Abstract
The synchronization and ovulatory responses of Sangsari cross bred ewes and metabolism of energy substrates in 8-cell stage embryos to hatched blastocysts stage produced in vitro or in vivo were investigated. Ewes were assigned randomly to receive 37.5 IU of porcine follicle stimulating hormone (FSH-P) daily for the 3 days preceding implant removal (Day 0). Synchronization of estrus was carried out using a 1.5 mg norgestomet (Crestar) ear implant for 12 days. Ewes in estrus were mated two to three times with rams of proven fertility. At the time of first mating each ewe was administered 1000 IU of human chorionic gonadotrophin (hCG) to induce ovulation. Surgical embryo recovery was performed on Days 4 and 6 after onset of estrus (Day 0) and recovered embryos were subjected to comparative metabolism studies with in vitro derived embryos at the same stage of development. The number of corpora lutea (CL), unovulated follicles and overall ovarian activity were recorded for each ewe during the breeding and non-breeding seasons. While the pattern of oxidation was similar among in vitro and in vivo derived embryos, a low pyruvate to lactate ratio was the preferred substrate of embryos derived in vitro. A high level of production of CO2 and lactate resulted from a stress response to the suboptimal culture environment. The first marked increase in the metabolism of glucose by ovine embryos was detected in compact morula stage, but there was no significant increase in the oxidation of glucose after the morula stage. Two different concentrations of glucose were compared, but this did not affect metabolism. However, the rate of incorporation and metabolism of glucose tended to be higher at the 0.56 mmol/L glucose dosage.