Elsevier

Theriogenology

Volume 63, Issue 1, 1 January 2005, Pages 219-238
Theriogenology

Reproductive soundness of captive southern and northern white rhinoceroses (Ceratotherium simum simum, C.s. cottoni): evaluation of male genital tract morphology and semen quality before and after cryopreservation

https://doi.org/10.1016/j.theriogenology.2004.04.007Get rights and content

Abstract

White rhinoceroses suffer from a low rate of reproduction in captivity. This study examines the role of male reproductive function as a contributing factor. We used ultrasonography to image accessory sex glands, testis and epididymis. Electroejaculation provided 36 ejaculates from 21 rhinoceroses. Based on the percentage of progressively motile spermatozoa, semen was categorized in three groups, high (I: >75%), intermediate (II: 50–70%) or low (III: <50%) quality. Only 52% of the males showed high semen quality. Ejaculates in the high motility category also had the highest proportion of morphologically intact spermatozoa. Both semen parameters, sperm motility and morphology, were found to positively correlate with size of the accessory sex glands. The semen category was associated with group size suggesting that the social status influenced functional reproductive parameters. Change of territorial status (n = 1) improved semen quality. Testicular fibrosis was characterized as a sign of reproductive ageing in all males older than 15 years of age (n = 13); although, this ageing process did not notably affect semen parameters. Furthermore, for the benefit of assisted-reproduction and genetic banking programs protocols for the storage of cooled semen and the cryopreservation of spermatozoa were designed using different cryodiluents. This report provides basic data for the evaluation of reproductive components and of breeding management in male rhinoceros. Our results indicate that low rate of reproduction in captivity can be attributed to reduced male reproductive fitness. Changes in management of white rhinoceroses may positively affect male reproductive function.

Introduction

Substantial knowledge on the reproductive physiology of the female white rhinoceroses has been gathered over the last 10 years [1], [2]. The impetus for these studies was a low rate of reproduction in the captive population [3]. Acyclic and erratic luteal activity, mating, conception and pregnancy failures and reproductive ageing have been identified in female white rhinoceroses that have low rate of reproduction [1], [4], [5], [6]. These problems are currently being addressed [7]. However, little emphasis has been put on the evaluation of male fertility. Considering that 81% of all male white rhinoceroses in the Species Survival Programs have not yet sired offspring [8], male fertility may represent a contributing factor to the reproductive failure of the captive population. Besides the description of different semen collection methods and basic reproductive data for three rhinoceros species [9], [10], to date analysis of reproductive fitness in a significant number of non-reproducing males has not been performed. Clinical examination of reproductive organs and assessment of semen quality have historically been used to predict potential fertilizing capability of stallions [11], [12].

In this study, reproductive tract ultrasonography and electroejaculation were used in tandem to obtain information on the reproductive parameters of the male white rhinoceros. The purpose of this study was to compare the reproductive efficacy of mature, non-reproducing males managed in groups with different male to female ratios. The effects of changing the housing management of male and resulting upgrade in social status on reproductive factors were instigated in one case. For the prevention of extinction and the improvement of assisted-reproduction programs and sperm banks of endangered species [13], freshly collected semen via electroejaculation was used to design protocols for storage of cooled semen and cryopreservation. This is an essential prerequisite for artificial insemination in rhinoceros.

Section snippets

Histology

Prior to the main investigations of this study, the genital tracts of two male rhinoceroses (28/21 years) were examined post mortem to establish further baseline values to existing data [10], [14]. The genital tracts were exenterated, frozen at −20 °C during shipment and dissected after thawing. The morphologic and ultrasonographic characteristics of the genital tracts were ascertained in a water bath before the testis, and epididymis were fixed in 10% formalin. After fixation, tissue samples

Semen collection and assessment

A total of 34 ejaculates were collected from 21 male rhinoceroses. The mean ejaculate volume of a white rhinoceros was 80.2 ± 13.0 ml. Semen quality varied considerably between rhinoceroses. The morphologic integrity of spermatozoa also differed significantly between the progressive-motility categories (P < 0.01; Table 2). The percentage of motile spermatozoa showed a significant positive correlation to the percentage of morphologically intact spermatozoa (Spearman r = 0.576, P < 0. 001). The

Discussion

To date, the reproductive status of male white rhinoceroses has scarcely been evaluated. This is mainly due to anaesthesia risks [16] and to the technical difficulties involved with fertility assessment of male white rhinoceros. The provided information about the reproductive status of 21 captive white rhinoceroses represents a substantial physiologic database on reproductive parameters in this species. The correlations discovered between the volume of the male accessory sex glands and the

Acknowledgements

The International Rhino Foundation and SOS Rhino, USA funded this work. The authors are grateful for additional financial support by the African Lion Safari ltd., Cambridge, Canada; Burgers’ Zoo, Arnhem, Netherlands; La Palmyre Zoo, France; Schwerin Zoo, Germany. Gratitude is extended especially to Igal Horowitz and Amelia Terkel form the Zoological Center Tel Aviv/Ramat Gan for their work and support, contributing a substantial number of animals to this study. The authors thank the staff of

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