Breedplan News
Issue 14
January 2004

Sex Selected Progeny
by Brian Sundstrom

Stud cattle breeders have long dreamed of predetermining the gender of some matings. Where A.I. is being used, sex-sorted sperm would be the way to do this -- how far has this technology advanced? The most promising technology at present is developed by the U.S. company XY Inc. They support research in this field in many countries including projects at Sydney University Vet School. Fiona Hollinshead, who has just completed a Ph.D. in Sydney, provided some of the following information. Other parts I have summarized from a phone discussion with Dr. Mervyn Jacobson of XY Inc.

The current XY Inc. system uses a modified flow cytometer (originally for blood separation) to ’draft’ or separate the male and female sperm. Female sperm have slightly higher DNA content, which allows separation of sperm as they flow ’in single file’ past UV laser and fluorescence detectors. They ultimately flow into two separate collection tubes. While this is done at an impressive 4,000/sec, it can still take approx. 15-20 minutes to produce a 2 million sperm straw (depends on factors such as qualityof the sample/ejaculate). Most Australian frozen semen straws have 25 million sperm, aiming to ’deliver’ 15 m. active sperm on thawing. XY Inc. has added technology developments that allow successful low-dose insemination from straws as low as 2 million sorted sperm.

The sorting equipment is currently very big and immobile, i.e. best where bulls are on site and fresh semen can be collected, sorted and then frozen. The most common beef cattle use at present is therefore in big A.I. centers. U.S. engineers hope more portable equipment will be available within a few years

Fiona has also experimented with sex-separation of frozen-thawed and liquid stored ram and bull semen. In one case, liquid stored semen came from Rockhampton. Both techniques showed promise, but require more semen to start with, as they contain a lower % of viable sperm than fresh semen.

XY Inc works with many domestic species including cattle, sheep , pigs, horses and dogs. Captive animal programs include elephants and dolphins and some endangered species where female numbers need rapid boosting. Some 150,000 ’totally normal’ sex-selected progeny have now been born. The first cattle from sex-sorted fresh semen and A.I. were in 1995; some of these have since contributed to further generations.

While the current technology sounds slow and expensive, the potential is enormous with, for example, juvenile IVF programs. Very young heifers, preselected on BREEDPLAN EBVs, could produce 50 or more eggs each and a straw of sexed sperm can fertilize up to 400 eggs! One of the large northern Australian pastoral companies has recently tried this with 40 heifers, to multiply some valuable new composite lines. I hope to be able to report on this next issue. The XY Inc system is now commercially available in the UK and Argentina with the US, Mexico, Brazil, Canada, China and Japan to follow shortly. Negotiations in Australia and NZ are in progress, with commercialisation planned within 1 to 2 years. It is hard to predict when sex sorted sperm will be more widely used in the average stud. Such technologies can improve rapidly, but are also at times frustratingly slow. I sense things are moving quite quickly, so watch this space or http://www.xyinc.com