الفهرس 
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Abstract
Sperm rheotaxis is established as a long-range guidance mechanism that helps in the guidance and selection of sperm cells inside the female reproductive tract. Sperm rheotaxis has attracted a lot of attention recently and has been used in sperm selection and semen evaluation. The objective of this study was to detect the impact of cryopreservation different steps on sperm rheotaxis, as well as test and establish sperm rheotaxis as a potential parameter in the evaluation of frozen semen in bull, and to study the influence of different microchannel dimensions on the percentage of sperm rheotaxis. This study is considered an important step for a better understanding of the causes of frozen semen reduced fertility in cattle, introducing new parameters for laboratory semen evaluation, and studying the interaction between sperms and the oviduct parts with different dimensions that will eventually lead to improved in vivo and invitro fertility results.
A total sperm number of 317,000 was obtained from six (6) healthy bulls with known fertility. Semen was analyzed inside a microfluidic platform for sperm rheotaxis and sperm kinematics (VCL, VSL, VAP, LIN, BCF). Through using a home-made computer-assisted sperm analysis (CASA) system along with subjective semen analysis (sperm motility, viability, and morphology).
The current study has been divided into 3 experiments. The first experiment studied the effect of various cryopreservation steps on sperm rheotaxis and sperm kinematics as several 41553 sperm for fresh semen, 7109 sperm for extended semen with yolk citrate, 3381 sperm for cryoprotectant added semen, and 112354 sperm for frozen semen were analyzed inside the microchannel using CASA. The results showed that the PR % was not significantly affected by any cryopreservation step. However, sperm kinematics were significantly changed. As velocity parameters (VCL, VSL, and VAP) were significantly reduced, progression parameters (LIN and BCF) showed a significant increase during the critical steps of cryopreservation (cryoprotectant addition and cooling/freezing step). Interestingly, abnormal backward-moving sperm cells were found to swim against the stream (PR in a backward movement). CASA analysis for These backward positive rheotactic sperms revealed significantly lower positive rheotaxis % than normal positive rheotaxis samples from the same bull. Furthermore, all sperm kinematics except BCF were found to be significantly higher in this abnormal sample.
The second experiment was to test and establish sperm rheotaxis as a parameter for laboratory evaluation of bull-frozen semen. So, 21 straws from 3 fertile bulls were analyzed using subjective analysis along with sperm rheotaxis and sperm kinematics using CASA. A large number of sperms were analyzed for each bull (bull 1 =31791, bull 2 = 34977, and bull 3 = 8369). The results indicate that bull 2 has the lowest motility and viability among the 3 bulls, which agrees with sperm rheotaxis and VSL which were also found to be significantly lower in bull 2. In addition, PR has a significant positive correlation with subjective analysis parameters (sperm motility and sperm morphology) and VSL.
The third experiment was designed to study the influence of microchannels of different dimensions on sperm rheotaxis and sperm kinematics. 2 rectangular microchannels were used for this purpose both have the same width (200 µm), but they were different in height as one of them have a height of 100 µm while the height of the other one was 20 µm. The channel with the greater height has a significantly higher PR as well as higher sperm kinematics (VCL, VSL, VAP, BCF) except linearity which was found to be significantly lower.