At the "Wildlife Conservatio Center Laboratory" in Tama Zoo, we work to support breeding in captivity.

One such method is the cryopreservation of semen. In order to ensure the survival of animals in zoos, it is essential that various individuals reproduce. Animals can usually only reproduce in the place and time in which they live. However, if semen can be preserved long-term, it may be possible to reproduce them through artificial insemination or other methods, transcending time and place. We are working on the cryopreservation of semen to expand the possibilities for breeding rare animals.

This year, we have conducted extensive research into the cryopreservation of semen from the endangered Chimpanzee species, and we are pleased to report that we have achieved a preservation method that shows promise for practical application for the first time.

Decky, a male Chimpanzee at Tama Zoo, possesses a valuable bloodline and is an individual we would very much like to see reproduce. Because Decky was raised by humans, he cannot mate naturally, but he hands his semen to his caretakers. In fact, being able to collect semen on a regular basis like this is a rare occurrence. For most animals, opportunities to obtain semen are very limited, and it is not easy to thoroughly consider preservation methods. However, with Decky's semen, we were able to seriously consider cryopreservation methods.

Freezing and preservation should be done as follows:
① The collected semen is examined under a microscope to check the percentage of motile sperm, etc.
② Mix in a special preservation solution so that the sperm do not die when frozen.
③ Place in a storage container and freeze using liquid nitrogen.
Later, the frozen semen will be thawed to check if the preservation was successful. Ideally, the semen should retain as much of its pre-freezing state as possible after thawing.

We will examine the semen under a microscope.	It will be stored in a liquid nitrogen tank.

We conducted freezing tests using several types of preservation solutions until the summer of 2021. However, when we thawed the samples later, unfortunately, in most cases, the sperm had become immobile.
Therefore, starting in September, we began freezing using a newly acquired human preservation solution. When we thawed it for the first time, I felt a mix of anticipation and anxiety. When I looked at the thawed semen under a microscope... "There are quite a few sperm moving actively!"
Compared to previous results, this was clearly closer to the pre-freezing state. We repeated the tests afterward and confirmed reproducibility. Currently, we freeze and store semen on the day we collect it in good condition.

This year, we also had the good news of successfully performing artificial insemination using Decky's sperm (not frozen) (details here). We will continue to cryopreserve frozen sperm in the hope that it will lead to future breeding.

[Takayanagi, Wildlife Conservatio Center Tama Zoo]

(March 11, 2022)