Insemination of mares with low numbers of either unsexed or sexed spermatozoa

Two experiments were conducted to determine pregnancy rates in mares insemi nated 1) with 5, 25 and 500 x 10(6) progressively motile spermatozoa (pms), or 2) with 25 x 10(6) sex-sorted cells. In Experiment 1, mares were assign ed to 1 of 3 treatments: Group 1 (n=20) was inseminated into the uterine bo dy with 500 x 10(6) pms. Group 2 (n=21) and Group 3 (n=20) were inseminated into the tip of the uterine horn ipsilateral to the preovulatory follicle with 25 and 5 x 10(6) pms, respectively. Mares in all 3 groups were insemin ated either 40 (n=32) or 34 h (n=29) after GnRH administration. More mares became pregnant when inseminated with 500 x 10(6) (18/20 = 90%) than with 25 x 10(6) pms (12/21 = 57%; P<0.05), but pregnancy rates were si milar for mares inseminated with 25 x 10(6) vs 5 x 10 pms (7/20 = 35%) (P>0 .1). In Experiment 2, mares were assigned to 1 of 2 treatments: Group A (n= 11) was inseminated with 25 x 10(6) spermatozoa sorted into X acid Y chromo some-bearing populations in a skimmilk extender. Group B (n=10) mares were inseminated similarly except that spermatozoa were sorted into the skimmilk extender +4% egg yolk. Inseminations were performed 34 h after GnRH, admin istration. Freshly collected semen was incubated in 224 mu M Hoechst 33342 at 400 x 10(6) sperm/mL in HBGM-3 for 1 hr at 35 degrees C and then diluted to 100 x 10(6) sperm/mL for sorting. Sperm were sorted by sex using flow c ytometer/cell sorters. Spermatozoa were collected at approximately 900 cell s/sec into either the extender alone (Group A) or extender + 4% egg yolk (G roup B), centrifuged and suspended to 25 x 10(6) sperm/mL and immediately i nseminated. Pregnancy rates were similar (P>0.1) between the sperm treatmen ts (extender alone = 3/10, 30% vs 4% EY + extender = 5/10, 50%). Based on u ltrasonography, fetal sex at 60 to 70 d correlated perfectly with the sex o f the sperm inseminated, demonstrating that foals of predetermined sex can be obtained following nonsurgical insemination with sexed spermatozoa. (C) 2000 by Elsevier Science Inc.