Sexed Semen has Arrived
Posted: June 8, 2005
After years of rumors that sex semen is just around the corner, it has arrived and is commercially available. Maximizing the potential benefits of incorporating sexed semen into your management program will take careful planning and realistic expectations for what the technology will provide. The process of sorting semen by sex is slow and expensive, but consistently yields 90% heifer calves. Sperm that have been treated with a fluorescent dye are sorted through a flow cytometer individually. The X chromosome (female chromosome) contains 4% more DNA than the Y chromosome and will fluoresce more brightly under a laser, which facilitates sorting the sperm by sex. You can generally expect to pay $50 or more per straw beyond what you would expect for non-sexed semen from the same bull. Some companies may offer young sire semen that has been sexed.
The slow sorting process necessitates that sexed semen will contain a lower concentration of sperm per straw (approximately 1.5 million) than non-sexed semen (approximately 20 million). This has a negative impact on fertility. Conception rate has been approximately 20% lower for virgin heifers in field trials using sexed semen. For this reason it is NOT recommended to inseminate lactating cows with sexed semen. Field research indicates that you can expect a 35%-40% conception rate for virgin heifers with well managed heifer reproduction programs.
Despite the cost and lower fertility of sexed semen, there are still many commercial applications with this technology. Any herd that is planning a future expansion should be using sexed semen. Increasing the number of heifers will allow a herd to expand internally, which has many advantages. Biosecurity risks associated with purchasing replacements will be eliminated. Herd growth will be at a steady rate, which will reduce some of the management challenges associated with making large jumps in herd size at one time. There will be challenges handling a growing heifer herd, but imagine having the replacements on hand to fill that new barn rather than having to purchase heifers and cows in a relatively short time frame once the expansion is completed! Some highly leveraged herds are operating under-capacity and are not able to purchase more animals. Those herds should be seriously contemplating sexed semen.
There are implications for sexed semen beyond growing your herd. Herds of any size will realize calving ease advantages when using sexed semen. Unfortunately, many producers are forced to hang onto a high SCC cow, or other problem cows to keep the barn full. With a ready supply of replacements, herds can cull more rigorously to create a healthier, more productive herd. Herds will be able to aggressively cull cows with Staph aureus mastitis and Johne's disease. Culling your low producers and problem breeders will also help improve your herd genetically.
Each producer will have to determine how to best incorporate sexed semen into their management system. Ideally, all heifers would be impregnated with sexed semen. Age at first calving might increase slightly because lower fertility will require more services. Researches at the University of Wisconsin-Madison have suggested using sexed semen for first services in your heifers, and then use non-sexed semen subsequently. This would provide over 60% female calves from first calf heifers with minimal impact on age at first calving. Herds with age at first calving lower than 24 months can probably use sexed semen for 2 – 3 services without risking an unacceptably high age at first calving. The researchers also explored the possibility of creating embryos through in-vitro fertilization with sexed semen and implanting them in heifers. The process could be cost effective if ovaries harvested from your better slaughter cows were used to provide oocytes.
Some Artificial Insemination cooperatives and smaller companies are now offering sexed semen. You will probably have to special order the semen so you will need to plan ahead. Sexed semen is here and now is the time to begin incorporating this technology into your management system.
C. D. Dechow, Assistant Professor of Dairy Cattle Genetics, Department of Dairy and Animal Science