Downside to feeding a low carbohydrate diet to performance horses
In 1986 the first commercially available high fat high energy feeds were introduced to the horse community in the High Plains and Intermountain West. Not only were these a new consideration in formulation but they started a new way of thinking about feeding horses. For years commercial horse feeds contained 2-3% fat and contained approximately 5-7% molasses to improve palatability and “hold” fines together. These new feeds were 8-10% fat and contained oats, barley and flaked corn as the primary ingredients with less than 1% molasses. Fast forward to the early 1990’s when university researchers demonstrated feeding higher fat content feeds could allow for smaller intake of the feeds and subsequently the carbohydrates they contained. These new feeding practices in some cases altered the horse’s attitude. Reducing the amount of “grain” may help decrease the anxiety of the horse; much like decreasing sugar intake can alter the behavior of children. Almost every feed company soon had a high fat feed designed for performance horses.
Also, during this time and into the early 2000’s, the number of horses “diagnosed” with Equine Metabolic Syndrome and Pituitary Pars Intermedia Disfunction (Cushing’s Syndrome) increased almost exponentially. Since both issues involve problems in glucose metabolism, the next step in feed formulation was for a high fat/high fiber feed with lower levels of sugar and starch. This is exactly what horses experiencing glucose/insulin metabolic issues require. While the right feed for this group of horses needing low sugar and starch, these same feeds found their way into the performance horse world. In the performance horse arena, there are now reports of issues that are often related to low carbohydrate intakes when these horses are required to compete over multiple days. To understand what is occurring and possibly causing the drop in performance from the first day of competition to the final day, you need to understand a couple of basic principles of exercise physiology. There are two basic types of exercise, low intensity aerobic and high intensity anaerobic. During aerobic exercise the horse has a enough supply of oxygen and can use body fat as the primary energy (fuel) source for work. As the level of exercise intensifies either from duration or effort, the amount of oxygen delivered through respiration is insufficient to maintain aerobic exercise and the horse may lack oxygen for aerobic muscle metabolism. In this situation the horse needs to use muscle glycogen as the energy (fuel) source. In most animals, body fat stores are many times larger than muscle glycogen levels. Muscle glycogen can only be efficiently replenished by feeding starches and sugars, i.e. carbohydrates. In the horse, it takes 48-72 hours for muscle glycogen to be replenished after strenuous exercise even when adequate carbohydrates are in the diet. In comparison, humans can replenish muscle glycogen in about 24 hours.
Now back to the possible issue of not feeding enough carbohydrates to the performance horse. Dietary fat(s) can’t be used by the body to synthesize muscle glycogen, only carbohydrates can do that. It is understandable why some of our performance horses have plenty of energy on the first and probably the second day of competition but lack the proper fuel to feed the muscles, rebuild glycogen stores and perform at an optimum level. These horses often “run out of gas” during subsequent days or runs. If this sounds like your horse and looks like your feeding program, you may benefit from adding a small amount of grain to your horse’s diet. Try adding a small amount of whole oats or flaked corn or mixed feed to your feeding program. For some horses, it may be as little as 0.5lb/d. It is important to provide the fuel the horse needs to compete in the events in which you participate and can recover after a strenuous work out. The gas tank needs to be refilled so that when it comes to the last days of competition your horse is fueled and ready, not out of gas. This might mean more checks cashed or titles earned during the show.