A novel semen extender to accelerate genetic improvement programs

Summary

Poor reproductive performance (McCosker et al., 2010) and variability in reproductive traits (Johnston et al., 2009) that impact productivity have been reported by northern Australian beef cattle producers. These producers have been slow to adopt assisted reproductive technologies (ART), with it estimated that less than 1% are utilising artificial insemination (AI) in their breeding and management programs. This is largely due to the logistical challenges associated with fixed-time AI (FTAI), namely precise timing of insemination in relation to ovulation. Traditionally, AI is done using sperm that have been cryopreserved, however this process causes significant damage to the sperm, reducing the number of viable cells following thawing and limiting their longevity within the female reproductive tract. This poses less of a challenge in dairy herds where AI can be performed on observed heat. By improving the logistics and flexibility around AI regimens and the viability of sperm intended for insemination, AI for selective breeding programs can become a feasible option for producers managing their herds extensively. To do so, we have developed a sperm storage medium capable of maintaining viability without chilling or freezing for up to 14 days following collection.

Objectives

Objective 1: Extender development - To develop and validate a novel, innovative sperm preservation medium that will maintain the viability of fresh-chilled semen for between 2 to 3 weeks after collection.

Objective 2: Extender validation - To confirm through laboratory testing and field trials the fertility of fresh-chilled sperm preserved in the novel medium in terms of iatrogenic damage to the sperm, pregnancy rates and weaning rates.

Key findings

The results of this project show the development of a medium capable of maintaining the fertility of bull sperm during ambient temperature storage. The developed medium ‘NEW Bull’ is compared to the current commercial sperm storage methods (cryopreservation and chilling) with significant improvements in motility parameters. Sperm stored in ‘NEW Bull’ for 7 days were used in a small field trial demonstrating field fertility.

Benefits to industry

‘NEW Bull’ will have many benefits to the industry once commercialised. For bull sperm intended for use within two weeks, ‘NEW Bull’ overcomes the need for cryopreservation. We hypothesise that by circumventing the freeze-thaw process of cryopreservation, sperm survival in the female reproductive tract after insemination will be enhanced, allowing for more flexibility in AI timings and higher pregnancy rates as the need for precise timing of insemination with ovulation will be reduced. Aside from its use in AI, ‘NEW Bull’ can also be used for storage of sperm for IVF and though we have not validated its use with sex-sorted sperm, we have every reason to believe that sperm can be supported before and after the sex-sorting process in this medium as well.

MLA action

Knowledge & IP Transfer Team to progress provisional patent and commercialisation pathway.

Future research

Optimisation of medium manufacturing and development of protocols for best use will need to be done for commercialisation including shelf-storage of the medium, best storage vessels for sperm after extension, and minimum sperm dose used for inseminations. Future research could also be done on determining if this medium is appropriate for use with other ruminants, or if similar media could easily be developed.