Improving bovine semen diluents: insights from the male and female reproductive tracts, and the potential relevance of cervical mucins

Abstract

The commercial applicability of bovine artificial insemination (AI) depends on the effectiveness of diluents for maintaining sperm fertility. Challenges faced by the AI industry due to recent advances in assisted reproduction, and the limitations inherent in using fresh and frozen-thawed sperm for AI, could be overcome with the development of better semen diluents. Research into the different microenvironments of bovine sperm as they progress towards maturity, capacitation and fertilisation is revealing various mechanisms that could be exploited to improve the formulation of semen diluents. These are reviewed here. A rationale for a more detailed investigation of bovine cervical mucus for factors that may allow further progress towards this goal are also discussed.Keywords: bovine sperm, semen diluents, artificial insemination ImplicationsArtificial insemination is used for almost 20% of breeding cows worldwide. There is a need for semen extenders that enhance and prolong semen fertility beyond that which is possible using existing commercial formulations for cryopreservation or liquid semen storage. This could allow the use of reduced numbers of sperm per insemination, enhance the use of bulls of high genetic merit, and facilitate the greater application of fresh and sex-sorted semen. Here we review current information on the microenvironments of sperm as they mature and migrate. We also discuss how this knowledge can be used in the design of next-generation semen diluents. IntroductionArtificial insemination (AI) has facilitated improvements to the genetic merit of dairy herds worldwide through provision of greater access to sires with favourable genetic traits, such as those relating to milk production and health. AI also allows easier herd management, reduces the risk of venereal disease, and improves farm safety. The semen extenders employed to successfully maintain the fertility of sperm are central to the widespread and commercial use of AI and these have been extensively reviewed (Vishwanath and Shannon, 2000;Vishwanath, 2003). However, current drawbacks to storage of sperm in a cryopreserved or fresh (liquid) state highlight the need for improvements to semen diluents.Cryopreservation of sperm facilitates its storage for indefinite periods. It is an indispensable technology to the AI industry internationally with 95% of AI worldwide carried out using frozen-thawed sperm (Thibier and Wagner, 2002). However, higher concentrations of sperm must be used per insemination dose to achieve non-return rates (NRRs) comparable to AI with fresh sperm (Vishwanath and Shannon, 2000). Sperm damage occurs during sperm cryopreservation as a result of mechanical stress to the plasma membrane and the generation of excess reactive oxygen species (ROS) (Bailey et al., 2000). This cryodamage is likely to account for the reduced viability of frozen-thawed compared with fresh sperm. However, cryocapacitation, a phenomenon of sperm cryopreservation (Bailey et al., 2000), could account in part for reduced fertility of frozen-tha...

Evaluation of three hormonal protocols for anovulatory lactating cows under regulations restricting the use of estrogenic compounds

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Review: The epic journey of sperm through the female reproductive tract

“…Sperm reservoirs have a remarkable ability to prolong the viability of sperm and, if we can understand how that is accomplished, we may be able to modify sperm diluents to lengthen sperm lifespan outside of the oviduct (McGetrick et al, 2014). Being able to store bovine sperm for several days would be advantageous in regions of the world where liquid nitrogen is not available or where fresh semen is used routinely due to short transportation times before use (Vishwanath and Shannon, 2000).…”

Editorial: International Cow Fertility Conference ‘New Science – New Practices’ in Westport, Ireland, in 2014

“…In a nonexpansion scenario, sexed semen may be used to increase the value of beef output from the dairy herd though market prices for sexed semen will be important. McGetrick et al (2014) discuss the potential to develop new improved semen diluents. This is based on the results of recent studies of bovine sperm as they progress towards maturity, capacitation and fertilisation.…”