Sperm motility, kinematics, morphometry and morphology over two seasons in free-ranging African elephants (Loxodonta africana)
Ilse Luther A B C , Liana Maree
A B , Antoinette Kotze B D , Thomas Hildebrandt E , Frank Göritz E , Robert Hermes E and Gerhard van der Horst A B F
+ Author Affiliations
- Author Affiliations
A Department of Medical Bioscience, University of the Western Cape, Private Bag X17, Bellville, 7535, South Africa.
B National Zoological Garden, South African National Biodiversity Institute, PO Box 754, Pretoria, 0001, South Africa.
C GEOsperm, Wildlife Reproduction and Biotechnology, PO Box 3300, Brits, 0250, South Africa.
D Department of Genetics, University of the Free State, PO Box 339, Bloemfontein, 9300, South Africa.
E Department of Reproduction Management, Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Straße 17, 10315, Berlin, Germany.
F Corresponding author. Email: gvdhorst7@gmail.com
Reproduction, Fertility and Development 32(4) 425-438 https://doi.org/10.1071/RD19182
Submitted: 21 September 2018 Accepted: 25 July 2019 Published: 24 January 2020
Abstract
This study aimed to address the lack of information on quantitative semen and sperm characteristics of free-ranging African elephants. Nineteen ejaculates were collected from 12 elephant bulls by means of electroejaculation in spring (Season 1, end of dry season, n = 7) and in autumn (Season 2, end of rainy season, n = 12). While most elephant cows are in oestrus in the rainy season, it is not evident whether sperm quality also improves during this period. Semen samples were assessed using computer-aided sperm analysis (CASA), brightfield microscopy and transmission electron microscopy. Seasonal differences and individual variation in sperm quality of bulls were apparent, with ejaculates collected during Season 2 revealing higher percentages for total motility, progressive motility, rapid-swimming spermatozoa and kinematic parameters compared with Season 1 (P < 0.05). Although normal sperm morphology percentage was similar over the two seasons, more sperm tail defects were found in Season 2 (P < 0.05). The baseline reference data and multivariate sperm parameter associations reported in this study can be used to predict elephant bull sperm quality and potential to fertilise. It is clear that CASA can detect subtle differences in sperm quality of African elephant ejaculates and should be the approach for future investigations.
Additional keywords: acrosome coverage, CASA, semen volume, sperm concentration, TEM.
References
Abaigar, T., Cano, M., Pickard, A., and Holt, W. V. (2001). Use of computer-aided sperm motility assessment and multivariate pattern analysis to characterise ejaculate quality in the Mohor gazelle (Gazella dama mhorr): effect of body weight, electroejaculation technique and short term semen storage. Reproduction 122, 265–273.| Use of computer-aided sperm motility assessment and multivariate pattern analysis to characterise ejaculate quality in the Mohor gazelle (Gazella dama mhorr): effect of body weight, electroejaculation technique and short term semen storage.Crossref | GoogleScholarGoogle Scholar | 11467977PubMed |
Amann, R. P., and Waberski, D. (2014). Computer-assisted sperm analysis (CASA): capabilities and potential developments. Theriogenology 81, 5–17.e3.
| Computer-assisted sperm analysis (CASA): capabilities and potential developments.Crossref | GoogleScholarGoogle Scholar | 24274405PubMed |
Andrabi, S. M. H., and Maxwell, W. (2007). A review on reproductive biotechnologies for conservation of endangered mammalian species. Anim. Reprod. Sci. 99, 223–243.
| A review on reproductive biotechnologies for conservation of endangered mammalian species.Crossref | GoogleScholarGoogle Scholar |
Andrews, D. F. (1972). Plots of high dimensional data. Biometrics 28, 125–135.
| Plots of high dimensional data.Crossref | GoogleScholarGoogle Scholar |
Arnold, D. M., Gray, C., Roth, T. L., Mitchell, S., and Graham, L. H. (2017). A simple, field-friendly technique for cryopreserving semen from Asian elephants (Elephas maximus). Anim. Reprod. Sci. 182, 84–94.
| A simple, field-friendly technique for cryopreserving semen from Asian elephants (Elephas maximus).Crossref | GoogleScholarGoogle Scholar | 28545986PubMed |
Barth, A. D. (2007). Evaluation of the potential breeding soundness of the bull. In ‘Current Therapy in Large Animal Theriogenology’. (Eds R. Youngquist and T. W. Youngquist.) pp. 229–239. (Elsevier: St. Louis, MO, USA.)
