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Equine Nutrition - be wary of false feeding economies

Article by Louise Jones

Equine Nutrition - feeding a horse on a budget

Many horses, especially performance horses, breeding stallions, and broodmares at certain stages of production, require additional calories in the form of hard feed. Whilst in the current economic climate, with rising costs and inflation, it might be tempting to look at lower cost feeding options; in reality, this could be a false economy. When choosing a feed, in order to ensure that you are getting the best value for money and are providing your horses with the essential nutrients they require, there are a number of factors to consider.

Quality 

The ingredients included in feed are referred to as the raw materials. These are usually listed on the feed bag or label in descending order by weight. Usually they are listed by name (e.g., oats, barley wheat) but in some cases are listed by category (e.g., cereals). Each raw material will be included for a specific nutritional purpose. For example, full-fat soya is a high-quality source of protein, whilst cereals such as oats are mainly included for their energy content, also contributing towards protein, fibre and to a lesser degree, fat intake.

Equine Nutrition - feeding a horse on a budget

Waste by-products from human food processing are sometimes used in the manufacture of horse feed. Whilst it is true that they do still hold a nutritional value, in most cases they are predominantly providing fibre but contain poor levels of other essential nutrients. Two of the most commonly used by-products are oatfeed and distillers grains. Oatfeed is the fibrous husks and outer layer of the oat and it mainly provides fibre. Distillers grains are what is left over after yeast fermentation of cereal grains used to produce alcohol. The leftover grain is dried and used in the feed industry as a protein source. Distillers grains can be high in mycotoxins, which are toxic chemicals produced by fungi in certain crops, including maize. Furthermore, despite being used as a protein source, distillers grains are typically low in lysine. As one of the first limiting amino acids, lysine is a very important part of the horse’s diet; horses in work, pregnant mares and youngstock all have increased lysine requirements.

Manufacturing equine feeds

Another ingredient to look out for on the back of your bag of feed is nutritionally improved straw, often referred to as “NIS”. This is straw that has been treated with chemicals such as sodium hydroxide (caustic soda) to break down the structural fibre (lignins) and increase its digestibility. Straw is a good example of a forage which contains filler fibre; in fact, you can think of it as the horse’s equivalent of humans eating celery. Traditionally, oat straw was used to make NIS, however many manufacturers now use cheaper wheat or barley straw due to the rising cost of good quality oat straw.  Not all companies state what straw is used and instead use generic terms such as cereal straw, which again, allows them to vary the ingredients used depending on cost and availability. 

By law, feed manufacturers must declare certain nutrients on the feed bag, one of which is the percentage crude protein. This tells you how much protein the feed contains. However, not all protein is created equal; some protein is of very high quality, whilst other proteins can be so low in quality that they will limit a horse’s ability to grow, reproduce, perform or build muscle. Protein ‘quality’ is often measured by the levels of essential amino acids (e.g., lysine, methionine) it contains. In most cases feed manufacturers do not have to list the amount of these essential amino acids; but looking at the ingredient list will give you a clue as to how good the protein quality is. Good sources of high-quality protein include legumes and soybean meal, whereas by-products often contain moderate- or low-quality protein, even though they may be relatively high in crude protein. 

Understanding more about the ingredients in your bag of horse feed will help you to assess whether they are providing good, quality nutrition. Feeds containing large proportions of lower quality ingredients will obviously be cheaper, but this could compromise quality of the products. The goal therefore is to ensure that the nutritional makeup of the products remains high quality and consistent. 

Cooking for digestibility 

Digestibility is a term used to describe the amount of nutrients that are actually absorbed by a horse and are therefore available for growth, reproduction, and performance. Understanding digestibility of energy sources—such as fibre, fat, starch, and sugar as well as protein, vitamin and mineral digestibility—is important when devising optimal diets for horses. 

cooking for digestibility in horse feed

Most of the energy in grains is contained in the starch; however, horses cannot fully digest starch from uncooked (raw) grains in the small intestine, which results in this undigested starch traveling into the hindgut where it will ferment and potentially cause hindgut acidosis. Therefore, in order to maximise pre-caecal digestibility, feed manufacturers cook the grain. Similarly, soya beans must be carefully processed prior to feeding them to horses. This is because raw soybeans contain a specific enzyme that blocks the action of trypsin, an enzyme needed for protein absorption.

