Dr. Kris Hiney

  • Obesity in Horses

    Written By Dr. Kris Hiney

    Just like in people, many horses suffer from obesity related health issues. Overweight horses can have more trouble with joint issues, suffer from exercise intolerance and can even develop metabolic problems. While many horse owners know the risks of having an overweight horse, it may be difficult to reduce weight in these horses – certainly the horse is usually an unwilling participant!  In this article we will address management techniques and dietary strategies designed to reduce weight, but still keep the horse physically and mentally healthy.
    First of all, which horses are good candidates for losing weight? Ideally most performance horses should have a body condition score around five. Horses that are slightly overweight, or have a body condition score of 6 or 7, shouldn’t be at a great risk for health issues, but certainly will perform better at a condition score of 5 or 5 1/2. Horses above a 7 have more risk of developing health issues such as insulin resistance, metabolic syndrome, or even Cushings in their later years. If the horse with a high body condition score also has uneven fat distribution, he is more likely to have metabolic issues, and may even be harder to remove weight from than a horse with a more even fat distribution (personal observation). Horses that have cresty necks, substantial amounts of fat over the tailhead, enlarged abdomens and fat in the area of their mammary glands or sheath fit this category.   It is more critical for these individuals to lose weight. Now that we have identified the horses which need to lose weight, let’s address a healthy weight loss plan.
    One of the first issues to address is the quality of the horse’s forage. Ideally we will feed dieting horses harvested forage/hay, rather than pasture as it is easier to monitor their intake. Horses that are overweight will do better on mature grass hay which has less caloric density than alfalfa or alfalfa-grass mix. When selecting hay, look for more mature hays that have been cut at a later stage of growth. Typically these will be coarser stems and have seed heads present in the hay. However, when looking for lower energy hays, don’t sacrifice the overall quality of the hay – it should not contain weeds, debris, dust, mold, etc. We are just looking for fewer calories, not hay that your horse shouldn’t eat! Once we have the correct hay type, the owner will have to limit their horse’s intake. This can often be confusing, as we typically teach owners to feed based on a percentage of the horse’s body weight. However, in this case, we have a horse that weighs too much, and is consuming more hay/forage than it should. Let’s take a look at the math involved to determine how much the horse should eat.
    For an example, we will start with a 1300 lb horse who has a body condition score of 8. If we looked up this horse’s energy requirements for maintenance, it would need 19.7 Mcals per day. But that energy requirement is based on a horse that is in a lean body condition. Remember that it takes more calories to maintain metabolically active tissue like muscle than it does fat.   So even if we fed our horse at its maintenance requirement, it is still receiving too much energy for its body type. We will now assume that for every body condition score we want the horse to lose, it should lose about 45 lbs. For our 1300 lb horse, our target weight is actually closer to 1165 lbs [1300 lbs-(45lbs x 3 body condition units)]. The maintenance requirement for the lean 1165 lb horse is 17.7 Mcal per day.    Using these numbers, we will calculate out how much hay this horse would need to provide that amount of energy. For this example, I will use a grass hay of advanced maturity with a caloric density of .86 Mcal/lb as fed. The amount of hay the horse would consume using our 19.7 Mcal figure would be 23 lbs of hay (19.7 Mcal/0.86 Mcal/lb), while the horse would receive 20.6 lbs of hay if we intend to provide 17.7 Mcal (17.7 Mcal/ 0.86 Mcal/lb). Let’s compare that with the standard feeding guidelines for horses based on body weight. If the target weight of our horse is 1165 lbs, and we fed at 2% of the target body weight, our horse would receive 23 lbs of hay. That certainly wouldn’t work because that would provide enough calories to maintain his current weight of 1300 lbs! So how much do we need to reduce his hay intake? If we feed the horse at 1.75% of its target body weight, the horse would receive 20.4 lbs of hay per day. However, even feeding at this rate will probably not get us to their target weight. Therefore, in order to really achieve weight loss in our horse, we should probably feed closer to 1.5 % of the horse’s target weight. That means our horse would only be eating 17.5 lbs of hay per day. For the horse owner, this means that in order to successfully achieve weight loss, we need to get a scale out to the barn, and physically weigh out the amount of hay the horse will consume in one day. While this may be time consuming, it is the most accurate technique to deliver the correct and consistent amount of calories.
    Now let’s talk about some other practical issues. A horse that is only consuming 1.5% of its target body weight is going to have some “free time” that it is not used to having. We need to provide mental stimulation for this horse or it may development unwanted stereotypies such as cribbing or wood chewing. Continual stalling would not be ideal as this will certainly lead to a great deal of boredom and frustration. If possible, the horse should be kept in a dry lot (free access to pasture certainly won’t help!) with secure fencing. Do not underestimate the horse’s ability to get through the fence to graze! Also, providing other horses with which to interact, stable toys, etc. will help relieve boredom. If you find your horse finishing his meals too quickly, putting the hay in a hay net which is tightly woven may also slow down his rate of intake and alleviate boredom. While these strategies may sound tedious, it is important in order to improve the overall health of your horse.
    Next month we will continue to discuss the dietary needs of a horse in a weight loss program, as well as how to safely use an exercise program to encourage weight loss.
  • Feeding Horses for the Prevention and Management of Laminitis

    Written By Dr. Kris Hiney

    Nothing is more devastating to the horse owner than to have a treasured partner be afflicted by the painful, crippling disease of laminitis. Laminitis can be a debilitating disease that may ultimately result in the death of the horse or humane euthanization. Unfortunately there are so many factors that can manifest in development of this syndrome that it can be difficult to sort through.
    To understand the development of laminitis one should really understand the physiology of the equine foot. Essentially the hard keratinized tissue which forms the hoof wall is held to the soft tissue by the interdigitation between the sensitive and insensitive laminae. The insensitive laminae (seen here in Figure 1) is formed in vertical sheets on the inside of the hoof wall. 
    Figure 1. An interior view of a horse’s hoof with the soft tissues removed. 1b. A schematic of the vertical lines of insensitive laminae lining the interior of the horse’s foot.
    Connecting to the insensitive laminae is the sensitive laminae, which is living tissue requiring an adequate blood supply of oxygen and nutrients to survive. When an alteration of blood flow or a vascular insult occurs inflammation or even death of the sensitive laminae can occur. The sensitive laminae ultimately stabilize the internal structures of the horse’s hoof, including the third phalanx (or coffin bone). When this stable connection is lost, the pull of the deep digital flexor tendon on the base of PIII rotates it out of place. This condition is referred to as chronic laminitis or founder.
    Figure 2. The sensitive laminae which connect the hoof wall to the horse’s foot.

    Figure 3. A foundered hoof where PIII has rotated out of place due to the pull of the deep digital flexor tendon.
     
