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Reproductive techniques

Antibiotics for the preservation of the koala (Phascolarctos cinereus) semen

Johnston, SD, O’Boyle, D, Frost, AJ, McGowan, MR, Tribe, A & Higgins, D 1998, Australian Veterinary Journal, vol. 76, no. 5, pp. 334-338.

From samples of koala prepuce and ejaculate collected using electroejaculation and artificial vagina methods, a range of bacteria was identified in koala semen, predominantly of the Corynebacterium genus but of unknown species. The antibiotics penicillin G at a dose rate of 1000-2000 IU/mL, and gentamicin at a dose rate of 100 to 200 µg/mL, had no detrimental effects on sperm motility within a 24-hour incubation period. Furthermore, the antibiotics inhibited the growth of bacterial contaminants in the semen.

  The type of bacteria most commonly detected in koala ejaculate and prepuce, corynebacteria, have been detected in the urogenital tracts of several other species. In addition to corynebacteria, inflammatory cells were detected in some semen samples that were concluded to be present as contaminants from the prepuce rather than from infections in the testicles or accessory organs. It is possible that Corynebacterium spp. can become pathogenic under certain conditions; however, these are yet to be described. Other organisms detected in semen were likely to be environmental or faecal contaminants. There was no significant difference in the motility of spermatozoa between semen samples treated with the antibiotics at the dose rates specified above and untreated samples; however, at the higher concentrations of 400 IU/mL of penicillin G and 4000 µg/mL of gentamicin, lower spermatozoa motility was detected after 4 hours and 22 hours of incubation at 16OC.

  Antibiotics can reduce the spread of pathogenic bacteria in semen by suppressing the growth of bacterial contaminants originating from the urethra, prepuce and penis, thereby delaying the expiration of stored spermatozoa. For this reason, antibiotics are often used in studies of marsupial sperm preservation, thus it is pertinent to describe and quantify the effects of these treatments on sperm survival in storage.

  This study may be the first to describe the bacterial flora of the prepuce and ejaculate not only of the koala but of any marsupial. It is important to note, however, that the authors of this study did not screen for all pathogens present in koala semen such as Chlamydia spp. and Mycoplasma spp. These findings are significant for improving practices to retain the quality of stored sperm for longer time periods than previously possible and thereby contribute to best practice in artificial insemination programs for koalas.


Summarised by Joanna Horsfall


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