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

• Published in: Theriogenology Vol. 48; no. 5; pp. 803 - 813
• Main Authors: Blondin, P., Guilbault, L.A., Sirard, M.-A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.10.1997
• Subjects: cow; embryo; FSH starvation; postmortem ovary; superovulation; FSH starvation; postmortem ovary; embryo; cow; superovulation
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/S0093-691X(97)00303-8

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 °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.