COMPARATIVE FEEDING VALUE OF A CUBED ALFALFA CORN PLANT PRODUCT AS ANEXCLUSIVE DIET FOR EXERCISING HORSES

In a switchback experiment, six mature Quarter Horse and Thoroughbred geldings weighing approximately 495 kg and in average body condition s core of 5.4 were fed two diets and exercised daily. Horses were random ly assigned to a conventional diet or alfalfa:corn plant cubes as an e xclusive diet. During the 21-day adaptation period, level of work incr eased daily digestible energy requirements to approximately 1.75 times maintenance. Sweat production was estimated on days 0, 7, 14 and 21. A 4-day digestion trial was conducted on days 17, 18, 19 and 20. Horse s performed a standardized exercise test on day 21 by galloping 18 min utes at a heart rate of 150 beats per minute followed by 2 minutes at 200 beats per minute. Venous blood samples, heart rates, respiration r ates and rectal temperatures were taken before exercise, immediately a fter and throughout recovery from the test. Then, the horses were abru ptly switched to opposite diets and the procedures were repeated. No n oticeable digestive disturbances occurred as a result of the abrupt in troduction of diets to horses. Furthermore, no ''cribbing'' problems o r apparent cases of choking were observed throughout the study. Horses consumed the cubed diet slower (P<.05) than the conventional diet. Ap parent digestibilities of dry matter, energy, crude protein, neutral d etergent fiber and acid detergent fiber were not different (P>.1) betw een diets. Only slight increases (P>.05) in body condition were observ ed at the end of each period. Heart rate, respiration and rectal tempe rature increased (P<.05) due to exercise; however, no dietary effects were observed. Horses exercised during period two had lower (P<.05) re spiration rates and rectal temperatures, indicative of easier heat dis sipation with decreased (P<.05) humidity. Plasma lactate and glucose c oncentrations increased with exercise. Overall, horses receiving the c ubed diet exhibited a tendency for higher (P=.08) plasma glucose conce ntrations. Values for plasma glucose were different (P<.05) between di ets at 30 seconds, 1, 2 and 5 minutes recovery. Water intake was not i nfluenced by diet. Sweat loss was similar among horses eating both die ts, and increased sweating was consistent with increased heart rate on the standardized exercise test day. The fecal: urinary ratio of water was slightly higher for horses consuming the cubed diet. However, the fraction of water intake lost through the combination of feces, urine and sweat was similar between diets. Results indicate that horses exe rted similar effort and were neither more nor less prone to early fati gue when fed either diet.