Insemination of heifers with sexed sperm

Data from inseminating 1,000 heifers consecutively with sexed sperm and 370 heifers with control sperm in 1 1 small field trials are summarized. Semen was from 22 bulls of unknown fertility of various beef and dairy breeds, a nd 6 inseminators participated. Freshly collected sperm were sexed using a MoFlo(R) flow cytometer/cell sorter(a) after staining sperm with the DNA-bi nding dye Hoechst 33342; the principle is that the bovine X chromosome has 3.8% more DNA than the Y chromosome. Accuracy approaching 90% males or fema les was achieved. There was little difference in pregnancy rates between se xed, unfrozen and sexed, frozen sperm. In 5 of 6 field trials. there was li ttle difference in pregnancy rates between insemination doses of 1.0 to 1.5 x 10(6) versus 3.0 x 10(6) sexed, frozen sperm. In the most recent trials, pregnancy rates with sexed, frozen sperm were within 90% of unsexed, froze n controls that had 7 to 20 times more sperm/insemination dose; however, in a few trials, control pregnancy rates were substantially higher than with low doses of sexed sperm. There were too few inseminations per bull to test bull differences in pregnancy rates rigorously. Insemination of sexed, fro zen sperm bilaterally into the uterine hems produced pregnancy rates simila r to insemination into the uterine body in 4 of 5 field trials. Pregnancy r ates among inseminators did not differ significantly. There was no excess e mbryonic death between 1 and 2 months of gestation with pregnancies from se xed sperm, and very few abortions occurred between 2 months of gestation an d term. Although rigorous epidemiological studies remain to be done, calves resulting from sexed sperm appear to exhibit no more abnormalities than co ntrols. (C) 1999 by Elsevier Science Inc.