MEDICAL ARCHIVES
08.02.2006
Feeding Horses under Hot Tropical Conditions
Most owners and riders of equestrian and show horses want their horses to be in good body condition, have a 'cool' temperament, maintain optimum coat condition and put effort and impulsion into their work.
Careful selection of feeds and feeding management, combined with routine health care and regular assessment of the horse's fitness for exercise will help achieve these aims.
The individual horse's needs must be taken into account when formulating and feeding a ration relative to the type and frequency of work, and its own likes and dislikes.
The stress of regular training, exercise under hot humid conditions and the horse'sappetite, temperament and ability to maintain optimum condition can all influence the type of feed and ration blend that will match its specific needs and ensure optimum performance.
Basic Requirements
The needs of equestrian, sport and pleasure horses vary in relation to the nutritional guidelines, as outlined in Table 1. The ration must be adapted to the individual horse's body size, desired condition, temperament and intensity of exercise on a day-to-day basis. Horses are always hungry and this increases the tendency for owners or riders to give them extra feed to keep them occupied and "happy".
Feeding Management - Feeding Energy Needs
An adequate intake of energy is required to maintain body condition, exercise capacity, body repair processes and ability to recover from repeated work. Simple guidelines for the balance of concentrates to roughage required for each type of equestrian activity in training and for competition are summarised in Table 1.
The body condition or body proportion, relative to frame size and gut size or "fill-out", will also influence the ration mix, with higher roughage intakes for horses that require a "filled-out" barrel and more substantial "gut" proportions.
It is important to feed strictly in proportion to the type, and duration, of work carried out each day, rather than feed in anticipation of training effort. A horse may not always be able to be worked to a set program due to weather, or soundness on a particular day, or the limited time that the trainer or rider has available to fully exercise the horse.
Horses that are only worked for 20-30 minutes daily, or on a sporadic basis, often do not require grain in their diets. They may maintain a suitable condition, a controlled temperament and satisfactory work capacity on a hay and pasture based diet
However, for horses that are worked regularly for 30-60 minutes each day, especially those in training for upper level competition, grains, preferably cooked, will need to be added to the diet to reduce the bulk of feed the horse has to consume to meet its needs.
Feeding too much energy on a low work or rest day can result in a horse becoming 'playful', "hyperactive", "energetic", "above itself, or 'too hard to handle', as well as increase the risk of muscle 'tie-up' or "set fast" cramps.
If a horse is not given its full or regular amount of work after receiving a normal work day breakfast, the next meal should be reduced in energy by limiting the grain intake, especially if raw grains, such as oats or barley, are used as the primary energy source.
In most cases, reducing the grain mix to 25-30% of the normal amount, and making up the bulk of the feed with chaff or hay will avoid the problems associated with overfeeding relative to exercise given on a particular day. This is particularly important with horses that have a "nervy" hyperactive temperament, or have a history of muscle cramping when work is resumed after a rest day.
Cool Energy Sources
Most equestrian and pleasure horse owners seek a "cool" energy source to help avoid horse handling problems associated with higher energy intake that is required to achieve and maintain fitness or a heavier body condition. Feeding too much raw grain as starch increases the risk of excess energy supply relative to work effort and can risk "hyper" or unsettled behaviour.
Oats is often avoided as an energy feed as it has a reputation for making a horse "hot headed" or 'energetic', which in most cases is caused by feeding excess to satisfy appetite demand or to maintain condition. However, there are 3 basic types of "cool" feed sources that provide "controlled', "calm" and sustained energy for equestrian activity.
Fibrous Feeds
Fibre is digested during fermentation in the large bowel (hindgut) by billions of micro-organisms to produce volatile fatty acids (VFA's). VFA's provide a slow release "aerobic" (metabolised using oxygen) and "cool" form of energy. Horses at pasture consuming 35kg of grass a day obtain 75-80% of their energy from VFA's, however, horses in race or advanced levels of eventing, polo or show jumping require a higher intake of grains with a greater energy density to limit the amount of feed they have to eat. The horse is more easily able to consume the 10-12kg bulk of the dry feed, which provides 70-75% of the energy for exercise from sugars, starches and fats and 25-30% from VFA's when the roughage intake is reduced to 50% by weight of the ration.
The most common forms of "fibrous" based energy included cracked lupins (they do not contain starch), cereal millrun (often In pellet form) or a cereal bran and pollard mix, hay and chaff based ration. These feeds are low in energy density, requiring larger amounts to meet a given energy need. The energy supplied by VFA's is slow to metabolise, producing a "sluggish", slow response form of energy as a 'calm' and 'cool' energy source for horses that become hyperactive when grain is included in their feed.
