The time interval between FSH-P administration and slaughter can influence the developmental competence of beef heifer oocytes.

Superovulation alone may not be enough to result in developmentally competent oocytes. The objective of this study was to determine if a time interval between FSH administration and slaughter and between slaughter and oocyte recovery could increase the percentage of embryos. Beef heifers (n = 20) were superovulated with 1 bolus injection of 25 mg, im FSH-P diluted in saline and then slaughtered at 24, 48 or 72 h after FSH injection and the ovaries transported to the laboratory at 30 degrees C. For 6 of the heifers that received FSH-P and were then culled at 48 h post treatment, oocytes were recovered 1 to 2 h post slaughter from the first ovary and 4 to 5 h from the second ovary. Ovaries from untreated cows were collected and served as controls. The results indicated that FSH-P and culling at 48 h produced 35% >/= 32-cell embryos, significantly more than FSH-P and culling at 24 and 72 h (19 and 14%, respectively; P < 0.05). Furthermore, FSH-P and culling at 48 h produced 25% >/= 64-cell embryos, significantly more than FSH-P and culling at 24 and 72 h and the nontreatment control group (5, 7 and 15%, respectively; P < 0.05). The FSH-P group culled at 48 h produced more >/= 32-cell embryos, with an average of 84 +/- 5 cells/embryo, than the treated groups culled at 24 and 72 h and the untreated group (52 +/- 6, 60 +/- 5 and 63 +/- 3, respectively; P < 0.01). Finally, oocytes left in the postmortem ovaries for 4 to 5 h resulted in higher rates (51% and 41%) of >/= 32- and >/= 64-cell embryos, respectively, compared with that of the untreated control animals (29 and 18%; P < 0.05), but these rates were not different from oocytes left in ovaries for 1 to 2 h (33 and 24%). It is concluded that culling at 48 h after FSH treatment, as well as the conditioning effect on oocytes in warm postmortem ovaries for 4 to 5 h, increases the number of competent oocytes.