For centuries, equine breeders have longed for the ability to select the sex of offspring. Now, thanks to a revolutionary breakthrough in biotechnology, foal sex selection may soon be a reality for breeders. A group of researchers at XY Inc., a recently formed biotech firm, selected the sex of a foal before the mare, Feisty, was ever impregnated. The new filly, an equine phenomenon named Call Me Madam, was delivered on a farm outside Ft. Collins, Colorado, on Aug. 6, 1998.
"We're elated, " says XY Inc.'s CEO, Dr. Mervyn Jacobson. "To produce a beautiful, live foal whose sex was predetermined 11 months earlier is a first on many fronts—scientific, economic and ecologic."
SORTING IT OUT
It's long been know that each egg produced by
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female mammals, including mares, contains an X chromosome, and that each sperm produced by a male carries either an X or a Y chromosome. Therefore, since all eggs are X-bearing, the sex of an offspring is determined by the sperm. An egg fertilized by an X-bearing sperm will result in an XX embryo, which will develop into a filly; the union of an egg with a Y-bearing sperm will yield an XY embryo, or a colt.
The ability to sort X from Y sperm is the key to predetermining the sex of offspring. Until recently, all attempts to accomplish that feat have ended in failure. However, Dr. Larry Johnson, who is conducting research at a U.S. Department of Agriculture (USDA) laboratory in Beltsville, Maryland, has found success. He was able to separate X- and Y-bearing sperm using a low cytometer, an instrument that sends a stream of cells past an analyzer and sorts them according to different characteristics. |
| In this case, sperm with X chromosomes were separated from those with Y chromosomes. The USDA now holds the patent on the technique, and XV Inc. is the only company in the world licensed to use the patented sperm-sorting techniques in nonhuman mammals.
THE ABCs of XY INC.
In 1996, XV Inc. was formed as a joint venture between Cytomation Inc. and Colorado State University Research Foundation to offer gender selection to the U.S. cattle market through sperm-sorting. Cytomation provides its unique MoFlo cell-sorting technology exclusively to XY Inc., and Colorado State University's Dr. George Seidel, a world-renowned reproductive physiologist and authority in low-dose insemination studies, serves as XY's director of science.
Dr. Seidel, who developed a technique that can establish successful artificial insemination in cattle using only 300,000 sperm, rather than the 30 million normally required, thinks that sex selection has the potential to greatly improve the breeding industry.
"Left to natural means, horses, cattle or other animals typically require millions of sperm per impregnation," says Dr. Seidel. "The sex of the resulting offspring is 50-50. The waste from unwanted sexes in animal-breeding industries is enormous."
Additions were made to XY Inc's team in 1997. The company acquired MasterCalf, a British firm engaged in similar work, and brought Dr. Jacobson on board to coordinate efforts between the research teams and bring sperm sorting to the market. Spurred by the success of the company's original mission to use sorted bull sperm to produce large numbers of calves of predetermined sex, XY Inc. then made the decision to apply its knowledge and experience to equine sex selection.
THE SELECTION PROCESS
The semen used to impregnate Feisty came from a stallion named Call Me Mr. Blue, a well-proven stud. Once collected, the semen sample was taken to the laboratory where the DNA, or genetic coding, in each cell was stained with a vital dye (one that does not damage living cells). The dyed sample then was passed through MoFlo, Cytomation's computerused flow cytometer, which can sort thousands of sperm per second. X-bearing sperm contain slightly more vital dye and, therefore, appear slightly brighter to MoFlo's laser detector than Y-bearing sperm. This subtle difference allows the instrument to sort the sperm and to discard any that clearly do not fall into the X or Y category.
An X-bearing sample of sperm from Call Me Mr. Blue was used to impregnate Feisty through oviductal insemination, introduced by flank incision. Thanks to the expertise of Dr.
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Seidel and his low-dose insemination technique, only 150,000 sperm were needed for successful fertilization, rather than the 500 million sperm normally required for equine artificial insemination.
THE FUTURE
Breeding Call Me Madam was just the first step, but it's a very important one. A well-designed program to bring foal sex selection to the horse world continues to unfold at XY Inc. Plans are under way to artificially inseminate several mares with fresh, low-dose sexed semen. Once this technique is accomplished, XY will pursue other methods of artificial insemination, such as using low-dose sexed semen that has been frozen and thawed (cryopreservation) prior to insemination. Successful cryopreservation of sexed semen will allow long-term storage and long-distance transport, and will open new and lucrative avenues in the breeding industry.
"Applications of advanced sperm-sorting for artificial insemination in the United States horse industry alone could be in excess of $300 million a year," says Dr. Jacobson, who added that the international market could more than double that projection.
Dr. Jacobson anticipates that the ability to select gender will be available to the horse industry in the near future, perhaps in as little as three years. XY Inc. plans to license universities, veterinarians and other groups to perform the semen sorting, but the operation will be costly to set up. A MoFlo unit costs $300,000 and requires a skilled operator. What should a breeder expect to pay? Well, breeding quality horses simply is not a low-budget operation. Dr. Jacobson estimates that "initially, it may cost about $5,000; however, prices should drop with time and increased availability. Of course, this cost does not include stud fees, which vary from stallion to stallion. In 1994 alone, horse breeders spent $548 million in stud fees and realized $3 billion in proceeds from horse sales.
While the cost to produce a sex-selected foal may be somewhat high initially, the savings in dollars and animals of unwanted sex should be well worth the cost. Consider competition horse breeders, who often view the "correct" sex of a horse as essential to winning. For example, male jumpers are preferred over females because males have more muscle mass and strength. The polo industry is among the most determined in its sex preference, as mares are thought to learn more quickly and be more agile on the playing field.
Brigitte Von Rechenberg, head of the muscular-surgical unit of the University of Zurich, Switzerland, and owner of top-class Arabian horses, summed it up this way: "From a horse breeder's perspective, time is money. A horse's gestation cycle typically is almost one year. That's a long and expensive wait for a foal that's the wrong sex. If breeders can select a foal's sex, they can plan and build their businesses based on what clients are interested in buying, breeding or raising for show."
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