Feeding Oil or Fat for Horses
Feeding Oil or Fat for Horses
The Domesticated Lifestyle
The modern, domesticated horse lives in an environment markedly different to the evolutionary one. Horses are often kept in paddocks and stables, restricting access to quality pasture. This, coupled with the high-energy demands of performance, can make safely meeting horses energy needs, a tall order.
The Grain Solution
Traditionally, horse diets have often included large quantities of grain (ie. starch) in an attempt to sate energy needs. However, horses have a limited capacity to digest starch and high starch feeding practices can result in starch overload into the hindgut (Kohnke et al 1999; Rowe et al 2001). A number of metabolic disorders - such as tying up, laminitis, colic, and excitable behaviour - are associated with high grain diets. Advances in feed processing technologies have reduced the risks associated with high grain feeding, but have not eliminated them.
So What Are Other Options for Nutritional Ergogenic Aids?
Ergogenic means ?work producing'. Nutritional ergogenic aids are those feeds which enable horses to perform to maximum potential. This paper focuses on those feeds that provide energy for performance.
Energy is derived from 3 sources only: Carbohydrate (including fibre, starch and sugars), protein & fats (Kohnke 1998). As noted, there are problems associated with the overfeeding of carbohydrates (starches and sugars can cause metabolic complications, and horses only have a limited gut capacity for the intake of roughages). Protein is not an efficient source of energy (Kohnke et al 1999). Also, protein, starches and fibre produce considerable metabolic heat waste (Kohnke 1998). So, equine nutritionists have arrived at feeding oil (in addition to a moderate level of grain) to provide energy for the modern performance horse.
A Note on Equine Exercise Physiology.
Horses require energy for performance in two forms
- Explosive - short duration, high intensity work (activities taking less than 3-5 minutes)
- Stamina - longer term activities requiring release of energy over a longer time
Racing, showjumping, polo
dressage, eventing, endurance
Energy supplied to muscles is in the form of ATP (Adenosine Triphosphate). Muscles contain only small ATP reserves which can only fuel exercise for a few seconds. The ability of the diet to produce ATP depends on the pathway by which the dietary ingredients are metabolised.
Aerobic and Anaerobic ATP production
ATP can be produced under anaerobic or aerobic conditions. Body glycogen stores yield ATP rapidly in anaerobic conditions, but this is highly fatigable. ATP can also be produced more slowly from fats and carbohydrates via the Aerobic process. This produces greater quantities of ATP for much longer than the anaerobic process. Glucose yields only 2 units of ATP under anaerobic conditions, whereas 18 times more ATP is produced under aerobic conditions. The form of supply of ATP is therefore critical for explosive and endurance muscular performance.
There are two basic types of skeletal muscle fibres. Fast-twitch fibres are responsible forexplosive activity of short duration. The anaerobic ATP process fuels fast-twitch fibres. Slow-twitch fibres are the second kind of muscle fibre and these are responsible for endurance. The aerobic ATP process fuels slow-twitch fibres.
Training to Facilitate the Aerobic Pathway
The aerobic metabolism provides energy for slow-twitch muscle fibres and therefore stamina. It also provides much of the energy for explosive exercise, which cannot be met by energy from the anaerobic process alone. Training the horse to facilitate aerobic metabolism, is advantageous to performance in all disciplines as a result of the elevated ATP production.
With training, horses have a higher number of mitochondria and enzymes in their muscles, which produce more energy. Training also increases the blood's ability to carry oxygen to the muscles, through increased haemoglobin concentration in blood. Training allows horses to carry out aerobic energy production more efficiently.
Feeding Oil or Fat to Horses
Concerns About Fat
Although horse diets have always contained small amounts of fat, nutritionists were initially circumspect about feeding horses higher levels of fat (Davison 2002) for a number of reasons:
Can Horses Digest and Metabolise Fat?
Unlike other livestock species, horses have no gallbladder (Fransdon and Spurgeon 1992). In the horse, bile is secreted fairly continuously from the liver and passes via a bile duct directly into the duodenum. This allows horses to digest fat quite efficiently. Diets containing up to 30% of the DE as fat (Kane et al 1979), were digested efficiently, without adverse digestive consequences. Research by Marchello et al (2000), indicated that horses fed diets containing 19.5 and 20% of the DE as fat, were metabolically capable of adapting to the increased dietary fat content as indicated by increased bile production and elevated HDLP and LDLP in blood serum. (Marchello et al 2000).
Is Fibre Digestibility Suppressed by Fat Supplementation?
