In the last two issues of Vetnotes we've discussed the technical aspects and some possible uses of the two new sheep drench families on the market.
Another application that both are a great fit for is something called ‘exit-drenching'. This is not a new concept in some respects. For example where ewes or ewe hoggets had been given a capsule or other persistent product pre-lamb, we have long recommended that they be given a one-off dose of a different (and highly effective) drug at the end of the product's payout time to remove any resistant worms that had established during the time the product was active.
So the point of exit-drenching is to use one chemical of known high efficacy to take out resistant worms that may have established a breeding population during a period of treatment with another chemical.
Aside from the capsule example, the other main use on sheep farms is going to be in lambs that are still on the farm in the autumn, after a summer drenching programme. On some farms, this will only be the replacement ewe hoggets; on many others, there will be trading lambs involved as well.
An example could be that all lambs grazing pasture are given a double combination at monthly intervals for 3 or 4 drenches, the following drench being one of the new actives. However, what drenches are used is heavily dependent on the farm's resistance status. Where it is minimal, there is an opportunity to save money - but you don't know until you find out!
Treating lambs in this way has been shown in modelling studies to be very helpful in slowing resistance development, where other measures to delay resistance are also in place.
The timing of the exit drench is a bit of a compromise. Leave it too late and there may already be significant autumn contamination by resistant worms; earlier on, there are more lambs to give that expensive drench to! Speak to one of us about the timing for your own situation.
A third application for the ‘exit' concept is where you are using a moxidectin-based product (Cydectin, Exodus) for Barber's Pole worm protection. After treatment with moxidectin, the drug is absorbed into the animal's body fat and is released over a period of weeks, initially in high concentrations but then ‘tailing off' over time. In this ‘tail' period, partially-resistant worms can establish. Although moxidectin has a claim for 5-6 weeks protection against Barber's Pole worm, the same is not true for the other worm species, and they will be coming under this ‘tail' effect from as early as a week after dosing. So knocking any of these out before they start laying eggs is a good plan. Therefore:
1. When using moxidectin, keep your dose intervals to around a month. You'll get excellent Barber's Pole control and be less likely to be creating resistance problems in other species.
2. Make sure moxidectin isn't the last drench that animals see in the autumn. Use another, highly effective short-acting product in animals treated with moxidectin - for lambs, around a month later, for ewes, when next convenient.
As mentioned above, the choice of product for exit-drenching will vary depending on what we know about the resistance status of the worms on your farm. Moderate to severe resistance to more than one of the common actives exists on a high proportion of farms in our database. If you have minimal resistance, you are in a fortunate position, but you don't know until you test. And it is not too late to do it this season.
Don't hesitate to get in contact with us regarding drench-testing, any questions you may have on exit-drenching, or indeed any other aspect of sheep worm management!
