Protein status of exercising Arabian horses fed diets containing 14% or 7.5% crude protein fortified with lysine and threonine

Ten Arabian horses (5 mares and 5 geldings averaging 436±17 kg) were randomly assigned to one of two dietary treatments: LP (7.5% CP fortified with 0.5% lysine and 0.3% threonine) or HP (14.5% CP). Diet composition and nutrient content are shown in Table 1.Horses were conditioned for nine weeks, then an exercise test was performed. It consisted of a warm-up followed by six, one-minute sprints at 10 m/s separated by four minutes of walking on a 6% slope. It concluded with a 30-minute recovery at the walk. Blood samples were taken every two weeks during the conditioning period as well as at rest, during the last 15 seconds of each sprint and at 5, 10, 20 and 30 minutes of recovery during the exercise test. Urine samples were obtained from mares every two weeks. Blood samples were analyzed for albumin, total protein, plasma urea-N (PUN) and creatinine. Urine was analyzed for urea, uric acid and creatinine. Horses were observed daily for clinical signs of protein deficiency. Effects of diet and time were evaluated by analysis of variance with repeated measures. During the conditioning period, there was no effect of diet on plasma albumin (P = .25), total protein (P = .72) or creatinine (P = .21). All values were within the normal ranges reported for horses. There was an effect of diet on PUN (P = .0001) with horses in the high protein group exhibiting greater PUN levels than horses in the low protein group. No difference in urine creatinine levels (P = .78) were observed. Urine urea (P = 0.011) as well as uric acid (P = 0.0001) were lower in the low protein group than in the high protein group. These differences are expected as a reflection of the different protein levels in the diet. During the exercise test, no differences in plasma albumin (P = .32), total protein (P = .81) or creatinine (P = .39) were observed. A greater PUN persisted in the high protein group (P = .0001). This was expected due to the difference in dietary nitrogen. No detrimental effect of the lower level of protein, fortified with amino acids, on protein status was observed during this experiment based on the measurements in this study. These results indicate that the restricted protein level fortified with limiting amino acids was adequate for conditioning and exercise over the nine weeks of the experiment. In a companion study, the lower level of protein fortified with amino acids moderated the acid-base responses to repeated sprints.1