Drench resistant worms on the NSW North Coast


In Spring 2020, 240 cross bred yearling steers sourced from across the north coast were used to test the efficacy of some commercially available worm control products.

Products Tested

  • moxidectin pour on
  • doramectin pour on
  • levamisole oral
  • oxfendazole oral
  • moxidectin + levamisole combination pour on

Key outcomes

  1. Haemonchus (barbers pole worm) and Cooperia were resistant to the single active doramectin pour on.
  2. Ineffective control of Haemonchus reduced weight gain by 10kg over 28 days, and those steers never caught up over the 90 day trial.
  3. The  levamisole and oxfendazole single active oral drenches and the moxidectin + levamisole dual active pour on were effective against Haemonchus and Cooperia.
  4. Moxidectin single active pour on was effective against Haemonchus but not Cooperia.
  5. Ineffective control of Cooperia had a minimal to no impact on animal weight gain.
  6. Where possible worms should be targeted with two different active ingredients, to protect weight gain and manage resistance. Using combination products or two or more products are both viable options.
  7. Worm testing and identifying key worm species is key to any effective worm control program.

Graph: Cumulative steer weight gains up to 90 days after treatment (DAT) after being treated with different worm control products.


The steers averaged 305kg LWT at the start of the trial and were allocated to one of 6 x 40 head treatment groups. Steers were weighed 6 times over the course of the trial, while faecal samples were collected 5 times, from 15 animals in each treatment group, to monitor worm egg counts and species.

The steers remained as a single herd up until day 0 (treatment day). Treatment groups were then separated for 3 days to prevent the pour on products being licked by other steers and were then run as a single mob for the duration of the trial. Steers rotationally grazed tropical pastures (paspalum, setaria, carpet grass) oversown with ryegrass.


Steer weight gain averaged 1.4kg/hd/d prior to treatments being applied. This dropped to 0.9kg/hd/d at 14 days after treatment (DAT), most likely due to social dislocation of the mob as treatment groups were separated.

Worm burdens impacted weight gains during this time and the steers treated with doramectin pour-on and control (no worm treatment) were around 10kg lighter than others at 28 DAT (Figure 1).

The steers were infested with both Haemonchus and Cooperia, although infection levels varied among the steers. The doramectin and control treatments had higher Haemonchus WEC than the other treatments (Figure 2). This resistance pattern mirrored steer weight gain (Figure 1), suggesting that Haemonchus had the greatest impact on animal performance.

Graph: Haemonchus worm egg counts in crossbred yearling steers up to 42 days after treatment (DAT) with a range of products.

For more information contact

Todd Andrews- Beef Development Officer
NSW Department of Primary Industries
0429 987 405