104 Teratospermia in tigers: Evidence for declining sperm quality over time
Authors: Herrick J. R. , Ploog C. , Santymire R. , Aaltonen J. , Traylor-Holzer K. , Byers O. , Armstrong D. , Harris T. 
Published: December 2018

Ejaculate traits in male tigers (Panthera tigris) were studied in the 1980s, but little work has been done on male tigers since then and the reproductive status of the current zoo population is not known. In order to characterise ejaculate traits in male tigers, semen was collected by electroejaculation (90 to 100 stimulations, 3 to 7V), subjected to a standard semen analysis (volume and pH and sperm concentration, motility, and morphology), and cryopreserved. To date, semen has been collected from 24 males (n=16 Amur tigers, Panthera tigris altaica, 10.3±1.1 y; n=7 Sumatran tigers, Panthera tigris sumatrae, 9.4±1.3 y; n=1 Malayan tiger, Panthera tigris jacksoni, 6 y), maintained at 18 USA institutions. Ejaculates (4.7±0.6 mL; pH=8.4±0.1) contained 240.3±54.9×106 spermatozoa, which yielded 357 straws of cryopreserved spermatozoa that were used to establish a Tiger Genome Resource Bank. The majority of the spermatozoa were motile (69.2±4.6%), but the proportion of spermatozoa exhibiting normal morphology was very low (18.7±3.3%) and similar between both Amur (20.0±4.8%) and Sumatran (16.3±5.2%) males, with the majority of abnormalities affecting the midpiece (retained cytoplasmic droplets, bent midpieces, or both). Previous studies of male tigers that utilised comparable anaesthesia regimens and collection techniques recovered similar quantities of semen (5 to 10mL), but the proportions of normal spermatozoa in those studies (&gt;65%) were very high (Wildt et al. 1988 Biol. Reprod. 38, 245; Byers et al. 1990 J. Reprod. Fert. 90, 119). Proportions of normal spermatozoa in the current study more closely resemble those reported for the teratospermic (&lt;40% normal spermatozoa) clouded leopard (Neofelis nebulosa, 18.5% normal spermatozoa, Pukazhenthi et al. 2006 Theriogenology 66, 1790) and cheetah (Acinonyx jubatus, 18.4% normal spermatozoa, Crosier et al. 2007 Reprod. Fertil. Dev. 19, 370), as well as the South China tiger (Panthera tigris amoyensis, 27% normal spermatozoa). The number of spermatozoa per ejaculate was also decreased in Amur tigers (190.1±67.7×106) compared to Sumatran tigers in the current study (362.9±99.5×106) and earlier studies of other Amur tigers (&gt;500×106). The reasons for this apparent decline in sperm quality are unclear, but reduced proportions of normal spermatozoa have been associated with reduced heterozygosity in small, isolated populations of felids (Florida panthers, South China tigers) or species that have been through a genetic bottleneck (cheetahs). Semen collections and evaluations will continue in order to determine if trends for compromised sperm quality are representative of the current SSP population(s) or an artifact of our reduced sample size. Additional studies investigating possible environmental, genetic, or nutritional influences on sperm morphology are also warranted.
This work is supported by grants from Association of Zoo and Aquarium’s Conservation Grants Fund and Point Defiance Zoo and Aquarium’s Dr. Holly Reed Conservation Fund.