Production of interspecies chimeric calves by aggregation of Bos indicus and Bos taurus demi-embryos.

Two experiments were conducted to produce interspecific chimeric calves by aggregation of B. indicus and B. taurus demi-embryos. In the first experiment, morulae, compacted morulae, and early blastocysts were collected nonsurgically from Brahman (B. indicus) and Friesian (B. taurus) donors. Embryos were bisected and one demi-embryo from each species was placed in a single zone pellucida. In the second experiment, Brahman (B. indicus) and Hereford-Shorthorn (HS) (B. taurus) demi-embryos were aggregated. The resulting 'chimeric embryos' were transferred nonsurgically to synchronous recipients immediately following microsurgery. Of 112 recipients of 112 chimeric embryos, 29 (26%) were pregnant at 60 days. Of these, 24 (83%) produced full-term calves and 5 (17%) aborted between 2 and 5 months' gestation. From the 24 full-term pregnancies, two sets of twins and 22 singleton calves were born. Of the 22 singletons, 15 were chimeric including six bull calves (one Brahman-Friesian and five Brahman-HS) that were overt chimeras. All the overt chimeras resulted from aggregation of halves of early morulae (precompaction).