Evaluation of enzyme activity in bovine semen.

The aim of this study was to investigate the activity of lactate-dehydrogenase (LDH), alkaline phosphatase (ALP), gamma-glutamyltransferase (GGT), creatinine kinase (CK) and total protein in semen obtained from bulls during winter season. Five animals were included in the trial. Enzymes were assayed by using commercially available kits and expressed as UI/l (Spinreact, Spain) in fresh and frozen seminal plasma and sperm cells. In fresh semen LDH, GGT and CK showed higher activity (P<0.05) in sperm cells respect to seminal plasma (11978 vs 709, 7854 vs 2086 and 1161 vs 203, respectively). In frozen samples LDH was higher (P<0.05) in sperm cells (243 vs 59) while an opposite trend was detected for GGT (28 vs 94). Conventional freezing caused a dramatic decrease of all enzyme levels in both seminal plasma and sperm cells after 6 months but enzymes showed a different decrease thus suggesting a specific sensitivity to freezing with an almost complete decrease up to 99.95% in sperm cells while seminal plasma LDH was the less inactivated (91.6%). Results confirm that enzymes are involved in bovine sperm metabolism ans suggest that they may represent sensitive markers for the evaluation of semen quality before and after storage . the evaluation of seasonality, time-dependent inactivation, as well as the correlation of enzymes activity to conventional semen parameters is in due course to develop an enzyme tool for the evaluation of semen quality.