Abstract
This paper describes a new method for producing identical twin calves developed from pairs of sex-predicted triplet demi-embryos, one of which used for embryo sexing. In addition, we compare this method with the conventionally used twin-bisection method. Bovine embryos (48) were collected 7 d after artificial insemination and then bisected in triplet by micromanipulation, after which one of monozygotic triplet from each embryo was subjected to a sex analysis. Those sexes were determined using the polymerase chain reaction (PCR) method (8/9, 89%) or cytogenic analysis (15/39, 38%, P<0.05). The all remaining 48 pairs of triplet embryos were evaluated as transferable after 20 h of culture in vitro. Of the resultant 23 sex-predicted pairs and 25 sex-incompletelypredicted pairs of demi-embryos, 31 pairs including both groups were nonsurgically transferred one or two demi-embryos into every 41 Holstein recipient. Twenty-two (54%) of the recipients became pregnant and produced 22 live offspring, of which five pairs were identical twins. The pregnancy rate and number of calves were not significantly different from those of conventional twin-bisection method, because 57% (51/89) of pregnancy resulted from twin-bisected embryos with 20 offspring and 14 pairs of identical twins. The sex of the resultant offspring produced using our method coincide with that predicted. These results indicate that the method used here is feasible for producing sex-predicted identical twin.
