The Effect of Dietary Protein Level on Exercising Horses

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Abstract
Six mature Quarter Horse mares were used in a crossover design to assess the effect of dietary protein level on metabolic response to exercise. After a 2-wk adaptation period to either a 12.9% (control) or an 18.5% CP (high-protein) diet, each mare performed a standard exercise test. The test consisted of a 15-min exercise period at 4.5 m/sec on a 9% grade motorized treadmill. Exercise resulted in an increase in heart rate (P < .001), but there was no difference (P > .05) between dietary treatments. In the jugular vein, lactate increased (P < .01) from 6.3 to 52.0 mg/100 ml in the control group and increased from 6.3 to 45.6 mg/100 ml in the high-protein group. There was an interaction (P < .05) between diet and exercise for lactate. Plasma NH3 increased (P < .001) during exercise, but not until the 15th min, at which time NH3 increased over fourfold in both groups. Dietary protein did not affect NH3; however, urea-N was higher (P < .001) in horses receiving the high-protein diet. Plasma alanine increased from 13.6 to 30.3 µmol/100 ml and glutamine increased from 49.3 to 62.5 µmol/100 ml in the control group. In the high-protein group, alanine increased from 10.2 to 25.8 µmol/100 ml, whereas glutamine increased from 39.3 to 49.2,µmol/100 ml. Our study detected no metabolic evidence for a detrimental effect of excess dietary protein in horses exercising on a graded treadmill at 4.5 m/sec for 15 min. Copyright © 1988. American Society of Animal Science . Copyright 1988 by American Society of Animal Science.