Aspects of the reproductive biology and breeding management of Asian and African elephants Elephas maximus and Loxodonta africana

International Zoo Yearbook

Volumn 40, Issue 1, 2006, Pages 20-40

  Hildebrandt, T B ^a   GOritz F ^a   Hermes, R ^a   Reid, C ^a   Dehnhard, M ^a   Brown, J L ^b  

^a LEIBNIZ INSTITUTE FOR ZOO AND WILDLIFE RESEARCH   (Germany)

^b SMITHSONIAN CONSERVATION BIOLOGY INSTITUTE   (United States)

Author keywords

African elephant; Asian elephant; Asymmetric reproductive againg; Contraception; Reproductive anatomy; Reproductive disorder; Reproductive medicine; Ultrasonography

Indexed keywords

EID: 85040404678     PISSN: 00749664     EISSN: 17481090     Source Type: Journal    
DOI: 10.1111/j.1748-1090.2006.00020.x     Document Type: Article

References (106)

1. Agnew, D. W., Munson, L. & Ramsay, E. C. (2004): Cystic endometrial hyperplasia in elephants. Veterinary Pathology 41: 179 – 183.
2. Allen, W. R., Matthias, S. S., Skidmore, J. A., Wooding, F. B. P. & Van Aarde, R. J. (1996): Feto-placental function in the African elephant. In Proceedings of the 13th International Congress on Animal Reproduction: 9 – 10. Stone, G. & Evans, G. Amsterdam: Elsevier.
3. Allen, W. R., Mathias, S. S., Wooding, F. B. P., Skidmore, J. A. & Van Aarde, R. J. (2001): Plac-entation in the African elephant, Loxodonta africana. I. Endocrinological aspects. Reproduction (Suppl.) 60: 105 – 116.
4. Amoroso, E. C. & Perry, J. S. (1964): The foetal membranes and placenta of the African elephant. Philosophical Transactions of the Royal Society of London B 248: 1 – 34.
5. Asa, C. S. (1996): Reproductive physiology. In Wild mammals in captivity: Principles and techniques: 390 – 417. Kleiman, D. G., Allen, M. E., Thompson, K. V. & Lumpkin, S. Chicago, IL: University of Chicago Press.
6. Balke, J. M. E., Barker, I. K., Hackenberger, M. K., Mcmanamon, R. & Boever, W. J. (1988): Reproductive anatomy of three nulliparous female Asian elephants: The development of artificial breeding techniques. Zoo Biology 7: 99 – 113.
7. Balke, J. M. E., Boever, W. J., Ellersiek, M. R., Seal, U. S. & Smith, D. A. (1988): Anatomy of the reproductive tract of the female African elephant (Loxodonta africana) with reference to development of techniques for artificial breeding. Journal of Reproduction and Fertility 84: 485 – 492.
8. Belterman, R. (2001): EEP Asian elephant studbook. Dataset. Rotterdam: Rotterdam Zoo.
9. Benz, A., Zenker, W., Hildebrandt, T. B., Weis-Sengruber, G. & Geyer, H. (2005): About the macroscopic and microscopic morphology of elephant’s hooves (elephantidae). Verhandlungsbericht ber Erkrankungen Zootiere 42: 167 – 170.
10. Blottner, S., Hingst, O., Hildebrandt, T., Göritz, F., Quandt, S. & Meyer, H. (1996): Testi-cular activity in subadult and adult African elephants. In Proceedings of the 13th international congress on animal reproduction: 11 – 12. Stone, G. & Evans, G. Amsterdam: Elsevier.
11. Brown, J. L. (2000): Reproductive endocrine monitoring of elephants: An essential tool for assisting captive management. Zoo Biology 19: 347 – 367.
12. Brown, J. L. & Lehnhardt, J. (1995): Serum and urinary hormones during pregnancy and the peri-and postpartum period in an Asian elephant (Elephas maximus). Zoo Biology 14: 555 – 564.
