Environmental aspects of Mortierella wolfii infection in cattle

Mortierella wolfii B. S. Mehrotra & Baijal, the main cause of mycotic placentitis in New Zealand, was frequently found in over‐heated, dark coloured, wet, and rotting plant material of pH 8‐9. Isolates were obtained from 62% of samples of rotting silage, 77% of rotting hay, and from soil around silage stacks and pits. No isolates were obtained from good quality silage or hay and very few from visibly mouldy material. The mycoflora of the rotting material was dominated by thermophilic fungi, including M. ambigua, Petriellidium boydii, Absidia ramosa, Coprinus cinereus, Scytalidium thermophilum , and Stilbella thermophila . Mortierella spp. were not isolated from the rotting surface layers of an unopened experimental silage stack in which the temperature had risen to 68°c during maturation. Material from the outer 2 cm supported M. wolfii growth in vitro . This suggests that M. wolfii belongs to the secondary succession which invades silage after the pit or stack has been opened, or hay after wetting during faulty storage. The morphological form in which M. wolfii occurs in the field was not determined.