Worm control and "refugia"
I strongly disagree with the idea of refugia for worm control in sheep. I've mentioned my thoughts on this a little here and there, but after some recent comments on our operation here on Caluka Farms from visitors, I thought I'd talk about it in a little more detail.
Even though we are having a very dry summer, we still have some green in all paddocks. Barbers pole worms can and are still very happy here. We have no cropping stubbles to put sheep on. We have no paddocks rested from grazing for 6 months. Every paddock is grazed at least once every 6-7 weeks, usually several weeks sooner.
I get told often how we are going to be a disaster for worms. Nah, I don't think so. It's a hurdle, but we have solutions. It's just not as easy as someone running 2 sheep/ha in winter and then throwing them onto bone dry crop stubbles over the summer with one drench just before they enter those paddocks. The heat and dry kills most of their worms and one shot of moxidectin will do the job. That's not an option for us.
I have intensive and extensive experience with herbicide resistant weeds. I think much is the same with drench resistance in worms (which are a nematode). So some basics we all must understand. Resistant genes are not created by us. They already exist. We just "select" those animals that have those genes by giving them a drench. The genes did not evolve. They already existed. We selected them. Another basic premise is, it is always a numbers game.
Many things eat sheep nematodes. Other nematodes. Some fungi and some bacteria. Heat and dry kills many of them. Time kills them if they do not get into a sheeps stomach. And, there are sheep with resistance to all worms and this is a multi-gene tolerance to the worms.
And a big one. Nutrition helps a lot for sheep to control and tolerate the worms. We do not have our nutrition perfect yet, but we have improved substantially and it is showing big results in our sheep.
So, refugia. For those who don't know what this theory is, it is the idea that you allow worms to be in a paddock so that when you drench sheep you put them into those wormy paddocks so that you dilute the worms in the sheep and you do not build up resistance.
Sigh. This is such bollocks to me. I dealt with this idea in the early days of managing herbicide resistant ryegrass. The reason some think it works is because they get to see ryegrass still dying from a herbicide that some ryegrass are resistant to. The idea was to allow some ryegrass to set seed and not see any herbicides. Some even promoted planting susceptible ryegrass so that when you spray it, it dies. It is such a stupid idea, but in their minds, the susceptible pollen would cross with the resistant pollen and dilute the resistance.
Back to the basics. We do not create resistance genes. We "select" for them when we drench or spray. Just because you may have flooded a paddock with susceptible genes, the resistant ones are still there. You just think you are controlling the worms because you are seeing lots of dead worms in the sheep. It is not a wise conclusion. The resistant genes are still there, and you will have lost yield to the crop or in the sheep by allowing so many weeds/worms to be there.
The idea of refugia for worms is folly.
It is always a numbers game. Always. If I drench with just moxidectin, as an example, and it kills 90% of the worms in the sheep, and 10% survive because of some level of resistance (ignoring survival for other reasons for the moment), then it is not only still very helpful to the sheep, but, it is easier for another product to kill the remaining 10%.
However, I speak to many farmers, and consultants :-(, who think using 2-3 active ingredients for worm control can be a disaster and select for highly resistant worms that are resistant to everything. Sigh, no. Back to the basics. It is a numbers game. It is always a numbers game.
Even if I used moxidectin and 10% resistant ones survive, and I used perhaps closantel with it and 0.5% resistant ones survived (ie they are resistant to moxidectin and closantel), it is so much easier for the sheep and other predators to control those remaining 0.5%. Remember, I did not create those 0.5% resistant worms. Their genetics were already there.
It is always a numbers game. Just by allowing masses of susceptible worms to be there so that you see your drench work, that does not mean you have reduced the resistance. You are making sure you have continual worm problems and sheep production losses.
Our strategy is to throw everything we can at the pest (the worms) to make life as difficult as possible for them from all angles. Every ram we purchase must have worm resistance. We always drench with 3-4 modes of action everytime we drench. We are intensely focussed on getting the pastures as healthy as possible. This includes doing what we can to keep adding more diversity and species that may have some benefit in reducing nematode numbers in the sheep.
Yes we rotationally graze and that can reduce worm numbers, but not really in our system. We do not want the pastures to become tall and rank, which is what will happen if we do not graze it for 6-months, all in an effort to let time happen and worms die. That's not an option. We are here to grow food and as much of it as efficiently as we can.
Genetic resistance is a big priority for us. We will not buy rams if the breeder does not measure worm resistance. By us having the best nutritious pastures we can with a diversity of species, and by using multi-mode drenches at every drenching, it then makes it so much easier for resistant sheep to control and suppress the remaining few worms.
When we only have a few worms on the paddocks and we have highly resistant genetics, then even less worms get returned to the paddock. Those few on the paddock are much more prone to having their numbers reduced even more by things that eat them, or a hot dry spell etc. We expect to get to the point where the resistance is so good in our sheep, and the pastures are really well fed and diverse, that drenching will be reduced substantially to maybe only once every 12-18 months, or longer.
There are already genetics that never need drenching even under immense pressure. I am chasing those to put into our flocks. Remember our slogan. Meat the way nature intended.
It is always a numbers game. Deliberately keeping numbers high is folly. You are not keeping resistance genes out of your paddocks. You are simply constantly having sheep production losses. Food for thought I hope :-).