    There are many reasons why blood flow can be disrupted to the equine digit. Laminits is often a systemic disease which is only visualized in the foot. While digestive issues lead the list of causes of laminitis there are other physical insults which can occur as well. When procuring wood shavings from a reputable dealer, care should be taken never to include those of the black walnut tree. These shavings contain the chemical juglone, actually a toxin which can kill other plants in the black walnut environment. Other physical causes are concussive trauma, from being ridden on hard surfaces resulting in decreased blood flow to the foot, and excessive loading (i.e., one limb is severely lame resulting in extra loading to the sound limb). Endotoxemia, such as what might be seen in a mare with a retained placenta, may also result in the development of laminitis.
     Nutritionally, a whole series of gastric insults can alter blood flow to the foot.  These include a carbohydrate overload (the classic example of the horse breaking into the feed bin) which leads to an alteration of fermentation in the hindgut.  In order to prevent starch from escaping enzymatic digestion in the small intestine and escaping to the hind gut, it is recommended to avoid a starch intake of more than 2-4 g/kg of body weight per meal. Therefore, a 500 kg horse should receive no more than 1-2 kg of starch per meal.  Pasture grasses have also long been known to precipitate bouts of founder, but typically only in susceptible populations. Ponies, and horses with thrifty genotypes are the most likely to suffer from pasture-associated laminitis. It is believed to be caused by a high level of fructans, although the quantity of fructans required to cause laminitis is unknown. Fructan content is known to vary with the time of year, with a higher content seen in the spring, when most pasture-associated laminitis occurs. Horses which are susceptible to pasture-associated laminitis should also limit their intake of pasture grass in the afternoon, when photosynthesis throughout the day has resulted in a higher level of fructans in the plant. The levels of water soluble carbohydrate gradually decline through the night, making grazing in the morning relatively safer. As the majority of horses which develop laminitis due so on pasture, rather than through the owner feeding excessive concentrates, at least some thought or caution should be used when grazing horses. Ideally horses should be introduced gradually to consuming fresh grass, and susceptible horses' grazing should be limited to when fructan concentrations are at their minimum.
    If a horse does develop chronic laminitis, unfortunately there is little the owner may do nutritionally to manage the horse. Obviously exposure to pasture grasses at peak times of fructan concentration should be avoided. Also, the horse should be managed to lower body weight to decrease the mechanical load on the laminae. Low energy forage should be the primary feed for the foundered horse. However, because low energy forages will typically be deficient in protein, minerals and vitamins, it is important to ensure that the horse is supplemented with a low energy concentrate to make up for dietary insufficiencies. As these horses are often in a great deal of pain, NSAID administration may often be needed, but can also contribute to gastrointestinal upsets. Alternatives to NSAIDS, such as Omega-3 fatty acid supplementation, may help to alleviate some discomfort, without the negative side effects.
    Overall, close attention to the diet of the horse, avoiding GI disturbances or causing fluctuations within the hind gut, and limiting grass intake during periods of time where fructan concentrations can be high, will hopefully prevent the horse from ever experiencing this deadly disease.

  • Feeding Horses with Respiratory Allergies

    Written By Dr. Kris Hiney

    Similar to people, horses can develop allergies to environmental contaminants that lead to asthma-like symptoms. In the equine world, this syndrome is referred to as recurrent airway obstruction (RAO). It was previously referred to as chronic obstructive pulmonary disease or (COPD) but due to dissimilarities with the syndrome observed in humans, RAO is now the preferred term. When some horses are exposed to dusts and molds, they develop allergies.  Why some horses do and others do not develop allergies is unknown. There is some evidence that this disease may be genetic. Horses born to affected parents are three times more likely to develop RAO than horses born to non-affected parents. Therefore, if you know your horse is predisposed to RAO, it is even more important to identify the symptoms and to properly manage its environment.
    Identifying RAO
    When the horse is exposed to an allergen, the body responds by increasing inflammation through the bronchioles coupled with bronchoconstriction.  The lungs increase in mucus production which the horse may not be able to clear easily. Frequently nasal discharge is seen, along with coughing, an increase in lung sounds and more distress during breathing. Lung sounds are typically heard with expiration, or the horse will “wheeze” when breathing out. Continual exposure to allergens may lead to fibrotic changes within the lungs. This will result in a horse which cannot take in oxygen to the same extent as an unaffected horse. You may notice that the horse has an increase in respiration rate over what is normally experienced during exercise, or he may become more exercise intolerant or fatigue easier. Horses with this syndrome which have had it more severely or more chronically may even develop a “heave line”. This is due to the hypertrophy of the abdominal muscles which must be used to assist the animal in breathing, rather than just solely using their diaphragm.
    Management of the RAO horse 
    As pollen and mold counts increase in the environment, horses with RAO will experience more symptoms or episodes of RAO. Often barns and stables are not designed with proper ventilation in mind. This contributes to a continual exposure of the horse’s respiratory system to particulate matter. Hay and straw bedding ideally should always be stored in a separate building from where horses are housed, and certainly not overhead. Additionally, the stalling area should be separate from the riding arena. All the dust that is kicked up while horses are exercising can greatly exacerbate the problem. Ever think about how much dust is stirred up into the air while the barn aisles are being swept? Ideally all of this dust exposure should be minimized and RAO affected horses removed from the barn whenever dust is stirred up. One of the best changes to management practices of the RAO horse is simply to house them outdoors. Often an improvement in airway function is seen within days.
    While horses stabled inside are clearly more likely to be exposed to particulate matter, horses on pasture during the summer can also have trouble. This even has its own nomenclature,  summer pasture associated obstructive pulmonary disease or SPAOPD. Horses with this syndrome should be kept off pasture during the summer months, but can be housed outdoors during the rest of the year. If horses must be housed inside, whether they are SPAOPD or perhaps competitive horses that must be stalled, it is imperative that the environment is as dust free as possible. Straw bedding may not be a great choice for RAO horses but shavings can also contain molds similar to those in hay and straw. High quality straw may actually be lower in spore count that some shavings. Alternative beddings may yield the best results such as cardboard or newspaper pellets. If straw or shavings are used, remove any RAO affected horses while bedding is introduced into the stalling area. Essentially, let the dust settle before the horse is put back into the stall!
    Feeding management
    Ideally the RAO horse should graze fresh pastures as much as possible, but obviously this is not always possible.  One of the most immediate dietary changes for the affected horse is to absolutely eliminate any moldy hay or straw that may be in the horse’s environment. While moldy hay should never be fed to horses, it is more critical with RAO horses.   One of the difficulties in finding suitable hays for RAO horses is that humans may not always be able to detect the presence of mold if it is not obvious. Try to find hay sources from a knowledgeable producer who bales high quality hay. The type of fungus which produces the most damaging fungal spores prefers relatively hot temperatures. This would be seen in poorly cured hay, or hay that is baled at too high of a moisture content. The heating which occurs during spoilage is a haven for these fungi.  Round bales may not be an ideal choice, unless they are stored completely inside and are never subject to any sort of spoilage. Additionally, round bales encourage the horse to almost bury their head within the bale, making the immediate breathing area of the horse very dusty. Completely pelleted diets might be a good choice for these horses at it greatly eliminates the dust exposure to the horse while feeding. The quality of the pellet is also critical. Uncoated pellets may break down more easily and have a substantial dust component. Hay cubes and haylage are also alternative feeding strategies.   Moistening the feed can also help in dust suppression prior to feeding. Hay only needs to be soaked for 30 minutes to achieve optimal dust suppression. Beyond that time no additional benefits are seen. However, the down side to soaking the hay is that some of the nutrients are leached out into the water, including P, K, Mg and Cu.
    Beyond eliminating dust and molds other dietary therapy may be aid the RAO horse. Supplementing RAO horses with additional anti-oxidants in the diet may be helpful. There is an increase in free radical formation or reactive oxygen species (ROS) in horses with lung inflammation. In fact, the increase in RAO may increase the upregulation of genes which produce inflammatory factors such as interleukins. Horses with RAO given a supplement of vitamin C and E plus Se resulted in less airway inflammation and an increase in exercise tolerance. Other natural sources of anti-oxidants such as sorghum and omega 3 fatty acids have not yet been studied for their effectiveness in RAO horses.   Additionally, due to the increased energy requirement just to breath, RAO horses are often underweight. The sustained stress to the horse’s system may also contribute to this weight loss. You may need to find a feed with an increase in energy density, such as a fat added feed to help maintain its body weight as well as additional anti-oxidants.
    If one follows these management guidelines carefully, RAO horses may be symptom free for years to come.   While pasture is ideal for RAO horses, performance horses which need to be stalled can be kept healthy with a rigorous adherence to maintaining a dust and mold free environment and proper dietary management.

