In the last issue we took a bit of a deviation from the normal path and pursued a discussion of equine nutrition. We briefly looked at the basics of a sound nutritional program for horses and it's importance. Over recent years an immense amount of research has been applied to the science of equine nutrition and physiology. One area in particular that has been pursued has been that of the energy component of the diet and how to address certain issues that are commonly seen in horses fed high levels of grains (starches, carbohydrates). Feeding of high or excessive starch levels from sources such as corn or other processed grains can lead to founder, laminitis and colic, all serious conditions in any horse but especially problematic in performance and work animals. This article will examine several concepts relating to energy nutrition in horses and some possible solutions.
Foraged Based Diets
Since forages make up the largest fraction of the diet, forages are, therefore, the most important and most significant source of energy. While this is a foregone fact, it is also true that many horse owners do not work on improving pastures. Attention to soil fertility, weed control, and grazing management is of exceptional importance. Grazing management is particularly important since a horse has the capability of grazing growing forages much more closely than cattle. Attention to pasture and overall forage quality can greatly increase the energy supplied by this portion of your operation and significantly reduce the amount of energy that must be supplemented in growing, breeding, performing or working animals.
Regular analyses of pastures and forages is very important as we have discussed before. This helps the producer to see what is being supplied by his pastures and how he may need to supplement the nutrient needs of the animals he owns. While we are concerned for providing adequate levels of nutrients, forage testing also helps us avoid potential problems from excessive levels of some nutrients. This is critical in equine operations utilizing significant amounts of lush forages in early spring and fall pastures where there is an increase risk of laminitis and colic caused by increased rapidly fermenting carbohydrate content in these plants. Researchers in Virginia found peak levels of these carbohydrates in forage samples taken in October and March. It has been suggested that producers restrict access to pasture for horses that have shown a greater risk to these metabolic problems. Additionally, careful pasture management can help control lush pastures and offset these difficulties.
Energy Production and Metabolism
As in all animals, the primary source of energy for cells and tissues is glucose, which is transported via the circulatory system to the cells. The level of glucose found in the animal can be referred to as the glycemic level and the capacity for this level to change (up or down) based on the consumption of a particular diet is referred to as the glycemic response.
Put another way, glycemic response is the relative response in blood glucose and insulin after eating a starchy food. Researchers with Kentucky Equine Research determined that the greatest glycemic response is from sweet feed, then oats, corn, and finally a high-fiber feed. Adding fat to a feed can reduce the glycemic response. In other words, by adding fat to the feed, the energy level is supported but the degree to which the glucose level in the animal is raised is diminished. Many researchers have found that feeds with a lower glycemic response could be beneficial to horses.
One reason for this is that researchers believe that feeding a supplement or feed which results in a high glycemic response (a high starch feed) to any horse that has been shown to have problems utilizing glucose or has insulin resistance, or is laminitic, might be detrimental. Currently a fair amount of research is underway to determine if these types of feeds might also be harmful to young (growing and developing) horses as well.
Not only does feed or grain type have an effect on the glycemic response; so does the processing method. For instance, steam-flaked corn was found to have the highest glycemic response (Gycemic Index Score of 144), ground corn was next (GIS = 109), and cracked corn has the lowest glycemic response (GIS=100). This is reflective of the starch availability or digestibility resulting from these different processing methods. As you can see, the flaked corn was significantly higher in it's capacity to increase blood glucose in the horse. Processing is important in feeds such as oats and barley since it can improve the digestibility of the product but in high starch ingredients such as corn, it is probably best to go with a process which does not produce such a high glycemic response.
Benefits of High Fat Diets
As we've mentioned earlier the use of fat in equine diets has received considerable attention over the last few years. Here are some things we know about the use of fats in equine diets:
*Energy feeds (supplements) can be made more energy dense by adding up to 10% additional fat or oil.
*Fats and oils contain 2.25 times more energy than carbohydrates (starch) and allow horse owners to provide the same amount of total energy with significantly less total daily intake of the overall supplement. This results in an opportunity to utilize a higher amount of forage in the animal's diet.
*Fats and oils, if used correctly, can be beneficial in putting weight on thin horses and have been shown to have “extracaloric” effects. In other words, they provide benefits above and beyond just increasing energy density of the diet.
*Fat-added diets increase fat percentage in mare's milk in early lactation and cause the overall fat content to stay higher as the lactation continues.
*Performance horses are able to spare muscle glycogen for short duration, exhaustive exercise by utilizing energy from fats while working aerobically (oxygen is still present in the blood and tissues and has not been consumed in the process).
