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Putting Weight on Skinny Horses Disclaimer
K Crandell PhD and P Huntington BVSc
Why is my horse so skinny and how can I put some weight on him?

Sometimes, trying to get weight on a poor doer can feel like banging your head against the wall. Whilst all around his lush green paddock, horses are getting round and fleshy with nothing but a sniff of grain, your horse bears an uncanny resemblance to your coat rack!

What is wrong with your horse? How can there be such a difference between him and his paddock mates?

Sometimes the answer can be as simple as feeding more calories, and sometimes the problem or static or dropping weight requires a deeper probe.

Don't despair! The answer to a beautiful rounded horse may not be out of reach. This article will try to explain some probable causes and possible solutions to give your horse every opportunity to gain weight.


Reasons for weight loss   Top
Insufficient caloric intake is the primary cause of weight loss in horses. There are various reasons for caloric deficiency including some that are easy to diagnose and correct (parasite burden, teeth problems) and some that may be impossible to diagnose without euthanasing the horse (physical problems with the digestive tract). Other reasons, not to be overlooked include psychological and environmental problems.

Teeth problems   Top
Probably the first thing that should be checked with a horse that fails to maintain weight is the condition of its teeth. Because of the nature of a horse's diet (mainly tough fibrous material), which requires a lot of chewing and grinding, which wears down the teeth, proper dentition is essential. If the horse's ability to grind down the food sufficiently is compromised for any reason, the enzymes and microbes of the gastrointestinal tract have a hard time continuing the digestive process and the result is a drop in condition.

The most common problem with the teeth of horses is the formation of sharp points through normal wear and tear along the outside or inside edge of the jaw causing laceration of the cheeks, gums or tongue. Chewing becomes very painful and the horse may reduce the amount of feed he consumes or eat more slowly. This problem can be alleviated by having your horses teeth rasped at least once yearly, but sometimes more often if your horse has a particularly bad problem or is old.

Horses have two sets of teeth in their lifetime, the milk teeth, present at birth are gradually replaced by permanent teeth as the horse reaches maturity. Sometimes, as the milk teeth are pushed out, a small fragment remains forming a kind of 'cap' over the new tooth. This can make chewing difficult and if noticed, should be removed.

Mouth infections, cracked, broken teeth or poor mouth conformation (eg parrot mouth) can also lead to reduced feed intake. Older horses have problems with lost or very worn molars and incisors leading to a reduced ability to crop grass and chew feed. This can be a major cause of weight loss in older horses. Some senior feeds are marketed as complete diets including forage, with small particle sizes. These feeds can also be moistened and made into a gruel, which does not require chewing.

Simply watching your horse whilst he eats can tell you much about his dentition. Slow eating, reluctance to drink cold water, tilting the head whilst chewing, wallowing food around in the mouth before swallowing, balling up food in the mouth and dropping food may all be indications of poor dental health in horses and should be investigated. It is also worth remembering that some horses with chronic dental problems causing weight loss show no outward symptoms at all, and in cases of gradual loss of condition bad teeth should still be investigated as a possible cause.

Parasites   Top
Internal parasites can be a major contributing factor to weight loss or inability to put on weight. Severe cases of parasitism are rare these days due to the wide use of new and improved de-wormers but where a horse is suffering from a large worm burden, the results on the digestive tract and the horse's ability to absorb and digest feed can be disastrous.

Parasites not only compete with the horse for the nutrients, they also cause damage to the digestive tract itself, reducing the surface area of the healthy gut thus reducing the guts' production of enzymes which are needed to prepare the food particles for absorption. Some nutrients are dependent on proteins in the diet to transport them across the stomach lining. As parasites compete with these nutrients for protein, the availability of those nutrients to the horse is also reduced. Damage by parasites can cause the intestinal lining to become swollen and inflamed. This draws water, electrolytes, sugars and amino acids (the building blocks of protein) out of the bloodstream and back into the gut, where they are passed through the digestive system and out in the manure.