  • Preparing for the Breeding Season

    Written By Dr. Kris Hiney
    While breeding season may be the last thing on anyone’s mind at this time of year, it will be coming soon. Now is the time to ensure that your mare or stallion is going to be at their optimal reproductive efficiency. While much of a mare's or stallion's fertility depends on other factors such as age, condition of reproductive organs, etc., there are some basic management steps we can take to ensure that as few cycles of inseminations are needed to get a mare pregnant. Multiple breeding attempts can quickly outstrip the original stallion breeding fee and be a significant cost to the mare owner. Often we forget that every shipment of semen may be an additional cost, followed by extra veterinary fees, mare board, etc. Therefore it is in the mare owner’s best interest to have her in optimal condition before the first breeding attempt ever occurs.
    So how do you prepare your mare and stallion in January to begin breeding anywhere from February to mid-summer? The easiest place to begin is to look at your horse’s body condition score. For a mare, we want her to be at a body condition score of at least 5 or 6 (see "Too Fat, Too Thin, or Just Right"). A mare in this condition would be a moderately fleshy mare whose ribs are covered by fat, has evidence of fat deposition behind her shoulder and over her tailhead, and whose back is level. Mares that are a higher condition score than that may still have no problem getting pregnant, but are unnecessarily obese. This may result in more wear and tear on her joints. Additionally, as there is no increase in reproductive efficiency, maintaining a mare in too high of condition may just be a waste of feed costs. Furthermore, if she has chronically been obese with localized fat deposition, she may even be at risk for metabolic syndrome or insulin resistance (see Equine Carbohydrate Disorders, Part 3: Metabolic Syndrome).  If your mare is diagnosed with metabolic syndrome, it is important to correct her metabolic profile and manage her carefully through the breeding season. Altered hormonal profile can impair her ability to become pregnant and certainly extra weight in a laminitic mare may increase her level of pain.
    If we look at the opposite condition and the mare is too thin, she will need more cycles to settle compared to a mare at adequate condition. She also may take longer to return to normal cyclic activity following winter anestrous (when mares cease to cycle due to the shorter day length). Thin mares' conception rates may be lower, and if she foals in a thin condition, she may take longer to begin cycling again. With so many negative effects of trying to breed a thin mare, one of the easiest ways to increase reproductive efficiency is to put weight on your mare!
    Stallions also use more energy in the breeding season due to the increase in their activity levels. Stallions which breed mares in an intensive live cover breeding system will of course need more energy than a stallion which is bred only once every other day. Stallions which are more extensively used would have energy requirements similar to a light to moderately exercising horse, and their maintenance requirements will also be elevated (see "Energy for Work").  Typically, stallions are simply more active during the breeding season as they exhibit their normal sexual behavior. Ideally, stallions should be maintained in a body condition score close to 5 throughout the breeding season.
    Beyond just meeting a stallion's energy requirements, feeding of Omega-3 fatty acids may help improve his reproductive efficiency. In a study by Harris, et al, published in 2005 in Animal Reproduction Science, stallions supplemented with dietary Omega-3 fatty acids increased their daily sperm output.  Furthermore, there was an increase in morphologically normal sperm in the supplemented group.  The greatest response was seen in the stallion with initially the most morphologically abnormal sperm. In this study, one stallion who was considered to be a “poor cooler” improved his post cooling progressive motility from 23 to 38% in a 48 hour test cool. Therefore, supplementation of Omega-3 fatty acids may be a valuable tool in improving the reproductive characteristics of sub-fertile stallions.
    Basic guidelines for increasing body weight and condition in horses are really no different for the broodmare or stallion than in other classes of horses. The quicker the gain is needed in the horse, the larger the increase in calories which must be offered daily. If you only have two months to get your mare in condition, you need to increase her energy intake by 30-40% to increase her body condition score by one number. If we have three months, which may be more realistic, the energy requirements increase by 20-30%. Remember, however, if you are trying to accomplish weight gain during the winter, she may also have an increase in energy requirements due to her need to thermoregulate. This will make weight gain more difficult. To add calories quickly to the diet, look for a fat-added feed that will be digested quickly and efficiently.  Remember that fat offers 2.25 x the calories that will be in grains which consist primarily of simple carbohydrates. Fat will also disrupt the metabolic profile of the horse to a lesser extent than a diet high in sugars and starches.
    Of course, beyond caloric intake, always ensure that your breeding horses are consuming a complete balanced diet in respect to all nutrients, have good health care and are suitable candidates for breeding. Breeding horses is a big responsibility in terms of the care and well-being of the mare, stallion and the subsequent offspring.