Barth, A. D., and Oko, R. J. (1989). ‘Abnormal Morphology of Bovine Spermatozoa’. (Iowa State University Press: Ames, IA, USA.)
Buranaamnuay, K., Mahasawangkul, S., and Saikhun, K. (2013). The in vitro quality of frozen–thawed Asian elephant (Elephas maximus) spermatozoa in semen supplemented with Equex STM paste and oxytocin during and after cryopreservation. Reprod. Biol. 13, 169–171.
| The in vitro quality of frozen–thawed Asian elephant (Elephas maximus) spermatozoa in semen supplemented with Equex STM paste and oxytocin during and after cryopreservation.Crossref | GoogleScholarGoogle Scholar | 23719124PubMed |
Campbell, R. C., Dott, H. M., and Glover, T. D. (1956). Nigrosin–eosin as a stain for differentiating live and dead spermatozoa. J. Agric. Sci. 48, 1–8.
| Nigrosin–eosin as a stain for differentiating live and dead spermatozoa.Crossref | GoogleScholarGoogle Scholar |
Chambers, J. M., Cleveland, W. S., Kleiner, B., and Tukey, P. A. (1983). Graphical Methods of Data Analysis. (Wadsworth: Belmont, CA, USA.)
Contri, A., Valorz, C., Faustini, M., Wegher, L., and Carluccio, A. (2010). Effect of semen preparation on CASA motility results in cryopreserved bull spermatozoa. Theriogenology 74, 424–435.
| Effect of semen preparation on CASA motility results in cryopreserved bull spermatozoa.Crossref | GoogleScholarGoogle Scholar | 20451996PubMed |
Craig, G. C. (1984). Foetal mass and date of conception in African elephants: a revised formula. S. Afr. J. Sci. 80, 512–516.
de Villiers, D. J. (1988). Musth and reproduction in the African elephant, Loxodonta africana. M.Sc. Thesis, University of Pretoria, South Africa.
Fickel, J., Wagener, A., and Ludwig, A. (2007). Semen cryopreservation and the conservation of endangered species. Eur. J. Wildl. Res. 53, 81–89.
| Semen cryopreservation and the conservation of endangered species.Crossref | GoogleScholarGoogle Scholar |
Flint, A. P. F., and Woolliams, J. A. (2008). Precision animal breeding. Philos. Trans. R. Soc. Lond. B Biol. Sci. 363, 573–590.
| Precision animal breeding.Crossref | GoogleScholarGoogle Scholar |
García-Osorio, C., and Fyfe, C. (2005). Visualization of high-dimensional data via orthogonal curves. J. Univers. Comput. Sci. 11, 1806–1819.
Gomendio, M., Malo, A., Garde, J., and Roldan, E. (2007). Sperm traits and male fertility in natural populations. Reproduction 134, 19–29.
| Sperm traits and male fertility in natural populations.Crossref | GoogleScholarGoogle Scholar | 17641085PubMed |
Graham, J. K., and Mocé, E. (2005). Fertility evaluation of frozen/thawed semen. Theriogenology 64, 492–504.
| Fertility evaluation of frozen/thawed semen.Crossref | GoogleScholarGoogle Scholar | 15946734PubMed |
Graham, L. H., Bando, J., Gray, C., and Buhr, M. M. (2004). Liquid storage of Asian elephant (Elephas maximus) sperm at 4°C. Anim. Reprod. Sci. 80, 329–340.
