Abstract
Modern cloning methods have become an important technology in artificial insemination which is used to create and maintain pools of genetically superior bull semen. In this study, semen from four identical quadruplet bulls (Q1, Q2, Q3, and Q4) produced by blastomere separation was analyzed to evaluate the differences in reproductive potential, if any, that existed between the identical quadruplet siblings. Analysis of fresh semen collected from 1994 to 1996, showed lower progressive motility and lower sperm concentration for one bull (Q3) compared to his identical brothers (P<0.05). Semen characteristics following freezing–thawing procedures have also been tested for these quadruplet bulls. The percentage of motility, progressive motility, and mean path velocity were lower in Q4 compared with Q1. Moreover, intracellular calcium level and P25b level (P25b is a sperm surface protein proposed to be a potential bull fertility marker) were lower in Q4 compared with his siblings (P<0.05). Cryodamage to Q4’s frozen–thawed spermatozoa were confirmed by a lower percentage of embryo development after in vitro fertilization. Thus, the higher instability of cryopreserved spermatozoa from Q4 and the lower semen production of Q3, compared to their siblings, indicate that differences in semen characteristics can indeed exist among genetically identical animals produced by blastomere separation.
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