ALTERATION OF FOLLICULAR DYNAMICS AND SUPEROVULATORY RESPONSES BY GONADOTROPIN-RELEASING-HORMONE AND FOLLICULAR STRUCTURE IN CATTLE - A FIELD TRIAL

A field experiment was conducted to determine the influence of follicu lar alteration on superovulatory responses. Ultrasonography was perfor med once daily over 4 d prior to gonadotropin treatment (Day 0), on th e day of estrus during superstimulation, and on the day of embryo coll ection to monitor follicular development. Animals were superstimulated between Days 8 and 12 of the estrous cycle. Follicular status was alt ered 2 d prior to initiation of superstimulation (Day 0) with GnRH (Cy storelin, 200 mu g im) administered with (GnRH-puncture group, n=31) o r without (GnRH-no puncture group, n=52) concomitant removal of the la rgest follicle by follicular aspiration. Responses were compared with those of an untreated control group superovulated 8 to 12 d after estr us (n=102). The proportion of animals with a high number (greater than or equal to 2) of large follicles (greater than or equal to 7 mm) on Day 0 was lower (P < 0.001) in the 2 GnRH-treated groups than in the c ontrol group, while the increase in the number of medium size follicle s (4 to 6 mm) on Day 0 was greater (P < 0.02) in the GnRH-puncture gro up. During superstimulation, the proportion of superovulatory cycles w ith a high follicular (greater than or equal to 10 follicles) response was similar in the control and GnRH-no puncture groups. Within the Gn RH-treated animals, follicular and ovulatory responses were greater in the GnRH-puncture than in the GnRH-no puncture group (P < 0.001 to P < 0.02). Despite these changes in follicular and ovulatory responses, however, the mean number of embryos produced did not differ (P > 0.1) among treatments (4.3 +/- 0.4, 3.7 +/- 0.7, and 5.4 +/- 0.8 in control , GnRH-no puncture, and GnRH-puncture groups, respectively). This was due primarily to an increase in the mean numbers of unfertilized ova ( P < 0.005) and in degenerated embryos (P < 0.06) in the GnRH-puncture group. Results indicate that the beneficial effects of treatment with GnRH and follicular puncture 2 d prior to superstimulation on follicul ar and ovulatory responses were limited by an increase in the number o f unfertilized ova and degenerated embryos. (C) 1998 by Elsevier Scien ce Inc.