"A 2005 study cited by FDA, on semen quality from two clones, found clones has a lower pregnancy rate (55% compared to 63%) than natural comparators and almost double the rate of spontaneous abortions. A 2004 study found that the range of rates of development to blastocyst for embryos fertilized in vitro by sperm from six bull clones was lower than that of comparators, while pregnancy and calcing rates of clones were 83%, compared to 90% for comaprators."