Horses possess complex, microbial systems in the hindgut for processing and deriving energy from dietary fibre. Like ruminants, horses rely on their microorganisms to derive energy yielding volatile fatty acids (VFA's) from cellulose and hemicellulose. In ruminants, >5% fat in the diet inhibits microbial fermentation due to death of cellulolytic bacteria (Brooks et al 1951) cited in Jansen et al (2000). Is the same true for horses?
Hughes et al (1995) reported that 10% (as fed) fat supplementation had no impact on overall digestibility of DM, but increased digestibility of NDF in horses. This was consistent with the findings with Julen et al (1995). Meyers et al (1987) reported no interaction between fat supplementation and fibre digestibility. Conversely, Jansen et al (2000) reported that fat supplementation at a rate of 37% of DE significantly reduced fibre digestibility. Digestibility was decreased by 8% for Crude fibre (CF), by 6.2% for NDF, and by 8.3% for acid detergent fibre (ADF).
Increased fibre digestibility associated with fat supplementation may be because the less starch in the diet reduces the suppressive effect of starch digestion on fibre digestion in the intestine. ie. Reduced starch intake may alleviate lowered caecal pH arising from hindgut fermentation of starch. The less acidic hindgut would facilitate proliferation and enhanced activity of cellulolytic bacteria, thereby increasing fibre digestion (Kohnke et al 1999).
Further, horses only digest fat in the small intestine, (Fransdon and Spurgeon 1992), which occurs prior to digesta entering the hindgut. This, coupled with the high digestibilities (75-90%) of fat, suggest that minimal fat should enter the hindgut. However, as dietary fat levels increase, the absolute level of fat entering the hindgut increases accordingly. If fat levels were sufficiently high, reduced microbial fermentation and fibre digestibility would result. Negative impacts on fibre digestibility should be avoided when feeding fat to horses, provided that a highly digestible fat source is fed at sensible levels (ie 250-500mL per day for horses in heavy work (Kohnke et al 1999)).
What Maintained the Interest in Feeding Fat to Horses?
Energy Density of Oil
Oil is very energy dense. It yields about 2? times more energy than starch or protein (McDonald et al, 1995; Kohnke 1998). This may be useful for a number of reasons including reduction in gut fill and reduction in feed intake required to sustain maintenance and exercise (Kohnke 1998)
Digestibility of Fat in the Horse
Fat is highly digestible in the horse, (Rich et al 1981; McCann et al 1987; Julen et al 1995), and an increased the proportion of fat in the diet further enhances the horse's capacity to digest fat (Orme et al 1997; Marchello et al 2000).
Horses may take between 3 (Potter n.d.; Hughes et al 1995) and 4 weeks (Julen et al 1995), to adapt to oil-supplemented diets.
Palatability of Oils
Horses readily accept oil-supplemented rations, provided that the oil is of high quality, not rancid, is introduced in a step-wise manner and does not constitute more than about 10-12% of the diet (Potter n.d.). If oil inclusion rates exceed 10% DM, acceptance may take longer (Potter n.d.). Horses exhibit a preference for vegetable oils over animal fats (Potter n.d.).
Cost and Availability
The fats fed to horses are typically readily available and relatively inexpensive energy sources.
Benefits for Horses in Hot Climates
The total amount of heat waste produced per unit of energy is different for different feeds with fats producing significantly less heat waste than fermentable carbohydrates, roughages and proteins (Kohnke 1998).
Further, fat metabolism, yields almost twice the water of protein and carbohydrate metabolism (Kohnke 1998). This may benefit horses that sweat profusely or undergo endurance training.
The combined effects of reduced thermal load and increased production of water may reduce heat stress in horses working in hot environments.
Fat as a ?Cool' Feed
When starch (typically in the form of grain), is fed to horses in large quantities, there is a risk of starch overload into the large intestine (Kohnke et al 1999). This can culminate in "fizzy" behaviour (Kohnke et al 1999). Reducing the amount of grain in the feed and instead meeting the energy need with fat, the risk of starch overload is also reduced. Hence, fat can provide a ?cool' source of energy, which is of consequence for performance horses that have a tendency to be excitable.
Benefits of Feeding Fat
Fat supplemented diets for horses have proven to be beneficial beyond that mentioned above. Adding fats to the diets of growing and breeding horses has increased milk energy yield in lactating mares and increased growth rate in weanlings (Scott et al 1989; Davison et al1991). However, the most exciting effects of feeding fat to horses have been observed in the equine athlete.
The effect of fat supplementation on muscle glycogen storage and utilisation has been widely tested. Other areas - such as effect of extra dietary fat on thermoregulation, energy requirement, management of Equine Rhabdomyolysis, and other exercise parameters - have also been explored.
Fat produces less heat waste per unit of energy and is more energy dense than carbohydrates and protein. Hence, partial replacement of carbohydrates in the feed with fat may assist in lowering thermal load.
Potter et al (1990) found that in both hot and temperate conditions, DE intake was lower in fat supplemented animals, regardless of season. This was interpreted as being the result of a decreased thermal load.
Cubit et al (2001) reported that the fat supplemented horses had mean body temperatures lower than those consuming high roughage and high grain diets.
Hence, provision of some energy in the diet with fat appears to reduce overall thermal load, and perhaps also DE requirements.
Role of Oil in Management of Equine Rhabdomyolysis
Equine rhabdomyolysis (?tying-up') is a broad term used to describe equine muscle disorders including EPSM and RER. Equine polysaccharide storage myopathy (EPSM) has been associated with dysfunctional carbohydrate metabolism. Horses suffering from EPSM must be provided with non-carbohydrate energy sources such as fat. Results to indicate a reduction in clinical signs in EPSM horses consuming a high fat, low carbohydrate diet (Valentine et al 1997).
Recurrent Exhertional Rhabdomyolysis (RER) is another form of Equine rhabdomyolysis. Horses suffering RER are frequently fillies, and tend to be nervous horses, (Geor and Valberg 2000). Starch feeding and excitement are both implicated as ?triggers' in RER, hence partial replacement of starch with fat in the diet may aid in the management of the condition (Geor and Valberg 2000).
The affect of dietary fat supplementation on the sparing, storage and increased utilisation of glycogen in skeletal muscle has been extensively investigated. Once adapted to higher levels of dietary fat, horses become more adept at transporting and digesting fat (Marchello et al2000) and can utilise fat for energy during submaximal (aerobic) exercise. This is achieved via fatty acid oxidation (Orme et al 1997; Geelen et al 2001).
Webb et al (1987), concluded that thoroughbred horses on a grain diet resorted to anaerobic carbohydrate metabolism to produce energy during an aerobic exercise test. The fat supplemented horses in this trial did not. Apparently, the fat supplemented horses utilised fatty acid oxidation as an energy substrate rather than the anaerobic metabolism of blood glucose and muscle glycogen. It is now well accepted that horses receiving fat supplemented diets employ fatty acid oxidation during aerobic exercise to meet energy needs (Kronfeld et al1994; Kohnke 1998), thereby sparing glycogen in skeletal muscles.
Elevated resting muscle glycogen concentrations in fat supplemented horses have been widely reported (Meyers et al 1989; Oldham et al 1990; Harkins et al 1992; Jones et al 1992; Scott et al 1992; Hughes et al 1995; Julen et al 1995). Meyers et al (1989) observed that concentration of glycogen in resting muscle increased concomitantly as level of fat supplementation was increased (from 0% to 5% to 10% of the diet).
However, some studies have reported no interaction between resting muscle glycogen concentration and fat supplementation (Eaton et al 1995; Orme et al 1997) and Geelen et al(2001) observed a drop in muscle glycogen concentration when fat was added to the diet.
However, the majority of research has found that added dietary fat promotes sparing and storage of muscle glycogen. Subsequently, horses appear able to utilise the greater muscle glycogen reserves during anaerobic activity. Meyers et al (1987), Oldham et al (1990), Jones et al (1992), Scott et al (1992), Julen et al (1994), and Hughes et al (1995) all observed increased utilisation of muscle glycogen in fat supplemented horses. This phenomenon has implications such as delaying time to onset of fatigue (Meyers et al 1989; Eaton et al 1995), and increased performance during high intensity (anaerobic) exercise (Webb et al 1987; Scott et al 1992).
Eaton et al (1995) found that run time to fatigue was increased during intense exercise in horses fed corn oil. Webb et al (1987) reported that cutting horses fed animal fat "worked harder" and performed a higher number of hindquarter turns during a workout. In horses performing a series of 600m gallops, Oldham et al (1990) reported that the fat supplemented horses were able to achieve higher velocities in the final 2 gallops at a constant heart rate. This was attributed to there being a greater amount of glycogen available for utilisation in the final 2 sprints. Thus, the evidence for fat supplementation resulting in increased muscle glycogen storage and utilisation during high intensity exercise is encouraging.
However, Eaton et al (1995) reported no change in muscle glycogen utilisation in anaerobically exercised, fat-supplemented horses. Harkins et al (1992) also reported no increase in muscle glycogen utilisation during intense work, despite noting an increase in muscle glycogen at rest in fat supplemented horses.
Predominantly, fat appears to serve as a useful energy substrate for submaximal exercise, and is related with a heightened capacity for high intensity work. The majority of research findings indicate this is due to improved muscle glycogen storage and utilisation. However, observations may be at least partially attributable to factors other than glycogen being affected by increased levels of fat in the diet.
