- Blood samples should be taken from either jugular or coccygeal veins with a minimal amount of stress. Lower concentrations of Pi and K have been documented in jugular compared to coccygeal blood samples as a result of salivary gland uptake. Blood samples from the mammary veins are not appropriate given the loss of nutrients into the mammary gland.
- Vacuum tubes are color coded (Figure 2) for specific diagnostic test procedures based on the specific anticoagulant or additive present in the tube (Table 1). Plasma from green top tubes is generally preferred, but red top (serum) tubes can be used. It is best to ask the laboratory which sample is preferred.
Table 1 - Description of blood collection tubes used for metabolic profiles Stopper Color Additive Sample Obtained Intended Use/Disadvantages
None Serum Routine use for all tests. Prolonged clot exposure results in decreased glucose and Ca and increased phosphorus. Hemolysis problems in poorly handled sample (Figure 3) Gray Na Fluoride or K Oxalate Serum Glycolytic inhibitor for sensitive glucose analysis Royal Blue Plastic Stopper
Serum, Plasma, or Whole Blood Trace mineral analysis, especially Zn Lavender EDTA Whole Blood, Plasma Routine use for Complete Blood Count/ EDTA chelates Ca, Mg and decrease enzyme activities Green Na Heparin Plasma, Whole Blood Routine analyses for either plasma or whole blood/ No effect on metabolites Red and Gray Serum Separator plug Serum During centrifugation gel plug moves to completely separate the serum from the clot/ hemolysis can be a problem
- All Samples should be properly identified with animal and group identification and date of collection. Use herd records to ensure the selected animals fit the defined group parameters, especially relative to parity and days in milk (or time relative to calving). Other pertinent information for interpretation of the metabolic profile would include milk production level, milk composition, pregnancy status, and body condition score. Again, metabolic profiling should only be used as a complement to more traditional diagnostic procedures.
- Recognize time of sampling relative to feeding and feeding management may also influence metabolite concentrations. If non-esterified fatty acid (NEFA) concentrations are of specific interest, then samples are best collected prior to the first primary feeding bout. If beta-hydroxy-butyrate (BHB) or blood urea nitrogen (BUN) is of primary interest, then samples are best collected when convenient and account for feeding time effects. This will be less of a concern in TMR-fed herds. If herds are being repeatedly sampled as a monitoring tool, samples should be taken at approximately the same time of day to minimize the diurnal and prandial variation between sampling periods.
- Meticulous effort should be taken to prevent hemolysis of any sample. All samples should be iced, but not frozen, immediately after collection and kept refrigerated until processed.
- Samples should be transported on ice (Figure 4) until properly refrigerator and shipped to the laboratory.
Figure 2. Color coded sample collection tubes commonly used for metabolic profiling.
Figure 3. Various stages of hemolysis in serum samples. Deeper shades of red indicate more severe hemolysis than lighter shades.
Figure 4. Samples properly stored in cooler on ice for transport after collection.