There are various methods of cooking including pelleting, micronizing, extrusion, and steam-flaking.  This is a fine art as, for example, undercooking soya beans will not deactivate the enzymes correctly, thus resulting in reduced protein absorption. On the other hand, overcooking will destroy essential amino acids such as lysine, methionine, threonine, and possibly others.

Variation in cooking methods, and hence digestibility, can have a direct impact on how the finished product performs. Your individual feed manufacturer should be able to tell you more about the cooking processes they use to maximise digestibility.

Micronutrient and functional ingredients specification

The back of your bag of feed should list the inclusion of vitamins, such as vitamin E, and minerals including copper and zinc. A lower vitamin and mineral specification is one way feed companies can keep the cost of their products down. For example, the vitamin E level in one unbranded Stud Cube is just 200 iu/kg—50% lower than in a branded alternative.

Equine Nutrition - feeding a horse on a budget

For most vitamins and minerals, the levels declared on the back of the bag/label only tell the amount actually added and do not include any background levels provided by the raw materials. In other marketing materials, such as brochures, some companies will combine the added figure with the amount provided by other raw materials in order to elevate the overall figure. For example, a feed with 50 mg/kg of added copper may list the total copper as 60 mg/kg on their website or brochure.  Whilst it is perfectly acceptable to do this, it is equally important to recognise that background levels in different raw materials can vary and hence should not be relied upon to meet requirements. To complicate this slightly further, chelated minerals (e.g., cupric chelate of amino acids hydrate, a copper chelate) may be included. Chelated minerals have a higher bioavailability, and so a feed with a high inclusion of chelated copper may perform as well as one that has an even higher overall copper level but does not include any chelates.

Equally important is the need to verify that any specific functional ingredients such as prebiotics or yeast are included at levels that are likely to be efficacious. 

Feeding rates

Equine Nutrition - feeding a horse on a budget

Whilst the cost of a bag of feed is undeniably important, another aspect that should be considered is the amount of feed required to achieve the desired body condition and provide a balanced diet. Feeding higher volumes of hard feed not only presents a challenge from a gastrointestinal health point of view but also increases the cost per day of feeding an individual. For example, the daily cost of feeding 8kg of a feed costing £400/€460 per tonne vs 5¼ kg of a feed costing £600/€680 per tonne are exactly the same. Plus, the lower feeding rate of the more expensive product will be a better option in terms of the horse’s digestive health, which is linked to overall health and performance. To keep feeding costs in perspective, look at the cost of feeding a horse per day rather than relying on individual product prices.

Consistency 

Consistency of horse feeds

When a nutritionist creates a recipe for a horse feed, they can either create a ‘set recipe’ for the feed or a ‘least cost formulation’. A set recipe is one that doesn’t change and will use exactly the same ingredients in the same quantities. The benefit of this is that you can rest assured that each bag will deliver the same nutritional profile as the next. However, the downside is that if the price of a specific ingredient increases, unfortunately, so will the cost of the product.

On the other hand, least-cost formulations use software to make short-term recipes based on the cost of available ingredients. It will use the cheapest ingredient available. When done correctly, they will provide the amount of calories (energy), crude protein, vitamins and minerals as specified on the label. However, the ingredients will change, and protein quality can be compromised. Often feed companies using least-cost formulations will print their ingredients on a label, rather than the bag itself, as the label can be amended quickly and cheaply, should they alter the recipe.

Checking the list of ingredients in your feed regularly should alert you to any formulation changes.  Equally look out for feeds that include vague ingredient listings such as ‘cereal grains and grain by-products, vegetable protein meals and vegetable oil’; these terms are often used to give the flexibility to change the ingredients depending on how costly they are.