  • Equine Carbohydrate Disorders Part 3: Metabolic Syndrome

    Written By Kris Hiney
    Imagine a bright spring day. You excitedly turn your horse out to indulge in the fresh spring grass as a special treat. You return in a few hours to collect your companion, but instead are met by an unhappy painful horse, slowly limping its way back to the gate.
    Sound familiar? Unfortunately for some owners, this is an all too real scenario. Many horses suffer from carbohydrate sensitivities, or metabolic syndrome, which make them extremely susceptible to changes in carbohydrates in the diet.  One may also hear these horses referred to as insulin resistant, almost like Type II diabetes in humans.  In recent years there has been an upsurge in the number of studies and articles written about metabolic syndrome in horses. While awareness in the general public has increased, many horsemen still wonder if their horse is, indeed, one of these individuals. Should they be paying strict attention to every type of carbohydrate their horse consumes? Should horses no longer consume grass? Does their horse need medication? How do you know if your horse truly has metabolic syndrome?
    Classically, horses with metabolic syndrome are described by a certain appearance. They are typically obese horses which gain weight readily, and are considered “easy keepers”.   Breeds with a higher prevalence of metabolic syndrome include the traditional easy keepers such as ponies, Morgans, and Paso Finos. However, metabolic syndrome  can be seen in a wide spectrum of breeds including Quarter Horses, Arabians and Thoroughbreds.  Beyond just being obese, metabolic horses tend to have regional adiposity, or specific fat deposits on the crest of their neck, over their tailhead, the sides of their abdomen and also in the scrotal or mammary area.  The size of the crest of the neck is often the best physical predictor of metabolic syndrome. The thicker the crest, the more likely the horse truly fits into this category. However, it is important to note that it is possible for leaner horses to also suffer from metabolic syndrome. Despite being lean these horses still demonstrate regional adiposity, along with a susceptibility to pasture associated laminitis, as well as insulin resistance. Therefore, if your horse shows symptoms, it may be wise to have it tested, despite it not being overly obese.
    Unfortunately the most common way horses are diagnosed with metabolic syndrome is the frequency of laminitic bouts. Usually this is seen following grazing on pasture, especially in the spring or fall.    These horses may be young or middle aged, which sets them apart from horses who suffer from Cushings disease. However, horses who suffer from metabolic syndrome early in life are certainly more likely to develop Cushings later on. Cushing horses are also distinct in the prevalence of hair coat which does not shed or long curly hair while the metabolic horse has a normal hair coat.
    Physiologically, these horses demonstrate insulin resistance.   Essentially they must secrete larger amounts of insulin compared to a normal horse, in order to stabilize their blood glucose levels. Therefore, their insulin levels remain higher in their bloodstream, which can have a cascade of effects on their body. They also present with elevations in blood lipids, as well as an increase in leptin. Leptin is a hormone secreted by fat cells or adipocytes, that normally helps in the feeling of satiety (or fullness). However, increased concentrations of leptin may contribute to inflammation in the body. Metabolic horses also have a lower resting thyroxine levels (T4) then their normal counterparts. However, the low level of T4 does not cause insulin resistance and metabolic syndrome, but rather is merely a consequence of altered metabolic profiles.
    So why are these horses so susceptible to laminitis? What could insulin resistance possibly have to do with painful feet? One of the commonalities between the myriad of disorders that can result in laminitis in horses is a disruption of the circulation to the hoof. Insulin is most commonly recognized for its role in glucose disposal, but it is a hormone with systemic effects. It is presumed that sustained hyperinsulinemia promotes vasoconstriction. It is already known that carbohydrate overload induces laminitis by creating vasoconstriction in the hoof, so the hyperinsulinemic horse may be even more susceptible to shifts in carbohydrate intake. This disruption of blood flow to the foot results in hypoxia and tissue damage to the sensitive laminae. Severe bouts may render the hoof wall unstable and allow the coffin bone to rotate downwards within the foot. This may lead to permanent alterations of the hoof structure.
    Testing for metabolic syndrome frequently involves blood sampling after a short period of fasting (typically 6 hours). Blood is analyzed for glucose and insulin levels that are above normal. The presence of altered adrenocorticortropin releasing hormone can also be tested if Cushings is suspected in an older horse.   Further testing can be done if horse’s insulin levels are within the normal range, but metabolic syndrome is suspected. Horses are again removed from feed, and a standard blood sample is taken. Horses are then given a bolus of glucose and then insulin to determine how the body metabolizes these compounds. This provides a more dynamic picture of the horse’s metabolic response to carbohydrates.
    If your horse has been diagnosed with metabolic syndrome, or has show signs of pasture associated laminitis, it is important to start them on a rigorous management protocol. First, as these horses have sensitivities to carbohydrates, concentrates should be removed from the diet. As these horses are typically obese anyhow, there is little need to supply concentrates to them anyhow. If the owner is concerned with mineral and vitamin intake, there are many products which are intended to complement forage only diets. Typically these are pelleted supplements which are fed at very low levels of intake. The obesity issue in the horse should also be addressed. Exercise should be increased to 5 days a week. Not only will this aid in reducing the body weight of the horse, but exercise also enhances glucose clearance from the blood in a non-insulin dependent manner. However, be sure that the horse is not recovering from any laminitic episodes. Pasture intake should also be limited in these horses. Horses should only have access to pasture for a short time or have access to a very small area. If more movement of the horse is desired, a grazing muzzle should be employed to prevent overconsumption of grass. The horse should receive an all forage diet, preferably of grass hay, with intake reduced in order to encourage weight loss. If weight loss is not able to be achieved at an intake of 2% of the body weight, then reduce feed intake to 1.5% of bwt. Unfortunately simple diet restriction may take a long time due to the efficiency of the horses prone to metabolic syndrome. If the horse has greater degrees of insulin resistance, it is advisable to monitor the non-structural carbohydrate composition of the hay, with it ideally below 10%.If horses have persistent issues with metabolic syndrome after calorie restriction, decrease in adiposity, alteration of diet, limitation of pasture intake and exercise have all been employed, then there are medical therapies which can be used. Levothyroxine is effective in improving insulin sensitivity. If all of these measures are followed faithfully, there is no reason that these horses cannot be returned to a metabolically normal state and enjoy a long healthy life.
    Next month: We will discuss other strategies that have been employed to assist the metabolic horse.

