Developing Optimal Sperm Cryopreservation for Genetic Management in the Giant Panda
The ex-situ giant panda population is not self-sustaining as many individuals do not reproduce primarily because of behavioral deficiencies and geographic isolation. Techniques including sperm cryopreservation and artificial insemination can improve captive genetic management by ensuring every individual reproduces, regardless of temperament or location.
To compare methods used for giant panda sperm cryopreservation, semen samples from five adult (5.5–20.5-year-old) males were collected, split into three aliquots and cryopreserved using three freezing methods: (1) manual 2-step, (2) automated Cryomed®, and (3) field-ready dry shipper. After cryopreservation, each sample was thawed at: (1) 22°C, (2) 37°C, and (3) 50°C. After thawing, samples were assessed for sperm motility (0–100%), forward progressive status (scale, 0–5; 5 is best) and intact acrosomes (0–100%).
Results indicated that all cryomethods resulted in high quality giant panda sperm post thaw. However, post-thaw sperm motility was higher (p<0.05) in the manual 2-step method thawed at 50°C (70.7±3.2%) and 37°C (68.5±2.9%) and dry shipper method at 50°C (69.5±3.4%) compared to the automated Cryomed® at 22°C (51.9±3.7%), but was similar (p>0.05) to the 2-step/22°C (63.8±2.5%), dry shipper/22°C (58.9±3.7%), dry shipper/37°C (62.9±3.6%), Cryomed®/37°C (60.3±3.5%) and Cryomed®/50°C (65.9±3.1%). Forward progressive status also was higher (p<0.05) using the dry shipper/50°C (3.6±0.1) and 2-step/50°C (3.5±0.1) than the Cryomed® at 22°C (2.9±0.1) and 37°C (3.0±0.1), but was similar (p>0.05) to other methods (2-step/22°C, 3.2±0.1; 2-step/37°C, 3.4±0.1; dry shipper/22°C, 3.2±0.1; dry shipper/37°C, 3.3±0.1; Cryomed®/50°C, 3.3±0.1). Acrosomal integrity did not differ (p>0.05) among cryomethods. These data demonstrate that all methods are effective and result in high-quality post-thaw sperm, but optimal cryopreservation methods for giant panda sperm are the 2-step manual and dry shipper technique when samples are thawed at 50°C.