88 Effect of Follicular Ablation and GnRH on Recipient Synchrony in Holstein Heifers

Abstract

In Holstein heifer recipients that are synchronized with a single dose of prostaglandin F_2α (PGF_2α), only 65% (on average) are eligible to receive an IVF embryo 7 ± 1 days after oestrus. The high variability in time to onset of oestrus after PGF_2α treatment and the small size of the corpus luteum (CL) on the day of embryo transfer (ET) may explain these results. Synchronizing ovulation might decrease the variability of the interval from treatment to ovulation and maximize the size of the CL. For this purpose, Holstein heifers were randomly allocated (using the lottery method of sampling) to 3 groups: (1) Control (n = 88), a single dose of PGF_2α (500 μg of cloprostenol, Merck, Darmstadt, Germany; Day 0) and transrectal ultrasonography of the ovaries on Day 0 to determine the diameter of the largest follicle, on Days 2, 3, 4, and 5 to determine occurrence of ovulation, and on Day 10 to determine presence and diameter of the CL; (2) follicular aspiration (n = 15), ultrasound-guided follicular aspiration (FA) 4 days before PGF_2α administration and ovarian evaluation as described above; and (3) FA + GnRH (n = 19), FA at Day –4, gonadotropin-releasing hormone (GnRH, 100 µg of gonadorelin acetate, Vetoquinol USA, Fort Worth, TX, USA) on Day 2, and ovarian examination as described in the control group. Data were analysed by one-way ANOVA and proportions by Chi-squared. The interval (days) from PGF_2α treatment to ovulation was not different among groups (3.2 ± 0.4, 3.1 ± 0.2, 3.0 ± 0.1, respectively). However, the variability (residuals) in the FA + GnRH group was the smallest (P < 0.05; high degree of synchrony) in the study (0.1 ± 0.1). Likewise, the FA group (0.5 ± 0.1) had a smaller interval (P < 0.05) compared with the Control group (0.8 ± 0.1). Interestingly, 86% of heifers from FA + GnRH group ovulated in a single day (Day 3; P < 0.05) compared with the FA and Control groups (55% and 53%, respectively). Considering the day of ovulation (only recipients that ovulated 2 to 4 days after PGF_2α treatment) and CL diameter (>20 mm; Nogueira et al. 2012 R. Bras. Zootec. 1, 2129-2133; Yoshida et al. 2012 Anim. Sci. J. 83, 207-212), heifers in the FA and FA + GnRH groups had higher proportion (P < 0.05) of animals selected to be transferred at Day 10 compared with the Control group (93%, 95%, and 67%, respectively). In conclusion, FA induced a more synchronous ovulation and increased the number of recipients ready to be transferred at Day 10 (7 ± 1 days after ovulation). These effects were further improved with the administration of GnRH.