Influence of a dominant follicle atresia and estradiol release by ovarian follicles during superovulation in cattle

Abstract

A total of 139 laparoscopies and 106 uterine flushings were performed in 28 female sheep of three different breeds (Finnish Landrace, Merino, German Blackface). Nine 1-year-old Finnish Landrace and German Blackface sheep were used as recipients. Oestrus was synchronised by intravaginal sponges and the donors were superovulated using either 16 mg follicle stimulating hormone (FSH-P) or 1500 IU pregnant mares' serum gonadotrophin (PMSG). Embryo collections were done by laparoscopy through three stab incisions in the area anterior to the udder. A uterine horn was punctured close to the uterine body and a flexible catheter was inserted into the tip of the uterine horn. It was necessary to clamp the tip of the uterine horn with grasping forceps and flush the uterine lumen twice to obtain high recovery rates. Superovulatory treatment led to an average of 4.7 ± 4.6 corpora lutea (CL) without differences between PMSG and FSH-P. A total of 226 ovine embryos were recovered of which 144 (63.7%) were fertilised, including 65 (28.8%) damaged morulae. The remaining portion consisted of 26.5% unfertilised ova and 9.7% empty zonae pellucidae. The embryo recovery rate using laparoscopic technology was approximately 75%. A repeated embryo recovery was possible up to three times on a monthly basis with an efficiency of approximately 75–80%. The fourth flush resulted in a significantly reduced recovery rate (47.4%). The limiting factor for continued laparoscopic embryo collection was the postoperative protrusion of the endometrium at the puncture wounds of the uterine walls. Laparoscopic transfer of eight freshly collected ovine embryos to four recipients led to one pregnancy. Transfer of ten frozen/thawed embryos to five recipients led to three pregnancies. All pregnancies resulted in the delivery of normal lambs.