Peace of mind

Lab testing horses feed - BETA NOPS registered feed manufacturers

Another important issue is that some companies producing lower-cost feeds may not have invested in the resources required to carry out testing for naturally occurring prohibited substances (NOPS) such as theophylline, banned substances (e.g., zilpaterol - an anabolic steroid) or mycotoxins (e.g., zearalenone). It is true that, even with the most stringent testing regime, identifying potential contamination is difficult; and over recent years, a number of feed companies have had issues.  However, by choosing a feed manufacturer who is at the top of their game in terms of testing and monitoring for the presence of such substances will give you peace of mind that they are aware of the threat these substances pose, and they are taking significant precautions to prevent their presence in their products. It is important to source horse feed from a BETA NOPS registered feed manufacturer at a minimum. It may also be prudent to ask questions about the feed manufacturer’s testing regime and frequency of testing.  

Supplements – to use or not to use?

A good nutritionist will be able to assess any supplements that are fed, making note of why each is added to the diet and the key nutrients they provide. It is easy to get stuck into the trap of feeding multiple supplements that contain the same nutrients, effectively doubling up on intake. Whilst in many cases this isn’t nutritionally an issue, it is an ineffective financial spend. For example, B vitamins can be a very useful addition to the diet, but if provided in levels much higher than the horse needs, they will simply be excreted in the urine. Reviewing the supplements you are feeding with your nutritionist to ensure they are essential and eliminating nutritional double-ups is one of the simplest ways to shave off some expense.

Review and revise

A periodic review of your horse’s diet ensures that you’re providing the best nutrition in the most cost-effective way. This will require the expertise of a nutritionist. Seeking advice on online forums and social media is not recommended as this can lead to misinformed, biased advice or frankly, dangerous recommendations. On the other hand, a properly qualified and experienced nutritionist will be able to undertake a thorough diet evaluation, carefully collecting information about forages, concentrates, and supplements. 

Equine nutritionists and feed bag labelling

Working with a nutritionist has many advantages; they will be able to work with you to ensure optimal nutrition, whilst also helping to limit needless expenses. Some nutritionists are better than others, so choose wisely. (Does the person in question have the level of qualifications?) Bear in mind that while qualifications can assure you that the nutritionist has rigorous science-based training, experience is also exceptionally important. Ask them about their industry experience and what other clients they work with to ensure they have the right skill set for your needs. In addition, a competent nutritionist will be willing and able to interact with your vet where and when required to ensure that the health, well-being, and nutrition of your horses is as good as it can be. 

There are independent nutritionists available, but you will likely incur a charge—often quite a significant one. On the other hand, the majority of feed companies employ qualified, experienced nutritionists and offer their advice, free of charge.

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The Role Vitamins Play in the Diet

Vitamins are a key part of the diet for racehorses and although the clinical signs associated with an overt deficiency or excess of one vitamin or another are rare, we should not presume that the level of vitamins provided in the diet is optimized for performance. Horses are, generally speaking, quite tolerant of sub-clinical deficiency or excess with regards to vitamins, and the margin of acceptable intake to prevent health issues is therefore relatively wide in most cases. However, maintenance of health is a separate issue compared to optimal performance, which is the ultimate target for horses in training.

Catherine Dunnett
 (14 October 2008 - Issue Number: 10)

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Racing Power- supporting muscular effort through nutrition


The powerhouse for a horse in training is found in its large muscle mass. Whilst genetic makeup within the Thoroughbred breed has a large impact on a horse’s innate racing ability, dietary factors will also influence subsequent performance.
Dr Catherine Dunnett (01 December 2007 - Issue Number: 6)

By Dr Catherine Dunnett

The powerhouse for a horse in training is found in its large muscle mass. Whilst genetic makeup within the Thoroughbred breed has a large impact on a horse’s innate racing ability, dietary factors will also influence subsequent performance.

 There are many elements found in a racehorse’s diet that will help to support muscle function. Hydrolysable carbohydrate (sugar and starch), assisted by fermentable fibre, will help to maintain important muscle stores of glycogen (a carbohydrate fuel).  Dietary electrolytes, which are integrally involved in muscle contraction, are essential to offset electrolyte loss in sweat. Key dietary antioxidants such as vitamins E and C and also antioxidant co-factors, such as copper, manganese, zinc and selenium, are also important as part of the body’s antioxidant team which strives to reduce the formation of free radicals or reactive oxygen species, and to limit their damaging effects on the body.  Free radical damage has previously been implicated in the process of exercise induced muscle damage.

