Dr David Gardiner, District Veterinarian for the Central North LHPA located at Mudgee, has been investigating worm problems on a sheep property near Gulgong.WormTesting indicates the problem worms are barber’s pole worm (BPW; Haemonchus contortus), black scour worm (Trichostrongylus) and small brown stomach worm (Ostertagia (Teladorsagia) circumcincta). At various times there are high BPW counts and clinical signs of haemonchosis. A DrenchTest (faecal worm egg count reduction test) in February gave these results (% reduction in egg counts): Ivermectin (IVM): 33% Closantel: 68% Benzimidazole (BZ) / Levamisole (LEV): 100% Moxidectin: 90% IVM/BZ/LEV: 100% LEV (double dose): 100% Untreated controls: mean WEC = 6384 (100% BPW).
The 100% results for BZ/LEV and for IVM/BZ/LEV might be largely due to the LEV component. Closantel at one third of the dose used here (the recommended dose) should be ~ 100% effective against BPW. Moxidectin, the most potent of the MLs available for sheep in AUS, only managed a 90% FECR.
Larval culture results raised the suspicion of Trichostronglyus and/or Ostertagia resistance to LEV and BZ as well.
One might not be surprised any more by this result in the New England region (northern NSW) or north coast, but it is somewhat more alarming in the Gulgong-Mudgee district further to the south.