New Zealand

Seasonal Spotlight


Worm Monitoring


Drench resistance is on the rise, and it will continue to do so if we continue to do the same thing! One of the easiest changes we can make is to increase our monitoring. This could be to check lamb or ewe worminess, check if the last drench worked or doing a full reduction test. Regardless of the type of test, we need to be doing more of them, as the information we get from monitoring will guide our next steps.

A fecal egg count (FEC) can be done at any time, in any class of stock to monitor how wormy your animals are. 2- tooth’s in lush grass might become daggy and you suspect worms, but a FEC may show there are none present and it’s just lush feed making them loose. Likewise, if you want to extend or shorten a drench interval, a FEC can provide some guidance, however it’s not absolute, as animals can be full of immature non-egg laying stages that still cause problems. It can also be a useful tool if you are changing or trialing management systems and want to keep an eye on progress. Fecal egg counts are very inexpensive and easy to do.

A drench check is a FEC taken 10-14 days after drenching and gives an overview of drenching efficacy. Fecal sample 10 drenched lambs and request a fecal egg count. If your drench is highly effective and these lambs have been drenched properly (dosed to heaviest, no one spat it out, gun was working well), there should be no eggs present. If eggs are seen, a proper reduction test would be a good next move.

Fecal Egg Count Reduction Tests (FECRT) provide the best information on the efficacy of the drenches tested - usually combinations and some single actives will be tested. This does involve some forward planning and a bit of extra work, but it will tell you the efficacy level of each product and what options you have available.

These tests are key tools in practicing good parasite management techniques. Ultimately, if you don’t look, you won’t know what is happening, and you won’t know if your current practices are working, or if you need to make a change.

Click here for more information on monitoring options and other parasite management tools, or call Zoetis technical services on 0800 ZOETIS, your veterinarian, or visit

Posted by Dr Victoria Chapman, Veterinary Adviser, Livestock.