Hi T (and WormMail mailing list)
Good questions. I will reply to this by way of a "WormMail" – not disclosing your details of course, as this may be of general interest. So, your questions/comments:In your last newsletter you listed activities that promote worm resistance. Could you please explain two of these:
· Drenching before moving to very clean pastures (especially stubbles),
· The treatment of ewes prior to lambing.
We drench and allow the stock (goats) to stay in the yards for a couple of hours before moving them to a new, clean pasture. Should I return them to the contaminated pasture?
We always drench 7-8 weeks prior to kidding and then give the kids their first drench at around 4 weeks of age. Why is this wrong?
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Some thoughts/answers:
* Often worm control decisions are a ‘Catch-22′: there is no perfect solution; and the choice is often between competing priorities.
*There are only two ways to avoid drench resistance: only use a drench that is 100% effective all the time (no such thing); or never drench (and never get worm-containing animals or faeces from anywhere else).
* Drenching before moving to very clean pastures:
* This is one of those Catch-22 situations
* On the plus side, drenching and moving to a very clean paddock is good because the rate of reinfection of animals is very slow. So, you get good worm control.
* On the down-side, you are likely to get increased selection for resistance because there are few worms ‘in refugia’ (few worms have escaped exposure to the drench). i.e. on that clean paddock, where you have put the freshly drenched sheep or goats, a large proportion of the worm population are individuals that have been exposed to and survived the drench. These breed and make a big contribution to the succeeding generation of worms on that paddock.
* I refer to ‘very clean’ paddocks here as ‘clean’ means different things to different people. A cereal stubble in Western Australia or the Riverina of NSW in December is likely to be orders of magnitude cleaner than your average ‘clean’ paddock in the NSW tablelands, for example.
* There is no easy way around this, but here we go:
Before moving stock to a very clean paddock, check that they DO need a drench (faecal worm egg count-WormTest). If they DO require a drench, you can delay the move after the drench, giving the drenched animals time to pick up some ‘unselected’ worms to ‘dilute’ the resistance worms left behind by the drench. The obvious question then is, how long do I delay the move? There is no one ‘size fits all’ answer to this unfortunately, because every situation is different. Sorry.
If you think a paddock has a high proportion of resistant worms on it, you can ‘dilute’ these worms by moving a wormy mob of sheep or goats onto the paddock from elsewhere on the property. Re-sowing, cropping, or hay-making are others ways to deal with the resistant worms (except around the edges of the paddock). All this requires individualised advice, however.
* Drenching pre-lambing, or kidding.
This point particularly refers to the use of long-acting products pre-lambing. It has been theorised for some time that this would encourage the development of resistance in worms, and Dave Leathwick presented experimental data in the Dec 2006 issue of the NZ Vet Journal to show that this is the case, at least in the NZ situation.
People of course give ewes a pre-lambing drench in part because of the ‘peri-parturient relaxation of resistance’ (PPRR), which means for several weeks post-lambing ewes lose some of their resistance to worms. This means the lambing paddock can get quite wormy (especially if the lambing paddock was not prepared properly), which then has a flow-on effect to the lambs, who are highly susceptible to worm-infection.
There is an upside and a down-side to using a long-acting drench pre-lambing. The upside is a nice clean lambing paddock, all going well. This means a good start in life for the lambs, and helps ewes to recover body-weight. The down-side is that there may be increased selection for drench resistance.
After the ewes have been treated with a long-acting product (LAP), the resistant worms that have survived the drench have a competitive advantage, as incoming drench-susceptible worms are killed by the LAP. Then the ewes starts regaining their ‘immunity’ or resistance to worms, which makes life even more difficult for drench-susceptible worms, as many of them, along with others, are prevented from establishing by the host’s immune system. This effect is more marked in ewes that have stronger host resistance (due to genetics x environment). This effect may be more marked in, say, NZ Romney Marsh sheep that have somewhat stronger host resistance than the average Merino.
A more general enunciation of this principle is to avoid unnecessary drenching of (relatively) immune animals; e.g. adults, especially dry adults, versus young sheep.
As to lambing ewes, or kidding does, a better way is to prepare the animals and the paddocks beforehand. Ewes that are in good condition when they lamb generally fare better worm-wise than their poorer mates, and their lambs do better as well. Paddocks that are prepared beforehand (so that they have good feed, and are not wormy) are also a part of the solution.
Of course sometimes you get stuck, especially in barber’s pole worm areas, and you have no option other than to use a long-acting drench.
* What about goats? (‘We always drench 7-8 weeks prior to kidding and then give the kids their first drench at around 4 weeks of age. Why is this wrong?’)
Ideally, you would have kidding paddocks prepared for the does (see above). And the does would kid in good condition.
Before kidding, you would do a WormTest to see if they need a pre-kidding drench. Unfortunately goats on the whole appear to be more vulnerable to worms than sheep – possibly because they evolved more as browsers than grazers?? – so a pre-kidding drench may often be required.
A big issue, especially for goat owners, is what to use?? The only registered drenches for goats in NSW are ones based on triclabendazole (a narrow-spectrum liver fluke drench), benzimidazoles(BZ; (broad-spectrum), morantel (Oralject; mode of action is similar to levamisole), and an organophosphate drench, triclorfon (Neguvon(R), available for use under permit against barber’s pole worm. More recently, a macrocyclic lactone-based product (abamectin; Caprimec(R)) has been registered for use in goats.
As to the BZs, it is very likely you have resistance to it in all the major roundworms. The scour worms are very likely resistant to morantel, with barbers pole worm a little less likely to be resistant, but more likely than resistance to levamisole (which is not registered for use in goats). Triclorfon will probably be effective against barber’s pole worm, but you might understandably have reservations about using an OP on goats pre-kidding, given the relatively narrow safety margin of OPs.
Abamectin (Caprimec(R)) has a relatively good chance of working on the scour worms in most areas of NSW, but there IS resistance in these worms to the ML family. It has a poorer chance of working against barber’s pole worm.
In short, don’t assume Caprimec will work, although it is likely to be better than other goat products on the market.
In short, you have to test your drenches. The simplest way to do this is by way of WormTest 7-14 days post-drench, in the case of short-acting drenches.
If Caprimec(R) works on your farm, I would seriously consider using it concurrently with an unrelated broad-spectrum active, with a view to extending the lives of both drenches. But you will need individualised advice on this.
As to drenching kids at around 4 weeks: in a very wormy environment they may well need a drench this young, but it would be better to do them older, with some monitoring of their condition – and worm egg counts – along the way.
Regards
Steve
Posted via email from vet26mi