GLYCOGEN STORES MUST BE REPLENISHED FOLLOWING EXERCISE


One of the most important functions of the diet is to replenish the horse’s energy stores in muscle on an ongoing basis.    A racing ration needs to support the synthesis of glycogen to maintain the store of this important fuel, which is used in increasing amounts during exercise.  Glycogen, which consists of a large branched chain of glucose units, is stored in both skeletal muscle and the liver and it represents one of the largest potential energy stores in the body. Horses being natural athletes, have a relatively large muscle glycogen store when compared to other species.  As the glycogen content of horse muscle is influenced by the proportion of different muscle fibre types present, this means that there is a genetic influence on the overall glycogen content.   
Fast twitch fibres (Type IIb), which are found in increased numbers in talented sprinting horses, store relatively more glycogen than the slower type I and type IIa fibres.  However, both diet and training can influence the level of glycogen stored in muscle.  Exercise training for example has been reported to increase muscle glycogen content by 30-60% in horses.

Logically, diet should have a significant effect on the storage of muscle glycogen as it provides the building blocks for glycogen synthesis.  Glycogen can be synthesised efficiently from dietary starch, which is another polymer of glucose found in cereals.  Glycogen can also be produced from certain glycogenic amino acids, released from the protein content of feed. In addition, propionic acid, which is a significant volatile fatty acid produced in the horse’s hindgut during the fermentation process, can also ultimately be converted to muscle glycogen.   In terms of the day to day diet, starch is by far the most direct and most efficient precursor for glycogen and so it is therefore not surprising that cereals, which are high in starch, have been the mainstay of racing diets for many years.

In recent years we have seen the introduction of racing feeds that are lower in starch and sugar than traditional racing rations, with a greater emphasis being placed on digestible fibre and oil as energy sources. Whilst there are many health benefits attributable to this type of diet, the effect of changing the level of starch in the diet on muscle glycogen should always be considered.

MUSCLE GLYCOGEN - 
AN IMPORTANT FUEL BUT NOT THE KEY FACTOR IN FATIGUE


Muscle glycogen is a major source of energy (ATP) to working muscle during intense exercise, which is characteristic of racing.  The amount of muscle glycogen used during training or racing will depend on its rate of utilisation, which in turn is affected by the speed and duration of the exercise undertaken.  In general terms, the higher the speed, the faster muscle glycogen is broken down and used. The duration of fast exercise is normally curtailed, which limits the overall amount of glycogen used.  During slower work, although the rate of glycogen utilisation is much lower, exercise can usually be continued for a much longer time allowing more glycogen to be utilised overall (see figure 1).

Total muscle glycogen content can be reduced by about 30% during a single bout of maximal exercise in horses.  However, as muscle is a mix of different fibre types, the depletion of glycogen in individual fibres may be greater than this depending on the pattern of fibre recruitment during the exercise.  Studies, however, have shown that even the IIB muscle fibres, which use glycogen at the fastest rate, are not totally depleted of glycogen following racing.  This supports the notion that although glycogen is an important fuel source for racehorses, glycogen depletion is not the most important factor in fatigue.  However, exercise studies do suggest that power output and exercise performance can be decreased in horses where muscle glycogen has failed to be adequately replaced following a previous race or piece of hard work.  This was the conclusion drawn by Lacombe and co-workers (2001) who reported that horses with replete muscle glycogen stores were able to run for longer periods during a maximal exercise test compared to horses whose muscle glycogen level remained low following a previous exercise bout.  
Whilst there are always horses that will buck the trend, this research emphasises the need to allow a suitable period of time between races, but also between bouts of fast work and subsequent racing to allow muscle glycogen stores to be replenished.

From a practical viewpoint, I would say that the ability of a racing diet to support muscle glycogen synthesis remains important.  In contrast to human athletes, muscle glycogen replenishment in horses is relatively slow.  Following racing or a hard work, research suggests that muscle glycogen can take up to 72 hours to return to pre-exercise levels when a traditional high cereal racing ration is fed.

