Conservation – novel concepts and methods

Revolutionary achievements in the fields of miniaturisation of technologies, from field and veterinary imaging techniques via computers to GPS satellite data and the continuous advances in biotechnology open totally new areas for conservation research. The application and refinement of these developments open tremendous opportunities for scientific research supporting wildlife conservation, one of the main goals of the IZW. Currently, we are engaged in the following topics.

Genome conservation to protect biodiversity

Genome resource banking can potentially offer a safeguard against gene loss by storing reproductive material from animals for future use. Cryopreserved samples can be stored for generations and may have direct impact on genetic management when thawed and used in assisted reproduction programmes. At the IZW, as part of programmes such as the ‘Frozen Ark’ or the ‘Felid Gamete Rescue’, a large collection of gametes, embryos, and testicular and ovarian tissue samples has been accumulated over the years. These samples provide an insurance against complete loss of an individual's precious genes. Based on species-specific cellular and molecular properties of germ cells, ovary tissue and embryos, customised methods of (cryo)preservation are continuously under development for various species. In combination with the adaptation of assisted reproduction technologies this will provide a more functional pool of stored gametes and embryos. Subsequently, distant, isolated, wild or captive populations can be easily linked through the use of cryopreserved samples without the risks of disease transmission or animal transport. Sample collection is performed from living animals or, as a rescue measure, from deceased or neutered valuable individuals.

Assisted reproduction

Assisted reproductive technology (ART) is as a significant tool in overcoming breeding problems in captivity and broadening the gene pool for species conservation in situ and ex situ. The modern methodology of ART includes hormonal monitoring of cyclic ovarian activity, artificial insemination, aspiration of oocytes, collection of spermatozoa, in vitro production of embryos and, finally, embryo transfer.

By definition, endangered species are species in which the population is small and dwindling, putting their genetic diversity and the survival of the species at risk. Development of species-specific assisted reproduction technologies is necessary for directing gene exchange. One important aspect when developing ART is the cognition of species specific reactions to the reduced gene pool. In this respect, shifting the sex of offspring either by new techniques or as a result of adaptation might play a considerable role.

Non-invasive and minimally invasive methods

Evaluating general health status, adrenal activity (stress) and reproductive functions to investigate reproductive health requires the development of non-invasive techniques to monitor reproductive cycles and the success of contraceptive methods. In recent years, improvements in endocrine monitoring, characterisation of reproductive cycles and the application of imaging techniques such as ultrasound and computed tomography facilitates the rapid development of innovative tools for research and reproductive monitoring in captive and free-ranging wildlife populations.

Camera trapping

Many wildlife species are extremely rare and cryptic and may rarely, if ever, be encountered. Today, new technical developments allow us to study these often highly threatened wildlife species.

Among these developments, camera-traps are a particularly popular tool for monitoring cryptic and rare wildlife. Their non-invasive character and their ability to quickly accumulate data over large areas with relatively little effort make them an ideal tool for wildlife monitoring and biodiversity assessments. To enhance systematic applications of camera-trapping and in collaboration with other researchers and institutes we recently developed a practical camera-trapping handbook for wildlife monitoring, targeting the logistically challenging rainforests of Southeast Asia. Another focus of our work is to disseminate and emphasise the challenges when analysing camera-trapping data by linking species ecology and survey design to advanced statistical concepts, with the aim to encourage adequate data collection and interpretation.

In situ field studies are, for example, in the tropical rainforests of Sabah, Malaysian Borneo, where our team rediscovered the hairy-nosed otter after 100 years, and obtained the first video footage of the sunda clouded leopard and the otter civet. With the data collected in these studies we were able to provide rigorous density estimates for the Sunda clouded leopard and the leopard cat using modern spatial capture-recapture models. A camera-trapping study carried out in collaboration with the Jaguar Conservation Fund in Emas National Park, in the Cerrado grasslands of Central Brazil, revealed that jaguars occur at very low densities and that they prefer to use areas of denser vegetation, concentrated along the park’s river valleys, as opposed to the more generalist puma.

