Steroid concentrations in follicular fluid aspirated repeatedly from transitional and cyclic mares.

The objectives of the present study were to determine follicular progesterone (P4) and estradiol-17beta (E2) in transitional mares and to compare follicular steroid concentrations between transitional and cyclic mares. Follicles > 8 mm were aspirated under transvaginal ultrasound-guidance 4 times at 3 to 4 day intervals (T1-T4) in Norwegian pony mares during vernal transition. During the breeding season, follicular aspirations were conducted in each mare on Day 6, Day 14 and Day 18 after ovulation of 3 separate estrous cycles (Day of ovulation = Day 0). Plasma and follicular fluids were analyzed for P4 and E2 with ELISA and RIA, respectively. Plasma P4 concentrations remained below 1 ng/mL throughout T1-T4, while the follicular P4 concentrations increased significantly to cyclic levels after the first transitional aspiration. Plasma E2 concentrations similarly remained at low levels during the course of the transitional aspirations, while the follicular E2 concentrations increased gradually over the 4 aspirations to cyclic concentrations. The mares ovulated on average 9.8 +/- 1.6 (mean +/- SEM) days after the last transitional aspiration, and 16.6 +/- 0.2, 11.3 +/- 1.5 and 23.2 +/- 4.4 days after aspirations conducted on Day 6, 14 and 18, respectively. The present study demonstrates that in the transitional mare newly developing follicles exhibit biosynthesis of P4 and E2. Furthermore, an increase in follicular steroid concentrations is not necessarily reflected in the peripheral steroid concentrations.

Effect of administering a crude equine gonadotrophin preparation to mares on follicular development, oocyte recovery rate and oocyte maturation in vivo.

In mares, the shortage of oocytes and the variability in nuclear maturation at a certain time of the oestrous cycle hinders the optimization of methods for in vitro maturation and in vitro fertilization. Increasing the number of small-to-medium-sized follicles available for aspiration in vivo may increase the overall oocyte yield. The aims of the present study were to investigate whether administration of crude equine gonadotrophins affects follicular development, oocyte recovery rate, in vivo oocyte maturation and follicular concentrations of meiosis-activating sterols. During oestrus, all follicles >/= 4 mm were aspirated from 19 pony mares (first aspiration: A1). Over the next 8 days, the mares were treated daily with either 25 mg crude equine gonadotrophins (n = 10) or physiological saline (n = 9). Between day 1 and day 8, follicular growth was monitored by ultrasonography. On day 8, all follicles >/= 4 mm were evacuated (second aspiration: A2) and nuclear maturation of the recovered oocytes was assessed after orcein staining. Follicular growth between A1 and A2, as well as the number and size of follicles at A2 were similar for control mares and mares treated with crude equine gonadotrophins. The oocyte recovery rates at A1 and A2 were similar. At A2, the oocyte recovery rate and oocyte maturation in vivo were not affected by treatment with crude equine gonadotrophins. The number of expanded cumulus oophorus complexes recovered from follicles

Repeated transvaginal oocyte aspiration in unstimulated and FSH-treated mares.

Transvaginal ultrasound-guided follicular aspiration was conducted repeatedly in 5 cyclic mares. Three techniques were used and the aspirations were performed either > or = 23 d apart (A1, B1, C1) or 6 d apart (A2, B2,C2). During the A1 and A2 aspirations, the follicular cavity was flushed manually 8 to 10 times with flushing medium-filled (60 ml) syringes, while an electrical aspiration pump was used for the B1, B2, C1 and C2 aspirations. Prior to aspirations C1 and C2, the mares were treated daily with porcine FSH (100 mg, im) for 4 d. Aspiration was conducted 24 h after the last FSH injection. A total of 212 follicles with diameters varying between 5 and 23 mm was aspirated. The oocyte recovery rate was significantly higher (P = 0.004) from aspirations conducted with a > or = 23-d interval (35.8%) than from those aspirated 6 d after the previous aspiration (18.4%). Mode of evacuation and flushing (pump or syringe) and FSH treatment of the mare had no detectable effect on the oocyte recovery rate or on the cumulus dimensions of the aspirated oocytes. More than 80 % of the oocytes were at the germinal vesicle or diakinesis stage.