2005/N03 Dung Beetles and Internal Parasites of Sheep

Summary

The project identified the dung beetles that attacked sheep faeces as being: native species O. atrox, O. australis, O. capella, O. chepara, O. dandalu and O. granulatus; and introduced species O. gazella, E. africanus, E. intermedius and O. pecuarius. Dung ball rollers Sisyphus sp. also removed sheep dung. The project originally intended to monitor dung beetle activity and then attempt to correlate this with worm egg counts in sheep grazing the monitored paddocks. This proved too difficult as many factors such as host immunity, age, etc. influence faecal egg counts.  Instead, the project moved to estimate numbers of infective larvae developing in sheep faeces attacked by dung beetles compared with dung beetle free faeces.  
Early experiments with infective larvae were confounded by low numbers of parasites developing in either control or dung beetle attacked faeces. A series of small experiments were undertaken to investigate larval culture techniques that both produced a large number of parasites but still could estimate the effect of dung beetles on the system.  These studies developed a culture container that could reliably recover larvae from buried faeces and also estimate the amount of faeces being attacked by dung beetles.  
The project found that burying sheep faeces manually actually enhanced the amount of larvae recovered compared with faeces on the surface of soil when moisture was limited. Larvae developing underground were found to stay there until there was sufficient moisture to allow them to move to the surface. If burying faeces by dung beetles was purely a mechanical movement of faeces, there would be a potential for larvae to develop underground and be sequestered there until rainfall enabled them to move to the surface.  These sequestered larvae could represent a time bomb for sheep farmers by commencing infection of sheep immediately following rain, even when the sheep grazing the pastures were parasite free prior to rainfall. However, when dung beetles were included in the culture containers the time bomb effect was ruled out. The action of dung beetles in burying faeces actually reduces the numbers of larvae obtained consistent with the total amount of faeces removed from the surface by the beetles.  Dung beetles were found to remove approximately 1g of faeces/beetle from freshly deposited sheep dung.  Thus dung beetle activity results in a reduction of parasitic larvae on pasture.