| Liquid storage of Asian elephant (Elephas maximus) sperm at 4°C.Crossref | GoogleScholarGoogle Scholar | 15036508PubMed |
Hanks, J. (1972). Reproduction of elephant, Loxodonta africana, in the Luangwa Valley, Zambia. J. Reprod. Fertil. 30, 13–26.
| Reproduction of elephant, Loxodonta africana, in the Luangwa Valley, Zambia.Crossref | GoogleScholarGoogle Scholar | 5035330PubMed |
Henkel, R., Kierspel, E., Hajimohammed, M., Stalf, T., Hoogendijk, C., Mehnert, C., Menkveld, R., Schill, W.-B., and Kruger, T. F. (2003). DNA fragmentation of spermatozoa and assisted reproduction technology. Reprod. Biomed. Online 7, 477–484.
| DNA fragmentation of spermatozoa and assisted reproduction technology.Crossref | GoogleScholarGoogle Scholar | 14656411PubMed |
Hermes, R., Hildebrandt, T. B., Blottner, S., Walzer, C., Silinksi, S., Patton, M. L., Wibbelt, G., Schwarzenberger, F., and Goeritz, F. (2005). Reproductive soundness of captive southern and northern white rhinoceros (Ceratotheruim simum simum, C.s. contini): evaluation of male genital tract morphology and semen quality before and after cryopreservation. Theriogenology 63, 219–238.
| Reproductive soundness of captive southern and northern white rhinoceros (Ceratotheruim simum simum, C.s. contini): evaluation of male genital tract morphology and semen quality before and after cryopreservation.Crossref | GoogleScholarGoogle Scholar | 15589286PubMed |
Hermes, R., Goeritz, F., Saragusty, J., Sos, E., Molnar, V., Reid, C. E., Schwarzenberger, F., and Hildebrandt, T. B. (2009). First successful artificial insemination with frozen–thawed semen in rhinoceros. Theriogenology 71, 393–399.
| First successful artificial insemination with frozen–thawed semen in rhinoceros.Crossref | GoogleScholarGoogle Scholar | 19007979PubMed |
Hermes, R., Saragusty, J., Goeritz, F., Bartels, P., Potier, R., Baker, B., Streich, J., and Hildebrandt, T. B. (2013). Freezing African elephant semen as a new population management tool. PLoS One 8, e57616.
| Freezing African elephant semen as a new population management tool.Crossref | GoogleScholarGoogle Scholar | 23936034PubMed |
Hildebrandt, T. B., Hermes, R., Saragusty, J., Potier, R., Schwammer, H. M., Balfanz, F., Vielgrader, H., Baker, B., Bartels, P., and Göritz, F. (2012). Enriching the captive elephant population genetic pool through artificial insemination with frozen–thawed semen collected in the wild. Theriogenology 78, 1398–1404.
| Enriching the captive elephant population genetic pool through artificial insemination with frozen–thawed semen collected in the wild.Crossref | GoogleScholarGoogle Scholar | 22898009PubMed |
Holt, W. V. (2000). Basic aspects of frozen storage of semen. Anim. Reprod. Sci. 62, 3–22.
| Basic aspects of frozen storage of semen.Crossref | GoogleScholarGoogle Scholar | 10924818PubMed |
Holt, W. V., and van Look, K. J. W. (2004). Concepts in sperm heterogeneity, sperm selection and sperm competition as biological foundation for laboratory test of semen quality. Reproduction 127, 527–535.
| Concepts in sperm heterogeneity, sperm selection and sperm competition as biological foundation for laboratory test of semen quality.Crossref | GoogleScholarGoogle Scholar | 15129008PubMed |
Holt, W. V., O’Brien, J., and Abaigar, T. (2007). Application and interpretation of computer assisted semen analysis in assisted breeding and comparative research. Reprod. Fertil. Dev. 19, 709–718.
| Application and interpretation of computer assisted semen analysis in assisted breeding and comparative research.Crossref | GoogleScholarGoogle Scholar | 17714625PubMed |
Howard, J. G., Bush, M., de Vos, V., and Wildt, D. E. (1984). Electroejaculation, semen characteristics and serum testosterone of free-ranging African elephants (Loxodonta africana). J. Reprod. Fertil. 72, 187–195.
| Electroejaculation, semen characteristics and serum testosterone of free-ranging African elephants (Loxodonta africana).Crossref | GoogleScholarGoogle Scholar | 6471047PubMed |
Imrat, P., Suthanmapinanth, P., Saikuhn, K., Mahasawangkul, S., Sostaric, E., Sombutputorn, P., Thongtip, N., Pinyopummin, A., Colenbrander, B., Holt, W. V., and Stout, T. A. E. (2013). Effect of pre-freeze semen quality, extender and cryoprotectant on the post-thaw quality of Asian elephant (Elephas maximus indicus) semen. Cryobiology 66, 52–59.
| Effect of pre-freeze semen quality, extender and cryoprotectant on the post-thaw quality of Asian elephant (Elephas maximus indicus) semen.Crossref | GoogleScholarGoogle Scholar | 23168056PubMed |
Imrat, P., Mahasawangkul, S., Thitaram, C., Suthanmapinanth, P., Kornkaewrat, K., Sombutputorn, P., Jansittiwate, S., Thongtip, N., Pinyopummin, A., Colenbrander, B., Holt, W. V., and Stout, T. A. E. (2014). Effect of alternate day collection on semen quality of Asian elephants (Elephas maximus) with poor initial fresh semen quality. Anim. Reprod. Sci. 147, 154–160.
| Effect of alternate day collection on semen quality of Asian elephants (Elephas maximus) with poor initial fresh semen quality.Crossref | GoogleScholarGoogle Scholar | 24832106PubMed |
IUCN (2013). The IUCN Red List of Threatened Species. Available at: www.iucnredlist.org [Verified 2 October 2019].
Jainudeen, M. R., Eisenberg, J. F., and Jayasingue, J. B. (1971). Semen of the Ceylon elephant, Elephas maximus. J. Reprod. Fertil. 24, 213–217.
| Semen of the Ceylon elephant, Elephas maximus.Crossref | GoogleScholarGoogle Scholar | 5551412PubMed |
Johnson, O. W., and Buss, I. O. (1967a). The testis of the African elephant (Loxodonta africana). I. histological features. J. Reprod. Fertil. 13, 11–21.
| The testis of the African elephant (Loxodonta africana). I. histological features.Crossref | GoogleScholarGoogle Scholar | 6066825PubMed |
Johnson, O. W., and Buss, I. O. (1967b). The testis of the African elephant (Loxodonta africana). II. development, puberty and weight. J. Reprod. Fertil. 13, 23–30.
| The testis of the African elephant (Loxodonta africana). II. development, puberty and weight.Crossref | GoogleScholarGoogle Scholar | 6066777PubMed |
Jones, R. C. (1973). Collection, motility and storage of spermatozoa from the African elephant, Loxodonta africana. Nature 243, 38–39.
| Collection, motility and storage of spermatozoa from the African elephant, Loxodonta africana.Crossref | GoogleScholarGoogle Scholar | 4621102PubMed |
Jones, R. C. (1978). Studies on the handling of spermatozoa from the African elephant, Loxodonta africana. Symp. Zool. Soc. Lond. 43, 261–269.
Jones, R. C., Rowlands, I. W., and Skinner, J. D. (1974). Spermatozoa in the genital ducts of the African elephant, Loxodonta africana. J. Reprod. Fertil. 41, 189–192.
| Spermatozoa in the genital ducts of the African elephant, Loxodonta africana.Crossref | GoogleScholarGoogle Scholar | 4431010PubMed |
Jones, R. C., Bailey, D. W., and Skinner, J. D. (1975). Studies on the collection and storage of semen from the African elephant, Loxodonta africana. Koedoe 18, a919.
| Studies on the collection and storage of semen from the African elephant, Loxodonta africana.Crossref | GoogleScholarGoogle Scholar |
Kerr, M. A. (1978). Reproduction of elephant in the Mana pools National Park, Rhodesia. Arnoldia. 8, 1–11.
Kiso, W. K., Brown, J. L., Siewert, F., Schmitt, D. L., Olson, D., Crichton, E. G., and Pukazhenthi, B. S. (2011). Liquid semen storage in elephants (Elephas maximus and Loxodonta africana): species differences and storage optimization. J. Androl. 32, 420–431.
| Liquid semen storage in elephants (Elephas maximus and Loxodonta africana): species differences and storage optimization.Crossref | GoogleScholarGoogle Scholar | 21127305PubMed |
Kitiyanant, Y., Schmidt, M., and Pavasuthipaisit, K. (2000). Evaluation of sperm acrosome reaction in the Asiatic elephant. Theriogenology 53, 887–896.
| Evaluation of sperm acrosome reaction in the Asiatic elephant.Crossref | GoogleScholarGoogle Scholar | 10730977PubMed |
Lebelo, S. L., and van der Horst, G. (2010). The ultrastructure of the Sertoli cell of the vervet monkey, Chlorocebus aethiops. Tissue Cell 42, 348–354.
| The ultrastructure of the Sertoli cell of the vervet monkey, Chlorocebus aethiops.Crossref | GoogleScholarGoogle Scholar | 20828773PubMed |
Lebelo, S. L., and van der Horst, G. (2016). Ultrastructural changes occurring during spermiogenesis of the vervet monkey, Chlorocebus aethiops. Asian J. Anim. Sci. 10, 247–254.
| Ultrastructural changes occurring during spermiogenesis of the vervet monkey, Chlorocebus aethiops.Crossref | GoogleScholarGoogle Scholar |
Lindeque, M. (1988). Population dynamics of elephants in Etosha National Park, SWA. PhD thesis, University of Stellenbosch, South Africa.
Lueders, I., Young, D., Maree, L., van der Horst, G., Luther, I., Botha, S., and Bertschinger, H. J. B. (2017). Effects of GnRH vaccination in wild and captive African elephant bulls (Loxodonta africana) on reproductive organs and semen quality. Plos One 12, e0178270.
| Effects of GnRH vaccination in wild and captive African elephant bulls (Loxodonta africana) on reproductive organs and semen quality.Crossref | GoogleScholarGoogle Scholar | 28915245PubMed |
Malo, A. F., Garde, J. J., Soler, A. J., García, A. J., Gomendio, M., and Roldan, E. R. S. (2005). Male fertility in natural populations of red deer is determined by sperm velocity and the proportion of normal morphology. Biol. Reprod. 72, 822–829.
| Male fertility in natural populations of red deer is determined by sperm velocity and the proportion of normal morphology.Crossref | GoogleScholarGoogle Scholar | 15576823PubMed |
Maree, L., and van der Horst, G. (2013). Quantification and identification of sperm subpopulations using computer-aided sperm analysis and species-specific cut-off values for swimming speed. Biotech. Histochem. 88, 181–193.
| Quantification and identification of sperm subpopulations using computer-aided sperm analysis and species-specific cut-off values for swimming speed.Crossref | GoogleScholarGoogle Scholar | 23331185PubMed |
Maree, L., Menkveld, R., du Plessis, S. S., and van der Horst, G. (2010). Morphometric dimensions of the human sperm head depend on the staining method used. Hum. Reprod. 25, 1369–1382.
| Morphometric dimensions of the human sperm head depend on the staining method used.Crossref | GoogleScholarGoogle Scholar | 20400771PubMed |
Miró, J., Lobo, V., Quintero-Moreno, A., Medrano, A., Peña, A., and Rigau, T. (2005). Sperm motility patterns and metabolism in Catalonian donkey semen. Theriogenology 63, 1706–1716.
| Sperm motility patterns and metabolism in Catalonian donkey semen.Crossref | GoogleScholarGoogle Scholar | 15763113PubMed |
Monfort, S. (2014). Mayday, mayday, mayday. The millennium ark is sinking. In ‘Reproductive Sciences in Animal Conservation’. (Eds W.V. Holt, J. Brown and P. Comizzoli.) pp. 15–31. (Springer Science and Business Media: New York.)
Nöthling, J. O., and Irons, P. C. (2008). A simple multidimensional system for the recording and interpretation of sperm morphology in bulls. Theriogenology 69, 603–611.
| A simple multidimensional system for the recording and interpretation of sperm morphology in bulls.Crossref | GoogleScholarGoogle Scholar | 18242677PubMed |
O’Brien, J. K., Steinmann, K. J., and Robeck, T. R. (2009). Application of sperm sorting and associated reproductive technology for wildlife management and conservation. Theriogenology 71, 98–107.
| Application of sperm sorting and associated reproductive technology for wildlife management and conservation.Crossref | GoogleScholarGoogle Scholar | 19010523PubMed |
O’Brien, J. K., Steinman, K. J., Monato, G. A., Love, C. C., and Robeck, T. R. (2013). Sperm DNA fragmentation and morphological degeneration in chilled elephant (Elephas maximus and Loxodonta africana) semen collected by transrectal massage. Andrology 1, 387–400.
| Sperm DNA fragmentation and morphological degeneration in chilled elephant (Elephas maximus and Loxodonta africana) semen collected by transrectal massage.Crossref | GoogleScholarGoogle Scholar | 23536498PubMed |
Pond, W., Church, D., Pond, K., and Schoknecht, P. (2004). ‘Basic animal nutrition and feeding’, 5th edn. (John Wiley and Sons: New York.)
Rittem, S., Imrat, P., Suthanapinah, P., and Mahasawangkul, S. (2010). Morphology and head morphometric characteristics of Asian elephant (Elephas maximus) spermatozoa as determined by computer-assisted sperm analysis (CASA). In ‘Proceedings of the EU Asia-Link Project Symposium on Health and Reproduction of Asian Elephants’. (Ed. C. Thitaram.) pp. 104–108. (Faculty of Veterinary Medicine, Chiang Mai University: Chiang Mai, Thailand.)
Rodrigues-Martinez, H., and Barth, A. (2007). In vitro evaluation of sperm quality related to in vivo function and fertility. In ‘Reproduction in Domestic Ruminants’. (Eds J. Juengel, J. Murray and M. Smith.) pp. 39-54. (Nothingham University Press: Nottingham.)
Ruedi, V. D., Kupfer, U., Gutzwiller, A., Rindisbacher, F., and Wiesner, H. (1981). Collection of semen from African elephant (Loxodonta africana). Planning of artificial insemination. In ‘Proceedings of the 13th International Symposium Dis. Zoo. Anim’. pp. 349–351.
Saacke, R. G. (2008). Sperm morphology: its relevance to compensable and uncompensable traits in semen. Theriogenology 70, 473–478.
| Sperm morphology: its relevance to compensable and uncompensable traits in semen.Crossref | GoogleScholarGoogle Scholar | 18495234PubMed |
Saragusty, J., Hildebrandt, T. B., Behr, B., Knieriem, A., Kruse, J., and Hermes, R. (2009). Successful cryopreservation of the Asian elephant (Elephas maximus) spermatozoa. Anim. Reprod. Sci. 115, 255–266.
| Successful cryopreservation of the Asian elephant (Elephas maximus) spermatozoa.Crossref | GoogleScholarGoogle Scholar | 19111407PubMed |
Schmitt, D. L., and Hildebrandt, T. B. (1998). Manual collection and characterization of semen from Asian elephant (Elephas maximus). Anim. Reprod. Sci. 53, 309–314.
| Manual collection and characterization of semen from Asian elephant (Elephas maximus).Crossref | GoogleScholarGoogle Scholar | 9835384PubMed |
Skinner, J., and Smithers, R. (1990). ‘The Mammals of the Southern African Subregion’. (University of Pretoria: Pretoria.)