Genetic analysis

Another way of acquiring data by non-invasive means is the sampling of material that is shed by animals (hair, faeces), followed by genetic analyses [in praxi, faeces are often also used for hormonal and microbiological analyses]. Shed material contains cells und thus DNA from the shedding individual which can be used to genotype the shedding individual. If applied to samples from many individuals, data can be used to infer population-wide information such as population size, sex ratio, allele frequencies and gene flow among populations and subpopulations.

While in principle very promising, this approach has to overcome several obstacles. Because the shedding individual is often not known, many samples are necessary (a so-called capture-mark-recapture approach) to infer the sought after information. In addition, shed material is always exposed (often for an unknown period) to destructive external factors such as UV-light, other organisms which feed on the shed material (e.g. microbes, insects) or rainfall which may result in the loss of the peripheral layer of intestinal cells covering, e.g. faecal material. These factors may hamper genetic analysis, rendering numerous samples uninformative. Despite these complications, these methods become more reliable and we have developed and modified procedures which were successfully applied to non-invasive genotyping of numerous wildlife species.

Females in many species produce estrous-related olfactory signals (pheromones) specifically directed towards males. These have already in some cases been used as excellent analytical indicators to predict the receptive period of a female (e.g. in elephants). Pheromones from males sometimes enhance reproductive functions in females such as the male effect in goats and sheep. This biostimulation may have great potential to support reproductive management as it could hasten sexual maturity, induce ovulation and reduce post-partum anoestrus and mating.

Monitoring reproductive health

Evaluating general health status, adrenal activity (stress) and reproductive functions to investigate reproductive health,  requires the development of non-invasive techniques to monitor reproductive cycles and the success of contraceptive methods. In recent years, improvements in endocrine monitoring, characterisation of reproductive cycles and the application of imaging techniques such as ultrasound and computed tomography facilitates the rapid development of innovative tools for research and reproductive monitoring in captive and free-ranging wildlife populations.

Non-invasive monitoring of hormones

At the IZW endocrinology laboratory, we are developing non-invasive methods to study the physiology of reproduction and stress in different wildlife species such as an enzyme immunoassay (EIA) for PGFM estimation in feces of the Iberian lynx (Lynx pardinus) for pregnancy monitoring and its differentiation from pseudopregnancy. Fecal PGFM levels before mating and after parturition were low. In pregnant females a distinct increase was observed after Day 45 postmating, culminating in peak levels around parturition, whereas PGFM levels returned to basal levels in pseudopregnant female (Fig. 1). By now the PGFM principle has been proved to be valid in six of the eight cat lineages.

Fig. 1: Course of fecal PGFM levels in samples collected from one pregnant and one pseudopregnant female Iberian lynx. The PGFM principle has also been proven to be valid in most of the species tested so far from the eight cat lineages.

We also developed an easy to manage PGFM assay to reduce the time between sampling and diagnosis. Pregnancy diagnosis can be performed based on two calibration standards from pregnant and pseudopregnant females when diagnosing samples from the last pregnancy trimester yielding only a weak yellow colorization in pregnant females (Fig. 2).

Fig. 2: Fast PGFM assay for pregnancy analysis in the Iberian lynx. Pregnancy diagnosis is performed based on reference samples from pregnant and non-pregnant lynxes.

In the brown bear (Ursus arctos) infanticide caused by males is an important cause of cub mortality. This project is a co-operation with the Scandinavian Brown Bear Research Project (SBBRP). We hypothesize, that infanticide is followed by an immediate resumption of female reproductive activity elicited by increasing estrogen levels and thus increasing fecal estrogen metabolites. In one female infanticide occurred early in June 2011. Until infanticide fecal estrogen metabolites (fEM) levels remained at basal. Infanticide was associated with an immediate increase in fEM. Thereafter six peaks of estrogen secretion were measured until end of June while the female was accompanied by males.

Two other focus species are the spotted hyena (Crocuta crocuta) and the cheetah (Acinonyx jubatus). In both species we aim to objectify adrenocortical activity (stress) based on measuring fecal cortisol metabolites. Before applying an assay so called biological validations must be performed. This can be realized applying so called ACTH challenges resulting in a pharmacological stimulation of the adrenal cortex to secrete cortisol into the blood followed by a corresponding increase of fecal cortisol metabolites (fGM). Three different assays based on different antibodies were proved for the cheetah. Whereas assay 1 and 2 didn’t demonstrate a distinct increase in fGM the use of assay 3 revealed an 18-fold increase of fGM (Fig. 3).

