Adult cell cloning has now been carried out in a wide range of different mammals including cows, pigs, goats and cats. However in every type of animal it is a very difficult process, with many clones failing for every one successful pregnancy. What is more, many of the animals born as a result of cloning have had serious defects, and have died at birth or had to be put down shortly afterwards.

Twin calves were produced as a result of adult cell cloning for the first time in Japan in 1998, but progress in cloning cattle has been slow, with a high proportion of birth defects and dead calves. There is a lot of interest in cloning commercial milk givers like cows because of their potential for producing therapeutic proteins in their milk, but success has been slow.

Finally, in 2002/3, a group in the US developed a technique for adult cell cloning in cattle which has given them a 1 in 7 survival rate instead of 1 in 20 – a substantial improvement. Whether the calves produced live long and healthy lives has yet to be seen.