The effect of estrous ewe serum and heparin on in vitro fertilization and subsequent embryonic development in sheep

The aim of the present study was to investigate the effect of adding estrous ewe serum (EES), heparin and BSA at different concentrations to synthetic oviduct fluid (SOF) during in vitro fertilization (IVF) on the cleavage rate and subsequent embryonic development. The three different treatments used were: (i) SOFaa (+3 mg/ml BSA) +20%, 10%, 5% or 0% EES (v/v); (ii) SOFaa (+5% EES) +3 mg or 0 mg/ml BSA; (iii) SOFaa (+5% EES) +10 IU, 5 IU or 0 IU/ml heparin. The addition of 20% EES to the fertilization medium significantly (P < 0.05) enhanced the cleavage rate (78.0 ± 4%) compared to 10% (72.6 ± 6%) or 5% (73.9 ± 2%) EES supplemental. However, blastocyst development rate per oocyte and per cleaved embryo was not affected. Oocytes fertilized in vitro with frozen-thawed semen treated with or without 5 IU/ml heparin significantly (P < 0.05) improved the cleavage rate (85.8 ± 4% and 86.7 ± 8%, respectively) and the embryonic development in vitro expressed as blastocyst development rate per oocyte (23.1 ± 2% and 22.8 ± 9%, respectively), compared to 10 IU/ml heparin (75.5 ± 10% and 18.8 ± 7%, respectively). The presence or absence of BSA in the IVF medium containing 5% EES did not influence the cleavage rate and subsequent embryonic development. Results show that 5–10% EES can improve the in vitro fertilization rate and a 70.8–86.7% cleavage rate may be obtained without the supplementation of heparin or BSA. The addition of heparin in the IVF medium was, thus, not essential for more acceptable fertilization rate under the present conditions and for subsequent blastocyst development, when using frozen-thawed semen.