Fig. 3: Fecal cortisol metabolites in a female cheetah subjected to an ACTH challenge (arrow). Three different assays were checked for their capability to detect a pharmacologically induced increase in fGM resulting in assay 3 to be suitable for this species.

Modelling the distribution and habitat requirements of populations and species

A key challenge in ecology is to understand the factors that determine the spatial distribution and abundance of organisms. This topic has relevance to conservation ecology because the characterisation of the essential habitats of species is essential to address the effects of degradation, loss of connectivity, fragmentation and loss of habitat on the viability of species. The understanding of how species respond to certain landscape elements is thus a prerequisite for effective nature conservation measures and habitat restoration efforts. At the IZW, we use different statistical methods to develop species distribution models for rare and endangered carnivores. The latest development is the use of isotope information in hair samples to deduce origins of migrating species.

As the IUCN identified large Southeast Asian animals as the one of three groups currently facing an extinction crisis, we have started to work on integrated conservation plans and use modern modelling techniques to improve the conservation of carnivores in Southeast Asia, and in particular in Borneo. Since 2008, the IZW conducts an in situ research and conservation project - Conservation of Carnivores in Sabah (ConCaSa) in Malaysian Borneo. In this project, non-invasive techniques (mainly camera-trapping) are used to investigate how three different forest management practices affect individual carnivore species in their abundance and the general mammal community composition. A particular focus was given to studying the habitat association and the resilience of highly threatened mammal species to anthropogenic habitat modifications. To tie in the field results with a landscape-scale approach, we synthesized the fragmented information of Bornean carnivores, resulting in a database with over 4000 occurrence records. Based on these, we produced species distribution models for 23 carnivore species, which will aid in the reassessment of the IUCN’s Red List accounts of these threatened carnivore taxa. Already in 2010 we applied a similar approach to one of the most threatened Southeast Asian carnivores, the flat-headed cat Prionailurus planiceps, and showed that this species faces a great risk of extinction as its distribution is restricted to tropical lowlands close to water resources - exactly the areas that show the highest deforestation rates in the world.

Selected publications

Ancrenaz M, Hearn AJ, Ross J, Sollmann R, Wilting A (2012) Handbook for wildlife monitoring using camera-traps. Japan International Cooperation Agency (JICA).

Dehnhard M, Finkenwirth C, Crosier A, Penfold L, Ringleb J, Jewgenow K (2012) Using PGFM (13,14-dihydro-15-keto-prostaglandin F2 alpha) as a non-invasive pregnancy marker for felids. Theriogenology 77: 1088-1099.

Fickel J, Bubliy OA, Brandt J, Mayer K, Heurich M (2012) Genotyping error rates in non-invasively collected samples from roe deer of the Bavarian Forest National Park. Mamm Biol 77: 67-70.

Hildebrandt TB, Hermes R, Saragusty J, Potier R, Schwammer HM, Balfanz F, Vielgrader H, Baker B, Bartels P, 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.

Saragusty J, Hermes R, Hofer H, Bouts T, Göritz F, Hildebrandt TB (2012) Male pygmy hippopotamus influence offspring sex ratio. Nat Commun 3: 697.

Sollmann R, Furtado M, Hofer H, Jácomo A, Tôrres N, Silveira L (2012) Using occupancy models to investigate space partitioning between two sympatric large predators, the jaguar and puma in central Brazil. Mamm Biol 77: 41-46.

Dehnhard M (2011) Mammal semiochemicals: understanding pheromones and signature mixtures for better zoo-animal husbandry and conservation. Int Zoo Yb 45: 1–25.

Drews B, Harmann LM, Beehler LL, Bell B, Drews RF, Hildebrandt TB (2011) Ultrasonographic monitoring of fetal development in unrestrained bonobos (Pan paniscus) at the Milwaukee County Zoo. Zoo Biol 30: 241-253.

