Effect of two feeds and submaximal exercise on plasma norepinephrine and epinephrine


Equine Research Centre, 3801 West Temple Avenue, Building 67, Pomona, California 91768, USA.


4 Arabian horses were used in a randomised, repeated measure design to examine plasma norepinephrine and epinephrine responses to 2 common feeds and subsequent exercise. On each of 4 sampling periods, 2 horses were fed one of 2 isoenergetic meals, either 100% corn or 100% alfalfa, at 22% of their estimated daily energy requirement. Two hours after the meal, each horse was exercised submaximally in 3 consecutive 10 min runs of increasing intensity. Mean ± s.e. heart rates were 132 ± 2, 140 ± 1 and 147 ± 2 beats/min, respectively. Norepinephrine values (nmol/l) were higher in resting horses fed alfalfa (mean ± s.e. 1.98 ± 0.25) than in those fed corn. Epinephrine values were not different between diets (4.48 ± 1.00 alfalfa and 3.86 ± 0.84 corn). During exercise, norepinephrine increased from 2.00 ± 0.45 to 3.24 ± 0.74 for alfalfa and from 0.80 ± 0.17 to 1.79 ± 0.29 for corn fed horses. There was a significant effect of meal with norepinephrine values being higher on alfalfa than on corn. During exercise, epinephrine levels did not change and there was no effect of feed type. These results indicate that a single high soluble carbohydrate meal, fed at 22% of NRC estimates, did not increase sympathetic activity during submaximal exercise.