Evidence suggests the effectiveness of drenches including triple combinations have changed dramatically for the worse.

In New Zealand the most up to date information we have on the level of drench resistance on sheep farms is the national survey conducted in 2006, and the 2016-2017 FECRT data from Gribbles Laboratories. Anecdotal evidence from veterinarians in the field and published case reports, would strongly suggest that our drench resistance status, particularly for triple combination drenches, has changed dramatically for the worse in very recent times.

It is important to your bottom line to know if the drench you are using on your farm is working. A drench that is not working can cost you 10-14% of your lamb carcass value, not to mention less hoggets up to weight for mating, and the extra feed the lambs will eat while they are on the farm for longer. Based on a $6/KGCW value for a 18kg CW lamb equates to a $13/lamb cost or loss in carcass value.  Doing a drench check (FEC Test) 7-10 days post drench administration is easy and inexpensive and something you should be doing each year to safeguard your income.

As triple drench resistance becomes more of an issue on a lot of farms the importance of the drenches containing the novel actives Derquantel (Startect®) and Monepantel (Zolvix Plus®) becomes greater, and how you should use them slightly different, depending on the farm’s resistance status. Startect (derquantel/abamectin combination) or Zolvix Plus (Monepantel/abamectin combination) can be positioned to achieve three different goals:

1) To protect your flock from resistance. This is using Startect or Zolvix Plus as a Quarantine drench to prevent the introduction of any resistant parasites with purchased stock.
2) To prolong the life of your older drenches. This is using Startect or Zolvix Plus as either an Exit or Knockout drench. An Exit drench is used after any long acting product and a Knockout drench is the replacement of one of the routine lamb drenches with a fully effective drench that is different from the routine drench. Both Exit and Knockout drenches are designed to remove resistant parasites that have survived the previous drenches used.
3) To perform better using a fully effective drench. On farms where triple drench resistance already exists, Startect or Zolvix Plus can be used strategically in lamb drenching programs. This ensures the lambs are receiving a fully effective drench, which not only kills the resistant parasites but also ensures lamb growth is not compromised.

Another important step is to ensure management changes are also made on farm so that refugia is created and pasture contamination is minimised. Just changing which drench you use is not good enough. Advice on effective stock integration and pasture management is vital, irrespective of the resistance status of the farm. Our veterinarians can help you slow down the development of drench resistance on your farm by discussing the appropriate management options, as well as the drench options for your farm. For practical parasite management solutions, speak to one of our vets or contact the Wairoa clinic on 8386099 or the Gisborne clinic 8679405.

Phil Ware (B.Agr)

Eastland Veterinary Services Trading Manager