Lipid Nutrition: Part 4, Omega-3 Fatty Acids

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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

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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.

Lipid Nutrition: Part 2, Performance Benefits of Fat

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Written By Dr. Kris Hiney
Last month we discussed the usefulness of fat in the equine diet, as well as some examples of typical feeds which contain fats. Fats are an easily digestible source of calories which can readily supply the extra energy that performance horses may need. Fat may lower the heat load on the horse compared to traditional diets, which may aid in performance in hot climates. Finally, fat may even help calm the horse compared to when they are fed high starch diets. But is there any other reason to feed fats that may help you get to the winner’s circle?
Fat Metabolism
Lipid2_skeet.bmp When horses are fed fat in the diet, their body responds by increasing the number of enzymes that are involved with lipid metabolism. These include the enzymes needed to remove fat from the bloodstream and enter muscle or adipose tissue, and those that ultimately oxidize the fatty acids. Feeding fat to horses results in a lowering of plasma triglycerides which is believed to be caused by a decrease in synthesis of triglycerides in the liver. The horse becomes more efficient at utilizing dietary fats for energy, rather than needing to use carbohydrate or protein.  This adaptation has repeatedly been shown to take at least three weeks after the change in diet.  Complete adaptation may take as long as 2-3 months.  Therefore, if switching your feeding regimen, don’t expect to see instantaneous results.
Exercise and Fuel Sources
rice branWhen fatty acids are oxidized in the body for fuel, their final metabolic pathway involves the Tricarboxylic cycle (TCA)* or Kreb’s cycle. This cycle is dependent on oxygen (through its connection to the electron transport chain) in order for it to work.   The TCA cycle supplies the bulk of Adenosine Triphosphate (ATP)** for horses when they are working aerobically, or at lower intensities. Technically, aerobic work is at a low enough intensity that the requirement of ATP can be met by the slower metabolic pathway of the TCA cycle.   At low intensities of exercise, fat typically supplies up to 50-60% of the calories needed.  All dietary energy sources – fats, carbohydrates and protein – can be utilized in aerobic metabolism, provided there is sufficient intake of oxygen.   That means that the horse’s heart and lungs can keep up in the race to deliver oxygen to the tissues. However, when the horse’s muscles are contracting faster or harder than the ability of the cardiovascular system to keep pace, they then enter into anaerobic metabolism. The horse must then switch to a different supply of fuel, primarily carbohydrate metabolism. They are simply working too hard for the aerobic system to keep up with the demands of the muscles for ATP. Therefore, horses undergoing intense exercise, or sprinting type of activities, must rely on their carbohydrate stores for energy. These include blood glucose, liver and muscle glycogen, and the body’s ability to perform gluconeogenesis (make glucose from other sources).
Can Fat Save Glucose?
It is presumed that due to the adaptation of the horse to become more efficient at fat metabolism, they are less reliant on their carbohydrate stores (blood glucose, muscle and liver glycogen) to supply their energy needs.    This should allow the horse to work longer before turning to carbohydrate metabolism. This may be advantageous for two reasons. One is that carbohydrate stores in the body are much more limited in comparison to lipid stores, and two, usage of carbohydrate through anaerobic metabolism can result in the production of lactic acid.  This may contribute to the onset of fatigue, due to depletion of energy sources or the accumulation of lactic acid. Therefore, fat fed horses may have some advantage in their resistance to fatigue.
