Synchronization of follicle wave emergence before ovarian superstimulation with FSH and ovum pick-up improves in vitro embryo production in pregnant heifers

Abstract

The objective of the present study was to evaluate effects of synchronization of timing of follicle wave emergence, before ovarian superstimulation and ovum pick-up (OPU), on ovarian response and embryo production in pregnant heifers. Pregnant (47-69 days of gestation) Holstein heifers (n = 64), 19.0 ± 0.3 months of age, were assigned in a completely randomized design to one of two groups: synchronization of follicular wave emergence using follicle ablation (Synchronized) or untreated control (Non-synchronized). Superstimulatory treatments consisting of 160 mg (280 IU) of porcine follicle stimulating hormone (p-FSH), administered in four decreasing dose treatments 12 h apart, were initiated 36 h after follicle ablation or at random stages of the follicular wave in heifers of the Synchronized and Non-synchronized group, respectively. Ovum pick-up was performed in all heifers 40 h after the last p-FSH administration and retrieved cumulus oocyte complexes (COCs) were subjected to in vitro embryo production (IVEP) procedures. Ultrasonography was performed immediately before OPU to determine number and size of ovarian follicles. Differences in treatment responses between groups were evaluated using generalized linear mixed models. Total number of follicles at the time of OPU was not different between treatment groups (P = 0.61), however, the number of small follicles (<6 mm) was greater (P = 0.05) in heifers of the Non-synchronized group, whereas number of medium size follicles (6-10 mm) tended (P = 0.09) to be greater in heifers of the Synchronized group. Heifers in the Synchronized group had a greater (P = 0.01) percentage of medium sized follicles and a lesser (P = 0.01) percentage of smaller sized follicles than heifers in the Non-synchronized group. There were no differences (P > 0.15) in total number of recovered COCs, or number of viable COCs between groups. Cleavage percentage (84.5% and 72.8%) and blastocyst percentage (48.2% and 33.4%) were greater (P < 0.01) in heifers of the Synchronized than Non-synchronized group, respectively. As a result, mean number of blastocysts per OPU/heifer was greater (P = 0.006) in the heifers of the Synchronized (8.9 ± 1.0) than the Non-synchronized (5.5 ± 0.9) group. In conclusion, synchronizing the time of follicle wave emergence in pregnant heifers, prior to ovarian superstimulation with FSH and OPU results in a greater superstimulatory response and oocyte competence leading to greater embryo production.

Keywords: Cattle; Follicle ablation; Follicular wave synchronization; In vitro embryo production; Ovum pick-up.