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Sexed Semen
Sexed semen is semen that contains X or Y bearing sperm and is used to produce progeny of a desired sex. The accuracy of methods used to sort semen based on sex can have an accuracy of approximately 90%.

History
The first sperm sorting technology was developed at Lawrence Livermore National Laboratory, where they were able to separate the X- and O- sperm in vole (Microtus oregoni) . Following this breakthrough, multiple different studies were carried out in order to develop a sperm sorting technology that could be used in domestic livestock species. In 1989, researchers at USDA Beltsville Research Center were able to achieve 81% males in rabbits inseminated with Y-chromosome bearing sperm and 94% females in rabbits inseminated with X-chromsome bearing sperm.

Flow Cytometry
The Beltsville Sperm Sexing Technology was one of the first patented semen sorting technologies. This technology is a flow cytometry technique. Essentially, this technology works by staining sperm DNA using the Hoechst 33342 stain, these sperm are then passed through specific wavelengths of a laser beam and the blue fluorescence released from the stained sperm is measured by a photomultiplier tube to be analyzed. The stream of sperm is then split into individual droplets by a crystal vibrator. The individual droplets are then separated based on their electrical charge, positive or negative. This difference in charge is due to the difference in DNA content of X- and Y-bearing semen, as X-baering sperm contains approximately 4% more DNA. A third stream of uncharged droplets is also collected but is discarded (sperm that could not accurately be sexed, no sperm, rarely two sperm, and dead sperm).

Advantages
Thus far, the use of sexed semen is mainly used in cattle breeding programs. The use of sexed semen has revolutionized animal breeding and improves productivity and profitability of livestock production, especially in cattle. For cattle production, sexed semen allows producers to increase the probability of producing progeny of the desired sex. In turn, this can benefit both cow and calf welfare. In the dairy industry, the goal is to produce heifer calves. Heifer calves are desired over bull calves because they help increase herd expansion and are generally worth more when sold than bull calves. Bull calves are generally of little value to producers and this tends to decrease the incentive to implant good husbandry practices for bull calves. In terms of cow welfare, sexed semen can reduce the risk of dystocia as heifers are generally lighter at birth than bull calves.

The use of sexed semen also has genetic advantages over conventional semen. Using sexed semen is estimated to increase herd genetic progress by 4.4%.

Disadvantages
The process of producing sexed semen is slow, making it difficult to make large quantities rapidly. This is why the sperm concentration is lower in doses of sexed semen as it is not practical to use large doses or the same dose used in conventional semen.

One of the main reasons for producers not adopting the use of sexed semen is the decreased conceptions rates. When comparing the conception rates of cows and heifers bred using sexed semen and conventional semen, the conception rate was higher for animals bred using conventional semen. The decreased fertility of sexed semen has been attributed to the lower concentration of sperm in sexed semen straws and the damage to sperm caused by the sex sorting process. This being said, good cattle management, semen handling and well trained inseminators can improve the conception rates of sexed semen.

Potential Future Possibilities for use of Sexed Semen
The main goal to improve the success of sexed semen is to make it more efficient. To do this, a production method that separates sperm at a faster rate needs to be developed. If sexed semen could be produced at a higher rate, it would allow larger sperm doses to be used and this would possibly increase the fertility of sexed semen. Also, larger scale production would make sexed less expensive and potentially adopted by more producers and producers of livestock other than cattle.