UTERINE HORN INSEMINATION OF HEIFERS WITH VERY-LOW NUMBERS OF NONFROZEN AND SEXED SPERMATOZOA

Experiments were conducted to determine 1) pregnancy rates of heifers inseminated with very low numbers of spermatozoa under ideal field con ditions, and 2) pregnancy rates with low doses of sexed spermatozoa. I n Experiment 1, semen from 3 Holstein bulls was extended to 1 x 10(5) or 2.5 x 10(5) sperm/0.1 ml, 2.5 x 10(6) total sperm/0.21 ml were used for the control. Semen was cooled to 5 degrees C, packaged into modif ied 0.25-ml French straws, and used 26 to 57 h after collection. Sperm atozoa were inseminated 24 h after detection of estrus into the uterin e horn of Holstein heifers ipsilateral to the ovary with the largest f ollicle, as determined by ultrasound 12 h after estrus was detected; s ide of ovulation was verified by detection of a corpus luteum (CL) by ultrasound 7 to 9 d post estrus. Pregnancy was determined 40 to 45 d p ost estrus. The side of ovulation was determined correctly in 262 of 2 86 heifers (92%), and pregnancy rates were nearly identical for ipsila teral and contralateral inseminations. Pregnancy rates were 48/118 (41 %), 56/111 (50%), and 35/57 (61%) for 1 x 10(5), 2.5 x 10(5) and 2.5 x 10(6) sperm per insemination (P<.05 between 1 x 10(5) and 2.5 x 10(6) ). There were no significant differences in pregnancy rates (P>.05) am ong the heifers for the 3 AI technicians or the 3 bulls. In Experiment 2, freshly collected semen was transported from Lancaster, Pennsylvan ia to Beltsville, Maryland, and sorted into X- and Y-sperm populations based on DNA difference using a flow cytometer/cell sorter over a 6-h period. Sorting rates were about 100 sperm/sec of each sex at similar to 90% purity. Sorted spermatozoa were shipped similar to 2600 km by air, and in most cases cooled to 5 degrees C during shipping over 6 h in an Equitainer. Heifers were inseminated with 1 to 2 x 10(5) sorted X- or Y-spermatozoa in 0.1 ml within 9 to 29 h of sorting. The insemin ate was either deposited into the uterine horn ipsilateral to the ovar y with the largest follicle as determined by ultrasound at the time of insemination, or half of the inseminate was deposited into each uteri ne hem. None of 10 heifers became pregnant when inseminated with sexed spermatozoa shipped at ambient temperature. Of the 155 heifers insemi nated with sexed spermatozoa cooled to 5 degrees C, 15 of 67 females ( 22.4%) inseminated 9 to 13 h post sorting calved, but only 2 of 78 (2. 6%) inseminated at 17 to 29 h calved. Fourteen of the 17 calves born ( 82%) were of the selected sex. (C) 1997 by Elsevier Science Inc.