Captive breeding of bonobos (Pan paniscus) has proven to be successful, but it remains a challenge to keep sufficient genetic diversity. Therefore, it would be beneficial to store valuable genetics by means of frozen semen followed by artificial reproductive techniques. In this study semen was successfully collected from 4 healthy adult bonobos, between 12 and 23.5 years old and 33.70 and 39.75 kg, using electro-ejaculation under general anaesthesia during management translocation procedures. Semen evaluation pre-freezing showed an average ejaculate volume of 450 µl (100–1000 µl), a total motility of 59% (40–80%), a viability of 69% (38–85%) and 58% (46–72%) normal spermatozoa. Mainly head (18%) and tail (16%) defects were detected on eosin nigrosin stain. Ejaculates were highly concentrated but due to high viscosity, non-homogenous and low volume samples, only estimations of concentration could be made. Ejaculates were split in two equal volumes and frozen in two different extenders, a 1-step Freezing Medium-TYB glycerol (IrvineScientific, Santa Ana, USA) and a 2-step Uppsala diluter.1 Ejaculates were gradually cooled to 5°C in two hours, subsequently stored in liquid nitrogen vapour for 20 minutes, and finally dropped into liquid nitrogen.2 After 48 hours of storage, post-thaw evaluation showed a loss of quality of 15% (5–30%) of motile sperm cells using IrvineScientific medium and 19% (5–30%) using Uppsala diluter. Post-thaw viability was 16% and 20%, respectively. Samples are stored for conservation matters and will be used in future breeding purposes to maintain genetic variety in captive populations.
The authors would like to thank Planckendael Zoo for their cooperation.
1. Peña A, Linde-Forsberg C. Effects of Equex, one-or two-step dilution, and two freezing and thawing rates on post-thaw survival of dog spermatozoa. Theriogenology. 2000;54(6):859–875.
2. Keller D. Bonobo semen analysis and cryopreservation. Bonobo Species Survival Plan; 2012.