13. Brown, J. L., Hildebrandt, T., Theison, W. & Neiffer, D. L. (1999): Endocrine and ultrasound evaluation of a non-cycling African elephant: Identification of a follicular ovarian cyst. Zoo Biology 18: 223 – 232.
14. Brown, J. L., Schmitt, D. L., Bellem, A., Graham, L. H. & Lehnhardt, J. (1999): Hormone secretion in the Asian elephant (Elephas maximus): Characterization of ovulatory and anovulatory LH surges. Biology of Reproduction 61: 1294 – 1299.
15. Carden, M., Schmitt, D., Tomasi, T., Bradford, J., Moll, D. & Brown, J. L. (1998): Utility of serum progesterone and prolactin analysis for assessing reproductive status in the Asian elephant (Elephas maximus). Animal Reproduction Science 53: 133 – 142.
16. Cooper, R. A., Connell, R. S. & Wellings, S. R. (1964): Placenta of the Indian elephant, Elephas indicus. Science 146: 410 – 412.
17. Craig, G. C. (1984): Foetal mass and date of conception in African elephants: A revised formula. South African Journal of Science 80: 512 – 516.
18. Czekala, N. M., Macdonald, E. A., Steinman, K., Walker, S. Garrigues, II, N. W., Olson, D. & Brown, J. L. (2003): Estrogen and LH dynamics during the follicular phase of the estrous cycle of the Asian elephant. Zoo Biology 22: 443 – 454.
19. Davis, S. & Bernirschke, K. (1991): Observations on the placenta of elephants. Verhandlungsbericht ber Erkrankungen Zootiere 33: 39 – 45.
20. Dehnhard, M., Heistermann, M., Goritz, F., Hermes, R., Hildebrandt, T. B. & Haber, H. (2001a): Demonstartion of 2-unsaturated C19-ster-oids in the urine of female Asian elephants, Elephas maximus, and their dependence on ovarian activity. Reproduction 121: 475 – 484.
21. Dehnhard, M., Hildebrandt, T. B., Rohleder, M., Strauss, G., Meyer, H. H. D. & Göritz, F. (2001b): Application of an enzyme-immunoassay (EIA) for rapid screening of 5alpha-pregnane-3,20-dione (DHP) in blood plasma of the Asian elephant, Elephas maximus. Berliner und Munchener Tierarz-tliche Wochenschrift 114: 161 – 165.
22. Dehnhard, M., Eulenberger, K., Ochs, A. & Strauss, G. (2003): Headspace solid-phase microex-traction (Spme) and gas chromatography-mass spectrometry (GC/MS) for the determination of 5a-Androst-2-en-17-one and -17/3-ol in the female Asian elephant: Application for reproductive monitoring and prediction of parturition. Journal of Steroid Biochemistry and Molecular Biology 84: 383 – 391.
23. Delsink, A. K., Van Altena, J. J., Kirkpatrick, J., Grobler, D. & Fayrer-Hosken, R. A. (2001): Field application of immunocontraception in African elephants (Loxodonta africana). Reproduction (Suppl.) 60: 117 – 124.
24. Dorresteyn, A. H. & Schaftenaar, W. (2004): Population management of Asian elephants in zoos and the related problems. In Proceedings of the 15th symposium on tropical animal health and production. Management of elephant reproduction: 39 – 44. Utrecht: Utrecht University.
25. Duer, C, Carden, M., Schmitt, D. & Tomasi, T. (2002): Utility of maternal serum total testosterone analysis for fetal gender determination in Asian elephants (Elephas maximus). Animal Reproduction Science 69: 47 – 52.
26. Fayrer-Hosken, R. A., Grobler, D. Van Altena, J. J., Bertschinger, H. J. & Kirkpatrick, J. F. (2001): Immunocontraception of African elephants. Nature 407: 149.
27. Fiess, M., Heistermann, M. & Hodges, J. K. (1999): Patterns of urinary and fecal steroid excretion during the ovarian cycle and pregnancy in the African elephant (Loxodonta africana). General and Comparative Endocrinology 115: 76 – 89.
28. Gaeth, A. P., Short, R. V. & Renfree, M. B. (1999): The developing renal, reproductive, and respiratory systems of the African elephant suggest an aquatic ancestry. PNAS 96(11): 5555 – 5558.
29. Göritz, F., Hildebrandt, T. B., Hermes, R., Quandt, S., Grobler, D., Jewgenow, K., Rohleder, M., Meyer, H. H. D. & Hofmann, R. R. (1999): Results of hormonal contraception programme in free ranging African Elephants. Verhandlungsbericht ber Erkrankungen Zootiere 39: 39 – 40.
30. Heistermann, M., Trohorsch, B. & Hodges, J. K. (1997): Assessment of ovarian function in the African elephant (Loxodonta africana) by measurement of 5a-reduced progesterone metabolites in serum and urine. Zoo Biology 16: 273 – 284.
31. Hermes, R., Olson, D., Göritz, F., Brown, J. L., Schmitt, D. L., Hagan, D., Peterson, J. S., Fritsch, G. & Hildebrandt, T. B. (2000): Ultra-sonography of the sexual cycle in female African elephants (Loxodonta africana). Zoo Biology 19: 369 – 382.
32. Hermes, R., Hildebrandt, T. B. & Goritz, F. (2004): Reproductive problems directly attributable to long-term captivity—asymmetric reproductive aging. Animal Reproduction Science 82-83: 49 – 60.
33. Hess, D. L., Schmidt, A. M. & Schmidt, M. J. (1983): Reproductive cycle of the Asian elephant (Elephas maximus) in captivity. Biology of Reproduction 28: 767 – 773.
34. Hildebrandt, T. B. (2001): Preliminary results of reproductive assessment of captive ‘breeding bulls’ in North America, Europe, and Asia. In Proceedings of the 5th annual international elephant research symposium, 2-3 June, 2000, Portland Zoo, Portland, Oregon: 6. Olson, D Portland, OR: Portland Zoo.
35. Hildebrandt, T. B. (2003): Aspects of male reproductive physiology and the phenomenon of temporary infertility in adult bulls. In Managing African elephant populations: Act or let die: 73 – 75. Utrecht: Utrecht University, Office for International Cooperation, Faculty of Veterinary Medicine.
36. Hildebrandt, T. B. & Göritz, F. (1995): Sono-graphic evidence of leiomyomas in female elephants. Verhandlungsbericht ber Erkrankungen Zootiere 36: 59 – 67.
37. Hildebrandt, T. B. & Göritz, F. (1999): Use of ultrasonography in zoo animals. In Zoo and wild animal medicine. Current therapy 4: 41 – 54.Fowler, M. E. & Miller, R. E Philadelphia, PA: W. B. Saunders Company.
38. Hildebrandt, T. B. & Schnorrenberg, A. (1996): Besteck zur kunstlichen Besamung von Elefanten. Deutsches Patentamt, Offenlegungsschrift, DE 196 06 925 A1.
39. Hildebrandt, T. B., Göritz, F., Pratt, N. C., Schmitt, D. L., Lehnhardt, J., Hermes, R., Quandt, S., Raath, J., West, G. & Montali, R. J. (1997): Assessment of health and reproductive status in African elephants by transrectal ultrasonography. JEMA 8: 44 – 48.
40. Hildebrandt, T. B., Göritz, F., Pratt, N. C., Schmitt, D. L., Quandt, S., Raath, J. & Hofmann, R. R. (1998): Reproductive assessment of male elephants (Loxodonta africana and Elephas maximus) by ultrasonography. Journal of Zoo and Wildlife Medicine 29: 114 – 128.
41. Hlldebrandt, T. B. Goritz, F. Hermes, R. Schmitt, D. L., Brown, J. L., Schwammer, H., Los-Kutoff, N., Pratt, N. C, Lehnhardt, J. L., MON-Tali, R. J. & Olson, D. (1999): Artificial insemination of African (Loxodonta africana) and Asian (Elephas maximus) elephants. Proceedings of the American Association of Zoo Veterinarians 1999: 83 – 86.
42. Hildebrandt, T. B., Fritsch, G., Hermes, R., Jewgenow, K., Rudolph, M., Maltzahn, J., Wiesner, H., Pratt, N. C, Neiffer, D., Schmitt, D. L. & Göritz, F. (1999): Ultrasound monitoring of the sexual maturation in the male elephant. Proceedings of the American Association of Zoo Veterinarians 1999: 203 – 204.
43. Hildebrandt, T. B., Göritz, F., Pratt, N. C., Brown, J. L., Montali, R. J., Schmitt, D. L., Fritsch, G. & Hermes, R. (2000): Ultrasonography of the urogenital tract in elephants (Loxodonta africana and Elephas maximus): An important tool for assessing female reproductive function. Zoo Biology 19: 321 – 332.
44. Hlldebrandt, T. B., Hermes, R., Pratt, N. C, Fritsch, G., Blottner, S., Schmitt, D. L., Ratan-Akorn, P., Brown, L. B., Rietschel, W. & Göritz, F. (2000): Ultrasonography of the urogenital tract in elephants (Loxodonta africana and Elephas maximus): An important tool for assessing male reproductive function. Zoo Biology 19: 333 – 345.
45. Hlldebrandt, T. B., Hermes, R., Jewgenow, K. & Göritz, F. (2000): Ultrasonography as an important tool for the development and application of reproductive technologies in non-domestic species. Theriogenology 53: 73 – 84.
46. Hildebrandt, T. B., Brown, J. L., Hermes, R. & Göritz, F. (2003): Ultrasound analysis of reproductive function in wildlife species. Conservation Biology 8: 166 – 182.
47. Hlldebrandt, T. B., Strike, T., Flach, E., Sam-brook, L., Dodds, J., Lindsay, N., Furley, C. F., Glatzel, P. S. & McGowan, M. (2003): Fetotomy in the elephant. Verhandlungsbericht ber Erkran-kungen Zootiere 41: 315 – 318.
48. Hodges, J. K. (1998): Endocrinology of the ovarian cycle and pregnancy in the Asian (Elephas maximus) and African (Loxodonta africana) elephant. Animal Reproduction Science 53: 3 – 18.
49. Hodges, J. K., Heistermann, M., Beard, A. & Van Aarde, R. J. (1997): Concentrations of progesterone and the 5a-reduced progestins, 5a-pregnane-3,20-dione and 3a-hydroxy-5a-pregnan-20-one, in luteal tissue and circulating blood and their relationship to luteal function in the African elephant, Loxodonta africana. Biology of Reproduction 56: 640 – 646.
50. Jainudeen, M. R., Mackay, G. M. & Eisenberg, J. F. (1971): Observations on musth in the domesticated Asiatic elephants. Mammalia 36: 247 – 261.
51. Jainudeen, M. R., Kartongole, C. B. & Short, R. V. (1972): Plasma testosterone levels in relation to musth and sexual activity in the male Asiatic elephants, (Elephas maximus). Journal of Reproduction and Fertility 29: 99 – 103.
52. Johnson, O. W. & Buss, I. O. (1967a): The testis of the African elephant (Loxodonta africana). I. histo-logical features. Journal of Reproduction and Fertility 13: 11 – 21.
53. Johnson, O. W. & Buss, I. O. (1967b): The testis of the African elephant (Loxodonta africana). II. development, puberty, and weight. Journal of Reproduction and Fertility 13: 23 – 30.
54. Jones, R. C. & Brosnan, M. F. (1981): Studies of the deferent ducts from the testis of the African elephant, Loxodonta africana. I. Structural differentiation. Journal of Anatomy 132: 371 – 386.
55. Jones, R. C., Rowlands, I. W. & Skinner, J. D. (1974): Spermatozoa in the genital ducts of the African elephant, Loxodonta africana. Journal of Reproduction and Fertility 41: 189 – 192.
56. Kähn, W. (1991): Atlas und Lehrbuch der Ultras-challdiagnostik. Gynakologische Untersuchung und Reproduktion. Pferd, Rind, Schaf Ziege, Schwein, Hund, Katze. Hannover: Schlutersche.
57. Kapustin, N., Critser, J. K., Olson, D. & Malven, P. V. (1996): Nonluteal estrous cycles of 3-week duration are initiated by anovulatory luteinizing hormone peaks in African elephants. Biology of Reproduction 55: 1147 – 1154.
58. Keele, M. (1997): Asian elephant regional studbook. Portland, OR: Metro Washington Park Zoo. (Electronic: QL737.P98 K44.).
59. Keele, M. (2004) North American regional studbook update 2002. Portland, OR: Oregon Zoo. (Electronic: QL77.5 S78 2004.).
60. Knobil, E. & Neill, J., (Eds) (1998): Encyclopedia of reproduction. New York: Academic Press.
61. Lair, R. C. (1997): Gone Astray. The care and management of the Asian elephant in domesticity. Bangkok: Food and Agriculture Organization of the United Nations (Regional Office for Asia and the Pacific: RAP).
62. Lange, A., Hlldebrandt, T. B., Strauss, G., Czu-palla, O. Göritz, F., Schaftenaar, W. & Schmitt, D. L. (1999): Moglichkeiten und Grenzen der Geburtshilfe bei Elefanten. Verhandlungsbericht ber Erkrankungen Zootiere 39: 47 – 58.
63. Laws, R. M. (1967): Occurrence of placental scars in the uterus of African elephants Loxodonta africana. Journal of Reproduction and Fertility 14: 445 – 449.
64. Laws, R. M. (1969): Aspects of reproduction in the African elephant, Loxodonta africana. Journal of Reproduction and Fertility, Suppl. 6: 193 – 217.
65. Leong, K. M., Ortolani, A., Graham, L. H. & Savage, A. (2003): The use of low-frequency vocalizations in African elephant (Loxodonta africana) reproductive strategies. Hormones and Behavior 43: 433 – 443.
66. Mariappa, D. (1986): Anatomy and histology of the Indian elephant. Oak Park, MI: Indira Publishing House.
67. Menon, V., Sukumar, R. & Kumar, A. (1997): A god in distress: Threats of poaching and the ivory trade to the Asian elephant in India. Bangalore: Asian Elephant Conservation Centre.
68. Meyer, H. H. D., Jewgenow, K. & Hodges, J. K. (1997): Binding activity of 5alpha-reduced gestagens to the progestin receptor in the African elephant. General and Comparative Endocrinology 105: 164 – 167.
69. Meyer, J. M., Walker, S. L., Freeman, E. W., Stei-Netz, B. G. & Brown, J. L. (2004): Species and fetal gender effects on the endocrinology of pregnancy in elephants. General and Comparative Endocrinology 138: 263 – 270.
70. Mikota, S. K., Sargent, E. L. & Ranglack, G. S., (Eds) (1994): Medical management of the elephant: 159 – 186. Oak Park, MI: Indira Publishing House.
71. Montali, R. J., Hildebrandt, T., Göritz, F., Hermes, R., Ippen, R. & Ramsay, E. (1997): Ultra-sonography and pathology of genital tract leiomyomas in captive Asian elephants: Implications for reproductive soundness. Verhandlungsbericht ber Erkrankungen Zootiere 38: 253 – 258.
72. Montali, R. J., Richman, L. K., Mikota, S. K., Schmitt, D. L., Larsen, R. S., Hildebrandt, T. B., Isaza, R. & Lindsay, W. A. (2002): Management aspects of herpesvirus infections and tuberculosis in elephants. In A research update on elephants and rhinos. Proceedings of the international elephant and rhino symposium, Vienna, June 7-11, 2001: 87 – 95.
73. Schwammer, H. M., Foose, T. J., Fouraker, M. & Olson, D. Münster: Schuling Verlag.
74. Niemuller, C. A. & Liptrap, R. M. (1991): Altered androstenedione to testosterone ratios and LH concentrations during musth in captive male Asian elephants (Elephas maximus). Journal of Reproduction and Fertility 91: 139 – 146.
75. Niemuller, C., Brown, J. L. & Hodges, J. K. (1998): Reproduction in elephants. In Encyclopedia of reproduction 1: 1018 – 1029.Knobil, E. & Neill, J. New York: Academic Press.
76. Olsen, J. H., Chen, C. L., Boules, M. M., Morris, L. S. & Coville, B. R. (1994): Determination of reproductive cyclicity and pregnancy in Asian elephants (Elephas maximus) by rapid radioimmunoassay of serum progesterone. Journal of Zoo and Wildlife Medicine 25: 349 – 354.
77. Olson, D. (2002): AZA North American African elephant. Sparks dataset. Indianapolis, IN: Indianapolis Zoo.
78. Olson, D. & Wiese, R. J. (2000): State of the North American African elephant population and projections for the future. Zoo Biology 19: 311 – 320.
79. Ortolani, A., Partan, S., Leong, K., Burks, K., Graham, L. H., Mellen, J. & Savage, A. (2000): ’Hey baby, I’m here!’: Advertisement of estrus in captive African elephants (Loxodonta africana). Advances in Ethology Suppl. 35: 52.
80. Ottow, B. (1955): Proboscidae In Biologische Anatomie der Genitalorgane und der Fortpflanzung der Säugetiere: 127 – 130. Jena: Verlag Fischer.
81. Perry, J. S. (1974): Implantation, foetal membranes and early placentation of the African elephant, Loxodonta africana. Philosophical Transactions of the Royal Society of London B 269: 110 – 135.
82. Plotka, E. D., Seal, U. S., Zarembka, F. R., Simmons, L. G., Teare, A., Phillips, L. G., Hinshaw, K. C. & Wood, D. G. (1988): Ovarian function in the elephant: Luteinizing hormone and progesterone cycles in African and Asian elephants. Biology of Reproduction 38: 309 – 314.
83. Poole, J. H. (1994): Sex differences in the behaviour of African elephants. In The differences between the sexes: 331 – 346. Short, R. V. & Balaban, E. Cambridge: Cambridge University Press.
84. Ratanakorn, P. (2000): Reproduction problems of Asian elephants (Elephas maximus) in Thailand. In Assessment and management of reproductive system in Asian elephants: 11 – 12. Bangkok: The National Identity Office, Secretariat of the Prime Minister.
85. Richman, L. K., Montali, R. J., Garber, R. L., Kennedy, M. A., Lehnhardt, J., Hildebrandt, T. B., Schmitt, D. L., Hardy, D., Alcendor, D. J. & Hayward, G. S. (1999): Novel endotheliotropic herpesviruses fatal for Asian and African elephants. Science 283: 1171 – 1176.
86. Riddle, H. S. & Rasmussen, L. E. L. (2001): Are female African elephants messaging through volatile chemicals? Studies from Europe, USA, and African groups. In Proceedings of the international elephant and rhino symposium, Vienna, June 7-11 2001: 29. Vienna: Schuling Verlag.
87. Roca, A. L., Georgiadis, N., Pecon-Slattery, J. & O’Brien, S. J. (2001): Genetic evidence for two species of elephant in Africa. Science 293: 1473 – 1477.
88. Schaftenaar, W. (1999): EEP-guideline. Captive elephant breeding: What we should do? Dataset. Rotterdam: Rotterdam Zoo.
89. Schaftenaar, W., Hildebrandt, T. B., Flugger, M., Göritz, F., Schmitt, D. & West, G. (2001): Guidelines for veterinary assistance during the reproductive process in female elephants. Proceedings of the American Association of Zoo Veterinarians 2001: 348 – 355.
90. Schmitt, D. L. & Hildebrandt, T. B. (1998): Manual collection and characterization of semen from Asian elephants (Elephas maximus). Animal Reproduction Science 53: 309 – 314.
91. Schulte, B. A., Feldman, E., Lambert, R., Renee, O. & Hess, D. L. (2000): Temporary ovarian inactivity in elephants: Relationship to status and time outside. Physiology and Behavior 71: 123 – 131.
92. Schulte, T. L. (1937): The genito-urinary system of the Elephas indicus. American Journal of Anatomy 61: 131 – 156.
93. Schwarzenberger, F., Strauss, G., Hoppen, H.-O., Schaftenaar, W., Dleleman, S. J., Zenker, W. & Pagan, O. (1997): Evaluation of progesterone and 20-oxo-progestagens in the plasma of Asian (Elephas maximus) and African (Loxodonta africana) elephants. Zoo Biology 16: 403 – 413.
94. Secundus, P. C. (A.D. 77): The historie of the world. Commonly called the natural history of C. Plinius Secundus: Book VIII: 192 – 234. Holland, P. (translator). London: Adam Islip, Printed 1601.
95. Sikes, S. (1971): The natural history of the African elephant. London: Weidenfeld & Nicolson.
96. Smith, N. S. & Buss, I. O. (1975): Formation, function, and persistence of the corpora lutea of the African elephant (Loxodonta Africana). Journal of Mammalogy 56: 30 – 43.
97. Smith, R. J., Muir, R. D. J., Walpole, M. J., Balm-Ford, A. & Leader-Williams, N. (2003): Governance and the loss of biodiversity. Nature 426: 67 – 70.
98. Sukumar, R., (Ed.) (1989): The Asian elephant: Ecology and management. Cambridge: Cambridge University Press.
99. Sukumar, R. (1994): Elephant days and nights. Dehli: Oxford University Press.
100. Swain, J. S. & Miller, R. R. (2000): A postcryogenic comparison of membrane fatty acids of elephant spermatozoa. Zoo Biology 19: 461 – 473.
101. Terkel, A. (2001): Overview of the African elephant EEP. In Abstracts of recent research on elephants and rhinoceroses: 133 – 135. Münster: Schilling Verlag.
102. Thitaram, C., Pongsopawijit, P., Jansittivej, S., Rojanaasathien, S. & Brown, J. L. (2004): Breeding management of the domestic female Thai elephant (Elephas maximus) population. In Proceedings of the 15th symposium on tropical animal health and production: Management of elephant reproduction: 44 – 48. Utrecht: Utrecht University.
103. De Villiers, D. J., Skinner, J. D. & Hall-Martin, A. J. (1989): Circulating progesterone concentrations and ovarian functional anatomy in the African elephant (Loxodonta africana). Journal of Reproduction and Fertility 86: 195 – 201.
104. Wiese, R. J. (2000): Asian elephants are not self-sustaining in North America. Zoo Biology 19: 299 – 309.
105. Wiese, R. J. & Willis, K. (2004): Calculation of longevity and life expectancy in captive elephants. Zoo Biology 23: 365 – 373.
106. Zwart, P., Ippen, R., Flügger, M., Göritz, F. & Hildebrandt, T. B. (1999): Post mortem findings in a 60-year-old Sri Lankan elephant (Elephas maximus maximus). Verhandlungsbericht ber Erkrankungen Zootiere 39: 143 – 148.