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Forage in Your Horse’s Diet

August 2017 by Tania Cubitt, PhD, HyGain Feeds, www.hygain.com.au

Forage, such as hay and pasture, is critical for the health and wellbeing of all horses. Understanding the design, function and reliance of the horse’s digestive system on forage is the first step in appreciating its critical value.  

Knowledge of what’s in forage, the types and physical forms of forage, and the importance of forage quality should be common for all horse owners. Finally, understanding how much forage a horse requires per day is essential in properly feeding any horse. So, let’s get started learning about forages for horses.

The digestive system

The unique structure and function of the horse’s digestive system is designed for the utilisation of forage. Horses are herbivores (plant eaters) that evolved on a high-fibre diet, spending 16 to 18 hours a day grazing. 

Fibre is the plant cell wall material, which consists of cellulose, hemicellulose, lignin and pectin. Fibre is largely indigestible as animals lack the necessary enzymes to break down fibrous material. However, the microbial population in the horse’s hindgut (large intestine) is able to break down (ferment) fibre, converting it into utilisable energy. 

Although lignin is completely indigestible, these microorganisms can partially digest cellulose and hemicellulose, and digest practically all pectin, mainly producing energy yielding compounds, called volatile fatty acids (VFAs). The horse’s hindgut is the largest area of the digestive system, making up over 65% of the digestive capacity. With a gastrointestinal tract designed to digest fibre, it is easy to see why forage is critical to the health of all horses.

What’s in forage?

Forage contains all of the essential nutrients required by horses - water, energy, protein, vitamins and minerals. Unfortunately, many horse owners only talk about, or judge, forage based on protein content. Forage should be judged by the levels of all nutrients, not any one single nutrient. The following are some of the nutrients that forage contains:

  • Water - Pasture contains large amounts of water, whereas preserved forages, such as hay and chaff, have been dried to prevent mould growth while in storage.
  • Protein - The protein content is highest in legumes, such as lucerne and clover, lower in grasses, and lowest in oat or wheaten chaff.
  • Fat - Forage contains a small amount of fat, high in omega 3 fatty acids.
  • Fibre - Fibre is the main component of forage. Not all of the fibre in forages is digestible with an overall estimate of digestibility of 40-50%.  
  • Minerals - A number of important minerals, such as calcium, phosphorus, potassium, copper, zinc, selenium and others are present. The mineral content of forage tends to be higher in legumes than grasses, but is dependent on soil conditions where the plants were grown.
  • Vitamins - The vitamin content of green forages is higher compared to bleached or damaged forage.

Types of forage

Forage comes in many different types and physical forms. In general, forages can be divided into two types - legumes and grasses. Legumes are plants, such as lucerne and clover. Generally, they provide more energy, and contain a higher protein and mineral content, particularly calcium, than grasses. 

Grasses that are fed to horses include many different species. The individual species of grass are further divided into those which grow well in colder climates - cool season grasses (e.g. ryegrass, orchard, oat and wheat) and those that grow well in hotter climates – warm season grasses (e.g. kikuyu, mitchel and kangaroo). Again, grasses typically contain less protein and more fibre compared to legume forages.

The physical form of forages fed to horses is also quite variable. The simplest form of forage is pasture. Pasture can contain both grass and legume plants.  Pasture plants can be selected to grow in all types of climates. Unfortunately, when conditions become harsh, such as during extreme heat or cold, pasture plants will quit growing and become dormant. At these times of the season, the horse must rely on physical forms of forage that have been stored.  

Hay is the most common form of stored forage. To make hay, plants are grown to a certain height or maturity, cut, dried to low moisture content and packaged into a bale. If the moisture content is greater than 15%, the hay will mould while in storage. Feeding mouldy forage is never recommended with horses since it can result in digestive upset or even death. 

Mould growth on forage results in the production of toxins that can cause digestive upset or death. Alternative feeds, such as HYGAIN® FIBRESSENTIAL® (35% crude fibre) or HYGAIN® MICRBEET®, are ideal as a substitute and partial replacement of traditional roughages. 

HYGAIN® FIBRESSENTIAL® includes highly digestible fibre sources, such as soybean hulls and legume hulls, that are high in the most digestible fibre - pectin. Since pectin is virtually totally digested by the horse, the feeds’ fibre level can remain high, but also have a moderate level of energy; so much so that soybean hulls can have a similar energy level as some oats, whilst having fibre levels similar to lucerne hay. 

For this reason, feeds which are high in pectin are often considered ‘super fibres’. These alternative feeds are easy to feed and provide superior conditioning, whilst significantly reducing the dust and inconsistency often associated with traditional forms of chaff. Furthermore, they are an ideal fibre source for dentally challenged horses as they can be soaked in water, which transforms the product into a soft mash. 

HYGAIN ZERO® (35% crude fibre) and HYGAIN® ICE® (25% crude fibre, approved by Laminitis Trust) have been formulated as high-fibre, low-starch feeds, which are fully fortified with vitamins and minerals. Highly lignified (stalky) feeds, such as straw and some cereal hays, are not very nutritious, but they keep the horse chewing and the digestive tract moving, which may reduce stable vices and stomach ulcers.

Forage quality

The main factors that influence the quality of forage are: species of plant, stage of maturity of the plant and the physical location where the plant was grown. As mentioned previously, legume plants (lucerne and clover) tend to be higher in protein, energy and calcium, compared to grass plants. 

Hence, legume forages are best suited for horses with elevated nutrient requirements, such as equine athletes, broodmares and growing horses. On the other hand, grass forages, because of their lower energy content, may be better suited to horses that gain weight easily or for pleasure horses.

The maturity of the plant is also a determinant of forage quality. The inside of plant cells consists of protein, fat and soluble carbohydrates (cell contents), whilst the outside (cell wall) consists of fibre. The inside of the cell is highly digestible (80-100%), whilst the cell wall is more limited (40-50%). 

The more mature (older) a plant becomes or the taller a plant grows, the smaller the proportion of cell contents and the larger the cell wall. As such, as plants mature, their digestibility and quality decreases. Due to the high fibre content of mature plants, they proportionally contain less energy, protein, vitamins and minerals. Pastures often become less digestible in mid-Summer and Autumn, due to the plants becoming tall and mature.   

The final determinant of forage quality is the physical location where the plant was grown. Different geographic regions contain soils with different nutrient densities. The nutrient content of the soil is reflected in the nutrient content of the plant. For example, plants grown in nutrient deficient soil will also be nutrient deficient and of lower quality.

How much forage should be fed?

Forage is the safest dietary ingredient that can be fed to horses. Horses require an absolute minimum of 1% of their bodyweight in forage dry matter per day. For a 500kg horse, this equates to just 5kg of forage per day. Racehorses are the only horses that would get down to this minimum amount of forage. A safer guideline is to provide horses with a minimum of 1.5% of their bodyweight in dry forage per day, which equates to 7.5kg of dry forage per day for a 500kg horse. So, how much forage will a horse actually eat?  

Maximum voluntary feed intake is 2-2.5% of bodyweight in dry forage per day, which is up to 12.5 kg of dry forage per day for a 500kg horse. When fed ad libitum (free access) forage, horses spend more time chewing and, thus, produce more saliva. As saliva contains bicarbonate - a buffering agent - it may reduce the acidity in the stomach, thereby, reducing the risk of acidosis and related disorders. It is, therefore, better to feed your horse several small meals per day, rather than two large meals.