The cause of the shorter gestation length for twin calves: A computer simulation

The possibility that the shorter length of gestation for twin calves is because pregnancy is determined by the earlier maturing twin has been investigated by computer simulation. The simulation indicated that this explanation alone could account for only about half the shortening of gestation for natural twin calves, and it is suggested that the combined actions of both twins is superimposed on the stimulus of the earlier maturing twin to initiate parturition. With mixed-species twins produced by embryo transfer, the immaturity of the more slowly maturing Bos indicus is such that it cannot cooperate with the earlier maturing Bos taurus cotwin to shorten gestation to appreciably less than is normal for single Bos taurus pregancies.