Fertility comparison of frozen bull semen stored in cryogenic deep freezer (-152 °C) and LN2 container.

The present study aimed to use cryogenic deep freezers that could be a feasible alternative for cryopreserved semen storage. A total of 284 straws from three Simmental bulls and 272 Simmental cows were used. The experimental group consisted of 151 semen straws that were stored at -152 °C for a week. Moreover, the control group consisted of 133 semen straws that were stored at -196 °C. Firstly, two samples per bull (n = 6) were examined in terms of sperm kinetic parameters by CASA. Furthermore, plasma membrane, acrosome integrity (PMAI) and high mitochondrial membrane potential (HMMP) were analyzed by flow cytometry. Then, artificial inseminations were performed on Simmental cows with 272 straws belonging to two groups. Then, 56th-day Non-return Rate (NRR56) was determined. All spermatological data were subjected to a linear mixed model. Chi-Square test was performed to NRR56 between storage temperature groups. Also, logistic regression analysis was used to examine the effect of bull, storage temperature and age of cows on pregnancy status. While age of cows was included in the final logistic regression model, effect of bull x storage temperature was not included because it was found as non-significant. The post-thaw PMOT and STR of cryopreserved bull semen, which was stored at -152 °C, had lower and statistically significant values (p < 0.05). However, frozen bull semen, which were stored at -152 °C, kept its fertility ability as which stored at -196 °C. Besides, NRR56 of semen stored at -152 °C and -196 °C were detected as 57.24% (83/145) and 55.91% (71/127), respectively (p > 0.05). Nevertheless, these results should be supplemented with more pre-freezing and post-thaw sperm quality analyses and more fertility data for increasing the accuracy of the method.