ATTEMPTS TO SYNCHRONIZE ESTRUS AND OVULATION IN MARES USING PROGESTERONE (CIDR-B) AND GNRH-ANALOG DESLORELIN

Forty Hanoverian mares received an intravaginal device containing 1.9 g progesterone (CIDR-B), which was inserted irrespective of their indi vidual cycles. At CIDR-B removal after 12 days, all mares were treated with PGF2alpha. Heat checks were made daily and all mares were examin ed both rectally and with ultrasound at 24 h intervals. A total of 15 mares (Group A) were implanted subcutaneously with a short-term implan t (STI) containing the GnRH analog deslorelin when the largest ovarian follicle had reached 40 mm in diameter or more, while another 15 mare s (Group B) received deslorelin STI on the third day of estrus; 10 mar es served as controls for groups A (C1) and B (C2). Following deslorel in treatments, mares were rectally examined at 12 h intervals until ov ulation had occurred. Treatment with CIDR-B sharply elevated periphera l blood-progesterone concentrations to levels similar to those seen du ring the CL phase in cyclic mares (3.5 ng/mL) and prevented estrus ons et, but did not prevent silent ovulation as observed in eight mares (2 0%). The number of large follicles increased while CIDR-Bs were in pla ce, and plasma concentrations of estradiol increased slowly. After CID R-B removal and PGF2alpha treatment, the onset of clinical estrus symp toms was synchronized, but ovulations were not. Treatment with deslore lin STI accelerated ovulations in groups A and B, with mean intervals of 47.2 +/- 7.1 and 48.8 +/- 7.1 h as against the 80.0 +/- 57.5 and 65 .3 +/- 42.9 h it took for follicles of equal size in the respective co ntrol-groups, C1 and C2, to ovulate. The percentage of mares that ovul ated within 48 h was 93.3% for groups A and B, and 44.4% and 55.6% for groups C1 and C2, respectively. (A vs. C1 and B vs. C2: p < 0.05). Tr eatment with deslorelin STI increased LH plasma concentrations for 48 h (p < 0.05).