131 EFFECT OF BREED AND FROZEN–THAWED RAM SEMEN ON IN VITRO FERTILIZATION AND OVINE EMBRYONIC DEVELOPMENT

Abstract

Ovine embryonic development was evaluated 8 days following in vitro fertilization, after using fresh or frozen–thawed Merino and indigenous (Pedi and Zulu) sheep semen. Semen used was collected twice weekly over a 3-month period with the aid of an electro-ejaculator. Following collection, semen samples were evaluated and semen with acceptable sperm motility and a percentage live sperm of 60% diluted with an egg yolk-based extender (Egg-Yolk Citrate). Semen samples were cryopreserved in straws with a programmable freezer to –130°C and then plunged into liquid nitrogen (–196°C) until used for IVF. Fresh and frozen–thawed semen was used to fertilize the matured oocytes in vitro. A total of 791 oocytes were fertilized using fresh semen and 802 oocytes fertilized using frozen–thawed semen. No significant differences were recorded between the fresh and frozen–thawed semen regarding the embryonic developmental stages. The performance of fresh and frozen–thawed semen followed the same trend, with the cleavage rate gradually declining with the progression in time and the embryonic developmental stage. The lowest developmental rate recorded was the occurrence of blastocyst formation, ranging between 0.4 ± 0.4% and 2.6 ± 1.0%. Regarding breed, no significant difference was observed from cleavage to the 2- to 4-cell stages. The use of fresh and frozen–thawed Zulu semen resulted in a significantly (P < 0.05) higher percentage of 8-cell development compared with the Pedi semen. However, the 8-cell embryonic stage recorded with the use of the Zulu ram semen (fresh and frozen–thawed), did not differ significantly from that of the Merino breed. No significant difference between the breeds regarding blastocyst formation was recorded. The overall cleavage rate, 2- to 4-cell, and blastocyst embryonic developmental stages following the use of fresh and frozen–thawed semen from the different rams were generally lower than those recorded by other researchers. The low blastocyst rates obtained warrant more research regarding the in vitro embryo production technique in order to improve the ovine blastocyst formation rate.