  • Equine Carbohydrate Disorders Part 2: Understanding the Terminology

    Written By Dr. Kris Hiney
    Last month we began a new series looking at carbohydrates commonly fed to horses, and the different forms they come in. We discussed the differences between simple sugars and polysaccharides and how the bonds which join these sugars have direct implications on how they are digested in the equine. We also discussed a few carbohydrates in particular in which many horse owners have particular interest, including fructans, which may carry health risks, and fructooligosaccharides, which can be used as digestive aids. In the following article I will attempt to define the wide array of terminology that one finds in equine nutrition, such as crude fiber, neutral detergent fibers, and non-structural carbohydrates, among others.
    Horses' diets primarily consist of plants which are largely made up of carbohydrates. Certainly plants also contain protein, lipids, vitamins and minerals, as well as water, but their primary composition is carbohydrates. If we use the carbohydrate definitions from last month, we know that the cell wall of plants is composed of cellulose, hemicellulose, lignin (which is indigestible by horses), beta glucans, gums and pectins. Inside the cell wall we find the more digestible cell contents which contain the simple sugars, starches, oligosaccharides and fructans. Often horse owners need to know what percentage of these compounds appear in a particular feedstuff. We use a variety of analytical methods to partition these carbohydrates into groups.
    Crude Fiber
    The most commonly used descriptor of carbohydrates on feed tags is usually crude fiber. Crude fiber content of a feed is determined using proximate analysis or the Weende system. Crude fiber is the residue remaining after subtracting water, lipids, proteins and the nitrogen-free extract from the feed. Nitrogen-free extract is said to represent mainly sugars and starches.   It uses a chemical method of solubilizing the feed using acids and bases. One of the problems in using crude fiber as a descriptor is that any lignin, cellulose or hemicellulose which is solubilized in the process is lost and appears in the nitrogen-free extract value for the feed. Thus, crude fiber values may actually underestimate the fiber value of the feed, and over estimate the nitrogen-free extract portion.
    NDF and ADF
    The Van Soest system of analysis improves on simple values of crude fiber, by separating out different fiber fractions into neutral detergent fiber and acid detergent fiber. These are the most common values which are reported if you have a forage analyzed. Unfortunately this method is most applicable to the value of feedstuffs for ruminants, rather than horses. Regardless, it still does offer the horse owner some important information. The neutral detergent fiber of a feed contains hemicelluloses, cellulose and lignin, although some soluble hemi-cellulose may escape into solution.    It does not provide information about fructans, pectins, gums, or beta glucans which are quite readily fermented by the equine digestive tract. Acid detergent fiber represents the lignin and cellulose content of the feed, as the hemicelluloses have been removed. The amount of hemi-cellulose in a feed, which is easily fermented by horses as well, is represented by the difference in value of the NDF and ADF value for the feed.
    Total Dietary Fiber
    Total dietary fiber is more frequently used in human nutrition, but may actually offer better information for species which are hind gut fermentors, as is the horse. Total dietary fiber combines many plant values together, and essentially represents the portion of the plant that resists enzymatic digestion which takes place in the small intestine. This includes the traditional fiber components of hemi-cellulose, cellulose and lignin, but also includes pectins, oligosaccharides, mucilages, gums, etc. which are often referred to as soluble fibers in human nutrition. Thus this method recovers more of the true fiber portion of the feed which is susceptible to fermentation in the horse and contributes to their energy supply. Unfortunately this method is not commonly used in commercial feed testing laboratories which serve the animal industry.
    Non-Fiber Carbohydrates (NFC)
    Now the definitions are going to start getting a little trickier, and the horse owner may encounter many different acronyms. Non-fiber carbohydrates, or NFC, represent the carbohydrates which are not in the cell wall and are not recovered when doing an NDF feed analysis.    The NFC is what remains after subtracting the NDF, protein, fat and ash. It represents the sugars, starches, fructans, galactans, pectins, beta glucans and organic acids. NFC is determined via a mathematical procedure and not a chemical analysis. You may also see values reported as NSC, which stands for non-structural carbohydrates. These values are actually determined chemically and differ from NFC in that NFC values may also include pectins and gums which will not appear when analyzed for NSC.
    WSC
    Confused? Let’s add some more letters. Water soluble carbohydrates are also used in equine nutrition to determine the most easily digested carbohydrate portion. The monosaccharides, disaccharides, oligosaccharides and some polysaccharides appear in this portion of feed separation. Compared to the NSC value for feeds, it would equal the WSC portion added to the starch content of the feed. Starch content of feed can also be analyzed separately as well.
    Finally, some equine specialists have suggested that carbohydrates need to be redefined in terms of horse nutrition. As they are hind gut fermentors, they handle carbohydrates much differently than do ruminants. Certainly, they also get much more use of cell wall components than do simple monogastrics. Many of the particular disorders found related to carbohydrate digestion in the horse may require us to look differently at feeds than is needed in other species. One of the suggested systems created by Rhonda Hoffman (currently of Middle Tennessee State University) is to separate equine carbohydrates into hydrolysable carbohydrates (CHO-H) subject to enzymatic digestion, and fermentable carbohydrates (CHO-F) which undergo fermentation in the hind gut. The fermentable carbohydrate fraction can further be defined as either rapidly fermentable carbohydrates (CHO-FR) or slowly fermentable (CHO-FS). Slowly fermentable carbohydrates would include those seen in NDF values, with the indigestible lignin portion removed from the value. The rapidly fermentable carbohydrates, whose presence can increase the energy content of a feed, include the oligosaccharides, fructans, beta glucans and pectins. Feeds higher in rapidly fermentable carbohydrates can offer more calories to the horse. Alternatively, some horse owners may need to be aware of the fructan content of feeds or forages in horses more prone to developing laminitis.
    So what values do you need to know and why should you care?
    In general, crude fiber values are listed on most feed tags. Typically the lower the crude fiber value, the higher the energy density of the feed. This is not true of feeds which are designed to have higher fat values, and may include fibers to provide a healthier type of feed for the horse. Owners who have horses with insulin resistance or metabolic syndrome, as well as PSSM horses, should try and choose feeds which are lower in the soluble carbohydrates such as sugars and starches. However, these values are not always provided on feed tags. Owners may also select away from forages which may be higher in sugars and starches as well for these particular types of horses with demonstrated metabolic disorders.
    Next month, we delve more deeply into particular carbohydrate disorders seen in horses.

  • Equine Carbohydrate Disorders, Part 1: Definitions and Relationship to Equine Diseases