Certainly research carried out in the past 3 years would suggest that a high glycemic racing ration would be better placed to support glycogen replenishment more quickly following racing or hard work.  There are many factors that affect the glycemic response to feed, which in simple terms describes the relative rise in blood glucose following feeding. The starch and sugar content of a feed, however, is one of the most significant factors affecting glycemic response.  Feeds that are high in starch and sugar e.g. a high cereal-containing mix produce a greater glycemic response compared with feeds that are very low in starch and sugar e.g. a forage only ration. 
Rate of glycogen synthesis following a glycogen depleting exercise bout was significantly higher in horses fed a high glycemic diet compared to those fed a very low glycemic control diet (Lacombe et al 2004, Lacombe et al 2006).  In addition, absolute glycogen concentration in muscle was significantly higher both 48 and 72 hours following exercise in the high glycemic group compared to the control horses and muscle glycogen concentration had returned to pre-exercise levels following 72 hours.   
 
The benefit of a high glycemic diet for glycogen repletion does, however, appear to be time dependent.  Jose-Cunelleras (et al 2006) reported a minimal difference in glycogen repletion in the first 24 hours following a glycogen depleting exercise bout between horses that were fed a high glycemic feed compared with a group where feed was withheld for 8 hours and another group of horses where only hay was fed.   A recent study also concluded that the route of administration of carbohydrate given post-exercise significantly affects the rate of glycogen replenishment.  Horses that were given an intravenous infusion of glucose following exercise exhibited significantly greater glycogen storage rates and glycogen concentration in the first 6 hours following exercise compared to horses fed a similar quantity of glucose orally.  In fact, the repletion of glycogen in response to oral glucose was minimal over this time period compared to the unsupplemented control horses (Geor et al 2007).
Whilst it is difficult to draw direct comparisons with feeding practices used in racing, it is worth appreciating the possible differences in the rate of glycogen repletion when very high glycemic feeds are fed compared to very low glycemic feeds.  The reality in many training yards I would suspect lies somewhere between these two extremes.

LOW GLYCEMIC 
DIETS CAN OFFER RACEHORSES MANY BENEFITS


There are many health-related benefits to feeding a ration that is lower in starch and sugar.  However, one should be mindful of muscle glycogen when considering horses that are consistently fed a low glycemic diet.  Specifically horses may be fed this type of ration because they are behaviourally more manageable, or because a specific condition such as the muscular disease recurrent exertional rhabdomyolysis (tying up) (RER) is present.

A low starch diet is actively encouraged for horses that suffer from RER.  McKenzie (et al 2003) reported that plasma creatine kinase activity (CK), elevations of which can indicate muscle damage, was significantly reduced following exercise in RER horses fed a low starch high fat diet versus a high starch low fat diet.   In addition, lower resting heart rates have also been reported in horses fed a low starch high fat diet compared to the reverse.  A lower resting heart rate may be beneficial especially in RER horses where it reflects a calmer horse as stress has been implicated as a trigger factor for the condition. 

The current thinking on feed for horses with RER continues to be a low starch and sugar diet supplemented with oil.  It is also important that the diet is well balanced, especially with respect to calcium and phosphorus.  Adequate electrolyte provision is equally important, as is the intake of antioxidants such as vitamin E and other related trace minerals such as selenium.  Any potential individual limitation in mineral or electrolyte absorption and retention should be investigated further with veterinary assistance in order that individualised adjustments can be made to the diet.

A SUPPORTING ROLE FOR PROTEIN IN MUSCLE RECOVERY


Whilst we are all no doubt aware that the amino acids that make up protein are important for muscle development and repair, protein and its constituent amino acids have received very little attention in horses in terms of their potential to limit exercise induced muscle damage and aid muscle recovery.

In human athletes, co-consumption of a protein and carbohydrate drink during and after exercise appears to limit exercise induced muscle damage, ultimately allowing faster recovery (Baty et al 2007; Saunders et al 2004).  Recent introduction of ingredients containing partially hydrolysed protein may improve absorption of these amino acids and peptides possibly offering further benefit.

Finally, some nutraceutical ingredients including carnitine and creatine have been hailed as being beneficial to muscle function and recovery in human athletes.  Creatine, which has been studied in the horse, has failed to offer any great advantage, largely due to its poor absorption.  Likewise, carnitine has been reported to improve muscle blood flow during exercise in humans, helping to reduce muscle damage.  However, this aspect has not as yet been investigated in horses and previous dietary studies with carnitine were not unequivocal about the ability of oral carnitine to increase muscle carnitine content.

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