STABILITY OF GAMMA-GLUTAMYL-TRANSFERASE ACTIVITY IN CALF SERA AFTER REFRIGERATED OR FROZEN STORAGE

Objectives-To examine stability of -glutamyltransferase (GGT) activity in stored serum from neonatal calves. Animals-10 commercial beef calv es between 36 and 60 hours old. Procedure-Serum samples were obtained from the calves, and each sample was divided into 8 aliquots. Serum GG T activity was measured on day 0 (fresh) and days 1, 2, 3, and 4 of re frigerated storage (4 C) and weeks 1, 2, and 3 of frozen storage (-20 C). Results-Serum GGT activities for each of the refrigerated aliquots did not significantly differ from day zero, with serum GGT activity ( expressed as a percentage of initial activity) > 99% on all 4 days. Se rum GGT activity in frozen aliquots decreased significantly after 1 an d 2 weeks of frozen storage, 97 and 98%, respectively; however, this d ecrease in GGT activity was not biologically significant. The observed GGT activity did not decrease significantly in the samples stored fro zen for 3 weeks; these samples retained 99% of initial activity. Concl usion-The observed stability of serum GGT activity indicates that seru m may be obtained, stored, and batch processed at a later time. This s tability during storage is important to the success of a bovine passiv e transfer monitoring program based on GGT activity.