Alteration of follicular dynamics and superovulatory responses by gonadotropin releasing hormone and follicular puncture in cattle: A field trial

Abstract

A field experiment was conducted to determine the influence of follicular alteration on superovulatory responses. Ultrasonography was performed once daily over 4 d prior to gonadotropin treatment (Day 0), on the day of estrus during superstimulation, and on the day of embryo collection to monitor follicular development. Animals were superstimulated between Days 8 and 12 of the estrous cycle. Follicular status was altered 2 d prior to initiation of superstimulation (Day 0) with GnRH (Cystorelin, 200 μg im) administered with (GnRHpuncture group, n=31) or without (GnRH-no puncture group, n=52) concomitant removal of the largest follicle by follicular aspiration. Responses were compared with those of an untreated control group superovulated 8 to 12 d after estrus (n=102). The proportion of animals with a high number (≥ 2) of large follicles (≥ 7 mm) on Day 0 was lower (P < 0.001) in the 2 GnRHtreated groups than in the control group, while the increase in the number of medium size follicles (4 to 6 mm) on Day 0 was greater (P < 0.02) in the GnRH-puncture group. During superstimulation, the proportion of superovulatory cycles with a high follicular (≥ 10 follicles) response was similar in the control and GnRH-no puncture groups. Within the GnRH-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 GnRHpuncture 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 follicular and ovulatory responses were limited by an increase in the number of unfertilized ova and degenerated embryos.