However, under hot and humid conditions, fibre based "cool" energy rations increase the amount of heat generated during fermentation or "heat waste" in the hindgut digestion processes. This adds to the total 'heat load* of exercise that is absorbed or less efficiently lost to the surrounding air in the environment, causing horses to sweat more heavily and "puff and blow" when working and during recovery as they off load heat from the lung surface.
High roughage intakes also increase gut fill and produce a "grass belly" appearance, which may detract from the horse's physical and athletic proportions and appearance in the show ring or dressage arena.
Supplements of Fat
Fat, in the form of vegetable oil (such as canola oil, which is good for cell membrane health and coat condition), palm and coconut oil (both of which are well digested) and sunflower oil (which turns rancid easily) is metabolised in the small intestine to free fatty acids. These provide a slow release "aerobic" form of energy. Copra (coconut) meal (7% fat), sunflower seeds (26% fat), cracked lupins (7% fat -do not contain starch) are often use to produce a 'cool' feed mix.
Up to 10% of oil by weight in a ration is well tolerated, although it must be introduced slowly over 10-14 days to enable the digestive system to adapt to breakdown fat and allow a horse to accept the taste and "mouth feel" of the fat.
For a 500kg horse, up to one cupful (250ml) of oil morning and evening can be used as a "cool" energy source for eventing, dressage or endurance training. For hacks, one cupful per day in a roughage-based diet is usually adequate. Again, oil-based cool feeds provide a "slow" low response form of energy.
The oil provides fatty acids for coat condition, (about 15mL/100kg body weight is required on a routine basis to assist coat condition), reduces dust when mixed into the feed and minimises the amount of "heat waste" from hindgut digestion as fat is only digested in the small intestine. Canola oil is regarded as one of the best natural vegetable oils, because it contains monounsaturated fats that do not turn rancid as quickly during storage, (corn and sunflower oil turns rancid quickly under hot storage conditions once opened). Canola oil also contains a higher proportion of Omega 3 to Omega 6 fatty acids for coat condition and natural body anti-inflammatory action.
Pryde's Easifeeds contain canola oil as an additional 'cool' energy and essential fatty acid source to the extruded base.
Extruded Feeds
Cooked starch in grain feeds is the most efficient and effective way of providing a "cool" energy source. Extruded (cooked) starches in grain release energy from the more complete digestion of starches to sugars in the small intestine. This helps to maintain blood sugar levels and muscle energy (glycogen) stores for exercise. Cooked starches release a 'cool' but responsive form of energy for working horses. Fats and fatty acids do not convert to muscle glycogen stores and only one VFA (propionic acid) can be used to produce muscle energy as glycogen.
Extrusion is a pressure cooking process in which controlled moisture and pressure combine to rapidly heat and cook the starch and protein content of cereal grains and oil seeds. The cooking temperature used in the production of Pryde's Easifeeds, for example, is carefully controlled to a maximum of 135°C for 15 seconds to avoid 'burning' the protein and fat content. The cooked food is rapidly cooled after extrusion to remove retained heat and minimise the damage to the natural vitamin content of the grain.
Extrusion expands the starch particles to form an open 'honeycomb' like structure (which is referred to as being "gelatinised"), as illustrated in Figure 1. This allows more direct and efficient digestive enzyme attack on the starch and proteins as the food passes through the small intestine.
Figure 1: This diagram illustrates the increase in digestive enzyme attack on cooked starch in extruded cereal grains.
As an example, around 30% of the starch content in raw, cracked or crushed corn is digested in the small intestine. Extruded or cooked starch in corn is 90% digested in the small intestine, as illustrated in Figure 2.
Extruding barley increases its starch digestibility in the small intestine from 23% to 70% or more, and makes it much more palatable to horses of all ages. Boiling whole barley increases starch digestibility to around 50% but damages the natural vitamin content more severely than extrusion.
Cooking by boiling the starch in barley, for example, improves the starch digestibility in the small intestine from 21% to around 50% (dependent on how long it is boiled), but the extrusion process increases starch digestion to 70-75%.
All Pryde's Easifeeds contain extruded grain bases. A feed such as EasiResult is formulated to meet the requirements for equestrian, show and sporting horses, without the 'fizz' and "fuss" of raw grain, and avoiding the slow, 'sluggish' response of high fibre or fat based feeds.
