EFFECTS OF PROCESSING AND STORAGE ON THE MEASUREMENT OF NITROGENOUS COMPOUNDS IN OVINE BLOOD

Four experiments were conducted to evaluate effects of processing and storage of sheep blood samples on measurements of ammonia N (AMN), ure a N (URN), total protein (TP), albumin (ALB), total globulin (GLB), an d the non-albumin non-globulin protein fraction (NAG). Experiment 1 co mpared the effects of using different anticoagulants. Blood samples (n = 15) were collected via jugular venipuncture into one of four evacua ted tubes: no anticoagulant, serum; sodium heparin, plasma; sodium flu oride and potassium oxalate, plasma; tripotassium-ethylenediaminetetra acetic acid (EDTA), plasma. Anticoagulant affected (P < 0.0001) metabo lite values, with TP, ALB, and GLB being higher in heparinized plasma, and URN, NAG, and AMN highest in serum. In addition, blood packed-cel l volume was 12% and 15% higher (P < 0.0001) in samples collected in h eparin and EDTA compared with samples collected in sodium fluoride and potassium oxalate. Experiment 2 investigated the effects of repetitiv e freezing and thawing (0-3 thaw cycles) of plasma samples (n = 15 blo od samples collected in tubes containing sodium fluoride and potassium oxalate). Repetitive freezing and thawing decreased (P < 0.0001) URN and NAG by 21% and 54%, respectively, the latter as a result of a 4-13 % increase (P < 0.0006) in ALB and GLB values. Experiment 3 evaluated the effects of storage length (0-26 weeks) and freezing temperatures ( -20 degrees C vs. -80 degrees C) on plasma samples (n = 16-20 blood sa mples collected in tubes containing sodium fluoride and potassium oxal ate). All nitrogenous metabolites were affected by length of storage ( P < 0.0001). Plasma AMN, URN, TP, and NAG were affected (0.0001 < P < 0.10) by storage temperature, and AMN, TP, GLB, and NAG measurements e xhibited a temperature X day interaction (P < 0.05). In general, TP an d NAG values declined with storage length, whereas URN, GLB, and AMN v alues increased. Plasma AMN increased 74% by Week 1 and 160% by Week 9 , and samples stored at -20 degrees C were 14% higher than samples sto red at -80 degrees C (P < 0.0001). Experiment 4 assessed the effects o f storage of whole blood samples (n = 15 blood samples collected for s erum) at 4 degrees C for 0-7 days. Serum URN and GLB decreased (P < 0. 0001), and TP and AMN increased (0.0001 < P < 0.02) with increasing re frigeration time. Standardized analytical procedures must be followed to obtain reliable nitrogenous metabolite measurements.