7 EFFECTS OF DIFFERENT TRYPSIN SOURCES AND CONCENTRATIONS ON THE VIABILITY OF BOVINE SPERM PRE- AND POST-CRYOPRESERVATION

The goal of this research was to investigate the effect of different sources and concentrations of trypsin on the viability of bovine sperm as a potential method for removing pathogens similar to the washing methods developed for embryos. Trypsin derived from porcine pancreas (Sigma-Aldrich, St Louis, MO, USA) at 2.5% and 0.25% was compared to the recombinant human sequence (TrypLE Select; Invitrogen, Carlsbad, CA, USA) at 10× and 1× concentrations. Cryopreserved bovine sperm (n = 3 bulls) were thawed and processed using discontinuous (90/45) Percoll density gradient centrifugation; the sperm pellets were then washed (10 min at 300g) in TL-HEPES Solution (Cambrex Corp., East Rutherford, NJ, USA) and then resuspended in 1 mL of the same medium. Aliquots of 200 µL of the washed sperm were then added to 1 mL of each of the 4 trypsin treatments as well as a negative control (without trypsin) and incubated at room temperature. Aliquots (25 µL) of each treatment were examined for progressive motility after 5 min. As a result, the control sperm (no trypsin) increased progressive motility by 6.7% and the 1× TrypLE treatment by 9.3%. However, the 10× TrypLE Select and the 10× and 1× porcine pancreas extracts decreased progressive motility by 8.3, 29.0, and 4.0%, respectively. The objective of the second experiment was to determine if the treatment of bovine semen with trypsin (1× TrypLE Select and 0.25% porcine pancreas extract) before or after cryopreservation would affect sperm quality as compared to cryopreservation without trypsin treatment. Raw semen (n = 6 bulls) was collected, evaluated, cryopreserved, and then thawed using a standard bovine method (Biladyl®; Minitube, Verona, WI, USA) without further treatment (control) or after treatment with one of two trypsin treatments (density gradient centrifugation with 1× TrypLE Select or 0.25% porcine pancreas extract in the 45% Percoll layer and a soybean trypsin in activator (Sigma) in the 90% layer) either before freezing (Treat–Freeze) or after thawing (Freeze–Treat). The results for the 6 individual bull samples were comparable and are presented as means (± SEM) compared to the cryopreserved control (no trypsin treatment). Using the Mann–Whitney Rank Sum Test, no differences (P > 0.05) were found in any of the parameters comparing the crypreserved controls (no trypsin treatment) and the 4 treatments: Freeze–Treat vs. Treat–Freeze using either the recombinant TrypLE Select (1×) or the porcine pancreas extract (0.25%). These results suggest that trypsin treatment, before or after cryopreservation, can be used safely on bovine sperm without affecting viability in vitro. Table 1.Comparison of cryopreserved bovine semen without and with various treatments