Measuring Serum Metabolites in Heifers

Blood metabolites were analyzed from a subset of heifers from each respective treatment (N = 30). Blood samples were collected at pasture turnout and at the final day of monitoring via jugular venipuncture into serum tubes (10 mL; Becton Dickinson Co., Franklin Lakes, NJ), allowed to clot for 30 min and centrifuged at 1,500 × g at 4°C for 20 min. Serum was separated and stored in plastic vials at −20°C until further analysis. Serum samples were analyzed for glucose and NEFA. Samples were analyzed using the Synergy H1 Microplate Reader (Biotek, Winooski, VT) with the Infinity Glucose Hexokinase Kit (Thermo Scientific, Waltham, MA) and NEFA-C Kit (WAKO Chemicals, Inc., Richmond, VA). The intra- and interassay CV was 2.62% and 3.41%, for serum glucose, respectively and 7.75% and 8.29%, for serum NEFA, respectively.