With excessive worm damage, muscle wastage may be evident as the body begins to break down its own protein stores (muscles) to support vital body systems. An effective program of de-worming, which could be designed by your vet who will know the area and specific problems of the region should keep parasites at bay and prevent weight loss problems associated with a worm burden. To test the efficacy of your worming program, talk to your vet about taking faecal samples and examining them for worm larvae throughout the year.

Digestive tract problems   Top
Weight problems may be caused by a physiological problem, which prevents food from reaching the intestines for digestion. Pain caused by nerve damage from equine protozoal myelitis, obstructions from strangles, abscesses or muscle weakness caused by hyperkalemic periodic paralysis or botulism can seriously alter a horses' eating habits and reduce appetite and feed intake.

Physical blockages such as abnormal growths in the oesophagus, scar tissue from past episodes of choking or foreign bodies lodged in the throat all narrow the passageway for food, making it difficult for the horse to swallow and may even cause chronic choke. The only way to effectively diagnose these problems is to perform an endoscopic examination or X-ray. If there is no way to clear the obstruction, special dietary arrangements should be made to allow the horse to swallow with more ease.

Gastric ulcers can cause reduced appetite as they cause pain and discomfort in the stomach. The incidence of ulcers in horses is quite high; studies have shown that approximately 80% of racehorses in training and 50% of other types of horses have ulcers. Horses that live on pasture for most of the day rarely develop ulcers. Ulcers are caused by excessive acid in the stomach usually associated with a high grain/low forage intake, meal feeding instead of continuous availability of forage and overtraining or stress of work. Symptoms of ulcers include irritability, picky eating, chronic colic, diarrhoea and inability to gain weight. Symptoms vary from horse to horse, with some showing one or two symptoms, others showing all and others no outward signs. Today we have a number of medications available to deal with ulcers including veterinary preparations designed to cure ulcers and antacids such as Kentucky Equine Research's own product Neigh-Lox. Although antacids cannot cure ulcers, they help to prevent gastric acid accumulation in the stomach and help to buffer excess acidity thus preventing ulcers from reoccurring.

In the small intestine, large intestine and caecum clinical conditions can alter the horse's ability to digest and utilise food. If nutrients move too quickly through the digestive system, as with diarrhoea, nutrients cannot be absorbed properly. There are a number of causes of diarrhoea in the horse including upsets in the balance of bacteria in the hindgut. There are many species of bacteria in the equine hindgut and if the population is disturbed the whole ecosystem of the hindgut can be affected. If bacteria are not functioning correctly, particles of food may not be sufficiently broken down for absorption, leading to diarrhoea. Another possible cause is viruses. These can cause sloughing of the intestinal lining and loosening of the faeces in the bodies attempt to flush out the pathogen.

Probiotics have been suggested to help treat diarrhoea caused by bacterial upset. They work by repopulating the hindgut with a number of species of good bacteria and are given through a nasogastric tube. Some endurance people have been known to use live yoghurt in horses feed as a natural probiotic. There are many commercially available lactobacillus and streptococcus faceum preparations as well as yeast products designed for daily use. Sometimes, when there is no apparent reason for a horse to be losing weight, a probiotic supplement can help to turn him around. They are also useful when horses are stressed after travelling or competition or after an illness requiring antibiotics.

Disease   Top
Chronic and acute disease can interfere with the horse's ability to maintain weight. There are many diseases contractible by horses, which can cause a disturbance in protein utilisation. Protein is important for rebuilding damaged and growing tissues, transporting nutrients through the blood, making blood-clotting factors and has a host of other functions. If the body cannot get enough protein in the diet, it begins to break down its reserves. As muscle is by far the biggest reserve of protein in the body, degeneration of muscle is the first response and may be the first noticeable indicator of protein deficiency, either from dietary insufficiency or from disease interfering with protein utilisation.

Chronic liver disease may result in weight loss due to the decreased ability to handle protein and fat properly. After absorption, dietary protein and fat make their way to the liver where they are directed to where they are needed in the body. If the liver is not functioning correctly, it affects many other body systems and results in weight loss. Liver function can be assessed by a simple blood test.