Effect of Fat on Other Exercise Parameters.
Various parameters relating to capacity for high intensity activity (other than glycogen), have also been measured in relation to high fat diets for horses.
That fat supplemented horses can perform work without typical reliance on carbohydrate energy substrates, indicates the utilisation of another energy substrate. Meyers et al (1989), Orme et al (1997) and Geelen et al (2001) all reported a decrease in blood lipid concentrations associated with a fat supplemented diet. Marchello et al (2000) notes that mechanisms for transport and digestion of dietary fats are elevated in horses adapted to fat supplemented diets. Perhaps although fat-adapted horses consume far greater quantities of fat, their blood lipid concentrations are lower because they are better able to transport, digest and metabolise dietary fat. This is beneficial in that it means carbohydrate energy substrates are spared for use in anaerobic activity.
Blood glucose data can provide insight into the horse's reliance on carbohydrate energy substrates. Fat-supplemented horses predominantly had higher blood glucose levels than grain controls (Webb et al 1987; Oldham et al 1990; Harkins et al 1992; Pagan et al 1995; Taylor et al 1995). Conversely, Pagan et al (1993) reported no change in blood glucose levels in fat supplemented horses and Meyers et al (1987) reported a reduction. Perhaps this reduction in blood glucose was due to the fact that less glucose precursors were available in diets containing less carbohydrate and more fat.
Hence, fat supplementation may spare blood glucose and instead result in preferential use of fatty acids as an energy substrate. Interestingly Pagan et al (1995) noted that horses supplemented with fat had an altered insulin response after feeding. They noted that feeding a fat supplemented diet resulted in a lower post prandial insulin response. A similar response was noted by Crandell et al 1998. This response may account for the higher glucose levels seen in the blood of fat supplemented horses. A manifestation of this occurrence long-term could be that fat-supplementation would result in less glycogen storage, (because glycogen storage is insulin dependent). If so, it is important that fat-supplemented horses also consume adequate carbohydrates for glycogen formation.
Blood lactate is the end product of anaerobic glycolysis. See figure 1.
FIGURE 1. Diagram of the cori cycle (Source: Lehninger et al 2000).
Findings in this area have been inconsistent. Data indicate that fat supplemented horses had higher blood lactate levels following high intensity exercise (Webb et al 1987; Pagan et al1993; Taylor et al 1995). This is in keeping with the theory that fat-supplemented horses store and then utilise more glycogen during anaerobic activity.
However, Meyers et al (1987) reported that fat supplemented horses had lower blood lactate following high intensity exercise than control horses. Considering that lactate is the end product of anaerobic glycolysis, this would indicate that less anaerobic glycolysis occurred in these horses during their anaerobic workouts. Hence, some other energy substrate must have been employed. The mechanisms by which this would occur are unclear.
Oxygen uptake, blood pH, respiratory quotient and ventilatory capacity all appear unaffected by fat supplementation (Meyers et al 1989; Taylor et al 1995). Some researchers have noted that heart rate is also unaffected by fat supplementation (Meyers et al 1989). Others have noted that horses fed fat have elevated heart rates following exercise compared with control animals (Webb et al 1987). It is possible that this is because fat-supplemented horses work harder during workouts (Meyers et al 1987, Oldham et al 1990).
Overall Effect on Aerobic Capacity
An increase in the oxidation of fatty acids and subsequent decrease in reliance on carbohydrate energy substrates has been observed during submaximal activity.
This action could be useful for horses undertaking a variety of classically "aerobic" disciplines such as dressage, droving, mustering and endurance. However, because the total contribution of the anaerobic system to high intensity exercise is only about 30%, aerobic metabolism is still of great importance in horses performing "anaerobic" pursuits (Davie 1999).
Overall Effect on Anaerobic Capacity
Due to the glycogen sparing effect of fat during aerobic activity, more glycogen is subsequently available for use during high intensity exercise. As discussed earlier, Webb et al (1987) and Oldham et al (1990) found that supplemental fats in horse diets enabled horses to work harder during high intensity exercise.
Largely this has been attributed to the alteration to glycogen storage and utilisation described. This may benefit horses undertaking anaerobic disciplines such as eventing, sprint racing, cutting, showjumping and polo.
Possible Reasons for Disparity in Results
Variances in experimental protocol - such as breed, sex and age differences, small sample sizes, and differences in discipline - are touted as being the causes underlying the variations in results obtained. Another variable - fat type - is considered in this paper.