Most studies of horses fed high fat diets have reported an increase in resting muscle glycogen stores. However, there have been a few reports which have shown an opposite effect of lowered muscle glycogen. In these studies, the horses were either untrained or receiving low intensity exercise. In studies which exhibit an increase in resting muscle glycogen, the horses received more intensive training, including sprinting exercise. This may be the key in seeing a response to the fat added diet. In addition, the amount of fiber and starch in the rest of the diets differed between studies, which also clouds interpretation. If horses do have higher glycogen stores at rest, it is unclear if this results in an increase in glycogen utilization during exercise. Some researchers found an increase in glycogen utilization while, again, others have found no change in glycogen metabolism during race simulations or long term sub-maximal exercise.   But would an increase in glycogen utilization improve performance? Again results are mixed. Horses fed 12% fat for four weeks improved their run time to fatigue in a high intensity exercise bout on a treadmill. Others have found increased performance in sprinting exercise and in a simulated cutting event, while some have found no clear advantage to feeding fat in improved performance.
Is Anything Consistent?
Lipid2_SkeetsSugarNSpice.jpgIn studies looking at blood metabolites in exercising horses fed a fat added diet, some consistent results have been seen. Feeding fat does decrease the exercise related drop in blood glucose. This is seen simultaneously with an increase in serum triglycerides and free fatty acids. Presumably these horses have indeed shifted toward a more efficient utilization of fatty acids during exercise, sparing their glucose stores. This seems to be supported by data which shows that horses on fat supplemented diets have a higher blood pH during exercise versus non-supplemented controls. The above effects are seen at lower intensities of exercise.  When the horse increases its ATP demand, they will need to draw more from anaerobic metabolism and must shift to carbohydrate usage.
So with all of these conflicting results, what should you believe? It is clear that feeding performance horses fat rather than carbohydrates is a much healthier alternative. High carbohydrate diets carry with them the risk of laminitis, colic, ulcers and insulin resistance. As of now, no negative effects of feeding fats to horses have been found. The potential benefits are many, including a potentially calmer horse, a decrease in reliance on blood glucose (at least at lower intensities), and a possibility of increased performance in anaerobic activities. With little to lose, and benefits to gain, it is no wonder fat added diets are so popular in the equine industry.
Next month – The usage of fat added diets in metabolic diseases.
* TCA – Tricarboxylic cycle, also known as Citric acid Cycle, has been described as the “central metabolic hub of the cell”. A sequence of reactions taking place in mitochondria where acetyl units attached to CoA are degraded to carbon dioxide and the electrons produced transferred to the coenzymes NAD⁺ and FAD.
**ATP – adenosine triphosphate, an adenine nucleotide used as the energy currency in metabolism. The free energy released when ATP is hydrolyzed is used to drive reactions in cells.

