animal breeding Determining sex from sperm

There is a commercial demand for the ability to predetermine the sex of livestock. For example, a producer may want female calves from the best cows for replacements and male calves for beef production. Dairy producers may want more females for replacing cows or for expansion of their herds. The sex of mammals is determined by the sex chromosomes, or X and Y chromosomes. Animals with two X chromosomes develop into females; animals with an X and a Y chromosome develop into males. Thus, the detection of X and Y chromosomes on sperm has been the focus of research to predetermine the sex of domestic animals.

In one process, sperm is pretreated with a dye that fluoresces when exposed to short wavelength light. The fluorescence is brighter from a sperm bearing X chromosomes, which contain about 4 percent more DNA than the Y chromosome. A stream of dyed sperm is passed through a flow cytometer, a computer determines the degree of fluorescence, and the sperm is separated into different containers. The success rate can be as high as 40 percent. When “sexed sperm” has been used on a commercial basis, though, it has had limited success. The conception rate using sexed sperm is lower in cows, though it is higher in primiparous cows. In addition, sperm are killed in the typing process, and the rate of sexing the sperm is slower than desired. While economical processing of sperm is just getting started, it is expected to become another useful tool in animal agriculture.