Effect of cryopreservation methods and precryopreservation storage on bottlenose dolphin (Tursiops truncatus) spermatozoa

Research was conducted to develop an effective method for cryopreserving bottlenose dolphin (Tursiops truncatus) semen processed immediately after collection or after 24-h liquid storage. In each of two experiments, four ejaculates were collected from three males. In experiment 1, three cryopreservation methods (CM1, CM2, and CM3), two straw sizes (0.25 and 0.5 ml), and three thawing rates (slow, medium, and fast) were evaluated. Evaluations were conducted at collection, prefreeze, and 0-, 3-, and 6-h postthaw. A sperm motility index (SMI; total motility TM] x % progressive motility PPM] x kinetic rating KR, scale of 0-5]) was calculated and expressed as a percentage MI of the initial ejaculate. For all ejaculates, initial TM and PPM were greater than 85%, and KR was five. At 0-h postthaw, differences in SMI among cryopreservation methods and thaw rates were observed (P < 0.05), but no effect of straw size was observed. In experiment 2, ejaculates were divided into four aliquots for dilution (1:1) and storage at 4 degrees C with a skim milk- glucose or a N-tris(hydroxymethyl)methyl-2-aminoethane sulfonic acid (TES)-TRIS egg yolk solution and at 21 degrees C with a Hepes-Tyrode balanced salt solution (containing bovine albumin and HEPES) (TALP) medium or no dilution. After 24 h, samples were frozen and thawed (CM3, 0.5-ml straws, fast thawing rate) at 20 x 10(6) spermatozoa ml(-1) (low concentration) or at 100 x 10(6) spermatozoa ml(-1) (standard concentration). The SMI at 0-h postthaw was higher for samples stored at 4 degrees C than for samples stored at 21 degrees C (P < 0.001), and at 6-h postthaw, the SMI was higher for samples frozen at the standard concentration than for samples frozen at the low concentration (P < 0.05). For both experiments, acrosome integrity was similar across treatments. In summary, a semen cryopreservation protocol applied to fresh or liquid-stored semen maintained high levels of initial ejaculate sperm characteristics.