How to preserve rhino sperm?

Catherine Reid’s task, supervised by team member Dr. Robert Hermes, is to look for new ways to preserve rhino sperm so that it can be used after months of preservation with minimal losses of fertility. A far-fetched topic for scientific work? Not at all, stresses Catherine Reid. The cryo-conservation of rhino sperm is very important for the conservation of threatened species. Catherine Reid: „Statistics show that the reproduction rate of captive White Rhinos is only about 8 per cent.” In European zoos, 55 per cent of all female animals are in the reproductive age, but so far, only 15 per cent of these animals have reproduced; most of them only once. „These numbers show that the population is not self-sustaining”, says Reid. All the more important is a way to conserve the sperm from male rhinos.

Asked, whether the team could not continue its work with fresh sperm, Reid answers: „This would limit the breeding possibilities.“ If the team used only fresh sperm, a suitable bull – fertile and not related to the female – must be nearby. That is not always the case. So, rhinos have to be transported over far distances for breeding projects. That is expensive and risky for the animals, and the chances of success are not very large. So far, an artificial fertilization was successful only twice world wide, and natural mating is rare. Particularly worrisome: The rarest rhino species – for instance the Sumatra Rhino and the Northern White Rhino – reproduce rarely in captivity. All the more important is a successful preservation of sperm cells by freezing. Thus, the sperm could be used after the death of a bull, livestock transports for mating could be abandoned, and large distances could be bridged by sperm transport. „Additionally, we could introduce new genes from wildlife populations into the breeding programmes of zoos without taking animals from the wilderness“, says Catherine Reid.

Now, what exactly does Ms. Reid investigate? In simple words, she is studying two different methods of freezing. „You can freeze sperm cells very fast with liquid nitrogen or you can freeze cells in two steps by first cooling them gradually“, says Reid. The fast method requires small quantities of sperm and can lead to crystallization which destroys cells or impairs their fertility. Therefore, she is working, together with her colleagues and supervisors at the IZW, on a slower freezing method that avoids crystallization and that can freeze larger quantities. First, the sperm cells are cooled down to 5 degrees Celsius, then the temperature is lowered to minus 50 degrees centigrade. „Beyond that, we are testing different additives to improve the fertility of the sperm celles after thawing.“

The scientist is working in Berlin with a scholarship from the local parliament (“Abgeordnetenhaus”). Recently, she presented her research project to experts from the foundation. It convinced the experts, and the foundation called “Studienstiftung des Berliner Abgeordnetenhauses” extended the scholarship.