Semen collection and seminal characteristics of the Australian saltwater crocodile (Crocodylus porosus)

Abstract

The development of a reliable non-invasive method of crocodile semen collection is fundamental for assessing male fertility and for implementing the benefits of artificial insemination for reproductive and genetic management of farmed populations and the captive breeding of endangered species. Following an initial description of male reproductive anatomy in the saltwater crocodile (Crocodylus porosus), this study developed a successful, reliable method of semen collection using cloacal digital manipulation of the terminal segment of the ductus deferens. Semen was recovered from 30 of 31 collection attempts from a total of 24 sedated males ranging from 197cm to 400cm in body length. Seminal characteristics (including abnormal sperm morphology) and bacteriology were documented for the first time. Mean (±SEM) seminal volume, pH, osmolality, sperm concentration, percentage of motile sperm and the percentage of sperm with an intact membrane measured 0.91±0.16mL, 7.3±0.1, 335.5±9.0mOsmkg-1, 2.29±0.26×109, 50.7±4.2%, and 79.9±3.6%, respectively. Sperm abnormalities included macro and microcephalic nuclei, teratoid spermatozoa, loose heads and a range of abnormal flagella. Most semen samples contained spermatozoa with what are presumed to be cytoplasmic droplets but the confirmation and then significance of this phenomenon as a sperm maturational pathology require further validation. In an attempt to develop targeted antibiotics for use in semen diluents, microflora of the penile shaft, sulcus and semen of a subset of crocodiles was analysed for culture and sensitivity. While a diverse range of bacteria were identified, the majority were sensitive to gentamicin. This study represents the first step towards assessment of breeding soundness examination and the use of artificial insemination technology in the saltwater crocodile industry.