Effects of cooling rate alterations in critical temperature range and supplementation of anti apoptotic proteins on cryosurvival of Buffalo bull sperm
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Date
2015
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Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana
Abstract
Present study was conducted to standardize the freezing protocol for cryopreservation of buffalo bull semen by applying different cooling rates in critical temperature range and asses the post thaw semen quality by using: a) CASA based motion traits b) Hypo - osmotic swelling test (HOST) c) percent viability test and d) percent sperm abnormalities. Semen was frozen by using nine different programmed freezing protocols including control freezing protocol having nine different cooling rates between 4 °C to -15 °C temperature range and 1 traditional vapour freezing protocol. Data was analyzed to find the best cooling rate between 4 °C to -15 °C temperature range. Similarly seven different programmed freezing protocols having 7 different cooling rates including control freezing protocol were used in -15 °C to -60 °C temperature range, but cooling rate in 4 °C to -15 °C temperature range was kept constant with best cooling rate that was obtained in 4 °C to -15 °C temperature range. From -60 to -140 °C temperature range, cooling rates -50 °C/min was same for each protocol except vapour freezing. The % HOST reactive sperm was significantly (P < 0.05) higher (30.60 ± 3.69) in the protocol with 30 °C/min in 4 to - 15 °C as compared to other protocols in this temperature range, however there was no significant (P > 0.05) difference in the % individual motility, progressive motility and various sperm kinetic parameters (VAP, VSL, VCL, ALH, BCF, STR and LIN), sperm size viability. Total sperm abnormality significantly lower (24.43 ± 2.33) in protocol with 30 °C/min in 4 to - 15 °C as compared to and vapour freezing (37.03 ± 2.8). The percent total motility (39.9 ± 3.3) in protocol with 50 °C/min in -15 to -60 °C temperature range was significantly higher than protocol with 20 °C/min (25.10 ± 3.35) within same temperature range and also percent progressive forward motility (34.2 ± 3.2) former protocol was significantly higher than later protocol (19.80 ± 3.24). Percent HOS reactive spermatozoa in protocol with 50 °C/min (25.0 ± 1.9) in -15 to -60 °C temperature range was different significantly (P < 0.05) higher than other protocols except protocol with 40 °C/min within same temperature range. Buffalo bull, semen freezing curve will be showing 30 °C/min cooling rate from 4 to -15 °C temperature range, 40 or 50 °C/min from -15 to -60 °C temperature range and 50 °C/min from -60 to -140 °C temperature range. Another way to improve the post thaw semen quality was supplementation of semen extender with caspase inhibitors (Z-DEVD-FMK, Z-LEHD-FMK and Z-IETD-FMK @ 2, 4, 6, 10, 20 µM) and Bcl-2 proteins (@ 5, 10, 15 µM). We found that supplementation of Z-DEVD-FMK and Z- LEHD-FMK to the semen minimize the apoptotic like changes that developed during cryopreservation in a dose dependent manner by maintaining mitochondrial membrane potential and prevent externalization of phosphatidylserine by keeping low phospholipase (PLA) A1 and A2 activity. Z- LEHD-FMK @ 2 µM resulted in significantly (P < 0.05) higher % individual motility as compared to other supplementation doses. Z-DEVD-FMK and Z-IETD-FMK to the semen extender did not enhance % individual motility @ all supplementation doses. We found that Bcl-2 protein supplementation @ 5 µM dose improved post thaw semen quality indicated by increase in the % sperms with low PLA activity (non apoptotic sperms) as compare to control