218 EJACULATE TRAITS OF THE NAMIBIAN CHEETAH (ACINONYX JUBATUS)—INFLUENCE OF ANIMAL AGE, SEASON, AND CAPTIVITY

Abstract

Wild cheetahs are threatened with extinction, and ex situ populations are not self-sustaining due to poor reproductive efficiency. Sperm cryo-preservation is a valuable tool for genetic management; however, increased knowledge of ejaculate traits is essential to improve cryopreservation protocols. The objective of this study was to characterize ejaculate traits of wild-born cheetahs in Namibia, Africa. Specifically, the influences of animal age, season and captive status on electroejaculate volume, sperm concentration, motility, forward progressive status (FPS scale 0-5, 5 = best), morphology, and acrosomal integrity were evaluated. Animal age was divided into categories: juvenile (14-24 mo; n = 16 males, 23 ejaculates), adult (25-120 mo; n = 76 males, 175 ejaculates), and aged (over 120 mo; n = 5 males, 5 ejaculates). Namibian seasons were divided into hot-wet (Jan-Apr), cold-dry (May-Aug) and hot-dry (Sep-Dec). Cheetahs were considered wild-caught (n = 29 males; 44 ejaculates) if trapped on farmland d30 days before semen collection. Raw ejaculates contained 69.0 ± 1.1% motile sperm (mean ± SEM) and 73.6 ± 1.5% sperm with intact acrosomes. Overall, 18.4 ± 0.9% of sperm were morphologically normal, with midpiece abnormalities being the most prevalent defects (?39%). To determine treatment differences, data were analyzed by General Linear Model procedures and means were separated with Duncan's multiple-range test. Juvenile cheetahs produced ejaculates with reduced (P < 0.05) sperm motility (56.7 ± 3.3%) and FPS (2.9 ± 0.1) compared to adult (69.8 ± 1.4% and 3.4 ± 0.1, respectively) and aged (78.9 ± 6.7% and 3.7 ± 0.3, respectively) animals. Ejaculates from juvenile animals also had reduced (P < 0.05) volume (0.69 ± 0.3 mL) and fewer (P < 0.05) total motile sperm (7.1 ± 9.3 × 10⁶) compared to adult (2.2 ± 0.1 mL and 42.3 ± 4.1 × 10⁶) and aged (2.3 ± 0.6 mL and 23.5 ± 20.0 × 10⁶, respectively) males. For all ejaculates combined, seminal quality was poorest during the hot-dry season with lower (P < 0.05) sperm motility and intact acrosomes as well as an increased (P < 0.05) percent of sperm with head abnormalities. Ejaculates from captive cheetahs (n = 68 males, 159 ejaculates) had increased (P < 0.05) volume (2.0 ± 0.2 mL) and intact acrosomes (80.1 ± 3.6%), but lower (P < 0.05) sperm density (14.3 ± 3.9 × 10⁶/mL) than wild-caught animals (1.5 ± 0.3 mL, 71.9 ± 4.6%, and 24.1 ± 5.1 × 10⁶/mL, respectively). These are the first large-scale data acquired to examine the reproductive biology of male cheetahs in Namibia, including those recently captured from the wild. Results reveal that this species demonstrates seasonal and age-based variations in ejaculate quality, and that all individuals (including those recently derived from the wild) produce unusually high proportions of pleiomorphic spermatozoa. These data are being used to select the ideal donor age and season during which spermatozoa should be collected for addition to a genome resource bank, thereby enhancing effective genetic management for cheetahs propagated ex situ.