Dr Brown Besier, DAFWA, Albany (brown.besier@agric.wa.gov.au)

Sheep drench figures – a recent snapshot

A recent Sheep CRC phone survey of producers across Australia reveals some interesting trends regarding sheep drench purchases, and an encouraging correlation with active information-seeking to choose drench types.

A major thrust in CRC extension messages is to ensure that drenches are fully-effective (as close to 100% as possible, and at least 95% effective), so very few resistant worms survive to add to future worm populations.  As importantly, drenches known to have high levels of resistance should be avoided unless a recent test shows they are effective.

Drench purchase trends

Encouragingly, 22% of drenches purchased were certain to be fully-effective (monepantel) or almost certain (triple combinations - three drench groups, including a macrocyclic lactone). Except on a small number of properties where resistance affects even the triple combinations, using these drench types is a sound basis for effective worm control, providing they are used at appropriate times. Not surprisingly, a larger percentage of producers in the main Barbers Pole worm regions (northern NSW and southern Queensland) purchased the top-line drenches (41%) at least once, compared with winter rainfall and other regions (29%) – a reflection of the importance of controlling the lethal Barbers Pole worm.  (Many producers in Barbers Pole worm regions also use organo-phosphate-based drenches against that worm, and these are almost always fully effective.)

Another 42% of purchases were of Moxidectin or Abamectin, the two most potent of the macrocyclic lactones (MLs) (not including long-acting forms). However, ML-resistance is present on almost all sheep properties in Australia, and in recent years has moved from affecting the less-potent Ivermectin to also becoming common in Moxidectin and Abamectin. As few drench resistance tests are now conducted, a real concern is that increasing (but initially invisible) resistance to these MLs will reduce the likelihood that the triple combinations – which include Abamectin – will be effective.

Surprisingly, some 20% of drench purchases reported in the survey were of the older, less-effective drenches, the white (benzimidazole), clear (levamisole) classes, and  the least –potent ML, Ivermectin.  Using these drench types will rarely give effective control of all sheep worms on a typical farm, and although levamisole may still be effective against Barbers Pole worm, this is increasingly less likely.

Information-seeking pays off

There was a clear trend towards use of the WormBoss website and purchases of the most-effective drenches by producers in the survey. As an example, nearly three times the number of producers who used WormBoss had bought monepantel compared with others (27% against 10%) in the major Barbers Pole worm regions, and in across other regions there was a nearly a two-fold difference.

The use of worm egg counts also correlates well with drench purchases in the mainly winter rainfall regions. Some 44% who worm-tested had purchased Monepantel and/or a triple combination, compared with only 19% who did not test. Conducting worm egg counts indicates an awareness of the importance of worm control and the need for objective information, and it is no surprise that these producers had also heeded messages regarding drench options.  (There was a smaller difference in the mostly-Barbers Pole worm region -  43% to 39% - possibly because worm egg counting is already undertaken more commonly than in other areas.)

It was surprising that there was little effect of WormBoss use or worm egg counting on the purchase of drenches to which resistance is common.  However, in some cases, white and clear drenches may have been to use in combination, such as with Naphthalophos or an ML. In summer rainfall regions, Levamisole would often have been bought in the expectation of control of Barbers Pole worm, although unfortunately this can no longer be assumed.

As few drench resistance tests are now conducted, it is especially important that drench choices are made using the best information available. WormBoss provides a comprehensive basis for planning worm control programs and selecting drenches, and the recent figures indicate that an increasing number of producers are aware of this.