Oats is actually well digested in the small bowel in amounts up to 1.5-2.0kg per feed, but higher intakes result in overload of raw starch into the hindgut, with corresponding increase in 'fizzy', hyperactive behaviour.
Protein
An adequate intake of protein is required to provide amino acids for the protein in the structure of body tissue and muscle, blood protein and structural protein in bone, hair and hooves. Refer to Table 1 for guidelines on protein requirements.
Most working horses on a lucerne based diet containing over 3kg of lucerne chaff or hay in total, will obtain an adequate amount of good quality protein to meet daily needs. Diets high in tropical grasses or cereal hay or chaff or grains may not provide an adequate intake of tissue growth amino acids, and an additional protein source may be required.
Common protein sources include cracked lupins (33%CP), canola meal (30%CP), soyabean meal (44%CP), full fat extruded soyabeans (38%CP) eg. Pryde's Protein-Pak, sunflower seeds (23%CP) and copra meal (20%CP but low in growth amino acids). Generally, 1-114 cups per day of a high protein meal (soyabean meal or Protein-Pak), 2 cups of a medium protein source (canola, lupins) or 3 cups of a lower protein food (copra and sunflower seeds - high in energy as oil) may be required on grass based diets.
Excess protein intake must be avoided, as it is not only expensive, but protein not absorbed from the small intestine is overloaded into the hindgut, where it is fermented by bacteria to produce heat (6 times more heat per unit weight than starches or fibre). This causes increased heat waste and results in sweating in the flanks and belly area, which leads to dehydration and heat stress under hot humid conditions. Diets containing high intakes of lucerne making up more than 40% of the total ration weight (lucerne contains 15-17% CP as compared to grass hay at 7-8.5% CP) can result in horses developing the "puffs", sweating more and increasing the risk of dehydration under hot conditions.
Fat
An adequate amount of fat is required to provide the fat soluble vitamins, such as Vitamins A and E in the diet, as well as fatty acids in the structure of cell membranes and for skin and coat condition. Vitamin A can be synthesised from B carotene in good quality hay, Vitamin D from sunlight (20 minutes per day) and Vitamin K by hindgut bacteria. Vitamin E must be provided by the fat contained in the feed, or as a supplement each day. Natural Vitamin A and E can be stored in the body for 3 months; in the liver for Vitamin A, in fat stores and muscle membranes for Vitamin E, but in hard work, Vitamin E acts in conjunction with Selenium as an antioxidant in muscle cell membranes.
Most horse diets contain 2-5% fat. Extra fat can be used as a "cool" source of energy (refer above) and to provide a higher energy dense food for horses that cannot consume a large bulk of feed, "picky eaters" and horses working over long distances that require minimum gut weight, but a high energy intake.
Fat, in vegetable oil, is energy "dense", containing over twice the energy of starches and proteins. For example, 1 cup (250ml or 230grams) of vegetable oil (eg canola oil) provides the same amount of digestible energy as 6 cups or VA litres (or 750g) of oats, or 3 cups of cracked raw com. High intakes of fat (above 3 cups daily) should be avoided as high fat can reduce the palatability of the feed and hamper storage and use of muscle glycogen in working horses, although lower supplementary intakes increase glycogen storage and have a glycogen sparing effect at slower speeds.
Fibre
Fibre is essential to open up the digestive mass, maintain active hindgut digestive fermentation of soluble fibres and cellulose in hays and pasture, and hold a reserve of water in the hindgut. As plants mature, there is an increase in non-digestible lignin fibre, which occurs in mature, stemmy hay and chaff. This bulks out the hindgut digestive tract, but does not contribute to energy production.
Horses do not 'do as well' if the hay is poor quality, as it is often not chewed sufficiently to ensure optimum digestive attack as well. Each one gram of fibre holds 4 grams of water in its porous structure (like a sponge), or each 1 kg hay holds up to 1-1% litres of water as it digests in the hindgut.
Fibre is contained in the roughage, chaff, hay and hulls or grains - oats contains 10% crude fibre, lucerne hay has from 22-30% crude fibre related to maturity at harvest and sunflower hulls has 50% crude fibre.
The concentrate to roughage ratio, as recommended in Table 1, provides a balance of fibre to meet digestive needs. However, high concentrate intake reduces hindgut digestive function and safety, resulting in risk of starch overload in grain based rations.