If the kidneys are malfunctioning, a large amount of dietary protein can be lost in the urine. Horses with kidney problems will usually drink large volumes of water and will urinate frequently. Kidney function can also be assessed by a simple blood test.

There are certain problems that can result in an abnormal increase in the amount of energy required to run normal body processes. Internal abscesses or cancerous growths will rob large amounts of energy from the horse, resulting in chronic weight loss. Horses with chronic obstructive pulmonary disease (COPD) also burn more calories because of the increased physical effort required to breathe. Pituitary adenoma (Cushing's syndrome) can also speed up metabolism, burning energy excessively even at rest. Common ailments such as heart murmur can also cause weight loss through disruption of blood flow carrying vital nutrients through the body

Environment   Top
Like humans, the horse's appetite can be affected by physical environment. If a horse is bored and unhappy, he may lose his appetite and develop vices such as cribbing, weaving or stall walking, thereby wasting energy and losing condition. The ideal solution to vices is to investigate the cause of the problem and attempt to fix it. This can be very difficult, and even if the cause is discovered, sometimes the behaviour pattern is so ingrained it becomes a habit that the horse will not break. The next best approach is to increase the caloric density of the diet.

Climate can also affect appetite. Horses can be reluctant to eat in very hot summer weather, or will be turned off feed that has gone bad after being stored in hot conditions for a period of time. It is wise to keep only small amounts of fresh feed in stock in hot weather. Appetite can be stimulated by adding commercially available supplements containing B-vitamins, which give the horse a boost and stimulate appetite. Working horses use more energy to work in the hot weather than in the cooler winter months. Their caloric intake should be adjusted to account for this or they may start to drop weight.

If your horse is kept in a herd environment and is low down the pecking order, this could affect his weight. He may be chased off food by the herd leaders and stand to the side wasting away whilst the other horses get fat. If this is the case, feeds of hay and grain should be well spaced, allowing horses to feel comfortable and unintimidated whilst eating. Placing a couple of extra servings of hay or grain in the field can also help to ensure that all horses get a share.

Chronic pain is often overlooked but can be a cause of chronic weight loss in horses. Discomfort not only reduces appetite, but also causes the body to release adrenaline (epinephrine) which puts the body in a state of catabolism. Catabolism causes the break down of body energy stores, resulting in weight loss. The presence and cause of low grade chronic pain is often hard to diagnose. If discovered, remedying the problem may solve the poor condition problem.

How to get weight on your skinny horse   Top
All your horses get a scoop of hard feed each, a few scoops of chaff and maybe a supplement thrown in for good measure. Feeding time is easy and takes no time at all. Some of your horses look great, fat and shiny, but the Thoroughbred who dropped a little weight last summer has not gained any weight since, in fact he seems to be getting thinner. He's getting exactly the same feed as the others so what's the problem? Could it be as simple as insufficient caloric intake, and if so, what can you do to encourage him to gain weight?

Sometimes, increasing a horses weight and condition can be as simple as adding more calories to the diet to meet his physical requirements. Other times, you may need to feed more calories than the horse actually needs to make up for physiological or environmental problems that cause him to either use more energy or reduce the amount of energy he can absorb from the feed.

What makes a healthy horse a poor doer?   Top
The main determinant is the metabolic rate, which can vary tremendously between horses. Metabolism is the speed at which the body burns fuel for energy in order to perform normal body functions. A slow metabolism requires very little energy to perform these functions whereas a fast metabolism requires substantially more energy and will require a higher caloric intake to maintain the same weight as the horse with the slow metabolism.

In general, metabolism is fairly breed specific, the terms 'hot blooded' and 'cold blooded' are generally indicative of a fast and slow metabolism respectively. For example, Thoroughbreds need to consume more calories per kg of body weight than draught horses. There are also variations within breeds; some Thoroughbreds keep condition quite easily, whilst others are more challenging when it comes to maintaining weight. Temperament can play a big part in a horse's ability to maintain weight and often goes hand in hand with metabolic rate. Nervous or tense horses tend to use more energy than calm ones.

