Nitrogen Metabolites During Exercise in the Horse

239 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.In experiment one, eight Quarter Horse mares were intravenously infused prior to exercise with either sodium acetate (control) or ammonium acetate to determine the effect of elevated ammonia (NH$\sb3$) levels on fatigue development and muscle metabolism. The horses were exercised on an 11% grade treadmill at 4.4 m/s, carrying 27 kg of lead. Time to fatigue was not (P $>$.05) different between groups. Middle gluteal muscle (im) NH$\sb3$ and lactate increased (P $$.05). Treatment did not (P $>$.05) affect plasma or im ala, glu or gln. Urinary orotic acid/creatinine ratio was not (P $>$.05) affected by exercise or treatment and suggests that the urea cycle was not impaired during exercise. These results did not show any metabolic evidence for a role of increased blood NH$\sb3$ in fatigue development at the level of the central nervous system.In a second experiment, six mature Quarter Horse mares were used in a crossover design to assess the effect of dietary protein level on energy and nitrogen metabolism during exercise. After a 2-wk adaptation to either a 9.0% (control) or an 18.5% crude protein (high-protein: HP) diet, each mare performed an exercise test (ET). The ET was performed in the absorptive stage of digestion and consisted of a 15 min exercise period at 4.5 m/s on an 11% grade treadmill. The dietary treatment did not (P $>$.05) affect heart rate or oxygen uptake; however, exercise resulted in an increase (P $$.05) effects due to treatment. A diet by exercise interaction (P $<$.01) occurred for plasma ala, being lower in the HP horses. Plasma urea-N, the urinary urea-N/creatinine and orotic acid/creatinine ratio were higher (P $<$.001) in the HP group. The excretion of urea-N in sweat was also higher (P $<$.001) in the HP group. Substrate utilization during exercise was not altered by excess dietary protein; however, excess protein stimulated nitrogen metabolism in the horse at rest, during submaximal exercise and during recovery.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD