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Wairarapa Drench Capsule Study

Key points from the famous Wairarapa capsule study

This large scale piece of research (14 separate trials on commercial farms) was going to give us the answers we needed to make better informed decisions on the need (or otherwise) for ewes to be treated with long acting (LA) anthelmintic products pre-lamb.

Now, the data has gone through intensive analysis, and two scientific papers have been produced; one detailing the biological and productive outcomes, and one applying a cost benefit analysis to these. So now we can give you some simple advice around pre-lamb worm treatments that is backed by actual data.

We get some assessment of this by people who are top notch at analysing and understanding what makes profitable and successful farming businesses.

The first piece of key information is this…The farms where there was no (or a very low) response to the LA treatments were those with a long-term history of a high performing, stable ewe flock with good feed levels and high level of management skill.

“There is no silver bullet as opposed to well fed animals”.

With LA treatments,

  1. Capsule treated ewes weaned heavier (average 3.2kg, range 1.8-4.9kg) and this was significant in 12 of the 14 trials.  
  2. Some of this benefit was carried through to the next tupping (average 2.5kg, but range -1.8 to +4.5kg). This reached significance in 9 of the 14 trials.
  3. Individual lamb weaning weight was better in capsule treated ewes’ lambs, but not by as much as you might think (average 1.5kg, range 0.34 to 2.88kg).
  4. Capsule treated ewes were cleaner (less daggy) than untreated ewes


“The positive ewe liveweight response was independent of ewe body condition; thin ewes did not respond better than well-conditioned ewes. But they still gained weight, which is important when you’re a thin ewe at lambing time!”

The fact that the weaning liveweight benefit did not carry through to tupping at the same magnitude indicates a period where capsule treated ewes did not gain weight as fast as the untreated ewes. Previous work has shown a temporary slackening in parasite immunity after LA treatments run out; the above finding is likely a reflection of this.

The following findings may challenge your assumptions if you are a keen user of LA products in your ewe flock:

1. Overall, capsule treatment did not improve the weight of lamb weaned per ewe. This ranged from -5.2 to a massive +15.6kg; and was driven by big differences in ewe and lamb survival between mobs not related to LA treatment. In 9 of the 14 trials the treated ewes reared less lambs than the untreated ones!

2. Thus some of the improved weaning weight of treated ewes is attributable to the fact that they reared less lambs, ditto for the improved individual lamb weaning weight.

3. In 8 of the 14 trials the increase in individual lamb weaning weight was not statistically significant.

4. On some of the farms 25-30% of the capsule response was attributable to the minerals in the product (B12 and Selenium).

5. Concurrent ‘mectin and white drench resistance was evident on a number of the farms with as many as 50% of the treated ewes having positive egg counts throughout the capsule payout period, with pure cultures Ostertagia being grown from these.


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