Different Types of Fat Fed
A variety of fats have been used in the research with soybean oil, corn oil and animal fat being the most common. Even though these fats vary considerably in lipid biochemistry, they are simply referred to in the research as ?fat'. Although the interest in feeding fats has stemmed from an interest in increasing the energy content and/or density of feed rations, it is possible that the type of fat fed may influence results.
Comparison of results reported in the literature explored appears in the table 1.
Table 1. Table comparing results with fat source used, from various papers reviewed.
It is evident that experiments using animal fat typically reported increases in both resting muscle glycogen concentrations, and in utilisation of glycogen during high intensity exercise. The same is generally not true for experiments that used vegetable fats.
This indicates that the type of fat which horses consume may have physiological repercussions, beyond that of simply providing an energy substrate. Hence, fat type could be at least partially responsible for the inconsistent experimental data available.
Trials Involving Various Fat Sources
Few trials have considered the effects of fat type fed on results obtained. However, a trial by Pagan et al (1993) explored the impacts of feeding Soyabean oil (10%), Coconut oil (10%) and a mixture (5% Coconut oil and 5% Soyabean Oil) compared to a traditional high carbohydrate diet. Horses were exercised anaerobically and results indicated that fat type did influence results obtained. The authors concluded that feeding supplemental fat altered the horses' response to a standard exercise test. Further, they noted that during the 8 minute gallop, blood lactate was lower and free fatty acids higher in the Coconut Oil group than the control and that blood ammonia was low in the Coconut Oil group throughout the exercise test.
In this paper the authors stated that "more research is needed to identify the role that chain length and degree of saturation play in fat metabolism during intense exercise in the horse".
Another KER trial, by Kennedy et al (1999) evaluated corn oil, rice bran and dry fat as energy sources for exercising horses. This trial further demonstrated the different impacts of different fat types on equine performance. In this experiment, Blood lactate, heart rates at a canter and gallop and triglyceride mobilisation, were all affected by type of fat fed.
These results suggest that further investigation into the differences between fats fed to horses is warranted.
Oils Aint Oils
All oils are not the same. Dietary fats predominantly consist of triacylglycerols (also known as triglycerides), (Chow (ed)1992). They consist of three fatty acids, each in ester linkage with a single molecule of glycerol (Lehninger et al 2000). Refer to Figure 2.
Figure 2. Diagram of a Triacylglycerol Molecule. (Source: Lehninger et al 2000).
The fatty acids are typically of an even carbon number and may be branched or unbranched. Animal fats tend to be unbranched (Stryer 1995). The fatty acid chain may be saturated, monounsaturated or polyunsaturated. Dietary fats typically contain all three of these fatty acids but the relative proportions of each type vary between different fat sources (Lehningeret al 2000).
Fatty acids that contain no double bonds between carbon atoms are known as saturated(Stryer 1995). Lauric acid and Myristic acid are saturated fatty acids. Dietary fats that are primarily comprised of saturated fatty acids are known as saturated fats. Coconut oil and beef tallow are examples of saturated fats.
Fatty acids that contain a single double bond between carbon atoms are monounsaturated(Stryer 1995). Oleic acid and Palmitoleic acid are monounsaturated fatty acids. Dietary fats that are primarily comprised of monounsaturated fatty acids are monounsaturated fats. Olive oil is a monounsaturated fat.
Fatty acids that contain >1 double bond between carbon atoms are polyunsaturated (Stryer 1995). Linoleic acid and Linolenic acid are polyunsaturated fatty acids. Dietary fats that are primarily comprised of polyunsaturated fatty acids are polyunsaturated fats. Sunflower oil, Corn oil and Soyabean oil are polyunsaturated fats.
The graph below shows the different proportions of saturated, monounsaturated and polyunsaturated fatty acids in some fats commonly fed to horses. It is clear that the various fats fed to horses are fundamentally different. Hence, they may be associated with different resultant physiological manifestations. The different levels of saturation of some fats commonly fed to horses are shown in Figure 5.
Figure 5. Graph showing the level of saturated, monounsaturated and polyunsaturated fatty acids in fats commonly fed to horses. (Source: Chow (ed) 1992).
The Fatty Acids Involved
Long Chain, Medium Chain and Short Chain Fatty Acids
Fatty acids can also be divided into 4 main groups based on chain length. Very short chain fatty acids have chain lengths of 8 to 10 carbon atoms or less, short chain fatty acids have less than 12 carbon atoms, medium chain fatty acids have 12 to 16 carbon atoms and long chain fatty acids have 18 or more carbon atoms (Chow (ed) 1992. See Figure 6.
Figure 6. Graph showing proportion of very short, short, medium and long chain fatty acids in some fats commonly fed to horses. (Source: Chow (ed) 1992).