    Written By Dr. Kris Hiney
    Equine disorders related to carbohydrate consumption have received much attention by owners and researchers alike, as of late. This has resulted in almost a mistrust or fear of feeding horses carbohydrates.  But in reality, almost all of the horse’s calories come from carbohydrates – there is no way to avoid them in the horse’s diet. What one must do is understand all of the forms in which CHO (carbohydrates) are found, identify horses at risk for CHO disorders and select the appropriate feeds to keep them healthy.
    To begin, carbodydrates are simply molecules composed of carbon, hydrogen and water. Monosaccharides are single units of sugars which vary slightly in their structure.  Common monosccahrides in the horse’s diet consist of glucose, galactose, fructose, mannose, arbinose and xylose. While these monosaccharides are not normally found in their single form in plants, they are joined together to make  longer polysaccharides. However, monosaccharides are produced through  enzymatic digestion by the horse.  Disaccahrides, then, are just two sugar units linked together. Common disaccharides include lactose (found in mare’s milk and is formed by glucose and galactose linked together) and maltose (two glucose units linked together).
    Figure 1. Glucose and galactose. The two structures only differ by the location of the hydroxyl group on the left side of the structure.
    Oligosaccharides are longer chains of a variety of monosaccharides linked together, typically between three and ten sugar units.  The primary oligosaccharides in the horse's diet are stachyose, raffinose and fructo-oligosaccharides (FOS).  FOS have received attention in animal nutrition as a way to supply pre-biotics to the animal. Pre-biotics are often oligosaccharides which are resistant to digestion in the foregut of the horse but are digested by bacteria in the hindgut. These supply a source of nutrition which supports the growth of beneficial bacteria and perhaps reduces the population of disease causing – or "pathogenic" – bacteria. In fact they are looked at as an alternative to feeding antibiotics in livestock. FOS are believed to alter the pH of the colon to a more favorable environment for the most productive bacteria. Mannose specific oligosaccharides are also thought to reduce the adherence of pathogenic bacteria to the epithelium of the gut wall. In yearling horses, feeding FOS reduced fecal pH and increased the production of volatile fatty acids from the hind gut. FOS supplementation also decreased the incidence of diarrhea when fed to foals. It has also been shown to have a protective effect on the development of foal diarrhea when fed to their dams. However, it is not known if that was an indirect effect passed through the milk, or if the foals simply ingested some of their dams' feed containing the supplement. While feeding oligosaccharides does not appear to have an immune boosting effect that has been suggested in other species, it does appear to have beneficial effects on gut health in the equine. Horses receiving FOS and challenged with a large barley meal had less lactobacilli in their colon compared to controls. Thus FOS may help prevent GI disturbances due to diet changes or CHO overload.
    Fructooligosaccharides also belong to the category of carbohydrates labeled as fructans.  Fructans are polysaccharides which have multiple fructose units. Inulin is also classified  as a  fructan. Many horse owners have heard of fructans as a risk factor for pasture associated laminitis. A sudden increase in fructans in the diet can alter the microbial population in the hindgut which may then subsequently lead to the development of laminitis. Fructan concentrations in grasses vary with both season and time of day.  Fructans and other starch concentrations are highest in the spring, lowest in the summer and intermediate in the fall. During the day, the process of photosynthesis results in the highest concentrations of fructans in the afternoon with sometimes half or less in the morning or evening hours.
    Other CHO include longer chains of sugar units and are known as polysaccharides. Most commonly we think of starches and fibers as the common polysaccharides in the equine diet. Starch occurs in either linear form known as amylose or branched form, amylopectin.  It is composed of only glucose linked by bonds that can be enzymatically digested by the horse. In contrast, cellulose is also a straight chain of glucose but is linked by a different type of bond , a beta bond, which must be broken by microbes. Fermentation of this fiber fraction results in formation of volatile fatty acids which are metabolized by the horse to produce energy. Pectin and hemicelluloses are also common polysaccharides found in the equine diet.
    Figure 2. Amylose is a chain of glucose units linked by alpha bond.
    Figure 3. Cellulose is a similar chain of glucose units, but linked by beta bonds instead, making it indigestible by mammals.
    Those CHO linked with alpha bonds can be digested in the foregut, allowing the monosaccharides to be absorbed intact. In contrast, cellulose, hemicelluloses, pectin, raffinose and stachyose, which contain beta bonds, will all need to undergo microbial fermentation to provide energy to the horse.   Hemicellulose, compared to cellulose, is a mixture of arabinose, xylose, glucose , mannose and galactose. Pectin is made up of beta linked galacturonic acid, arabinose and galactose. Pectin and hemi-cellolose are more rapidly fermented than cellulose and increase the digestibility of the feed if present in a greater proportion.
    Now that we know what different types of carbohydrates exist in the horse’s diet, let’s look more closely at some differences that occur in forages. Typically, forages should always make up the bulk of the horse’s diet. They are made up of structural CHO which make up the cell wall as well as some indigestible lignin.  The plant cell wall is made of cellulose, hemicelluloses and pectin. Forages also have non-structural CHO or NSC in the cell content, though certainly not as much as concentrates. The NSC is a mixture of monosaccharides (glucose, fructose, etc.) and disaccharides as well as starch and fructans.
    If we compare common forages, cool season grasses are made up of primarily cellulose, then hemi-celluose and the fairly small amounts of pectin. Cool season grasses include Kentucky Bluegrass, orchard grass, fescues and ryegrass.  Legumes, which are typically high in digestible energy are relatively higher in pectin. Legumes would include alfalfa, clover, lespedeza and peanuts. Warm season grasses grow and mature more rapidly and have much more cell wall/kg DM and thus much more fiber. Warm season grasses include Bermuda grass, switchgrasses, and bluestem. Therefore warm season grasses at a later stage of maturity may be ideal for horses with carbohydrate sensitivities. In general, there is a higher proportion of cell content in a younger, or more immature plant. This makes grasses or hays harvested at an earlier stage more digestible.
    Interestingly, the storage form of CHO in legumes and warm season grasses is primarily starch, while cool season grasses prefer to store energy in the form of fructans with much less starch. There is also a limit to how much starch the chloroplasts of warm season grasses and legumes can contain, yet there is no limit to fructan accumulation. Fructan also accumulates more to the base of the plant and more so in the stem than in the leaf. Cool temperatures and droughts (which typically don’t go together) may also increase the fructan production by the plant. Anything that promotes photosynthesis but retards growth ends up increasing NSC (lots of light with cool temperatures).   Therefore, be especially careful to observe growing conditions, especially if the horses are consuming cool season grasses and have carbohydrate sensitivities.

