by Lewis Kahn, Executive Officer, ParaBoss

The average age of sheep producers has increased from 51 to 56 years, the use of worm egg counts was down and practices that will encourage drench resistance are still widely used. These results were just some from a large national survey reporting the practices used by Australian sheep producers to control worms, flies and lice.

The recently-released national survey results from 2011 highlight that many producers have not fully embraced an effective and sustainable approach to worm control.

The survey, completed by over 1000 sheep producers across Australia, was conducted by Professor Steve Walkden-Brown and Dr Ian Reeve from the University of New England. Australian Wool Innovation Limited and Meat and Livestock Australia have supported the study, which provides a good national perspective and comparison to an initial survey of nearly 2300 producers in 2003.

The number of worm treatments given to adult ewes across the nation averaged 2.1 in 2003 and 2.7 in 2011 with most treatments given in the New England of NSW (Figure 1). This is a region endemic for barber’s pole worm and it received 1000 mm (40") in 2011, which was 200 mm more than the annual average.

Pleasingly, the number of combination treatments used in 2011 was 43%, which is an important means of controlling drench resistance. A combination contains two or more active ingredients (e.g. albendazole + levamisole) that each target the same worms. The chance of a worm being resistant to all active ingredients in the combination is much lower than for each individual active on its own.

Of concern was that the remaining 57% were single active treatments, with moxidectin and ivermectin most likely to have been given alone. Monepantel (Zolvix) was also mostly given alone, but it is not available as a combination treatment. The best time to use combination treatments is before drench resistance emerges.

The factors most commonly nominated as very important for deciding if worm treatment was required were worm egg counts, time of year, and, in barber’s pole regions, exercise intolerance. Worm egg counts were used by only 21% of producers in 2011, despite being seen as very important, which was lower than the 44% of producers who used worm egg counts in 2003. This was disappointing as worm egg counts can give an early warning of production loss before signs are obvious.

Drench resistance testing has been conducted in the last five years (2007–2011) by 29% of sheep producers (unchanged from 2003, Figure 2). Drench resistance is said to be present when a drench causes the egg count to be reduced by less than 98%. Only fifty five percent of producers thought they had resistance to benzimidazole and levamisole drenches, 12% thought they had resistance to ivermectin, 28% to abamectin and 21% to moxidectin. On average, 48% of sheep producers said they didn’t know the drench resistance status of drench groups on their farms.

When compared to actual resistance test results, this suggests that many sheep producers either underestimate or don’t know the extent of drench resistance on their farms. A recent compilation of the results of 390 resistance tests on Australian farms was carried out by Playford et al (accepted for publication in AVJ). This reports that resistance against benzimidazole and levamisole was present on 96% of farms, and against ivermectin, abamectin and moxidectin on 87%, 77% and 54% of farms respectively. These conflicting estimates of drench resistance highlight the need to test for drench resistance and to schedule these tests every 2–3 years.

Drenching remains the main technique to control worms, used by 87% of sheep producers, but paddock spelling, cropping and cattle/sheep alternations are all well used with importance varying among regions (Figure 3). Integration of a range of worm control techniques is an important component of a good worm control program.

Figure 3. Percentage of producers using various worm control techniques within each region. Note that rams with ASBV relates to selecting rams that have Australian Sheep Breeding Values for low worm egg count.

Figure 4. The percentage of sheep producers using 1, 2, 3, 4 or unspecified number of drench actives in quarantine treatments of newly introduced sheep averaged across all regions.

There was a low use by sheep producers of worm-resistant rams, selected using Australian Sheep Breeding Values (ASBV) for low worm egg count (Figure 3). On average, 13% of producers used rams selected for resistance to worms but only 62% of these rams were selected on the basis of ASBV for worm egg count, which is the gold standard.

Introductions of sheep occurred on 57% of properties and some form of quarantine worm treatment was given by 67% of producers. Ideally a quarantine treatment should include a combination of no less than four unrelated drench actives, with one of these being monepantel (Zolvix). In contrast, most producers used a single active drench for sheep introductions, which leaves the risk of importing drench resistant worms onto the farm (Figure 4).

On a final note, 5% of sheep producers had used WormBoss to make a change to worm control and another 16% had visited the site. But we have to do better because 38% had heard of WormBoss but not visited the site and a further 41% of producers had not heard of WormBoss. Even though we have more than 5,000 people visit WormBoss each month, it is clear that we need to keep spreading the word.

Results for flies and lice will be covered in future ParaBoss newsletters.