The term “metabolic horse” is more and more commonly heard in the equine industry due to a high prevalence of horses with conditions such as Equine Metabolic Syndrome (EMS), Pars Pituitary Intermedia dysfunction (PPID), Polysaccharide Storage Myopathy (PSSM), Insulin Resistance (IR), obesity and laminitis. “Metabolically challenged” simply means that the horse is in a physiological state where certain metabolic functions (e.g. nutrient metabolism, hormonal and immune function) are compromised, possibly leading to a variety of health issues. Although a metabolic disease is what typically comes to mind when thinking of metabolically challenged horses, there are a variety of other, more subtle, conditions that may induce such a state. For example aging horses, those recovering from surgery or horses undergoing some form of stress. A clear understanding of metabolic states in which the horse may need specialized management and nutrition is important to avoid health problems.
COMMON METABOLIC ILLNESSES IN HORSES
- Insulin resistance: is a condition where the body’s sensitivity for the actions of the hormone insulin is decreased. This hormone is important for the uptake of blood sugar (glucose) into tissues that utilize it for energy and is a key regulator of many other physiological functions. A typical symptom of this condition is a high level of insulin in the blood in attempt to compensate for decreased sensitivity. This abnormality can lead to various other problems, such as inflammation and development of laminitis and is a common underlying feature of many metabolic disorders.
- Laminitis: is a severe and often detrimental hoof problem where the inner layers of the hoof wall become inflamed. If allowed to progress or in case of acute laminitis, this can lead to detachment of the hoof bone from the hoof wall (“founder”). This is very painful and often difficult to treat, in particular in the advanced stages which often result in euthanasia. Acute laminitis is a common secondary complication in case of ingestion of large quantities of grain (starch/sugars), consuming grass in early spring or late fall that is high in non-structural carbohydrates (fructans) or in events of colic. However, chronic laminitis is also commonly associated with metabolic and hormonal disturbances such as in case of obesity, IR, EMS or PPID.
- Obesity: is a common and prevalent issue in the equine population and yet many owners fail to recognize its important relevance to the overall health of the horse. Fat tissue was once considered to be a “storage” site for excess energy, however it is now well known that fat is an “active” tissue and is involved in many different metabolic functions. For example, it is able to secrete molecules that are involved in inflammation and therefore obesity is now called a “low grade chronic inflammatory state”, which in turn can cause other metabolic disturbances such as IR and abnormal fat metabolism. Even though some breeds may be genetically predisposed to develop obesity (the so called “easy keepers”), it is almost always a combination of continuous dietary energy intake above requirement and a lack of exercise.
- EMS: is a condition characterized by three features: generalized obesity with abnormal fat distributions (fat depositions in typical places such as the tail head, behind the shoulder and a typical “cresty” neck), known or suspected IR and some form of foot abnormalities with a predisposition to laminitis. Although some breeds are genetically predisposed (“easy keepers”), environmental influences still have the biggest impact on whether or not the horse will eventually develop EMS.
- PPID: is a disease most commonly seen in old horses and is caused by neuronal defects in the intermediate lobe of the pituitary gland. This gland is responsible for the secretion of many essential hormones and therefore dysfunction leads to metabolic disturbances. Typical symptoms may include a long, curly hair coat, muscle wasting, increased thirst and frequent urination, abnormal fat deposits, hoof problems with increased risk of laminitis and IR.
- PSSM: is a clinical condition where a dysfunction of the enzyme responsible for glycogen synthesis (storing energy) in the muscle can lead to a variety of problems such as poor performance, loss of athletic function and can even become life threatening. In some breeds, this condition is associated with increased insulin sensitivity.
CONSIDERATIONS WHEN FEEDING THE METABOLICALLY CHALLENGED HORSE
- Non-structural carbohydrates (NSC)Even though NSC (sugars and starch) are a major energy source, it is not advisable to feed large quantities of it to the metabolic horse without risk of aggravating the condition, in particular relative to obesity and insulin metabolism. Since insulin levels are affected by glucose concentrations in the blood, being cautious with dietary administration of NSC is very important. NSC will mostly be digested in the foregut and are absorbed as glucose. Feeds that include grains such as corn and barley, which are high in NSC, will result in a high blood glucose level after a meal and should therefore be avoided. It is also not advisable to feed a lot of sweet feed, since it typically contains molasses (rich in sugar).In addition to forage, feeds and ingredients lower in NSC such as wheat bran, beet pulp, soybean hulls are more appropriate for certain types of metabolic horses.
