Time of Feeding Before Competition

One of the most frequently asked questions regarding feeding performance horses is when to feed before a competition.

To answer this, three experiments were conducted by Kentucky Equine Research (KER) to evaluate if feeding hay with and without grain affects glycemic response and hematological responses in Thoroughbred horses at rest and during a simulated competition exercise test (CET) on a high-speed treadmill. The first experiment evaluated how feeding forage along with grain influences plasma variables and water intake. The second experiment was conducted to determine whether these changes affect exercise performance. The third experiment was performed to determine how forage alone affects exercise response.

Feeding hay either before or with grain significantly reduced the glycemic response of the grain meal. Insulin production post feeding was also reduced. In addition, when hay was fed, total plasma protein (TP) became significantly elevated within one hour. Interestingly, feeding only grain resulted in essentially no change in TP, even though the level of grain intake was the same that elicited a large change when hay alone was fed. Water intake was significantly influenced by time of hay feeding.

Following hay feeding, water intake was greatly increased. The increase in water intake also corresponded to increased TP, suggesting that decreased plasma volume may have triggered a thirst response. Feeding grain before exercise with or without hay reduced free fatty acid availability and increased glucose uptake into the working muscle. This would not be beneficial for horses competing in the speed and endurance phase of a three-day event.

Feeding only forage before exercise had a much smaller effect on glycemic and insulin response to exercise than a grain meal. Additionally, feeding forage did not affect free fatty acid (FFA) availability. In horses fed a pre-exercise meal of hay, TP was elevated before and during exercise, and heart rate was elevated during the gallop in the horses receiving ad libitum hay the night before exercise. Both of these responses in the hay-fed horses were probably due to increased gut fill and a movement of water from the plasma into the gut. Horses that grazed in paddocks the night before exercise did not suffer from reduced plasma volume or elevated heart rates during exercise. This is probably because water was able to equilibrate between the plasma volume and gut so there was no reduction in plasma volume before exercise.

The results of these experiments indicate that feeding hay along with grain will result in a decrease of plasma volume and increase in body weight which may be detrimental to performance. Feeding grain with or without hay two hours before exercise will reduce FFA availability and increase glucose uptake by the working muscle. This is probably not desirable during prolonged exercise.

Feeding only forage before competition does not appear to interfere with FFA availability and has no adverse effects other than possibly reducing plasma volume and increasing body weight. If forage is fed in small amounts or if time in a grass paddock is limited, then these effects will probably be minimal. Because completely withholding forage may lead to stomach ulcers, the slight risk of reduced plasma volume and increased gut fill is more than outweighed by the potential benefit to the horse’s long-term health and well-being.