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 rand omly 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 nutr ient 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 sample s were taken every two weeks during the conditioning period as well as at r est, during the last 15 seconds of each sprint and at 5, 10, 20 and 30 minu tes of recovery during the exercise test. Urine samples were obtained from mares every two weeks. Blood samples were analyzed for albumin, total prote in, plasma urea-N (PUN) and creatinine. Urine was analyzed for urea, uric a cid and creatinine. Horses were observed daily for clinical signs of protei n deficiency. Effects of diet and time were evaluated by analysis of varian ce with repeated measures. During the conditioning period, there was no eff ect of diet on plasma albumin (P = .25), total protein (P = .72) or creatin ine (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 pr otein group exhibiting greater PUN levels than horses in the low protein gr oup. No difference in urine creatinine levels (P = .78) were observed, Urin e 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 expecte d as a reflection of the different protein levels in the diet. During the e xercise test, no differences in plasma albumin (P = .32), total protein (P = .81) or creatinine (P = .39) were observed. A greater PUN persisted in th e high protein group (P = .0001). This was expected due to the difference i n dietary nitrogen, No detrimental effect of thr lower level of protein, fo rtified with amino acids, on protein status was observed during this experi ment based on the measurements in this study. These results indicate that t he restricted protein level fortified with limiting amino acids was adequat e for conditioning and exercise over the nine weeks of the experiment. In a companion study, the lower level of protein fortified with amino acids mod erated the acid-base responses to repeated sprints.(1)