The "dilution effect" in stallion sperm.

Dilution of semen to less than 20 × 10(6) sperm/mL has been reported to decrease sperm quality in multiple species, a phenomenon known as the semen "dilution effect." Critical evaluation of stallion semen diluted to these concentrations, however, has not been reported. This study evaluated sperm motion characteristics (percent total motility [TMOT], percent progressive motility [PMOT], curvilinear velocity [µm/s], and percent straightness) and plasma membrane integrity (percent plasma membrane intact [PMI]) in semen samples diluted to 2.5 × 10(6) sperm/mL with the addition of 0%, 7.5%, or 25% seminal plasma (groups T-2.5/0, T-2.5/7.5, and T-2.5/25, respectively), or after simple dilution to 30 × 10(6) sperm/mL (group T-30), or simple dilution to a ratio of 3:1 (extender:semen; group T-3:1SD). Evaluations were performed immediately after semen collection (T0), and after 24 and 48 hours of cooled storage (T24 and T48, respectively). The PMI and TMOT were the highest in group T-3:1SD at T0. At T24, the PMI in groups T-30, T3:1SD and T3:1/30, and T-2.5/0 were higher than that in the other groups (P < 0.05), whereas TMOT in group T-3:1SD was higher (P < 0.05) than that in all other groups except T-30. By T48, no difference was detected for PMI among groups T-3:1SD, T-30, and T-2.5/0; for TMOT among groups T-3:1SD, T-30, and T-2.5/0, and T-2.5/7.5 (P > 0.05), whereas PMOT was the highest in groups T-2.5/0 and T-2.5/7.5 (P < 0.05). These findings revealed that treatments in which semen was diluted to a concentration of 2.5 × 10(6) sperm/mL had lower initial PMI, TMOT, and PMOT, but semen quality did not decline after 24 and 48 hours of cooled storage. In this study, TMOT and PMI in dilute semen were less than those in more concentrated semen at T0. This effect, while significant, was small and less apparent after cooled storage.

Recovery of mare oocytes on a fixed biweekly schedule, and resulting blastocyst formation after intracytoplasmic sperm injection.

Oocytes may be collected from live mares from either the stimulated preovulatory follicle or from all visible immature follicles. We evaluated the yield of mature oocytes, and of blastocysts after intracytoplasmic sperm injection (ICSI), for both follicle types. In Experiment 1, mares were assigned to Progesterone (1.2g biorelease progesterone weekly) or Control treatments. Transvaginal aspiration of all follicles was performed every 14 d. Overall, 596 follicles were aspirated, with a 54% oocyte recovery rate. There was no difference between treatments in number of follicles punctured (9.0 to 9.1) or oocytes recovered (4.8 to 5.0) per mare per aspiration session. Of 314 oocytes recovered, 180 (57%) matured in culture. Thirty-six mature oocytes were subjected to ICSI; 33% formed blastocysts (63% per mare per aspiration session). In Experiment 2, the preovulatory follicle was aspirated every 14 d for three to four cycles. Prostaglandin F(2 alpha) was given on Days 6 and 7 after aspiration. A follicle >or=25 mm in diameter was present on Day 13, the day of deslorelin administration, in 23 of 24 cycles, and ovulatory response (granulosa expansion) was seen in 24 of 25 follicles aspirated. Blastocyst development after ICSI was 41% per injected oocyte, or an estimated 33% per mare per aspiration session. We concluded that both aspiration of immature follicles and aspiration of the preovulatory follicle can be performed effectively every 14 d without monitoring ovarian follicular growth. As performed in these separate experiments, aspiration of immature follicles provided more blastocysts per aspiration session.