The message in this area has not really changed in the last few years and that is that the whole flock use of these products does accelerate the development of drench resistance.  You can have maximum productivity or maximum sustainability (minimum drench resistance), but you can’t really have both.  Where each farmer sits is really a matter of personal choice and some thought needs to be given to the extent to which these products are used on farms.  In other words first decide if, and to what to extent, you are going to use these products – having said that it is too early to decide yet – don’t be forced into making purchases for an event several weeks away when you can’t predict what conditions are going to be like at the time.  Factors such as ewe condition, feed ahead, pregnancy status and the parasite challenge are not known. 

The second decision to be made is (assuming some product is going to be used, however you may well not use any) what product, and this is where things get messy.  Note that some of the advertising used by some of the companies is extremely selective in the information provided – any point no matter how minor, where their product is superior is pushed to the extreme while any bad points, no matter how major, are ignored.  I have already seen examples of this on TV.


There are quite a wide range of capsules and injections available – five different capsules and roughly eight different injection products.  There is absolutely no doubt that from the resistance development point of view the No 1 choice for minimising this on the overwhelming majority of farms will be Bionic Combination capsules.  At the other end of the scale the worst products in this regard, in my opinion, are the moxidectin (Cydectin) injection products.  This is because they all have relatively long periods of sub-lethal activity (the so-called tail) where more resistant worms can survive while more susceptible ones are killed off giving an advantage to the more resistant ones.  The other point I wish to reinforce from the last newsletter, to counter some of the afore mentioned advertising, is that the new so called Cydectin LA (long acting) is only long acting against one worm type down here.


In summary don’t rush into any decisions yet and obtain veterinary advice over the best option for you – if this is to do nothing we will advise that.  One bit of good news is that capsules have reduced in price a bit and which means that Cydectin LA is about the same price as the capsules, hence you will get far more bang for your buck out of a correctly chosen capsule.


Written by John Smart BVSc

Extract from July 2008 - Sheep Newsletter