  • Minimizing the Stress of Weaning

    Written By Dr. Kris Hiney

    The fall season is here and with it often comes the time for weaning our foals. Many successful weaning strategies exist but it is important for the manager to choose the optimal one for their facilities and management style. These decisions are important and can affect the growth, well being and even the future behavior of your foal.
    When is it appropriate to wean?
    Foals can be weaned at any age provided their proper nutrition and socialization skills are ensured. Foals whose dam’s may die at birth are obviously “weaned” from their dam at an extremely young age. While it is preferable to find a willing nurse mare, and it is even possible to induce lactation in a non-pregnant mare, many owners choose to put the foal on a liquid diet of formula designed to match the mare’s own milk.  Specialized milk replacer, goat’s milk and supplemented cow’s milk can all be used successfully.  Prior to doing so, it is important to ensure that the foal has received adequate amounts of high quality colostrum, as the proteins found in the milk replacer may block the later absorption of immunoglobins from colostrum. Colostrum content quickly decreases in post-partum mares and should have been harvested within the first three hours post parturition of the donor mare.
    Orphaned foals must be fed frequently , initially from a bottle, but can then be taught to drink from a pail, similar to calves. Initially the foal should be fed at 5-10% of its body weight in the first day, and then increase to 20-25% of its body weight by day 10. Solid feeds can be introduced early, as the foal would typically begin to ingest feed in imitation of its dam after only one week of being born. Milk replacer pellets are available, and can help supplement the foals’ initial liquid diet.   Foals can be weaned from this liquid diet by 10-12 weeks of age. Most importantly, some sort of companion should be found for the foal. Often orphan foals develop undesirable behaviors as they have no guidance from a mature horse as to what constitutes appropriate social behavior. Typically, orphaned foals view humans as their peers, which may result in some rather inappropriate rough play!
    With the exception of extremely early loss of the dam for a variety of reasons (death, injury, sales, etc.) most managers choose to wean foals between three and six months of age. In the feral state, foals typically are self weaned by 35 weeks of age or between eight and nine months. At five months all foals spend 50-70% of their day consuming solid feed, compared to about 2% of the day suckling. Mare’s milk production also begins to drop off by three months of age, at which time foals are consuming a high percentage of natural feeds through grazing, hay or concentrates.  It is advantageous to introduce the foal to the feeds it will be consuming post-weaning to ensure an easier and more stress-free transition. This will also help prevent fluctuations in growth rates that may place the foal at risk for developing developmental disorders.
    After insuring that the proper diet is being fed (see previously related articles concerning protein, energy and minerals for growth), the management system used is important to consider. Foals weaned in isolation (such as confined in a box stall) show more incidences of stereotypies (such as weaving, cribbing and wood chewing) and are more vigilant (less time standing relaxed) than foals weaned in pairs. Foals weaned in stalls also show more abnormal behaviors such as stall licking, kicking, rearing and pawing than weanlings weaned in a paddock. Even horses stabled for the first time as two year olds exhibited much less aberrant behavior and were more relaxed when stalled in pairs versus singularly.
    Therefore the ideal management system would wean the foals with a counter-part, rather than in isolation. For example, at our facility we wean the foals by removing the dams, with foals remaining in the same pasture and with the same herd mates with which they have been raised. This results in very little stress (at least as exhibited by vocalizations and seeking of their dam) which is frequently resolved within two days post weaning.   Even in this system we wean in pairs, whether or not this actually relieves stress for the weanling. If raising only one foal, it is advisable to seek out an older quiet pasture mate, or even to find another youngster to raise with it. Many horse owners find themselves in a similar situation and may be willing to board another weanling or send theirs as a companion.
    Alternative strategies include gradual weaning, in which the mare and foal are separated, but are allowed all behaviors except nursing. Typically this is done over a fence that the foal simply cannot nurse through. After one week, the mare is removed completely. Foals weaned in this manner, exhibit less stress and have lower levels of cortisol (a stress hormone) than foals which are weaned abruptly. However, these foals are no different than abruptly-weaned foals after two weeks. The advantages to this system may simply be a lessened possibility for injury or disease.
    Weaning stress may also make the foal more susceptible to diseases. Because of this, be sure that the foal is in good health prior to weaning (we typically have vaccinated the foal and ensured a high immune status prior to weaning) and there are no undo stressors. For instance, plan the time of weaning for when the climate is not too adverse (either too hot or too cold/wet).   Because the mare and foal may show high stress and try to re-unite, check that the facilities used for weaning are extremely safe. Expect that maiden or younger mares may exhibit a longer period of time in which they still call for or seek out their foals. Halter breaking is not advisable right at the time of weaning either, as the foal is already stressed and more reactive. Ideally foals are handled from birth, which can lessen the stress of procedures often introduced at this time (vaccinations, deworming, farrier care, etc).
    Care of the mare is simple, with usually a decrease in ration quality or quantity from that received as a lactating mare. Although her udder will fill initially, it is important to not milk the mare, as this will only further stimulate lactation. The udder should become soft within a week of weaning.   She can then be returned to her pre-foal life, whether that is as a riding horse, a gestating mare, or simply a mare of leisure.

    By thinking through the weaning system and the safety and nutritional needs of both mare and foal, the stress of “growing up” for the foal can be greatly minimized.

  • Lipid Nutrition: Part 4, Omega-3 Fatty Acids

    Written By Dr. Kris Hiney
    In previous articles we have discussed the many benefits of feeding fats to horses. Typically these fats in feeds are vegetable oils, or even occasionally animal fats. We have not yet discussed specifically the type of fat in the diet. However, researchers in human and animal medicine have much information supporting the idea that specific types of fatty acids can provide numerous health benefits. This month we look at the science behind Omega-3 fatty acids and begin the process of understanding the terminology used.
    Omega-3 fatty acids
    So what makes Omega-3 (or “n-3”) fatty acids so unique? Quite simply, it’s just the location of the double bonds which occur between the carbons in the fatty acid chain. The location of these bonds are what provide these fatty acids with their naming system.  Omega-3 fatty acids have the last double bond placed three carbons from the methyl end of the carbon chain, which is the opposite end from the attachment to the glycerol backbone in a triglyceride. Compare this to the Omega-6 fatty acids (or “n-6”), which have their last double bond six carbons in from the methyl end. This simple change in location of a double bond can have tremendous impact on the metabolism of these fats in the body.
    Essential fatty acids
    Previously we mentioned that horses must ingest certain fatty acids in their diet as they do not have the capability of synthesizing them in great enough quantities. These include linoleic acid and linolenic acid. Both of these fatty acids are 18 carbons long but differ in the number and placement of the double bonds.  Linolenic acid has three double bonds with the last one placed three carbons from the methyl end.  Thus, it is an Omega-3 fatty acid.  Linoleic acid has two double bonds, with the last double bond six carbons from the methyl end and is an Omega-6 fatty acid. These two fatty acids represent the essential fatty acids that horses must consume. These fatty acids do occur in forages and concentrates such as corn and oats, just in smaller quantities than we think about in more fat rich feedstuffs. Typically there will be more Omega-3 fatty acids in forages, especially pasture grasses, while grains will contain more Omega-6 fatty acids.
                  Linoleic Acid Molecular Diagram               Linolenic Acid Molecular Diagram
    The horse, as well as humans, must consume these fatty acids as we both lack the necessary enzymes to build these structures on our own. However, we do possess the enzymes needed to elongate these fatty acids to more complex fatty acid structures.  These elongation enzymes are shared by both linoleic and linolenic acid in their metabolic pathway. Their products in turn can be used to synthesize a whole host of biologically active compounds.  Linolenic acid can be elongated to eicosapentanoic acid or EPA, a twenty carbon fatty acid with five double bonds, and docosahexaenoic acid or DHA, a 22 carbon fatty acid with 6 double bonds, as well as others. Both EPA and DHA are Omega-3 fatty acids, due to their origin from an Omega-3 fatty acid. Linoleic acid is elongated to arachidonic acid, a twenty carbon fatty acid chain with four double bonds which is, of course, an n-6 fatty acid.   These fatty acids can be used to synthesize eicosanoids, which are biologically active lipids.
    Eicosanoids have hormone-like activity which is typically mediated locally within a tissue. These include prostaglandins, thromboxanes and leukotrienes.   These compounds differ by their structure and perform a host of activities within the body. All of these compounds are necessary for normal bodily function, but an imbalance can contribute to a disease state. Prostaglandins can effect smooth muscle contraction, vasodilation, inflammation, pain, and fever, as well as gastric acid and mucus secretion. Leukotrienes are released during the inflammatory process and can contribute to inflammation and bronchoconstriction. While their role may be to aid in healing the damaged tissue, overproduction of leukotrienes can contribute to asthma or allergic reactions. Finally, thromboxanes cause the aggregation of platelets and constriction of blood vessels. Again, all of these compounds are part of normal bodily function, but their potent effects can contribute to the diseased state.
    So how do Omega-3 fatty acids fit into this story of thromboxanes and leukotrienes? When animals ingest greater quantities of Omega-3 fatty acids, these fatty acids can displace arachadonic acid in the cell membrane. Thus, there is less arachadonic acid available to be released and formed into eicosanoids.   Increased linolenic acid also decreases the amount of linoleic acid which is elongated simply due to a competition for the same enzymes. The elongation products of linolenic acid and subsequently EPA may also directly counter act some of the inflammatory products of arachadonic acid metabolism. Thus increased consumption of Omega-3 fatty acids may aid in decreasing inflammation in the diseased state.
    Feeding Omega-3 fatty acids may be helpful for horses which may have chronic pain or inflammation. Traditionally horsemen have used NSAIDS, or Non-Steroidal Anti-Inflammatory DrugS, to manage pain and inflammation. When we provide NSAIDS these compounds act by blocking the activity of enzymes which cause the release of inflammatory agents.  However, NSAIDS are not specific and block the activity of both cox-1 and cox-2. These enzymes are essential in the conversion of arachidonic acid to progstaglandins.  Cyclo-oxygenase 1 unfortunately is also intimately involved with the formation of thromboxane in platelets and in gastromucosal integrity. It is the inhibition of cox-1 which leads to the formation of ulcers in horses which have long term NSAID administration. However, many specific cox-2 inhibitors have been produced (Celebrex® and Vioxx®).
    Sources of Omega-3s for horses
    Compared to humans, it may be harder to increase the consumption of Omega-3 fatty acids in horses, but not impossible. Typically the greatest concentration of Omega-3 fatty acids is found in marine fish. Certainly fish oils have been fed to horses, but there may be limits in the acceptability of fish oil by the horse. Flaxseed, however, is also an excellent source of Omega-3 fatty acids, has a slightly sweet, nutty, whole-grain flavor and aroma, and is readily accepted by horses. Many flax products are now offered to the horse owner.  Increasing consumption of fresh grass will also boost the Omega-3s in your horses’ diet.
    Next month we continue to look at Omega-3 fatty acids in the horse’s diet and examine some of the available literature concerning their effects in the horse.