Lipid Nutrition: Part 1, Feeding Fat to Horses

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Written By Dr. Kris Hiney

This month we begin a series looking at the value of incorporating fat into the diets of our horses. We will discuss how fat is digested and handled in the equine, the types of fats fed to horses, and the many beneficial effects that can be realized through the addition of fat to the diet of our horses.
Fat digestion
Feeding fat to horses became more popular in the 1980’s and has continued to see an increase in the share of the feed market. Most feed stores now offer a selection of fat added feeds, or specific fat supplements. While one may not think of horses as a species that routinely consumes fats, horses can handle fats quite well in their digestive system. Lipid digestion occurs primarily in the small intestine, via the production and release of digestive enzymes and bile salts. As the horse does not possess a gall bladder, bile salts are continually released into the intestine. Fats that are added to the diet in the form of oils or fat are very well digested, typically up to 90%. Comparatively, naturally occurring fats in the diet (muchsmaller percentages of fat are actually present in forages and cereal grains) are less well digested, between 40-50% for forages and 50-75% for grains. Addition of fat to the diet does not alter digestibility of other components of the diet, unless the amount of lipid exceeds 22% of the total diet. However, typically this is not a concern, as acceptability and practicality of such diets make them improbable. There are some published studies which do report a lowered fiber digestibility in horses fed soy oil, however, these horses were also rapidly introduced to the fat in the diet. Ideally horses should be gradually transitioned onto a higher fat diet in order to adapt and increase the necessary fat digesting enzymes in their system. This should take place over one to two weeks, depending on how much fat is being added to the diet.
Acceptability
Palatability of fat added feeds is quite good, especially if supplied by vegetable oils. Typical vegetable oils include corn oil, soybean oil, canola oil and linseed oil. Horses will consume animal fats and fish oil, but typically not as readily as vegetable sources. The acceptability of fats in the diet is good up to about 15% of the diet. After that consumption rates do drop off.   There are commercially available feeds which have a higher percentage of fat, but these are typically extruded feeds which are more acceptable. Again, these are fed at a smaller percentage of the diet, such that 15% of the total diet is never exceeded. When feeding fat added feeds, it is important to realize that they do have a shorter shelf life than non-fat added feeds. This is due to the peroxidation that takes place, especially in polyunsaturated fats. These feeds then develop an off taste and flavor. If your feed smells rancid, it is best to avoid feeding it. Storing feeds in a cool, dry area will help to preserve their shelf life as well. These feeds often have anti-oxidants added to them to aid in protection against oxidation. Some products, such as Omega Horseshine, specialize in stabilized fats with a prolonged shelf life, up to 12 months.
Benefits to feeding fat
The most readily realized benefit to adding fat to the diet is in order to help meet the animals’ caloric needs. Fat is very readily digestible as already stated, and is much more energy dense than other components of the horse’s diet. Compared to proteins and non-structural carbohydrates which contain 4 Mcal/kg, fat is 2.25 times more energy dense at 9 Mcal/kg. Thus inclusion of fat allows a horse to gain weight much more readily or conversely, need to consume less feed to obtain the same amount of calories. Lowering the total amount of feed may be advantageous to horses working in hotter climates as it lowers the total heat production associated with digestion. Furthermore, fat itself is a relatively cool feed, as there is no fermentation and thus heat production associated with its digestion. Replacing high energy cereal grains with fats is an additional benefit, as less digestive risk is associated with feeding fats. Horses fed large amounts of cereal grains over time are at greater risk for ulcer formation, potential development of  stereotypies such as cribbing, laminitis and insulin resistance. This does not mean that starch needs to be eliminated from normal equine diet (the exception are horses with metabolic disorders which render them more sensitive to starch in the diet), but fat can make a very useful substitution. Another benefit to replacing starch in the diet with fats appears to be a calming effect on the horse. Horses fed fat added diets compared to typical sweet feeds have been found to be  less reactive to novel stimuli. Therefore, there is a second reason that fat is a cool feed, not only does it produce less heat during digestion, but it appears to “cool” the hot minded horses. Now obviously it is not a substitute for proper training and exercise!
Essential fat and fatty acids
 Horses must also consume some amount of fat for normal body functio. Lipids are used in the synthesis of steroid hormones, and  all of the fat soluble vitamins (ADEK) are contained within the fat portion of the feed.  However, the exact amount of fat necessary in the diet of the equine has not been determined. Additionally, the horse, like all other animals, must consume its essential fatty acids, linoleic (18:2 omega 6) and linolenic acid, (18:3, omega 3) from the diet. They lack the enzymes necessary to produce these particular fatty acids within the body. Important sources of these fatty acids include pasture grasses, canola oil and linseed oil or flax seed.
Practical guidelines for feeding fat to horses.
As stated previously, most fats in horse feed actually come from vegetable oils. The oils can either be extracted and purified, or the actual oil seed can be fed. Examples of common oilseeds include cottonseeds, soybeans, canola and flaxseeds. If these seeds are referred to as meal, such as cottonseed meal, the fat has already been extracted and then they are being fed typically for their high protein content, not for additional fat. Thus, feeding linseed meal provides a much diferent percentage of fat compared to feeding flax, despite it being the product of the same plant! Pure vegetable oils can also be fed to horses as a top dressing to their feed. One cup of vegetable oil provides as many calories as 1.5 lbs of oats or 1 lb of corn, allowing you to decrease the amount of cereal grains fed.   If feeding a fat added feed, typically these feeds will allow you to feed less concentrate for a similar work class of horse, due to the increased caloric density of the feed. The benefit of feeding a fat added feed, rather than top dressing, may be in its simplicity, as well as the fact that these rations are rebalanced with the knowledge that the horse may consume total less feed. However, if you are just top dressing fat to existing feeds, and thereby decreasing the total amount of feed, be sure that the total diet still meets the horse’s other nutritional requirements.
In the next part, we will discuss the potential for performance enhancing effects of feeding fat beyond merely an easy way to supply calories.