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Characteristics of koala (Phascolarctos cinereus adustus) semen collected by artificial vagina

Johnston, SD, O’Callaghan, P, McGowan, MR & Phillips, NJ 1997, Journal of Reproduction and Fertility, vol. 109, no. 1, pp. 319-323.

An artificial vagina is recommended as a simple, reliable and non-invasive method of semen collection from koalas in captivity. Out of 90 attempts, 40% resulted in collection of a complete ejaculate comprising a rubbery copulatory plug fraction and a sperm fraction with high motile spermatozoa content. No semen was collected in 38% of trials, while only partial ejaculates were collected in 14.5% of trials. Urine was detected in 4.5% of samples, and 3% of semen samples were collected after the koala’s ejaculation behaviour had ended.

  An artificial vagina designed for use in sheep was resized to suit the male koala. The device was lined with soft rubber and warm water, inflated and lubricated. An oestrus female koala was used as a ‘teaser’ by allowing a male to commence copulation before the penis was redirected into the artificial vagina. Once the male had finished thrusting, his sample was transferred into a collection vial. The male would subsequently end the interaction by separating from the female, during which the artificial vagina remained over the penis in case of late ejaculation. While the procedure was mostly successful in collecting complete ejaculates, some did not separate into the plug and fluid components, and these were termed ‘partial’ ejaculates. For the complete ejaculates, the mean mass of the copulatory plug was 0.78 g and the mean sperm fraction volume 0.73 ml. The percentage of spermatozoa demonstrating forward motility was 70.7% and of abnormal spermatozoa 26.9%. Percentage forward spermatozoa motility was negatively correlated with the number of sperm abnormalities observed.

  Previously, the most common technique used to collect spermatozoa from marsupials was electroejaculation, which is quite invasive compared to the artificial vagina collection technique. The tested device proved to be effective for semen collection by taking advantage of the male koala’s natural sexual behaviours. Once copulation has commenced, the erect penis continues to be thrusted towards the female while the male secures her with a neck bite, making the penis easy to manipulate for seminal collection with minimal disruption to the koalas. Failure to collect samples in some cases may have been due to inconsistent libido, aggression, the temperature of the artificial vagina, use of a non-compliant teaser female, or simply a rejection of the device. A possible function of the copulatory ‘plug’ which was usually ejaculated following the sperm fraction is to avoid the ejaculate exiting the female given her upright and arboreal position; however, more investigation would be required to determine its precise purpose.

  Due to its non-invasiveness, ease of use and effectiveness for collecting ejaculate, the artificial vagina is a near-ideal method for semen collection in captive koalas. The procedure is limited, however, by the need for oestrus ‘teaser’ female koalas, making it potentially unsuitable for only small captive populations or indeed free-ranging males.

 

Summarised by Joanna Horsfall

 

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