Jewgenow K, Wiedemann C, Bertelsen MF, Ringleb J (2011) Cryopreservation of mammalian ovaries and oocytes. Int Zoo Yb 45: 124–132.

Kanagaraj R, Wiegand T, Kramer-Schadt S, Goyal SP, Anwar M, Harihar A (2011) Assessing habitat suitability for tiger in the fragmented Terai Arc landscape of India and Nepal. Ecography 34: 970-981.

Loi P, Fulka J, Hildebrand T, Ptak G (2011) Genome of non-living cells: trash or recycle? Reproduction 142: 497-503.

Roellig K, Drews B, Goeritz F, Hildebrandt TB (2011) The long gestation of the small naked mole-rat (Heterocephalus glaber RUPPELL, 1842) studied with ultrasound biomicroscopy and 3d-ultrasonography. PLoS ONE 6.

Saragusty J, Arav A (2011) Current progress in oocyte and embryo cryopreservation by slow freezing and vitrification. Reproduction 141: 1-19.

Schroeder K, Drews B, Roellig K, Menzies BR, Goeritz F, Hildebrandt TB (2011) In vivo tissue sampling of embryonic resorption sites using ultrasound guided biopsy. Theriogenology 76: 778-784.

Sollmann R, Furtado M, Gardner B, Hofer H, Jácomo A, Tôrres N, Silveira L (2011) Improving density estimates for elusive carnivores: Accounting for sex-specific detection and movements using spatial capture-recapture models for jaguar in central Brazil. Biol Cons 144: 1017-1024.

Behr B, Rath D, Mueller P, Hildebrandt TB, Goeritz F, Braun BC, Leahy T, de Graaf SP, Maxwell WMC, Hermes R (2010) Feasibility of sex-sorting sperm in rhinoceros species. Reprod Domest Anim 45: 5.

Dehnhard M, Fanson K, Frank A, Naidenko SV, Vargas A, Jewgenow K (2010) Comparative metabolism of gestagens and estrogens in the four lynx species, the Eurasian (Lynx lynx), the Iberian (L. pardinus), the Canada lynx (L. canadensis) and the bobcat (L. rufus). Gen Comp Endocr 167: 287-296.

Finkenwirth C, Jewgenow K, Meyer HHD, Vargas A, Dehnhard M (2010) PGFM (13,14-dihydro-15-keto-PGF(2 alpha)) in pregnant and pseudo-pregnant Iberian lynx: A new noninvasive pregnancy marker for felid species. Theriogenology 73: 530-540.

Franz M, Kramer-Schadt S, Kilian W, Wissel C, Groeneveld J (2010) Understanding the effects of rainfall on elephant-vegetation interactions around waterholes. Ecol Model 221: 2909-2917.

Peppin L, McEwing R, Ogden R, Hermes R, Harper C, Guthrie A, Carvalho GR (2010) Molecular sexing of African rhinoceros. Conserv Genet 11: 1181-1184.

Roellig K, Goeritz F, Hildebrandt TB (2010) Ultrasonographic characterisation of prenatal development in European brown hares (Lepus europaeus PALLAS, 1778): an evolutionary approach. Reprod Fert Develop 22: 448-458.

Saragusty J, Hildebrandt TB, Bouts T, Göritz F, Hermes R (2010) Collection and preservation of pygmy hippopotamus (Choeropsis liberiensis) semen. Theriogenology 74: 652-657.

Saragusty J, Walzer C, Petit T, Stalder G, Horowitz I, Hermes R (2010) Cooling and freezing of epididymal sperm in the common hippopotamus (Hippopotamus amphibius). Theriogenology 74: 1256-1263.

Smitz J, Dolmans MM, Donnez J, Fortune JE, Hovatta O, Jewgenow K, Picton HM, Plancha C, Shea LD, Stouffer RL, Telfer EE, Woodruff TK, Zelinski MB (2010) Current achievements and future research directions in ovarian tissue culture, in vitro follicle development and transplantation: implications for fertility preservation. Hum Reprod Update 16: 395-414.

Walzer C, Goritz F, Hermes R, Nathan S, Kretzschmar P, Hildebrandt T (2010) Immobilization and intravenous anesthesia in a Sumatran rhinoceros (Dicerorhinus sumatrensis). J Zoo Wildl Med 41: 115-120.

Wilting A, Cord A, Hearn AJ, Hesse D, Mohamed A, Traeholdt C, Cheyne SM, Sunarto S, Jayasilan M-A, Ross J, Shapiro AC, Sebastian A, Dech S, Breitenmoser C, Sanderson J, Duckworth JW, Hofer H (2010) Modelling the species distribution of flat-headed cats (Prionailurus planiceps), an endangered South-East Asian small felid. PLoS ONE 5.

Wilting A, Samejima H, Mohamed A (2010). Diversity of Bornean viverrids and other small carnivores in Deramakot Forests Reserve, Sabah, Malaysia. Small Carniv Conserv 42: 10-13.

Behr B, Rath D, Hildebrandt TB, Goeritz F, Blottner S, Portas TJ, Bryant BR, Sieg B, Knieriem A, de Graaf SP, Maxwell W M C, Hermes R (2009) Germany/Australia index of sperm sex sortability in elephants and rhinoceros. Reprod Domest Anim 44: 273-277.

Behr B, Rath D, Mueller P, Hildebrandt TB, Goeritz F, Braun BC, Leahy T, de Graaf SP, Maxwell WMC, Hermes R (2009) Feasibility of sex-sorting sperm from the white and the black rhinoceros (Ceratotherium simum, Diceros bicornis). Theriogenology 72: 353-364.

Braun BC, Frank A, Dehnhard M, Voigt CC, Vargas A, Göritz F, Jewgenow K (2009) Pregnancy diagnosis in urine of Iberian lynx (Lynx pardinus). Theriogenology 71: 754-761.

Göritz F, Dehnhard M, Hildebrandt TB, Naidenko SV, Vargas A, Martinez F, Lopez-Bao JV, Palomares F, Jewgenow K (2009) Non cat-like ovarian cycle in the Eurasian and the Iberian lynx - Ultrasonographical and endocrinological analysis. Reprod Domest Anim 44: 87-91.

Hermes R, Behr B, Hildebrandt TB, Blottner S, Sieg B, Frenzel A, Knieriem A, Saragusty J, Rath D (2009) Sperm sex-sorting in the Asian elephant (Elephas maximus). Anim Reprod Sci 112: 390-396.

Hermes R, Göritz F, Portas TJ, Bryant BR, Kelly JM, Maclellan LJ, Keeley T, Schwarzenberger F, Walzer C, Schnorrenberg A, Spindler RE, Saragusty J, Kaandorp S, Hildebrandt TB (2009) Ovarian superstimulation, transrectal ultrasound-guided oocyte recovery, and IVF in rhinoceros. Theriogenology 72: 959-968.

Hermes R, Göritz F, Saragusty J, Sos E, Molnar V, Reid CE, Schwarzenberger F, Hildebrandt TB (2009) First successful artificial insemination with frozen-thawed semen in rhinoceros. Theriogenology 71: 393-399.

Hildebrandt TB, Drews B, Kurz J, Hermes R, Yang S, Göritz F (2009) Pregnancy monitoring in dogs and cats using 3D and 4D ultrasonography. Reprod Domest Anim 44: 125-128.

Hildebrandt TB, Roellig K, Goeritz F, Fassbender M, Krieg R, Blottner S, Behr B, Hermes R (2009) Artificial insemination of captive European brown hares (Lepus europaeus PALLAS, 1778) with fresh and cryopreserved semen derived from free-ranging males. Theriogenology 72: 1065-1072.

Jewgenow K, Göritz F, Vargas A, Dehnhard M (2009) Seasonal profiles of ovarian activity in Iberian lynx (Lynx pardinus) Based on urinary hormone metabolite analyses. Reprod Domest Anim 44: 92-97.

