A paper on artificial insemination with x- and y-bearing bovine sperm was presented at the annual conference of the International Embryo Transfer Society was held in Salt Lake City, Utah in January, 1996. The study was a cooperative effort of Colorado State University (G.E. Seidel, G.R. Welch, M.D. Holland, and Z. Brink), USDA's Agricultural Research Service in Beltsville, MD (L.A. Johnson), Atlanta Breeders Cooperative in Lancaster, PA (C.A. Allen) and Duo Dairy in Loveland, CO (M.B. Cattell).
Semen was collected from bulls in Pennsylvania, diluted 1:4 with a buffered extender and transported to Beltsville, MD where it was sorted on DNA content at room temperature using a flow cytometry procedure. Sorting rates were up to about 2 million sperm of each sex in about five to six hours. These sorted sperm cells were approximately 90% pure -that is the x- bearing group was about 90% x and the y- bearing group was 90% y.
Sorted sperm were then concentrated by mild centrifugation to 2 million sperm per milliliter. Sortedsperm were shipped by air to Colorado either at 5ø C (about 41ø F) or at ambient temperature.
Heifers or nonpregnant dry cows detected in estrus on the dairy in Colorado were inseminated within 9 to 29 hours after the end of the sperm sorting session. Semen was deposited deep in the uterine horn on the same side as the ovary with the largest follicle as determined by ultrasound just before insemination. In contrast to frozen-thawed semen containing 10 to 30 million sperm cells, these cows and heifers received only 100 to 200 thousand sperm cells.
When sperm was shipped at ambient temperature, none of 10 cows and heifers conceived. However, if sperm was cooled to 5ø C, 14 of 29 were pregnant at 4 weeks after breeding and 12 of 29 (41%) were still pregnant at 8 weeks after breeding. Using ultrasound at 60 to 70 days after breeding, 10 of 12 (83%) fetuses were of the predicted sex, one was of the opposite sex, and one could not be determined. The accuracy of fetal sex closely corresponds with laboratory analysis of the DNA Content of sorted sperm (ie. about 90%). This also agrees with field trials in Scotland where in-vitro fertilized embryos were transferred and carried to term.
In another replicate 33 heifers were inseminated with 0.05 mL of semen (about 50 to 100 thousand sperm) into each uterine horn without use of ultrasound. Only 3 were pregnant at 4 weeks and only 1 at 8 weeks. A third replicate used 38 heifers in a herd near Beltsville. None of those became pregnant after insemination about 22 hour after sorting.
Differences in bulls could account for some of the differences in replicates in pregnancy rates. Other factors may include timing of insemination after sorting, or perhaps insemination techniques differed some among replicates.
What does all this mean? Sorting semen into x-and y- bearing sperm populations is possible but does take more time than conventional handling of sperm. Use of lower semen doses than regular AI does result in pregnancies but at lower rates than optimum at this time.
With current pregnancy rates at about 40%, and accuracy of sex at 90%, how much are you willing to pay for semen giving a 36% chance (.90 x .40) of the gender of your choice (plus a 4% chance of calf of opposite sex)? This method is commercially available in Scotland and it may be available soon in New Zealand and within a year or two in the United States. The process is not practical for regular artificial insemination because fewer than half a million sperm can be separated per hour. First applications will likely be restricted to deep uterine insemination, intratubal insemination, or in-vitro fertilization with embryo transfer. Certainly the potential for extremely valuable offspring will enhance the likelihood of use of such technology. Certainly the extra time it takes to prepare semen will have a cost associated with it.
However, the fact that it can be done is positive. With more research and perhaps screening out bulls that do not work well, this technology may well find its way into the management of our cattle herds.