*Increased stamina and delayed onset of fatigue is a benefit from the use of fat-inclusive diets.
Let's look at some of these factors more closely. A number of studies of the feeding of fat discovered that there was almost 100 percent absorption of various fat sources--corn oil, peanut oil, soy oil, soy lecithin, tallow, and fat blends. It should be noted here that not all studies agree with these results and that some have shown varying degrees of absorption depending on the source. These fat sources were not shown to depress digestion of fiber or nutrients although it has been observed that dietary fat levels should be kept under a certain level – about 8 to 10 percent depending on the application. However, a study in The Netherlands showed that diets very high in fat might cause enough fat to enter the large intestine to depress fiber fermentation by bacteria. We see a similar effect to this in cattle if the dietary fat level exceeds seven percent. Fortunately since horses digest most of the fat in the stomach and small intestine before the fat ever reaches the large intestine where the bacterial population is located, the amount of fat that can be fed is significantly higher.
One interesting study showed the effects of various fat sources fed to horse on the level of lactate produced. You may recall that it is the accumulation of lactate in the muscles that causes the soreness we feel after exercise we are not accustomed too or after periods of excessive activity. The same is true in horses. In this study a control group was compared to horses fed a dry fat source, corn oil and rice bran. Muscular accumulation of lactate (after exercise) was significantly lower in the horses fed rice bran (~20% fat) as compared to those fed corn oil. The rice bran fed horses also exhibited a lower heart rate during exercise (at gallop) compared to the other sources.
One primary reason researchers are interested in the use of fat is related to the effect on glycogen stores in muscle tissues. Glycogen is a compound similar to carbohydrates which animals use to store energy in muscle tissue. When needed, an animal can “mobilize” this glycogen, converting it to glucose for use in the cells. Researchers with Texas A&M University have shown a moderately high-fat diet in horses produces a glycogen "sparing" effect that increases glycogen stored in muscle. In other words under performance or work situations, animals on the higher fat diets will require that less of their stored glycogen be mobilized to provide energy for the tissues.
A very important consideration is that horses have to be adapted to the higher dietary fat. Horses placed on the higher fat levels will not see this glycogen sparing effect immediately, and should be adapted for a period of up to three weeks. A typical horse diet contains two to three percent fat and subsequently they are not adapted to fat as a fuel source. Subsequently they have to be adapted physiologically to the different energy source. Also, depending on the fat source there may be differences in palatability, especially when using animal fats or tallows that have been shown to be less palatable than oils. Incorrect top-dressing of fats and oils can also contribute to digestive disorders or can cause horses to go off feed. Products such as rice bran are palatable and also contribute other nutrients such as protein, minerals and vitamins to the diet where as fats and oils contribute only fat and energy.
Yet another factor in fat research in horses has been related to the exact fatty acid profile being fed. The benefits of omega-3 fatty acids have been widely promoted in human and canine nutrition. Omega-3 and omega-6 have been recognized to contribute to normal cell function and help prevent immune disorders, skin conditions, inflammatory conditions, and certain disease conditions. There is considerable interest in the dietary ratio of omega-6:omega-3 fatty acids; in particular, diets that promote an increase in omega-3 relative to omega-6 fatty acids are advocated because of purported health benefits. One equine study showed that feeding fish oil (a good source of omega-3 fatty acids) increased omega-3 fatty acids in the horses' blood serum profiles. As a result, the omega-6 fatty acid concentration was lower, as was the omega-6:omega-3 fatty acid ratio. Changes in blood levels of insulin, free fatty acids, and glucose during an exercise test may indicate that insulin sensitivity and glucose metabolism was affected for the better by the fish oil. The main problem here, as we referenced above, is palatability. Fish oil is not palatable and must be used carefully and judiciously.
Obviously the feeding of horses is much more than providing pasture and some sweet feed. The serious horse owner and trainer must become well informed of the nutritional needs of the various classes of horses he may have on his farm at any given point and time and must feed them accordingly in order to maximize their growth and performance. Additionally, new research and concepts may go against much of what is considered traditional feeding practice, especially in performance and work animals but the results are there and these have shown to greatly benefit the animal. It is very much to the benefit of the owner and his horses to become familiar with current research and what options are currently available to build an exceptional equine nutrition program.
Dr. Steve Blezinger is and nutritional and management consultant with an office in Sulphur Springs Texas. He can be reached at Route 4 Box 89 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org.