Amid the proliferation of heavily promoted false claims, there now is a procedure for sexing sperm that, indeed, works with 90% accuracy. The procedure is not perfect, but it continues to be improved. The sexing procedure is remarkably fast in some respects; nevertheless it takes more than an hour to accumulate enough sexed sperm to make up a conventional dose of semen for AI. For this reason, fewer sperm are packaged per dose of sexed semen than for routine AI. While the sexing process damages sperm slightly, the damage is considerably less than occurs due to freezing.
Although the above limitations are true, flow cytometry/cell sorting has now been used to produce thousands of sexed calves and hundreds of sexed offspring in other species. Accuracy of sexing has been proven over and over to be around 90%, and the incidence of abnormalities in offspring appears to be no different from offspring produced by conventional AI.
The flow-sorting sexing procedure was first developed at the U.S. Department of Energy’s Lawrence Livermore Laboratory in California, and refined and then patented by the U.S. Department of Agricultures’ Beltsville, MD Laboratory. Because of this patent, royalties will be paid to the US government whenever sexed sperm are sold.
The main principles involved in sexing sperm are quite simple:
1. Half of the sperm produced by a male have an X-chromosome, and result in female offspring. The other half of the sperm have a Y-chromosome, and result in male offspring.
2. The bovine X-chromosome has 3.8% more DNA (genetic material) than the Y-chromosome.
3. The dye, H33342, binds to DNA quantitatively, that is, the more DNA, the more H33342 that binds.
4. When a certain wavelength of light is beamed at H33342 bound to sperm, the dye fluoresces, giving off intense blue light.
5. X-sperm with bound H33342 give off 3.8% more blue light than Y-sperm with bound H33342.
6. The flow cytometer/sperm sorter has all the components needed to accomplish the steps just described, including a laser to provide the correct wavelength of light to excite the dye, a detector to measure the amount of light, and a computer to analyze the information.
7. The flow cytometer/sperm sorter also has additional critical components. Sperm are pumped through a thin vibrating tube that breaks the stream of exiting fluid into small droplets that contain sperm. Droplets containing X-sperm are given a positive electrical charge and deflected into a collection tube for sperm to produce heifers. Droplets with Y-sperm are negatively charged and deflected into a collection tube for sperm to produce bull calves. Dead sperm, and those that cannot be sexed, are not collected.
Thus, the sperm sexing procedure is a set of steps based on well known principles. The sperm are sorted, one at a time, at speeds of over 10,000 live sperm/second (5,000 of each sex) under ideal conditions. The sperm exit the equipment at 60 miles per hour and are collected in tubes containing fluid to cushion their fall. After collection, the sperm are frozen, thawed, and inseminated using techniques similar to those used for routine AI.
Hopefully frozen, sexed sperm will be available for purchase in the U.S.A. sometime next year. Large-scale field trials are being conducted to continue to improve the sexed-sperm product.