 As the eggs in a female canine are only fertile during the estrus phase of the estrous cycle , the eggs could only be harvested during a three @-@ week period each year . Due to complexities with removing eggs from canine ovaries the eggs had to be extracted from the oviduct , which required constant monitoring to achieve . The nucleus of each egg was replaced with the cell from the ear of the adult dog and then electrified and fused using a chemical reaction . The embryos were then transferred to the surrogate dogs . Three of the surrogate mothers became pregnant and two successfully gave birth . Snuppy , the first to be born , survived while the other died two weeks after birth . This process of cloning Snuppy took nearly three years of intensive effort . 
