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Lamb drenching 101

Most New Zealand farm systems rely on some level of drench input into lambs to keep them alive and growing over their first year of life.

Whether your lambs get one or two drenches with the luxury of some type of specialist forage crop, or whether they head back out onto the hills where they were born and a regular monthly drench, it’s important that the treatment they are given is effective.

If I’m using a combination drench it should be effective, right?

For two decades, NZ parasitologists and vets have promoted the use combination drenches to help delay resistance.  The genes that give worms the power to survive a drench chemical are different for each drench family, and each worm species. Where there are low levels of pre-existing resistance, using chemicals in combination is an effective strategy, because it knocks out those small numbers of worms that have resistance genes for one chemical, and keeps the resistant worms at such a low level that there is very little risk of them breeding with each other.

However, for many NZ farms the move to combinations was made well after there was significant existing resistance to one or more of the drench families, so the resistance-delaying power of the combination drenches was already compromised.

And on many farms none of the other known resistance-delaying strategies were employed, meaning that combination drench resistance is becoming increasingly common.

Even a triple combination could be letting resistant worms through. If you don’t know; test. A drench check 10 days after the first lamb drench can give you an early warning that worms are being left behind. All you need is 10 separate fresh faecal samples (warm enough that the inside of the pottle should steam up after you place the sample in it), bring them to the clinic and we’ll do the rest.

Combination drench products can settle out in storage. We try to stock brands that are less prone to this; but shake the DRUM of drench well before you decant it into the backpack you are going to use for drenching.

Are you delivering the correct dose? If your drench gun is delivering 1ml less than you think, you could be underdosing your lambs by 5kg; this is 20% for a 25kg lamb!

Calibrate your gun – check the actual volume that the gun is delivering. They vary as to which part of the plunger corresponds with the volume graduation on the side of the barrel. For some it is the first rubber bit, for some it is the steel/plastic base of the plunger or the O-ring in this – CHECK – or you may be under-dosing.

An easy way to calibrate your gun is to deliver a number of squirts into a cup and suck the expelled drench back up with a syringe. Measure the volume and divide by the number of squirts you made. DON’T use a cheap measuring cup or the free giveaway cylinders that come with drench. Medical/veterinary syringes are manufactured to tight specifications to deliver an exact volume. Use a syringe!

Not all drench products are compatible, sometimes only a small amount of an incompatible chemical can upset the formulation of the product you are using. A good example of this is where you have used a backpack for one product, not had time to clean it and then tipped another product in.

It is a bit tricky to make general recommendations on cleaning drench guns as the brands do vary in what they are compatible with; it pays to check the instructions.

For most oral drench guns, and for backpacks, squirt the unused drench back into the original container; wash through with warm water and mild detergent. Once washed, guns should be lubricated; liquid paraffin is a really good choice (we stock this), although some of the plastic guns state that vegetable oil should be used.

Some drench formulations do not mix well with water, so dry your gear well before the next use.