Slow drench resistance

Each year, sheep farms inevitably face the catch-22 when using drenches as part of their worm management plan. Drenching is important to protect your lambs from the impact of worms. However, each drench promotes the development of resistance. 

Drench resistant worms pass their genetic code to their offspring resulting in more worms surviving each drench, creating a cycle of more resistant worms and poor stock performance. In fact, drench resistant worms have the potential to cost sheep farmers tens of thousands in lost productivity¹, including:

» compromising the ability for ewe lambs to reach target weights and impacting the development of their skeletal and reproductive systems

» resulting in a 14 percent loss of carcass value in lambs over a four-month period1

» jeopardising the lamb finishing system.

One method to slow the development of drench resistant worms is to replace one of your autumn lamb drenches with Zolvix™ Plus. Because it contains monepantel, an active not available in other drenches², Zolvix Plus is termed the 'knock out' drench. Worms on your farm may not have been repeatedly exposed to this active ingredient, making it a highly effective drench and an excellent alternative to your current or ‘routine’ drench to prevent the spread of resistance genetics.

For greatest impact, use Zolvix Plus in autumn on lambs grazing where most of the routine drenching occurs because this is where the drench resistant worms are concentrated. The timing is vital as you are influencing the genetics of the worm populations on your farm. Waiting until winter or when lambs go onto a crop can result in little, if any, impact. The use of highly effective drenches is also important, as any resistant worms remaining in their gut have a three-week advantage over worms susceptible to drenches. This can be monitored using a ‘drench check’ faecal egg count 7 to 14 days after drenching. 

Worm populations that can breed without being exposed to drenches, otherwise known as refugia, are critical when slowing resistance and are an integral part of your worm management system. Combining your refugia strategy with the autumn drench, Zolvix Plus, into your farm system will give you the upper hand in the fight against drench resistance.

Talk with your PGG Wrightson Technical Field Representative about integrating Zolvix™ Plus into your animal health programme.

ZolvixTM Plus is registered pursuant to the ACVM Act 1997. No. A011107.

¹Sutherland I.A. et al (2010). The production costs of anthelmintic resistance in sheep managed within a monthly preventive drench program. Veterinary Parasitology 171(3-4):300-304.

²Leathwick, D.M. et al. (2009). Managing anthelmintic resistance: Modelling strategic use of a new anthelmintic class to slow the development of resistance to existing classes. New Zealand Veterinary Journal 57(4):181–192.