Fertility of sperm from a tetraparental chimeric bull

Comparison of hybrid and purebred in vitro-derived cattle embryos during in vitro culture

Frozen-thawed spermatozoa collected from a beef bull (Japanese Black) were used for in vitro fertilization (IVF) of matured oocytes obtained from dairy (Holstein) and beef (Japanese Black) females. Embryos were examined for fertilization, cleavage rate, interval between insemination and blastocyst production (experiment I), total cell number per embryo and sex ratio during blastocyst formation (experiment II), and blastocyst production rate of zygotes that developed to 2-, 4-, and 8-cell stages at 48h post-fertilization (experiment III). Fertilized oocytes were cultured in vitro on a cumulus cell co-culture system. The fertilization and cleavage rate of oocytes groups were similar, however, the blastocyst production rate was greater (P<0.05) in hybrid than from purebred embryos (27% versus 20%). Development of blastocysts produced from hybrid embryos developed at a faster rate than blastocysts produced from the straightbred embryos. In hybrid embryos, blastocyst production was significantly greater on day 7 (56%) and gradually decreased from 20% on day 8 to 17% on day 9. In contrast, blastocyst production rate from the purebred embryos was lower on day 7 (17%), increasing on day 8 to 59% and then decreased on day 9 to 24%. The total number of cells per embryo and sex ratio of in vitro-produced blastocysts were not different between hybrid and purebred embryos. The number of blastocysts obtained from embryos at the 8-cell stage of development by 48h post-fertilization (94%) was greater (P<0.01) than the number of zygotes producing blastocysts that had developed to the 4-cell stage (4%) and the 2-cell stage (2%) during the same interval. These results show that the blastocyst production rate and developmental rate to the blastocyst stage were different between hybrid and purebred embryos, and that almost all of the in vitro-produced blastocysts were obtained from zygotes that had developed to the 8-cell stage 48h post-fertilization.

The effect of sperm-oocyte incubation time on in vitro embryo development using sperm from a tetraparental chimeric bull

The present study was designed as 5 x 4 factorial to investigate the effects of using sperm from 5 bulls, and varied sperm-oocyte incubation times (5, 10, 15 and 20 h) on the fertilization, cleavage rates and blastocyst formation on an in vitro bovine embryo production system. The bulls included a tetraparental Chimera, its sires (Japanese Black and Limousin), its maternal grand-sires (Japanese Brown and Holstein). The proportion of polyspermy, 2-pronuclei formation, fertilization, cleavage and development to blastocyst were affected (P < 0.001) by the duration of sperm-oocyte incubation, as well as by the interaction between bulls and their corresponding sperm-oocyte incubation time. Blastocyst rate observed after 5 h in oocytes inseminated with Chimera, Japanese Black and Limousin were higher (p < 0.05) than those observed at 20 h incubation. The proportion of blastocysts from oocytes inseminated with Japanese Black observed at 10 h of incubation did not differ from that of Chimera, but both were higher (p < 0.05) than those observed for the Limousin, Japanese Brown and Holstein sires. The present study showed that there was an effect by the duration of sperm-oocyte incubation on in vitro embryo development. The optimal time of sperm-oocyte incubation for the Chimera was similar to that of its sires (Japanese Black and Limousin) but differed from its maternal grand-sires (Japanese Brown and Holstein). The fertilization rates for the sperm from the Holstein bull increased up to 15 h suggesting that this might be the only bull that would benefit from a long incubation period for insemination.