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

Abstract

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 (~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.