  • Lipid Nutrition: Part 3, Benefit of Fats - Aid for Tying Up

    Written By Dr. Kris Hiney

    Last month we discussed the potential performance-enhancing benefits of feeding fats to exercising horses. These included a lowering of the thermal load on the horse, increasing its aerobic capacity, and perhaps even increasing their anaerobic energy stores in the form of muscle glycogen. Clearly, feeding fat has many advantages for the average horse.  Fat can even be used as a nutritional management technique for horses that may suffer from repeated bouts of tying up. This month we will examine two particular types of muscle disorders which may actually benefit from the addition of fat to the diet.
    Tying up in horses is usually seen as stiffness in the back or hindquarters, reluctance to move, cramping of the muscles or muscle fasciculation’s, profuse sweating, and may be accompanied by head nodding or pawing. The horse is extremely uncomfortable and should not be forced to continue to exercise.
    Tying up syndrome may have a multitude of causes. Horses may tie up due to electrolyte imbalances from prolonged exercise or sweating, or even if they have HYPP. However, some horses may chronically tie up, usually after they have been given a period of rest. Traditionally this syndrome was referred to as Monday morning sickness or Azoturia. It was seen in work horses which would experience muscle cramping soon after beginning work following a weekend of rest. However, now we know much more about this disease, its underlying causes, and its treatment.
    Horses which tie up chronically typically fit into separate breed types. In Thoroughbreds, this is commonly seen when the horse is already fit, and may be under a period of stress. It also occurs following time off or rest. Thoroughbreds typically have a syndrome referred to as “recurrent exertional rhabdomylosis, ” or RER. This disease is also seen in Arabians and Standardbreds, but less frequently than in Thoroughbreds. The underlying cause in these horses is that the calcium channels in the muscle do not work properly.  The release of Ca results in muscle contractions following nerve stimulation. However, in these horses, the threshold of muscle contraction is due less to the abnormalities in the calcium channels.
    Another disorder which is frequently seen in stock horse breeds and draft horses is related to storage of muscle glycogen. This disease, characterized by abnormal accumulations of glycogen in the muscle, is referred to as “polysaccharide storage myopathy,” or PSSM. Owners may initially not even know their horses have this disease, as the average age of first clinical symptoms is 6 years, with a range from 1 year of age to 12 years. Horses with PSSM have increased insulin sensitivity, combined with an abnormally high rate of activity of the enzyme which produces glycogen. When presented with glucose from nonstructural carbohydrates in the diet, these horses rapidly clear glucose from their blood and store it in the muscle. Due to their abnormal metabolism, they also seem to be unable to properly mobilize their own lipid stores. Ironically it is during aerobic exercise that these horses experience clinical symptoms, usually within 20 minutes of the beginning of exercise.
    Dietary management
    Although PSSM and RER horses have different disorders which lead to their tying up, they do share similarities in their management. Confinement without exercise should be avoided in these horses. If they do need time off, turn out is a must. However, if your horse merely stands at the gate waiting to come back in, alternative strategies should be developed. This could include lunging or providing a more active buddy which will encourage your horse to move around.
    The diet of the horses should be changed, with more stringent requirements for the PSSM horse. Grass hays should be used with a low content of non-structural carbohydrates, ideally under 12% of the diet for the PSSM horse. For RER horses, a goal for the overall diet should be less than 20% of their caloric intake as non-structural carbohydrate.   Traditional horse grains should be avoided, especially those containing molasses. Rather, they should be replaced with low starch, high fat concentrates, or, even, just add vegetable oil to their grain.  Frequently the PSSM horses, which are usually easy keepers, can meet their digestible energy requirements by forage alone, but more heavily exercising horses may need fat to supply their calories. In addition, clinical signs of PSSM may not resolve unless fat is added to the diet.
    Why does fat help?
    For the horse with PSSM, adding fat to the diet gives the horse an available source of long chain fatty acids that can be metabolized during exercise. Remember that these horses do not seem to be as able to mobilize their own lipid stores due to abnormal feedback from glucose metabolism. In addition, feeding fat may help these horses adapt to using fat for fuel during aerobic exercise and help to prevent episodes of tying up. However, caution must be used with these horses to avoid obesity. While RER horses don’t have a glycogen disorder or have an inability to efficiently use fat, addition of fat to the diet of these horses also appears to be helpful. Presumably this may be due to the calming effect of fat in the diet, which may make these horses less reactive. As their tying up bouts are frequently associated with times of stress (when the horse is nervous or excited) it may just be a shift in behavior which helps prevent their tying up.
    Bottom Line
    If your horse suffers from one of these diseases, it can be managed with diet and exercise. Avoid diets high in nonstructural carbohydrates, supplement the diet with fat, and be sure to balance properly for minerals and vitamins. Do not neglect these horses in their stall – regular exercise is key! With careful management, your horse can lead a normal, pain free life.

    Next month: The benefits of Omega-3 fatty acids in the horse’s diet.

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