The equine digestive system has developed to obtain most of its energy through microbial fermentation of fiber in the hindgut. Therefore it is advisable to ensure forage forms the foundation of every horses’ diet. In metabolic horses, where there is often a problem with obesity, forage can easily be the only form of feed if all nutrient requirements can be met. It is however important to inform yourself about the nutritive value of the forage (hay analysis!) because some may still contain considerable amounts of NSC. For example cool season grasses (timothy, orchard) are often higher in NSC than warm season grasses (bermuda, bahia). Furthermore, older, “stemmy” grass/hay will be lower in NSC and might therefore be more useful in obese/EMS horses compared to young, fresh hay. Older hay can also be fed in larger amounts to prevent boredom while not exceeding energy requirements.Soaking the hay (min. ~12h) might reduce some of the NSC levels in the hay, however, other valuable nutrients may be lost as well.Caution should be used when turning the horse out on pasture since it is difficult to control NSC and calorie intake, in particular for overweight horses. For example, grazing on early spring/late fall pasture, high in fructans, is a big risk factor for metabolic issues and should therefore be avoided. Restricted grazing for shorter periods and at certain times of the day/year (when NSC are lowest) or the use of a grazing muzzle may be a good option. However, in many cases (obesity, EMS, IR, laminitis) horses may have to be kept off pasture completely and be supplied with hay in a dry lot area. In case of metabolic horses that are not obese (PSSM, PPID) feeding highly digestible fiber sources such as non-molassed beet pulp and rice bran (higher in fat) are a good option to give extra calories. Additionally, the daily amount of forage for these horses can be increased to supply extra energy.
- Low starch, high fiber fortified feeds
As the prevalence of metabolic horses rose so did the demand of the equine industry for feeds safe to be consumed by these type of horses. The feed industry responded by manufacturing concentrates low in starch and sugars and high in fiber. If a forage-only diet is not able to meet requirements or in cases where horses are unable to consume the necessary quantities of forage (teeth issues, older horses) these concentrates are of particular interest (Cavalor FiberForce). Most high quality fortified feeds are formulated with easily digestible fiber ingredients to support healthy gut function and provide necessary energy without overloading the digestive system (Cavalor Strucomix). Additionally, some may have beneficial supplements (vitamins, minerals, herbs, pre-and/or probiotics) which can further improve the health of the metabolic horse. In general, it is advisable to divide daily concentrate portions into multiple, smaller meals a day to lower the glucose and insulin responses.
- Low starch, high fat fortified feeds
In addition to carbohydrates, fats can serve as an excellent energy source for the horse. In contrast to NSC, horses are less sensitive to higher fat concentrations in the feed and are able to tolerate and digest it well. With a lower risk of digestive upset or metabolic disturbance of glucose and insulin levels, fat is often considered a “safer source” of energy. In some metabolic horses where obesity is not a factor (PSSM, some older horses, PPID), fat can be a substitute when extra energy is needed in the diet. However, caution should be given to the quality of the feed as fat may oxidize and cause the feed to become rancid. Additionally, there is little scientific evidence on the effects of feeding long term (several years) high fat diets, which could potentially affect liver function.Several feed companies now carry low starch-high fat feeds (Cavalor FiberForce), however, if added topically on the feed (oils), horses will need to be adapted slowly to about ½ to 1 cup a day (depending on the amount of energy needed) over several weeks.
- Ration balancers and supplements
Even though we want to avoid a diet high in NSC it is important that all other nutrient requirements are met. In particular vitamins and minerals are important to support healthy metabolism and immune function. When feeding a high quality complete feed, supplementation may not be necessary. However, in case of a forage based diet, it is important to ensure all other nutrient requirements are met. This can be done with supplements or ration balancers (Cavalor 50/50, Cavalor WholeGain), which are low in energy but highly dense in all other nutrients to fill in the gaps where forage leaves off.Many supplements are available and marketed as being beneficial in metabolic disorders including magnesium, chromium and cinnamon. However, most evidence is anecdotal rather than scientific. Promising results however, have been obtained from studies supplying prebiotic fibers such as psyllium and fructooligosaccarides (Cavalor Vitaflor 365, also present in Cavalor Strucomix and Cavalor FiberForce), which significantly improved insulin sensitivity and/or reduced glucose and insulin responses. Good quality supplements to support immune function and overall health may always be beneficial as well (Cavalor Hepato Liq, Cavalor Digest, Cavalor Resist).
When managing the metabolic horse it is important to consider each case individually and talk with a veterinarian to make a correct diagnosis of the condition and discuss any nutritional strategies.
In any case, forage should be the foundation of the diet which can then be supplemented if needed. Know the nutrient value/quality (hay analysis!) of your hay or pasture to make sure you feed right at, or slightly under (when feeding for weight loss), requirements.
Be careful with pasture turn-out in particular at certain times of the year. Keeping the horse in dry lots with hay, may be the better option, in particular in the case of laminitis or weigh loss programs.
Avoid high levels of NSC but make sure all nutrient requirements are met either with a high quality low starch – high fiber/fat feed (Cavalor FiberForce, Cavalor Strucomix) or a ration balancer (Cavalor 50/50, Cavalor WholeGain), to support and improve healthy metabolism.
In addition to an appropriate feeding program, physical activity has scientifically shown to improve many metabolic disorders and SHOULD be part of a management program in metabolic horses if possible. Close monitoring of weight and body condition score will help to maintain the horses at a healthy weight or monitor weight loss if needed.