Fatty acids of different chain lengths are metabolised differently. Long chain fatty acids pass through the lymphatic system and then to the liver before providing an energy source. Conversely, fatty acids with chain lengths less than 14 Carbon atoms long are absorbed intact, directly from the stomach into the venous circulation (Chow (ed) 1992), are oxidised, and can provide a ready source of energy (Lambert et al 1997; Pehowich et al 2000).
Fatty Acid Profile of Fats Commonly Fed to Horses
A variety of fats are fed to horses and consequently they receive a variety of fatty acids. Figure 7.
Figure 7. Graph depicting the fatty acids present in some fats commonly fed to horses. (Source: Chow (ed) 1992).
Fats fed to horses are very different in their composition of fatty acids, chain length and degree of saturation.
Responses of Non-Equid Species to Different Types of Fats
Experimentation into the responses of animal species to different dietary fats has been conducted a two main levels- health and sports performance. However, whilst animal and human studies provide insight into the effects of dietary fat intake per se different types of dietary fat, and species differences may be significant and not all findings may be applicable to horses. Further, the levels of fat referred to in human studies as ?high fat' and ?low fat', represent much higher absolute levels of fat than that fed to horses.
Dietary fats and Their Effect on Health
Given that the focus of this paper is sports performance, the effects of dietary fat on health will be dealt with only briefly.
The Link Between Dietary Fats, Cholesterol and Coronary Heart Disease.
The excess intake of dietary fat, and of certain specific fats has been implicated in causing high serum cholesterol (considered a predisposing factor in Coronary Heart Disease (CHD) in humans (Elson, 1992; Sircar and Kansra 1998; Mendis et al 2001)). Saturated fats, specifically coconut oil have been identified as the most hypercholesterolemic dietary fats in humans and hamsters (Trautwein et al 1997; Katan et al 1994). However, other studies have reported that rats fed heated and fried coconut oil had lower levels of liver cholesterol than those fed polyunsaturated oils (Narasimhamurthy &http://www.foxtons.co.uk/
Raina 1999). This might indicate that whilst polyunsaturated fats reduce cholesterol levels in serum, they result in increased cholesterol storage in organs such as the liver, and that for saturated fats, the opposite occurs. Whatever the case, studies on traditional peoples consuming diets high in saturated fat (predominantly from coconuts), revealed that CHD is very rare in these people, much more so than in Western cultures (Lindeberg et al 1997; Mendis et al 2001).
The Link Between Dietary Fats and Cancer.
In humans nd rodents, dietary fats have been implicated in carcinogenesis, partly via the mechanism of oxidative DNA damage (Loft et al 1998). Loft et al (1998) found high total energy intake (rather than simply high fat intake), to be the major cause of oxidative DNA damage in rats, irrespective of degree of saturation of dietary fat consumed. D'Aquino et al (1991) reported that unlike coconut oil, fish oils are highly susceptible to oxidative deterioration and challenge the antioxidant defence system in rats, thereby increasing susceptibility of tissues to free radical oxidative damage.
An experiment involving tumour-bearing mice indicated that the level of dietary linoleic acid consumed was proportional to the weight of their tumours and to the number of macroscopic metastases. Mice that consumed proportionally more saturated fatty acids (in the form of coconut oil) had lighter tumours and fewer macroscopic metastases (Rose et al 1993).
Reddy (1992) noted that diets containing coconut oil, olive oil or fish oil had no colon-tumour enhancing effects regardless of whether they were fed at rates of 23% or less. However rats fed diets containing 23% corn oil, safflower oil, beef tallow or lard had increased incidence of colon tumours.
The links between dietary fats -their type and level of consumption- and impact on CHD and carcinogenesis are poorly understood. However, it appears that coconut oil may play a non-promotional role with regard to carcinogenesis.
Dietary Fats and Their Role in Sports Nutrition
Carbohydrates have traditionally been the energy sources of interest in human sports nutrition (Manore et al 2000), but now fat is in the limelight.
Dietary fat and its Impact on Plasma Free Fatty Acids and Triglycerides.
Like horses, human athletes fed high fat diets have an increased capacity for fatty acid oxidation during exercise (Helge 2000, Marchello et al 2000). In horses, fat-supplementation is linked with a decrease in blood lipids (Meyers et al 1989; Orme et al 1997; Geelen et al 2001), whereas in humans it has no effect on plasma or muscle lipid concentrations at rest.
The type of fat consumed also influences the effect on blood lipids. Human endurance athletes consuming high polyunsaturated fat diets had lower plasma triglyceride levels compared to the athletes consuming diets rich in saturated fat or carbohydrates (Lukaski et al 1984). Thus both level and type of dietary fat influence potential for exercise in humans, and the same is likely to be true for horses.