Lermen D, Blomeke B, Browne R, Clarke A, Dyce PW, Fixemer T, Fuhr GR, Holt WV, Jewgenow K, Lloyd RE, Lotters S, Paulus M, Reid GM, Rapoport DH, Rawson D, Ringleb J, Ryder OA, Sporl G, Schmitt T, Veith M, Muller P (2009) Cryobanking of viable biomaterials: implementation of new strategies for conservation purposes. Mol Ecol 18: 1030-1033.

Lopes CAP, dos Santos RR, Celestino JJD, Melo MAP, Chaves RN, Campello CC, Silva JRV, Bao SN, Jewgenow K, de Figueiredo JR (2009) Short-term preservation of canine preantral follicles: Effects of temperature, medium and time. Anim Reprod Sci 115: 201-214.

Lueders I, Niemuller C, Pootoolal J, Rich P, Gray C, Streich WJ, Hildebrandt TB (2009) Sonomorphology of the reproductive tract in male and pregnant and non-pregnant female Rothschild's giraffes (Giraffa camelopardalis rotschildi). Theriogenology 72: 22-31.

Mohamed A, Samejima H, Wilting A (2009) Records of five Bornean cat species from Deramakot Forest Reserve in Sabah, Malaysia. Cat News 51: 12-15.

Portas T, Johnston SD, Hermes R, Arroyo F, Lopez-Fernadez C, Bryant B, Hildebrandt TB, Göritz F, Gosalvez J, 2009: Frozen-thawed rhinoceros sperm exhibit DNA damage shortly after thawing when assessed by the sperm chromatin dispersion assay. Theriogenology 72: 711-720.

Reid CE, Hermes R, Blottner S, Goeritz F, Wibbelt G, Walzer C, Bryant BR, Portas TJ, Streich WJ, Hildebrandt TB (2009) Split-sample comparison of directional and liquid nitrogen vapour freezing method on post-thaw semen quality in white rhinoceroses (Ceratotherium simum simum and Ceratotherium simum cottoni). Theriogenology 71: 275-291.

Saragusty J, Hermes R, Göritz F, Schmitt DL, Hildebrandt TB (2009) Skewed birth sex ratio and premature mortality in elephants. Anim Reprod Sci 115: 247-254.

Saragusty J, Hildebrandt TB, Behr B, Knieriem A, Kruse J, Hermes R (2009) Successful cryopreservation of Asian elephant (Elephas maximus) spermatozoa. Anim Reprod Sci 115: 255-266.

Yang S, He X, Niu Y, Hildebrandt TB, Jewgenow K, Goeritz F, Tang X, Chang Y, Zhou Q, Ji W (2009) Ovarian response to gonadotropin stimulation in juvenile rhesus monkeys. Theriogenology 72: 243-250.

Baudi DLK, Jewgenow K, Pukazhenthi BS, Spercoski KM, Santos AS, Reghelin ALS, Candido MV, Javorouski ML, Muller G, Morais RN (2008) Influence of cooling rate on the ability of frozen-thawed sperm to bind to heterologous zona pellucida, as assessed by competitive in vitro binding assays in the ocelot (Leopardus pardalis) and tigrina (Leopardus tigrinus). Theriogenology 69: 204-211.

Dehnhard M, Naidenko S, Frank A, Braun B, Göritz F, Jewgenow K (2008) Non-invasive monitoring of hormones: A tool to improve reproduction in captive breeding of the Eurasian lynx. Reprod Domest Anim 43: 74-82.

Dehnhard M (2007) Characterisation of the sympathetic nervous system of Asian (Elephas maximus) and African (Loxodonta africana) elephants based on urinary catecholamine analyses. Gen Comp Endocr 151: 274-284.

Hermes R, Saragusty J, Schaftenaar W, Göritz F, Schmitt DL, Hildebrandt TB (2008) Obstetrics in elephants. Theriogenology 70: 131-144.

Hildebrandt T, Drews B, Gaeth AP, Goeritz F, Hermes R, Schmitt D, Gray C, Rich P, Streich WJ, Short RV, Renfree MB (2007) Foetal age determination and development in elephants. Proc R Soc Lond B 274: 323-331.

Yang S, Shen Y, Niu Y, Hildebrandt TB, Jewgenow K, Goeritz F, He X, Zhou Q, Ji W (2008) Effects of rhFSH regimen and time interval on ovarian responses to repeated stimulation cycles in rhesus monkeys during a physiologic breeding season. Theriogenology 70: 108-114.

