan, which is deposited in connective tissue in the legs, possibly causing swelling and STOCKING UP, LAMENESS and DSLD in horses (Halper, J. et al  BMC Veterinary Research 2006,2:12doi:10.1186/1746-6148-2-12).

It is suggested that selecting low NSC feeds that don?t overload the intestines causing abnormal growth of benign microbes (DYSBIOSIS) is a possible means of possibly reducing the effects of some of the  feed related metabolic disorders.

  1. Large Intestines

The small intestines has a maximum capacity to digest sugars and starch, and feeding too much starch can cause starch overload, ie the sugars and starch flow into the hind gut. The hindgut contains a population of microorganisms similar to that in the rumen of cattle. If cattle are overfed on grain, this causes acidosis (grain poisoning). The same effect occurs in horses. The additional sugar/starch is fermented by the microbes, and converted into acids, which are normally absorbed across the wall of the hindgut gut to provide energy. If the rate of fermentation is too high, the microbes produce high levels of acids, which are both absorbed, and also cause a decline in pH (acidity). These acids can cause  cell wall damage and leakage of nutrients and microbial toxins  into the blood stream. The  effect of hindgut acidosis causing LAMINITIS is well described by Dr Chris Pollitt  in EQUINE LAMINITIS for Rural Industries Research and Development Corporation Pub.No.01/129).

Hind gut acidosis is also implicated in causing HOT and FIZZY behaviour in horses.

Feeding low NSC feeds therefore will reduce the flow of fermentable carbohydrates into the hindgut, and therefore reduce the production of acids.

Pulse feeding

A pasture trail was conducted in which feeds with various levels of NSC were fed to grazing horses Richards. N. Feeding to maintain insulin sensitivity. Proc. Australasian Equine Sc. Symp., Vol 3, 2010 pp30. These included a sweetfeed (33% NSC), a pelleted feed (25% NSC) and CoolStance copra meal (11% NSC). Circulating glucose was measured for 6 hours after pulse feeding.

It can be seen that there was an immediate glucose spike after pulse feeding the sweetfeed and pelleted feed with NSC>20% (Richards, N. et al, 2011 in press).

The CoolStance copra meal (NSC 11%) did not increase blood glucose levels above that in the pasture fed horses, and did not cause a  glucose spike.  The pasture trial suggests some high energy feeds such as copra meal can be pulse fed, and yet be digested as a ?slow feed?.

Is low NSC enough.

CoolStance copra meal is a low NSC and high DE (digestible energy) because it contains a combination of oil and digestible fibre.  Some low NSC feeds are created by diluting a high NSC feed with poorly digestible, low NSC fillers and so they are low NSC and low DE. These feeds are usually unsuitable for performance horses because the DE content is too low.  Feeds for most pleasure horses must be selected with a low NSC, and a high DE


  1. Slow feeding is the natural state for the horse
  2. Supplementary feeding is necessary for the modern horse
  3. Shock/pulse feeding is a function of human lifestyle and work hours
  4. Some concentrate feeds are ?fast foods?
  5. NSC = GI = sugar and starch content of the feed.
  6. Feeding above 12% NSC, and not increasing work level may contribute to many metabolic disorders
  7. There is no labelling requirement for NSC content in a feed.
  8. Careful consideration must be given to match the feed with activity level, ie do not overfeed a high NSC feed and underwork
  9. Some concentrate feeds such as CoolStance copra meal can be pulse fed, and yet be digested as a ?slow feed?.

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