Improved quality of cryopreserved cheetah (Acinonyx jubatus) spermatozoa after centrifugation through Accudenz.

Sperm cryopreservation, in combination with assisted reproductive techniques, is a valuable tool for the genetic management of endangered felids. However, the acrosome of the cheetah spermatozoon is especially sensitive to cryopreservation, with approximately 40% of spermatozoa experiencing acrosomal damage immediately after thawing and then another approximately 15% loss during the next 4 hours in vitro. Additionally, thawing causes a reduction in sperm motility by approximately 20% with another decrease of approximately 12% during subsequent incubation in vitro. We hypothesized that slow removal of glycerol from cryopreserved cheetah spermatozoa using an Accudenz gradient would improve acrosomal integrity, sperm motility longevity, and structural morphology. Accudenz was compared with traditional cheetah sperm processing methods for glycerol removal that involves washing, multistep resuspension, and swim-up processing. Electroejaculates (n = 21 total from 8 males) were washed in Ham F10 medium, and sperm pellets were resuspended in TEST-yolk buffer with 0% glycerol. Samples were cryopreserved in straws in 4% final glycerol, thawed, and assessed for percent intact acrosomes (% IA), percent motility (% M), and forward progressive status (FPS; scale, 0-5). Sperm motility index (SMI) was calculated as (% M + [FPS x 20]) / 2. In study 1, glycerol removal by centrifugation through an Accudenz gradient (4%, 10%) was compared with traditional sperm washing (control) and multistep resuspension protocols. At each time after centrifugation (hourly for 4 hours), % IA was improved (P < .05) for Accudenz (range, 36%-39%) compared with control (30%-33%) and multistep (29%-33%) treatments. In study 2, a modified Accudenz protocol was compared with traditional washing and was found to improve (P < .05) SMI (range, 52-64) compared with controls (range, 41-52) at each time postthaw after centrifugation. In study 3, swim-up processed sperm were compared with those treated by centrifugation through Accudenz and traditional sperm washing for improving sperm morphology. The percentage of structurally-normal sperm recovered postthawing increased (P < .05) for both the Accudenz (38%) and swim-up (33%) treatments compared with controls (21%). Percent IA and SMI also were improved (P < .05) for Accudenz (range, 39%-47% and 46-59, respectively) compared with controls (range, 26%-33% and 40-53, respectively). Results indicate that using Accudenz for glycerol removal from cryopreserved cheetah sperm mitigates the significant loss in sperm quality that occurs after freeze-thawing. This alleviation of cellular damage resulting from cryopreservation contributes to a more than 10% improvement in overall sperm motility and, more importantly, allows retention of 40% or more of sperm with intact acrosomes.

Ejaculate traits in the Namibian cheetah (Acinonyx jubatus): influence of age, season and captivity.

The objective was to examine the influence of animal age, season and captivity status on seminal quality in wild-born cheetahs (Acinonyx jubatus) in Namibia, Africa. Animals were divided into three age categories: juvenile (14-24 months; n = 16 males, 23 ejaculates); adult (25-120 months; n = 76 males, 172 ejaculates); and aged (>120 months; n = 5 males, 5 ejaculates). Seasons were categorised into hot-wet (January-April), cold-dry (May-August) and hot-dry (September-December). A comparison between freshly wild-caught (n = 29 males, 41 ejaculates) and captive-held cheetahs (n = 68 males, 159 ejaculates) was also conducted. Raw ejaculates contained 69.0 +/- 1.1% motile spermatozoa (mean +/- s.e.m.) with 73.6 +/- 1.5% of these cells containing an intact acrosome. Overall, 18.4 +/- 0.9% of spermatozoa were morphologically normal, with midpiece anomalies being the most prevalent (approximately 39%) defect. Juvenile cheetahs produced ejaculates with poorer sperm motility, forward progressive status, lower seminal volume and fewer total motile spermatozoa than adult and aged animals. Spermatogenesis continued unabated throughout the year and was minimally influenced by season. Proportions of sperm malformations were also not affected by season. Ejaculates from captive cheetahs had increased volume and intact acrosomes, but lower sperm density than wild-caught counterparts. In summary, Namibian cheetahs produce an extraordinarily high proportion of pleiomorphic spermatozoa regardless of age, season or living (captive versus free-ranging) status. Young males less than 2 years of age produce poorer ejaculate quality than adult and aged males. Because (1) all study animals were wild born and (2) there was little difference between freshly caught males and those maintained in captivity for protracted periods, our results affirm that teratospermia in the cheetah is mostly genetically derived. It also appears that an ex situ environment for the Namibian cheetah can ensure sperm quality comparable with that for free-living males.

Cryopreservation of spermatozoa from wild-born Namibian cheetahs (Acinonyx jubatus) and influence of glycerol on cryosurvival.

Sperm cryopreservation is a valuable tool for the genetic management of ex situ populations. This study was conducted to assess: (1) semen characteristics of wild-born cheetahs; and (2) the impact of three types of glycerol influence (duration of exposure, temperature, and method of addition) on sperm cryosensitivity. To evaluate the impact of duration of glycerol exposure, spermatozoa were incubated in Test Yolk Buffer (TYB) with 4% glycerol at ambient temperature (approximately 22 degrees C) for 15 vs. 60 min before cryopreservation. To evaluate the influence of temperature and method of glycerol addition, spermatozoa were resuspended at ambient temperature either in TYB with 0% glycerol followed by addition of 8% glycerol (1:1 v/v; at ambient temperature vs. 5 degrees C) or directly in TYB with 4% glycerol. All samples were cryopreserved in straws over liquid nitrogen vapor and evaluated for sperm motility and acrosomal integrity after thawing. Semen samples (n = 23; n = 13 males) contained a high proportion (78%) of pleiomorphic spermatozoa. Ejaculates also contained a high proportion of acrosome-intact (86%) and motile spermatozoa (78%). Immediately after thawing, a significant proportion of spermatozoa retained intact acrosomes (range, 48-67%) and motility (range, 40-49%). After thawing, incubation in glycerol for 60 min at ambient temperature before freezing decreased (p < 0.05) sperm motility and acrosomal integrity at one time-point each (pre-centrifugation and post-centrifugation, respectively). However, method or temperature of glycerol addition had no (p > 0.05) impact on sperm cryosurvival. In summary, (1) wild-born cheetahs produce high proportions of pleiomorphic spermatozoa but with a high proportion of intact acrosomes; and (2) resuspension in 4% glycerol, followed by exposure for up to 60 min at ambient temperature, had minimal effect on sperm motility and acrosomal integrity after cryopreservation. Results indicate the feasibility of cryopreserving cheetah spermatozoa under field conditions, providing a user-friendly method to capture and store gametes to enhance genetic management.