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Beyond the Bale : December 2018
62 ON FARM The results from an AWI-funded project undertaken by The University of Sydney have determined that ‘sexed semen’ technology is effective enough to enable woolgrowers to choose whether they want male or female lambs via artificial insemination (AI). SEXED SEMEN VIA AI TO ENABLE SELECTION OF RAM OR EWE LAMBS The ability to choose the production of either male or female lambs would provide a number of benefits for the wool industry. Sex preselection can streamline flock management, reduce costs associated with progeny testing, allow woolgrowers to focus selection on a ewe line, and can improve the rate of genetic gain under certain breeding strategies. At present, these benefits are not being taken advantage of due to a lack of availability of commercialised semen sexing for sheep. However, AWI’s ‘sexed semen’ project aims to deliver a reproductive technology which is already very prevalent in the dairy cattle industry. The project recently conducted an insemination trial in Victoria at Paul Walton’s Wurrook Merino Stud, with Livestock Breeding Services inseminating about 300 ewes to test the fertility of fresh sexed semen that had been ‘sorted’ to contain female X-chromosome-bearing sperm. The results obtained are encouraging. Fertility following laparoscopic AI was excellent with non-sexed control semen inseminated at normal commercial doses achieving 78% pregnancy, while fresh sexed semen resulted in pregnancy rates as high as 65% depending on sperm dose used. Importantly, a significant skew in sex-ratio was achieved at lambing with an indicative success of 93.4% female lambs born to the ewes inseminated with the ‘female X-chromosome-bearing sperm’. These results support the commercial feasibility of fresh ‘sexed ram semen’. Additional research to deliver frozen sexed ram semen is already under way. HOW THE RESEARCHERS SEX SEMEN The only method capable of repeated, proven production of pre-sexed offspring is the ‘flow cytometric’ sex-sorting of sperm. “It's a pretty technical process I've got to admit,” said Associate Professor Simon de Graaf, who along with Dr Jessica Rickard is undertaking the research at The University of Sydney in partnership with Sexing Technologies. “It’s a long way from a ram just doing his thing in the paddock.” The way it works is an ejaculate of semen is collected in the same way as prior to semen freezing for normal AI programs. “But instead of sending it straight for freezing, we add a fluorescent dye that binds with the DNA inside of the sperm. Of the two types of sperm, the female X chromosome bearing sperm has more DNA so takes up more dye than the male Y bearing sperm. “So when the sperm are sent through the flow cytometer and exposed to UV light, the X bearing sperm fluoresce brighter than the Y bearing sperm. We're then able to place a charge on the droplet of fluid that each sperm is contained in – for example the female sperm might be given a positive charge and the male sperm given a negative charge. Then just like sheep going through a set of drafting gates we're able to send the sperm through electrostatic drafting gates and push them to one side or the other, so the female sperm goes into one tube and the male sperm go into another tube. “We then process them and end up with a population of sperm which is either male or female and can then be used for artificial insemination.” The accuracy of the process depends on how fast the semen is processed through the flow cytometer. The slower the speed, the more accurate the process; but if it’s too slow then the procedure becomes economically non-viable. “Shooting the sperm through the flow cytometer at 80 km/h may sound fast, but it still only equates to around 8,000 sperm of each sex produced per second, so when you consider the standard AI dose contains 20 million motile sperm it can take quite a while. Setting the machine at about 90% accuracy seems to be the sweet spot – where you can expect 90% of your lambs to be the required sex, either male or female, and it doesn't slow things down too much.” Dr Jessica Rickard and Associate Professor Simon de Graaf who are undertaking the research at The University of Sydney.
In the Shops - March 2019