Dietary Fat and its Impact on Glucose Metabolism.
In exercise-trained, fat-adapted rats and humans muscle glycogen was during submaximal exercise (Jansson and Kaijser 1982, Nakamura et al 1998), and an alternative energy substrate - presumably fat - was utilised. Increasing the availability of free fatty can slow muscle and liver glycogen depletion by promoting fat utilisation (Lambert et al 1997), a factor linked with prolonging time to fatigue. However, the full gamut of results from various studies, is less clear.
Whilst fatty acid oxidation is enhanced in humans consuming high fat diets, muscle glycogen storage can be compromised, glycogen utilisation reduced and performance at moderate and high intensities hindered (Helge 2000).
Rats fed high fat diets had elevated blood glucose concentrations and reduced muscle glycogen utilisation (Antoniak et al 1998). Highly saturated fat-supplemented diets reduced the content of glycogen in the liver and muscles. As the blood glucose content was high and the muscle glycogen concentration low, perhaps a diet high in saturated fat inhibits the tissue reactivity to or plasma levels of insulin (Antoniack et al 1998). The consumption of certain types of fat, can lower insulin levels in pre-ruminant calves (Piot et al 1999). Bizeau and Hazel (1999) noted that type of dietary fat can influence glucose metabolism, with coconut oil diets favouring gluconeogenesis and reducing reactivity to insulin. Pagan et al (1995) and Crandellet al (1998) noted that fat supplemented horses exhibited reduced insulin responses, although these animals consumed soybean oil (a polyunsaturated fat) and not coconut oil (a saturated fat). Perhaps these results arise from diets containing inadequate levels of carbohydrate with which to replenish glycogen stores.
The actions of high fat diets, on glucose metabolism are questionable. They may be of detriment to performance in various non-equid species via reducing uptake of glucose from blood and subsequently reducing concentration and therefore utilisation of glycogen in the liver and skeletal muscles. Conversely, various research with horses indicates that fat supplementation actually increases storage and utilisation of muscle glycogen.
Medium Chain Triglycerides in Sports Nutrition.
Medium chain triglycerides (MCT's) are fats rich in fatty acids 12 to 16 carbon atoms in length. The smaller molecular structures of MCT's make them more water-soluble than long chain triacylglycerides (LCT's). Whereas chylomicrons carry LCT's via the lymph system before reaching the blood stream, MCT's are carried to the liver directly in the venous portal blood (Chow (ed) 1992). That MCTs don't have to be carried by chylomicrons may be significant for horses. Although horses have LDLP and HDLP, they do not possess chylomicrons. Harris (1997) states that "It is known that in the adult horse, the transport of various lipoprotein fractions is dissimilar to that in other mammals, because an adult horse does not appear to have any chylomicron lipoproteins" (Watson 1991).
Unlike ingested LCT's, which are largely unavailable during intense exercise, MCT's do not undergo degradation and re-esterification, but are instead absorbed intact, readily oxidised, and can thus provide a source of ready energy (Lambert et al 1994; Pehowich et al 2000).
Consuming MCT's in combination with carbohydrate has the effect of sparing muscle carbohydrate stores during long bouts of submaximal cycling exercise and improves time trial performance (Lambert et al 1997). This suggests that specifically when MCT's are consumed in conjunction with a source of carbohydrate, fat oxidation is enhanced and body carbohydrate substrates are spared. Further, when cyclists were properly fat-adapted, resistance to fatigue almost doubled during low to moderate intensity exercise (Lambert et al 1997). So, although a minimal consumption of MCT's may not aid performance, (Hawley et al 1998), the combined consumption of MCT's in addition to a source of carbohydrate, may prove to be a useful ergogenic aid for human, and perhaps also equine athletes.
In human sports nutrition, MCT's are a potentially useful fat-based ergogenic aid and this may be similarly true for horses. Coconut oil is one of the best natural sources of MCT's. In the next section, coconut oil and its potential as a useful energy supplement for performance horses will be discussed.
Pagan et al (1993) stated that "Perhaps Coconut Oil, with a large percentage of both saturated and medium chain fatty acids can be mobilised and oxidised quickly enough to produce a significant amount of energy during intense exercise". For this reason, and those previously outlined, the ergogenic potential of coconut oil warrants investigation.
About the Oil from Cocus nucifera
The fruits of the coconut palm, give rise to coconut oil. The fruit is two-thirds oil and the oil is usually expelled mechanically (Enig 2000). Coconut oil is highly stable and resistant to oxidation (rancidity), a trait possessed by very few seed oils (Enig 2000).
