Jianhong Hu
College of Animal Science and Technology, Northwest A&F University

Artificial insemination (AI) is the most widely used biotechnology for genetic improvement through banks of frozen spermatozoa in bull. However, the genetic impact in the AI industry is limited by the efficiencies of semen production, 40-50% of viable sperm lose their integrity or functionality during the freezing-thawing process. Nevertheless, the cryo-damage induced by the cryopreservation can be minimized and significant improvement can be obtained through the use of optimizing cooling rate and cryoprotectant. In recent years, numerous studies have confirmed that the LDL extracted from egg yolk is successful for cryopreservation of semen from boars, bulls and dogs. Trehalose is a non-permeant cryoprotectant known to protect the sperm membrane structure from oxidative and cold shock damage during the freezing-thawing process. Otherwise, there are many methods to detect frozen-thawed semen quality, such as sperm motility, sperm survival time and sperm antioxidant enzymes activity, which can not only forecast sperm fertilizability, but also reflect the differences of freezing resistance in diverse individual sperm. HSP90 is localized in sperm tail in all species examined and the presence of HSP90 can play a role in mediating the fertilizing ability of sperm. Sperm exposed to 8% LDL exhibited the greatest percentages of sperm motility, acrosome integrity and membrane integrity. No difference was observed for membrane integrity between 8% and 9% LDL groups. The extender supplemented with LDL did not exhibit improvement in SOD levels. However, 8% LDL group favored the highest antioxidant activities of CAT, GSH-Px and GSH in comparison to other groups (7%, 9% LDL and the control). Sperm cryopreserved in the extender containing 8% LDL in place of egg yolk exhibited the greatest percentages of post-thaw sperm motility, acrosome integrity and membrane integrity, and favored the highest antioxidant activities of CAT, GSH-Px and GSH. The replacement of egg yolk by LDL in the composition of extenders was beneficial for bull sperm cryopreservation. The effects of varying doses of trehalose on in vitro semen quality parameters and antioxidant activities of frozen-thawed bovine semen were determined in our study. The extender supplemented with 100 mM trehalose exhibited the greatest percentages of sperm motility, acrosomal membrane integrity, and plasma membrane integrity. Extender supplemented with trehalose did not affect SOD levels. CAT and GSH-Px activity were demonstrated to be greater with the supplementation of trehalose. Extender supplemented with trehalose reduced the oxidative stress induced by freezing-thawing and improved parameters of bovine semen quality. The antioxidant characteristics of trehalose may be related to its effectiveness in membrane cryopreservation. The expression of HSP90 was associated with semen characteristics. Related coefficient between HSP90 expression and sperm motility, membrane integrity, acrosome integrity are 0.364, 0.447 and 0.402, respectively. The higher expression of HSP90 prognosticated high motility and freezing resistance of sperm after frozen-thawed. The expression of HSP90 could be utilized in developing a reliable and simple method to determine the bull sperm freezing resistance.