Fassbender M, Hildebrandt TB, Paris MCJ, Colenbrander B, Jewgenow K (2007) High-resolution ultrasonography of xenografted domestic cat ovarian cortex. J Reprod Develop 53: 1023-1034.

Fickel J, Hohmann U (2006). A methodological approach for non-invasive sampling for population size estimates in wild boars (Sus scrofa). Eur J Wildl Res 52: 28-33.

Hermes R, Göritz F, Streich WJ, Hildebrandt TB (2007) Assisted reproduction in female rhinoceros and elephants - Current status and future perspective. Reprod Domest Anim 42: 33-44.

Hildebrandt TB, Hermes R, Walzer C, Sos E, Molnar V, Mezosi L, Schnorrenberg A, Silinski S, Streich J, Schwarzenberger F, Goeritz F (2007) Artificial insemination in the anoestrous and the postpartum white rhinoceros using GnRH analogue to induce ovulation. Theriogenology 67: 1473-1484.

Jewgenow K, Paris MCJ (2006) Preservation of female germ cells from ovaries of cat species. Theriogenology 66: 93-100.

Portas TJ, Bryant BR, Goeritz F, Hermes R, Keeley T, Evans G, Maxwell WMC, Hildebrandt TB (2007) Semen collection in an Asian elephant (Elephas maximus) under combined physical and chemical restraint. Aust Vet J 85: 425-427.

Yang S, He X, Hildebrandt TB, Jewgenow K, Goeritz F, Tang X, Zhou Q, Ji W (2007) Effects of rhFSH dose on ovarian follicular response, oocyte recovery and embryo development in rhesus monkeys. Theriogenology 67: 1194-1201.

Yang SH, He XC, Hildebrandt TB, Zhou Q, Ji W Z (2007) Superovulatory response to a low dose single-daily treatment of rhFSH dissolved in polyvinylpyrrolidone in rhesus monkeys. Am J Primatol 69: 1278-1284.

Voigt CC, Streich WJ, Dehnhard M (2007) Assessment of fecal testosterone metabolite analysis in free-ranging Saccopteryx bilineata (Chiroptera: Emballonuridae). Acta Chiropterol 9: 463-475.

Dehnhard M, Hildebrandt TB, Knauf T, Jewgenow K, Kolter L, Göritz F (2006) Comparative endocrine investigations in three bear species based on urinary steroid metabolites and volatiles. Theriogenology 66: 1755-1761.

Göritz F, Neubauer K, Naidenko SV, Fickel J, Jewgenow K (2006) Investigations on reproductive physiology in the male Eurasian lynx (Lynx lynx). Theriogenology 66: 1751-1754.

Jewgenow K, Naidenko SV, Goeritz F, Vargas A, Dehnhard M (2006) Monitoring testicular activity of male Eurasian (Lynx lynx) and Iberian (Lynx pardinus) lynx by fecal testosterone metabolite measurement. Gen Comp Endocrinol 149: 151-158.

Kalz B, Jewgenow K, Fickel J (2006) Structure of an otter (Lutra lutra) population in Germany – results of DNA and hormone analyses from faecal samples. Mamm Biol 71: 321-335.

Si W, Hildebrandt TB, Reid C, Krieg R, Ji WZ, Fassbender M, Hermes R (2006) The successful double cryopreservation of rabbit (Oryctolagus cuniculus) semen in large volume using the directional freezing technique with reduced concentration of cryoprotectant. Theriogenology 65: 788-798.

Si W, Wang H, Reid C, Hildebrandt TB, Ji WZ (2006) Effect of sugar type on the survival of frozen-thawed rhesus monkey (Macaca mulatta) sperm. Am J Primatol 68: 103-108.

Zhou Q, Yang SH, Ding CH, He XC, Xie YH, Hildebrandt TB, Mitalipov SM, Tang XH, Wolf DP, Ji WZ (2006) A comparative approach to somatic cell nuclear transfer in the rhesus monkey. Hum Reprod 21: 2564-2571.