Repro­duc­tion of the Indian rhi­noc­eros faces greater dif­fi­cul­ties than was pre­vi­ously recog­nised. Researchers from the Ger­man Leib­niz Insti­tute for Zoo and Wildlife Research Berlin (IZW) together with Amer­i­can col­leagues dis­cov­ered that benign vagi­nal and cer­vi­cal tumours cause infer­til­ity even in young females. This sub­stan­tially affects breed­ing suc­cess in zoos.

At the age of three years Indian rhi­noc­er­oses become sex­u­ally mature. They can reach an age of up to 40 years. Although females should repro­duce until the very end of their life, on aver­age the females in zoo­log­i­cal gar­dens give birth to their last young at the age of 18 years. This is revealed by records in the inter­na­tional stud­book for Indian rhi­noc­eros which reg­is­ters the life his­to­ries and repro­duc­tive suc­cess of all 189 Indian rhi­nos liv­ing in zoos world­wide. The researchers found another curios­ity while inves­ti­gat­ing the stud­book: If rhi­nos gave birth to their first young by the early age of five years, they pro­duced up to six juve­niles. Rhi­nos with an age at first repro­duc­tion older than that rarely gave birth to more than two calves.

It is known that female Indian rhi­nos often suf­fer from tumours in the repro­duc­tive tract. Robert Her­mes, Frank Göritz und Thomas Hilde­brandt, all vet­eri­nar­ian sci­en­tists at the IZW, and their col­league Mon­ica Stoops from Cincin­nati Zoo analysed ultra­sound data of 23 female Indian rhi­nos. Over the last 20 years these ani­mals were exam­ined sev­eral times. The study results are pub­lished on 26 March in the jour­nal PLOS ONE.

Robert Her­mes, lead author, vet­eri­nar­ian sci­en­tist, Leib­niz Insti­tute for Zoo and Wildlife Research Berlin, Germany »

The find­ing: “Already at the age of 13 years all ani­mals had devel­oped tumours! The tumours grow rapidly, uncon­trolled and life­long until the vagina and cervix are com­pletely cov­ered in them.” This process may be asso­ci­ated with necro­sis and inflam­ma­tions. “Besides the pain which the female must be expe­ri­enc­ing because of the tumour, the mat­ing act becomes almost impos­si­ble and even if suc­cess­ful, there is no free pas­sage avail­able to the sperm any­more,” explains Robert Hermes.

Look­ing for an organ­ism with com­pa­ra­ble tumours the researchers found an unex­pected model species — the human being. “Eighty per cent of all women have such leiomy­omas at the onset of their menopause. Leiomy­omas can already start to develop in ado­les­cence and they grow as a func­tion of ovar­ian activ­ity. In con­trast to the rhi­nos the mostly benign tumours in women are located in the uterus and remain with­out symp­toms,” says Her­mes. Because of the spe­cial hor­monal con­di­tion dur­ing preg­nancy or lac­ta­tion, leiomy­omas do not grow dur­ing these peri­ods. Fur­ther­more women, who gave birth to at least one child, have a 40 % reduced risk to develop leiomyomas.

This anal­ogy pro­vides an indi­ca­tion why those female Indian rhi­nos who have their first preg­nancy at a younger age pro­duce a higher num­ber of off­spring than females whose first preg­nancy is delayed to an advanced age: Preg­nancy inhibits tumour growth. This also sug­gests a prospec­tive ther­apy for ani­mals that suf­fer from inflam­ma­tion and pain because of mas­sive tumours. “By sup­press­ing ovar­ian activ­ity, we should be able to induce the menopause, thus putting a halt to fur­ther tumour growth,” Her­mes stated.

Indian rhi­nos (Rhi­noc­eros uni­cor­nis) are threat­ened with extinc­tion. Only 2,900 ani­mals remain in the wild and they are listed Vul­ner­a­ble by the IUCN Red List of Threat­ened Species™. Robert Her­mes cau­tions: “We should not rely on higher rates of repro­duc­tion in free-​living Indian rhi­nos than those in cap­tiv­ity,” says Robert Her­mes. “Zoo­log­i­cal gar­dens are respon­si­ble for a coor­di­nated breed­ing pro­gramme which uses the genetic diver­sity of the entire pop­u­la­tion. It would be dis­as­trous, if only because of early tumour dis­eases breed­ing is con­fined to only a few ani­mals who may pro­duce a high num­ber of off­spring and the major­ity bear fewer or no calves.”

The authors strongly rec­om­mend to start breed­ing at an early stage and to opti­mise breed­ing con­di­tions to max­imise the chance of females becom­ing preg­nant.

Most zoos hes­i­tate too long until the con­di­tions for nat­ural mat­ing are cre­ated — some­times 12 or 13 years, deplores Her­mes. “This is too late, since all female Indian rhi­nos do already have tumours in this stage of life. More than one calf is then unlikely.” Because sev­eral Indian rhi­nos usu­ally grow up in close prox­im­ity in zoo­log­i­cal gar­dens, young females may not have a reg­u­lar ovu­la­tion. In such cases, assis­tance is nec­es­sary. There is a wide range of meth­ods: from a hor­monal impulse to a more active sup­port for search­ing a suit­able partner.

The above Eng­lish ver­sion of the news item is reprinted from mate­ri­als avail­able at Sci­enceDaily. Orig­i­nal text is edited for con­tent and length.
(Source: Forschungsver­bund Berlin e.V. press release, 26.03.2014)

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