Endangered species are living organisms that are nearly to be extinct due to decreasing population due to several physical factors. Preserving them expensive but necessary in order to further study the genetic relationship of the existing species and to fully understand the physiology of every species on earth.
The main priority of preservation of endangered species is the careful handling of organism reproduction. Some of the animals that are extinct in the wild are being studied and the sex cells are being collected and fertilized in vitro. There is a big risk in doing that since there is a big chance for these cells to die while on experimentation and the sources are extremely limited. Scientists are preventing the sex cells from dying while on a culture and keeping them alive while they are being brought back inside the female's body.
They need to understand the overall physiology of a particular animal since they may not respond on that method.
They are trying to preserve the animal and keep them from going instinct. By collecting the sperm and ova, if anything happens they can use science to bring the organism back to life.