A thin horse requires enough energy in its diet not only to maintain proper body functions but to increase muscle and fat reserves until it has reached the desired condition score. Feeding 2.5% body weight for maintenance at a skinny horses' current weight will only succeed in keeping it's weight static, to increase weight and condition, you must set a goal and feed at a rate corresponding to the desired body weight.

Horses that have lost weight slowly over a period of time by breaking down fat and muscle stores will look emaciated with poor muscle definition and protruding bones. The simplified solution to poor weight is therefore to increase the caloric content of the diet whilst ensuring adequate protein content. This can be done by increasing the daily intake of the three major ingredients of a typical horse diet, fibre, starch and fat. Each is utilised in a slightly different way in the horses body, and whilst increasing one ingredient may be favourable in one horse, it does not follow that all thin horses will respond as well to the same manipulation.

Fibre   Top
Fibre is the most important, most underestimated constituent of any horse diet. It is also the safest to increase in an effort to get a horse to gain weight. Some horses can maintain their weight on fibre sources (i.e. chaff, hay or grass) alone, even if they are in light work. For the poor doer, fibre is not sufficient to maintain weight alone, but there are strategies that can allow the horse to derive as much benefit as possible from it's fibre source.

The fibre portion of the plant is made up primarily of cellulose, hemicellulose (digestible fibre) and lignin (indigestible fibre). Cellulose and hemicellulose are broken down in the hindgut by the microbial population residing in the caecum and large intestine. Fibre is broken down into volatile fatty acids (VFA's), a useable form of energy for the horse. VFA's are readily absorbed into the bloodstream where they are transported to sites which need energy or stored in the form of fat or glycogen. Lignin is the structural support of the plant and is not digestible by the microbial flora. As a plant matures, the proportion of lignin increases and consequently the digestibility of the forage decreases, therefore the longer and more mature the grass, the less digestible the forage. Rigid stalked plants such as grass have a higher proportion of lignin than leafy plants such as lucerne. As a rule, if there is more leaf than stem in a forage source and if the stems have not matured enough to become stiff and inflexible, the digestibility of the forage will be higher. Fresh green spring grass will have more digestible fibre per kg than parched summer grass and hay or chaff cut prior to maturity will have more nutritional benefit than hay or chaff which is allowed to mature before cutting. Pasture is also more digestible than hay or chaff because the drying process involved results in digestible fibre losses.

If you compare the energy content of lucerne and grass hays, lucerne provides the most energy to the horse kg for kg. However, a low quality long stemmed lucerne hay is not a rich source of energy and would compare with an average quality grass hay. Maximising forage quality should always be the first adjustment when trying to achieve weight gain. Adding clover increases the energy and protein content of a mixed hay. Horses will generally eat clover hay better than other types of hay and therefore clover is particularly good for poor doers or picky eaters.

When good quality forage in the form of chaff, hay or pasture is not available, or if the horse does not readily eat hay, there are alternative sources of fibre such as lupins, copra meal, soy hulls, wheat bran and lucerne chaff or pellets. Overseas, beet pulp is a common fibre source being around 80% digestible fibre compared to 50% for average hay, however beet pulp is not yet available in Australia. Soy hulls are the by-product of soybean production and are the skin of the bean (not the husk or pod). Soy hulls are commonly used in commercial horse feed overseas and are a good source of digestible fibre. Lupins are a very common horse feed. Digestible fibre makes up a major part of the energy available from lupins.

Wheat bran is commonly thought of as a fibre source, but actually only contains about the same amount of fibre as oats. Wheat bran does contain a relatively high proportion of digestible fibre and starch but it also contains a lot of phosphorus, which can potentially disrupt the calcium and phosphorus ratio of the diet. Wheat bran works best as a complement to a diet high in lucerne hay or chaff because of the large amount of calcium in lucerne.

