Effects of brief postponement of the preovulatory LH surge on ovulation rates and embryo formation in eCG/prostaglandin-treated heifers

The aim of this study was to investigate whether prolongation of the period of preovulatory follicular development after superovulation reduces hetero geneity of oocytes of stimulated follicles with respect to the potential to mature, to ovulate, to be fertilized and to develop into embryos. Heifers were treated with eCG on Day 10 and prostaglandin (PG) 48 h later. At the t ime of eCG administration some of the heifers received a norgestomet implan t (N) to suppress the LH surge. After 96 to 104 h, N was removed and an LH surge was induced with GnRH (G) (N/G); the other animals served as controls . Matured oocytes (Experiment A: n=9, 139 [N/G] and 11, 125 [Control] heife rs, oocytes), zygotes and oviducts (Experiment B: n=8, 44 [N/G] and 9, 72 [ Control] heifers, zygotes) and embryos (Experiment C: n=11, 205 [N/G] and 1 1, 165 [Control] heifers, embryos) were collected at 22 to 26 h, 38 to 52 h and 7 days after the LH surge, respectively. Hatched blastocyst formation of matured oocytes (Experiment A) was analyzed after 11 days of IVC after I VF. In vivo fertilization rate of zygotes, the presence of periodic acid-Sc hiff (PAS) positive granules in the oviduct (Experiment B) and stage of dev elopment of embryos (Experiment C) were analyzed stereomicroscopically. The mean interval between PG and the LH surge was 53.8+/-3 (SD) (N/G) vs. 42.4 +/-4 h (Control). The maximum peripheral estradiol-17 beta concentration (5 29+/-36 [SEM] [N/G] vs. 403+/-17 pmol/L, [Control]) and the response to sup erovulation (25.4+/-2 [N/G] vs. 18.7+/-2 [Control]) were higher in N/G than in Control heifers. Hatched blastocyst formation rate (37.4 [N/G] vs. 33.6 % [Control]), in vivo fertilization rate (69.0+/-14 [N/G] vs. 73.0+/-10% [C ontrol]) and the yield of total embryos (3.8+/-1 [N/G] vs. 5.6+/-2 [Control ]) did not differ between groups. The percentage of heifers with abundant P AS-positive granules in the distal ampulla (0 [N/G] vs. 31% [Control]) was reduced after N/G treatment. Prolongation of the period of preovulatory fol licular development increased the number of mature follicles and ovulations but did not result in higher embryo yield, possibly because of an impaired oviductal environment. (C) 2001 by Elsevier Science Inc.