Coconut oil typically contains 49% Lauric Acid, 18% Myristic Acid, 8% Palmitic Acid, 8% Caprylic Acid, 7% Capric Acid, 6% Oleic Acid, 2% Stearic Acid and 2% Linoleic Acid (Enig 2000). Coconut oil is fundamentally dissimilar to many other fats typically fed to horses in terms of fatty acid composition, degree of saturation and high content of medium chain fatty acids.
Coconut oil, and specifically lauric acid (a fatty acid in coconut oil) is touted as possessing antibiotic, antiprotozoal, antifungal, antiviral and anticarcinogenic properties. Whilst some of these claims are only supported by anecdotal evidence, lauric acid has been scientifically proven for is antibiotic, antiviral, antifungal and antiprotozoal actions (Kneiflova et al 1992; Sutter et al 2000). It is presumed that these functions explain its presence in human milk (Hollingsworth 2000).(However, it is interesting to note that mare's milk does not contain lauric acid (Csapo et al 1995)). Further, Lauric acid forms the basis of the medical disinfectant ?Lautericide' (Kneiflova et al 1992). Hence, coconut oil may have beneficial traits, which extend beyond the realm of simple nutrition.
Coconut oil and it's Potential as an Ergogenic Aid for Performance Horses
Coconut oil is rich in medium chain triglycerides, fats which behave differently to the LCT's more commonly fed to horses. At least in humans, MCT's are absorbed differently to LCT's and provide a ready energy source for athletes. Although it is unknown if a similar action would occur in horses, the fact that MCT's do not have to be transported by chylomicrons could be beneficial to horses (as horses lack chylomicrons).
To properly ascertain the results of horses consuming coconut oil, feeding and performance trials must be carried out. Trials would need to involve a reasonable number of horses (so as to have the potential to achieve statistically significant results), and adequate carbohydrate would need to be fed along with the coconut oil. Parameters such as muscle glycogen concentrations and utilisation rates at rest and after submaximal and anaerobic activity, plasma glucose and insulin would need to be recorded.
It is worth noting that numerous informal trials using copra meal (8-10% coconut oil) indicate its usefulness as an ergogenic aid. All horses on both the ?Spring Valley Heritage Horse Ride' (Broome to Sydney in 3 months) and the ?Ride For Youth' (Darwin to Adelaide), consumed a diet of medium quality hay +2-4kg copra meal + a vitamin and mineral supplement each day. After travelling these significant distances on this diet, all horses were well muscled, conditioned and very healthy during and at the end of each ride. In these diets coconut oil provided a high proportion of the energy (other than that provided by roughage).
The Way Forward
There are no ?silver bullets' in horse nutrition. The ability of horses is limited by genetics, but for horses to perform to genetic potential requires optimal nutrition.
Starch has traditionally provided the extra dietary energy required for performance. However, despite extensive research and application of new technologies, the problems associated with feeding starch have not been overcome.
The option of feeding horses the balanced and natural diet on which they evolved is, in most cases, unfeasible due to space, time and financial constraints. Besides which it is most unlikely that the natural diet of horses would suffice to meet the energy needs demanded of many performance pursuits.
Of the few alternatives that remain, feeding supplemental fat appears to be the most feasible.
Should We Feed Fat to Horses?
Current research indicates that fat supplementation is a viable energy source for performance horses which is of greater benefit than simply caloricifically. However, almost all studies investigating the effects of fat supplementation on horses have been relatively short term, involved a small number of horses and produce results which are not always highly repeatable. In order that more confidence be placed in the long term feeding of fats to horses, studies need to be of longer duration, involve more horses and more consistent results are necessary. The best type of fat for horses should also be ascertained.
Which Fat is Best?
Numerous fat sources for horses - ranging from plain seed oils to blended, flavoured oils (eg. ?Enhance' and ?Vitamite Omega 3 Oil')- are available today. Copra meal , soybean meal and stabilised rice bran are further fat sources. Coconut oil is another alternative. Anecdotal evidence suggests that it is generally well accepted by horses (Kempton, T.J. 2002, pers. comm., 10 April), but currently it is not yet widely available in Australia. The MCT content peculiar to coconut oil make it an interesting and potentially valuable ergogenic alternative, however formal feeding trials are needed to better clarify its effects in horses.
These oils vary biochemically and consequently, each may produce different results in terms of horses health and performance. So which oil is best for performance horses? Further research is required to better understand the usefulness of specific oils, rather than just ?fats'per se, and specifically research on coconut oil with its abundance of MCT's may prove particularly worthwhile for equine athletes.
*Anaerobic means in the absence of oxygen
*Aerobic means in the presence of oxygen
*HDLP = High density lipoproteins
*LDLP = Low density lipoproteins