Lucerne pellets can be used as a supplement to average quality chaff or hay. Lucerne cut for pellets is harvested when the digestible fibre of the plant is at its peak. It is advisable to feed some hay or chaff along with these pellets to maintain gut fill. Hay and chaff are also important for their laxative effect. Using pellets alone may increase the risk of colic. Lucerne pellets however can be very useful for older horses that have difficulty chewing regular chaff or hay due to poor dental health. Cubes can be soaked for a few hours and stirred in with grain to create a kind of gruel which is easier to eat for older horses.

Supplements are available that may help with fibre digestion in the horse. Yeast (specifically Yea-Sacc1026) has been researched and found to improve fibre digestibility. Some commercially available feeds now come with yeast already added, otherwise yeast supplements can be purchased and added to your horses regular ration. Some probiotics are also thought to improve digestibility, especially where the microbial population of the hindgut is compromised. Various combinations of yeast and probiotics are also available to maximise regeneration and efficiency of the microbial population.

Starch   Top
When a horse cannot maintain weight on grass or hay alone, the addition of starch in the form of grains has been the most traditional method of increasing the energy density of the diet. Utilising energy from starch is very efficient because of the simple enzymatic process involved in its breakdown. It takes fewer kg's of grain to get the same amount of energy as a much larger volume of roughage. Grains are an excellent source of starch to the horse, but can be hazardous to digestive health if fed to excess.

The starch molecules in grains are complex polysaccharides, which are digested in the small intestine by the enzyme amylase, which breaks polysaccharides up into simple sugars. These sugars are easily absorbed into the bloodstream and are transported in the blood to where they are required or stored as muscle glycogen or adipose for later use.

The limiting factor of starch digestion is the production of amylase in the intestinal tract. Amylase production has been shown to be quite variable between horses. If amylase production is too low, much of the starch passes through to the large intestine for digestion. In the hindgut, the amount of energy extracted from the grain is reduced. Large amounts of grain in the hindgut causes microbial upset and makes the pH of the hindgut more acidic, possibly leading to problems such as laminitis and colic.

Starch molecules come in different sizes, some more easily digested than others. The starch molecules contained in oats for example are smaller than those in corn and barley and are more easily digested by amylase. Oats are well digested in their natural state and do not require processing for good utilisation. If corn and barley are treated with heat, the nature of the starch molecule is altered and it becomes more easily digested. Therefore, for some grains it is better to feed them steam rolled, steam flaked or micronised to get full nutritional value. The processes of pelleting and extruding also improve enzymatic digestion of many grains. When comparing prepared horse feeds, look for those using mainly heat processed grains to allow for optimal digestion in the small intestine.

It is often tempting to try and increase a horses weight simply by throwing more grain in the bucket, but it should be noted that there are inherent dangers with feeding excessive amounts of grain. Unfortunately, there is a point at which the amount of grain can actually harm your horse and make him less able to absorb the calories he requires from the diet. Some horses are hypersensitive to starch overload making the situation even more critical. The microbial balance of the hindgut becomes upset as the capacity of the small intestine is overwhelmed by the volume of grain; lactic acid is produced in the hindgut making the environment more acidic, which kills off the microflora. As the bacteria die they produce endotoxins which can cause colic and laminitis.

Stomach ulcers may also develop from high grain diets, further reducing the absorptive capacity of the gastro intestinal tract and causing more discomfort to the horse, which reduces his appetite even further. The horse may also lose his appetite for forage and thus begins to drop weight once more no matter how much grain you can get him to consume. Horses require a minimum of 1% bodyweight in forage every day to maintain a reasonable balance of the microbial population. The rest of the diet should be designed around the minimal forage requirement. The practice of adding more grain in an effort to increase weight and condition can spiral into a vicious circle that can cause serious damage to the horse if it goes too far.

