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 the critical value of forage. Knowledge of what’s in forage, the types and physical forms of forage, and importance of forage quality should be common knowledge 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 in learning about forages for horses with this article by Dr Stephen Duren.
The digestive system
The unique structure and function of the horse’s digestive system is ideally suited for the utilisation of forage. As such, horses are classified as herbivores or ‘plant eaters’. They are also referred to as ‘hindgut fermenters’ since the back portion of the digestive tract is a large fermentation vat. The horse’s hindgut is a large balloon-like area consisting of the cecum and colon. It is the largest area of the digestive system, making up over 65% of the digestive capacity.
Billions of bacteria and protozoa live in this portion of the digestive tract. These micro-organisms work together to break down (ferment) plant fibre from forage. It is the presence of these micro-organisms in the hindgut that allows horses to utilise forage. Without these micro-organisms, the horse would not be able to digest forage. The intestinal micro-organisms produce energy-yielding compounds called volatile fatty acids, as well as amino acids and B vitamins that can be absorbed by the horse. With over 65% of the horses’ digestive system geared towards digestion of forage, 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.
While protein is certainly important, other nutrients are often as important. 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 along with a brief explanation:
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, which is high in omega 3 fatty acids.
Fibre – Not all of the fibre in forages is digestible, with an overall estimate of digestibility ranging from 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 is dependent of soil conditions where the plants were grown.
Vitamins – The vitamin content of green forages is higher compared to sun-bleached or weather-damaged forage.
Types and physical forms 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. They are capable of fixing their own nitrogen and, therefore, they have higher protein content. Legumes also contain less fibre and more of that fibre is un-digestible fibre compared to 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, such as ryegrass, orchard, oat and wheat, and those that grow well in hotter climates – warm season grasses, such as 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 (colic) or even death. Mould growth on forage results in the production of toxins that can cause colic or even death.
Forage that has been stored initially as hay can then be further processed into other physical forms. These forms include pellets or chaff. These physical forms of forage are not more digestible than the hay they were made from, but instead, they simply add convenience in handling or feeding. Alternative fibre sources include fibre pellets or cubes like beet pulp, soy or hay pellets.
In the Hygain range, HYGAIN® FIBRESSENTIAL® are highly digestible fibre nuggets that are easy to feed and provide superior conditioning, whilst significantly reducing the dust and inconsistency often associated with traditional forms of chaff. Aged horses or horses with poor teeth may benefit from hay sources that have been further processed into pellets, cubes or chaff. It is an ideal fibre source for dentally-challenged horses as it can be soaked in water, which transforms the product into a soft mash.
Forage quality
The main factors that influence the quality of forage are specie of plant, stage of maturity of the plant and the physical location where the plant was grown. As mentioned previously, legume plants, such as 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 broodmares and growing horses. On the other hand, grass forages because of the lower energy content may be better suited to horses that gain weight easily or for show horses.
The maturity of the plant is also a determinant of forage quality. The more mature a plant becomes or the taller a plant grows, the lower the quality.
As plants mature, digestibility decreases due to an increased amount of fibre to keep the plant upright. 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. Forage quality can be determined to a limited extent by visual inspection of the forage. Visual inspection can include looking at the leaf to stem ratio, the length of the seed head, the colour of the plant, and the presence of dust or mould.
Higher quality hays will have more leaves than stems, a short seed head, be green in colour, and smell fresh with no dust or mould. A more accurate evaluation of forage quality can be acquired via a laboratory analysis. First, a representative sample of forage is sent to the laboratory for chemical analysis. The results will then provide accurate determination of energy, protein, vitamin and mineral content. Laboratory analysis can also be used to determine the presence of harmful mould.
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 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 eat? Conservative estimates are for horses to consume a maximum of 3.5% of their bodyweight in dry forage per day. This is a whopping 17.5Kg of dry forage per day for a 500Kg horse.
Summary
Forage is the most important dietary ingredient for horses. The digestive system of the horse is designed to digest forage.
There are many types and physical forms of forage. All forages fed to horses should be of good quality. Forage should be offered free-choice to horses unless your horse is obese or somehow sensitive to something in forage. Feeding large volumes of forage will maximise digestive health and minimise the amount of grain that will need to be provided to the horse.