Excessively high fibre diets increase the volume required to digest the fibre in the hindgut, producing a 'hay belly' or 'grass bell/ type appearance, heavy gut weight as a result of water trapped in the fibre which tends to tire a working horse more easily. Increased fibre intakes from oats or good quality hay are helpful to provide digestive 'heat' from fermentation under cold conditions to maintain body warmth. However under hot humid conditions, high fibre intakes produce more heat during hindgut fermentation, which adds to the heat load and risk of sweating and panting, although adequate water reserves are held in the hindgut to counteract fluid loss from sweating.
The minimum intake of fibre should be around 1.0% of body weight (or 5kg for a 500kg horse), but under hot climates this can be reduced to 0.75% safely, provided raw grain intake is not excessive, or to an absolute minimum of 0.5% roughage where lucerne hay and oats are fed for energy and roughage.
The combination of a diet that is adequate in fibre, with extruded grains and fats for 'cool' responsive energy is ideal under hot, humid conditions, with adequate salt and electrolyte intake and free access to water at all times.
Minerals and Vitamins
The basic needs for calcium, trace-minerals and major vitamins are outlined in Table 1. Horses in hard work on grain and hay based rations that are competing on a regular basis often benefit from additional B-group vitamins in the feed mix or as a supplement to help maintain metabolic function, the appetite and assist recovery from hard exercise.
Pryde's Easifeeds contain a cold-pressed pellet to meet the needs of specific levels of exercise in working horses. The pellet ensures stability and prevents sifting out of the vitamins and minerals, Extra vitamins, such as Vitamin A in a supplement such as Balance™ with trace-minerals combined with vegetable oils, may be beneficial to ensure optimum coat condition in show horses.
Electrolytes and Water
Under hot humid conditions, it is important to provide an adequate volume of water. Lightly worked horses can drink from 25-60 litres a day, or more as the temperature and humidity increases. Water must be provided on a free-choice basis at all times. This is particularly important for horses that are working under hot conditions and those that sweat heavily.
Supplements of salt up to 50-60 grams daily in addition to that contained in a prepared feed, as well as heavy sweat electrolyte mixtures such as Heavy Sweat Electrolyte Mix™, may be necessary to replace sweat loss under hot humid conditions or under extremely hot conditions in working horses.
Summary of Feeding Equestrian Horses Under Hot Conditions
- Provide free-choice cool, clean water at all times, up to 50-60 litres minimum each day.
- Supplement with salt and electrolytes relative to the amount contained in prepared mixes and sweet feeds.
- Provide 'cool' low heat waste feeds, such as extruded feeds and oils, combined with adequate,
but not excessive intake of roughage to maintain hindgut digestion and water reserve. - Pryde's EasiResult™ and EasiSaver™ are ideal as a 'cool* feed base for hot climates.
- Work horses early in the morning or late in the afternoon so that they can cool down under cooler conditions. Hose with colder water on the neck, shoulders and under the belly area to increase heat transfer after exercise. Scrape off water from the coat within 30 seconds to remove heat, do not allow a horse to "drip dry" under hot humid conditions with no airflow as the warm water trapped in the coat will insulate against heat loss.
- One method that is used in hot, humid conditions, during the hottest time of the day, is to soak a hessian strip about 2 meters long by 500mm wide in cold water and place along the back of the horse from the withers to the tail butt area. Hessian is preferred because its open weave structure allows heat to escape as the water is evaporated. The hessian acts as a "wick" to absorb and evaporate moisture to cool the skin surface. Directing the airflow from a fan onto the body will assist in evaporating the moisture from the hessian bag, and thus more efficiently dissipate heat. Repeat 2-3 times daily under hot conditions.
- Dampen all feeds, particularly the evening feed, to provide increased moisture intake as well as reduce dust in the feed.
- Consider pre-cooling horses prior to exercise under hot conditions - hose with cold water (except under the saddle area) and warm-up the horse with a wet coat - it will evaporate the moisture to cool the skin for 10-15 minutes as it works, reducing overall sweat and fluid loss during the training sessions.
- Heavy sweat loss of salts especially potassium and chloride, can increase the risk of "spooky", "flighty" behaviour, rather than "fizzy" or "hyper" behaviour, Provide heavy sweat electrolyte supplement such as Heavy Sweat Electrolyte Mix™, to replace salts lost under hot, humid conditions.
- Horses can be allowed to drink cold water at intervals when they are being exercised for long periods, provided exercise continues immediately to warm the water volume consumed. Once a horse finishes work and is cooling out, offer only small quantities of cold water of 1-2 litres initially, then larger volumes after 10-15 minutes to avoid gut "cramping" and discomfort.
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