As with forage digestion, there are numerous supplements available to aid with starch digestion or utilisation. Adding enzymes to the diet has not been greatly researched but is based on sound theory. If amylase is the limiting factor of starch digestion in the small intestine, then adding amylase to the diet may reduce the amount of feed passing through to the hindgut. Although there are a few commercial feeds and supplements available which contain enzymes, their efficacy is questionable. Enzymes are proteins which are very sensitive to temperature and pH fluctuations and become denatured (inactive) if subjected to hot or highly acidic environments such as the stomach. It is arguable that any enzymes can survive the acidity of the stomach to make it to the small intestine.

Supplemental chromium may improve the metabolism of starch. Chromium influences the way the body handles the rise in blood glucose resulting from starch digestion and the consequential rise in insulin. Chromium yeast has been used effectively in reducing the incidence of chronic laminitis in some ponies and in reducing the incidence of chronic tying up in horses that cannot tolerate a high grain diet. Recent research has shown that chromium can enhance glucose metabolism in young horses, which reduces insulin and cortisol levels after feeding grain. This may be useful in reducing the risk of OCD in young horses.

Fat   Top
These days, it is not uncommon to add fat to a horses diet. Whether it is added to increase the calorie density of the diet (ie more calories per kg) or as an alternative to adding more grain, fat has become a popular additive to horses diets. Fats in the form of oils, rice bran, linseed, sunflower seeds or commercial high fat feeds are all popular. Traditionally, fat was given to give the coat a healthy shine, but recent research has shown that fats not only are a great energy source for horses but can have performance enhancing properties too. Adding fat has also proved to be an invaluable tool for putting weight on a poor doer. Advantages of feeding fat include: it is more concentrated, you feed less to get the same benefits, energy from fat does not make a horse 'fizzy' like grain, horses on high fat diets exhibit more endurance.

There are differences between the available sources of fat that make one more useful than the other in different circumstances. As far as palatability goes, vegetable oils and particularly corn oils are much more palatable than animal fats. Vegetable oils are also much more digestible by the horse with excessive feeding of animal fats (or any fat if fed in high enough volumes) leading to loose faeces: a sign of improper digestion and microbial upset in the hindgut. All oil supplementation should begin slowly with small quantities at first, giving the digestive system time to acclimatise to the new energy source a little at a time.

Another common source of fat is rice bran. Rice bran is an excellent product for improving body condition in horses but it must be stabilised soon after it is separated from the rice kernel to prevent oxidation (making it rancid). Stabilised rice bran is fed as a solid and is more convenient than oil for many horse owners. It is very popular in the United States and has just become available in Australia as a pelleted supplement called Equi-Jewel. Rice bran is an excellent combination of fat from rice oil and highly digestible fibre and can be added to the grain or be used to replace some of the grain with horses that are starch sensitive. Rice bran is extremely palatable to all horses and can be used to add calories without the 'fizz' of grain.

Other sources of fat include linseed, sunflower seeds, full fat soybeans and coconut meal (copra meal). Seeds provide fat but if the quantity of seeds fed gets too high, consumption becomes very slow and some horses simply give up and refuse to eat them. Roasted soybeans are also great in small quantities but will increase the protein percentage too much if fed in larger quantities. Copra meal can be an excellent and palatable low-grade source of fat and digestible fibre but is not stabilised and so can sometimes be slightly oxidated by the time it reaches the feed bin. Linseed should not be fed raw but should be boiled for a period of time first to inactivate an enzyme that can release a toxic cyanide molecule when the seed is wet.

A high fat diet is invaluable for achieving weight gain in skinny horses as long as the gastrointestinal tract of the horse can tolerate the fat. Normally horses have no trouble digesting the fat as long as it is introduced gradually into the diet. The greatest advantage of using fat as an energy source is that it helps to avoid excessive grain intake. Dietary fat works best when fed in conjunction with grain and/or highly digestible fibre sources. Many new products are becoming available which incorporate high fat levels with high fibre ingredients such as soy hulls.
 

Kathleen Crandell, Ph.D and Peter Huntington B VSc
Kentucky Equine Research (Australasia)
112B Martin St Brighton
VIC 3186



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