Not Feeling Hungry? Why Overtraining May Put A Horse Off His Feed

by | 06.26.2017 | 1:21pm

When a racehorse goes off its feed, something is wrong. The horse may have caught a bug, it may have a digestive problem, or it may be in pain. If an examination shows nothing significant, the problem may be overtraining.

When horses do not get adequate rest between workouts, several physiological responses can activate the satiety center in the horse's brain, causing the horse to stop eating. One of these responses occurs when horses are pushed so hard they have to dip into the glycogen reserves stored in their muscles to meet the demands of acute exercise. The breakdown of muscle and other tissues resulting from acute exercise also dumps waste products into the bloodstream, decreasing appetite.

Overtraining can also deplete nutrients from the horse's body, such as important B-vitamins that are essential in the production of energy.

“Interestingly, one of the old trainers' treatments for track-sour horses was to feed them brewer's yeast. One of the nutrients in high concentration in brewer's yeast is Thiamine, a B-vitamin necessary for energy metabolism,” said Dr. Gary Potter, consulting nutritionist and professor emeritus of equine science at Texas A & M University.

Gastric ulcers plague many racehorses, and going off feed can either cause ulcers or be a result of them. When the stomach does not have some type of food in it for the stomach acid to digest, the acid begins to digest the stomach lining instead, and the resulting erosion is an ulcer.

“Most of this whole syndrome can be avoided if trainers will learn how to objectively measure physical fitness in horses, give the horses sufficient rest between workouts in the training phase, and know objectively when they are as fit as they are going to be for the task at hand,” Potter said. “What I mean by sufficient rest is time to allow the horse's physical, physiological, and biochemical mechanisms to return to homeostasis [internal balance] before the horse is worked hard again.”

Perhaps surprisingly, it takes significantly less work for a horse to maintain a level of fitness than it does to attain that level of fitness, but the key is knowing when they've had enough work to get there. Potter strongly recommends trainers use a heart monitor to guide their horses' fitness programs. A heart monitor is a device connected to the horse by two electrodes placed at the armpit on one side and the withers on the other side. The heart monitor produces a digital readout of the horse's heart rate in a receiver worn on the rider's wrist.

When a horse works at a heart rate above 170 beats per minute, it begins to break down stored energy reserves.

“When that happens, it typically takes a horse nine to ten days without further anaerobic work to recover fully,” Potter said. “They can do slow work—at a heart rate of 150 or less—during the recovery period, but they must not do hard work during that period if they are to fully recover.

“The speed at which a horse can work at a heart rate of 170 increases until the horse reaches fitness for a given level of work, then it flattens out. That, in itself, can be used to objectively measure the effectiveness of the work program.

“Typically, a horse's heart rate will reach greater than 230 beats per minute at the end of a race or hard workout. When a horse reaches maximal fitness for a given level of work, the heart rate at the end of the workout will be cut in half in three to five minutes after the work stops. The length of time it takes for a horse to cut the maximum heart rate in half following a hard workout also can be used to measure the progress toward fitness for a given work load because it will be reduced as the horse becomes fit. Any time a horse is worked hard outside these parameters, they were not given sufficient rest between workouts.”

The LARC Test ( is another way to analyze a horse's fitness by calculating how quickly it recovers from exercise. The smartphone application was developed by Argentinian veterinarian Dr. Maria Cecilia Tula and has been used successfully on racehorses in South America. About once a week after a breeze, at five minutes and eight minutes post-work, blood and vital signs are taken from the horse and the resulting data is entered into the application along with training conditions, such as level of humidity and track surface. The LARC Test analyzes the data and delivers the results, which the trainer can use to modify the training program for that horse.

Potter stressed that all horses are individuals that can vary widely in how they respond to training.

“That is why trainers need to use objective measures of fitness on each horse and not 'cookie cutter' them all using the same training program,” he said.

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