Spinage, C. (1994). ‘Elephants’. (Poyser Natural History: London.)
Thongtip, N., Mashasawangkul, S., Kornkaewrat, K., Saikhun, J., Angkawanish, T., Jansittiwate, S., Boonprasert, K., Suthanmapinanth, P., Kaewmanee, S., Wajjwalku, W., Songsasen, N., Pinyopummintr, T., and Pinyopummin, A. (2006). Evaluation of post-thaw motility of Asian spermatozoa frozen in TEST+5% glycerol media using computer-assisted sperm analysis. In ‘The 2nd Symposium on the Asian Zoo and Wildlife Medicine and the 1st Workshop on Zoo and Wildlife Pathology AZWMP’. (Eds W. Banlunara, P. Ingkaninun, K. Sanshu, and K. Promngram.) pp. 15. (Tiranasar Press: Bangkok, Thailand.)
Thongtip, N., Saikhun, J., Mahasawangkul, S., Kornkaewrat, K., Pongsopavijitr, P., Songsasen, N., and Pinyopummin, A. (2008). Potential factors affecting semen quality in the Asian elephant (Elephas maximus). Reprod. Biol. Endocrinol. 6, 9.
| Potential factors affecting semen quality in the Asian elephant (Elephas maximus).Crossref | GoogleScholarGoogle Scholar | 18346275PubMed |
Thurston, L. M., Watson, P. F., and Holt, W. V. (1999). Source of variation in the morphology characteristics of sperm subpopulations assessed objectively by a novel automated sperm morphology analysis system. J. Reprod. Fertil. 117, 271–280.
| Source of variation in the morphology characteristics of sperm subpopulations assessed objectively by a novel automated sperm morphology analysis system.Crossref | GoogleScholarGoogle Scholar | 10690194PubMed |
van der Horst, G., and Maree, L. (2010). SpermBlue: a new universal stain for human and animal sperm which is also amenable to automated sperm morphology analysis. Biotech. Histochem. 84, 299–308.
| SpermBlue: a new universal stain for human and animal sperm which is also amenable to automated sperm morphology analysis.Crossref | GoogleScholarGoogle Scholar |
van der Horst, G., Seier, J. V., Spinks, A. C., and Hendricks, S. (1999). The maturation of sperm motility in the epididymis and vas deferens of the vervet monkey, Cercopithecus aethiops. Int. J. Androl. 22, 197–207.
| The maturation of sperm motility in the epididymis and vas deferens of the vervet monkey, Cercopithecus aethiops.Crossref | GoogleScholarGoogle Scholar | 10367241PubMed |
van der Horst, G., Maree, L., and du Plessis, S. S. (2018). Current perspectives of CASA applications in diverse mammalian sperm. Reprod. Fertil. Dev. 30, 875–888.
| Current perspectives of CASA applications in diverse mammalian sperm.Crossref | GoogleScholarGoogle Scholar | 29576045PubMed |
Vutyavanich, T., Piromlertaorn, W., and Nunta, S. (2010). Rapid freezing versus slow programmable freezing of human spermatozoa. Fertil. Steril. 93, 1921–1928.
| Rapid freezing versus slow programmable freezing of human spermatozoa.Crossref | GoogleScholarGoogle Scholar | 19243759PubMed |
Wittemyer, G., Northrup, J., Blanc, J., Douglas-Hamilton, I., Omondi, P., and Burnham, K. (2014). Illegal killing for ivory drives local decline in African elephants. Proc. Natl. Acad. Sci. U S A 111, 13117–13121.
| Illegal killing for ivory drives local decline in African elephants.Crossref | GoogleScholarGoogle Scholar | 25136107PubMed |
