Targeted Selective Treatment

Protecting drench performance in cattle systems

In the sheep industry we’ve had more than a decade of activity aimed at prolonging the useful life of the anthelmintic drenches that are so important for controlling internal parasites in young stock.

AgResearch’s multiple studies into drench resistance clearly showed the protective effect of using combination products as opposed to single actives. However simply changing what you purchase without changing what you practice will have a limited impact on slowing the development of resistance.

Terms such as refugia, co-grazing and selective treatment are finding their way into day to day language and farmers are finding ways to fit them into their systems to protect the performance of the anthlemintics we use. Remembering of course that we can achieve a lot through good nutrition to minimise our dependence on anthlemintics!

In the beef and dairy grazing worlds we need to be similarly looking at tools to add to combination drench use to maintain the efficacy of the drugs we have.

The concept of refugia entails leaving some parasites ‘unselected’ by drench. The easiest way to apply this is to ensure that un-drenched animals graze the same areas as animals under regular drench treatment. Thus, the worms that survive and develop on pasture are not solely those which have survived the drench treatment. In sheep breeding systems refugia can be easily provided via undrenched ewes, used in a planned way.

However, on beef rearing and dairy grazing blocks suitable older animals may be in short supply, and their efficacy in providing effective refugia is not well understood.

An area that is attracting some research attention both here in New Zealand (NZ) and overseas is the concept of ‘Targeted Selective Treatment’ (TST), whereby not all young cattle in a mob are drenched at the same time, allowing some animals to provide a source of unselected parasites to dilute out any that may be surviving the drench treatment.

EID (tagging with electronic tag) via the NAIT (National Animal Identification and Tracing) system has provided us with a simple way to apply this concept in any young cattle grazing system should we choose.

A TST programme can run thus: Calves are yarded for weighing, a liveweight gain target is set; (say 600g/day for dairy grazers or 800g/day for R1 bulls) animals which have exceeded the target go straight back out onto good feed, those who have not, receive a drench and then join the mob. It may seem frightening to leave calves undrenched but much of the work done to date demonstrates that there is minimal liveweight cost to this system when feed levels are good, and there are farmers around NZ employing this system and dropping their drench inputs substantially.

Work with dairy grazers by Lincoln University showed that a TST regime reduced anthelmintic use by 74% on one farm and 47% on another. The first farm had a high proportion of adult animals on the calf grazing area and thus likely much lower larval challenge.

While it makes great sense to consider a system that not only improves sustainability and saves money, you do need to be committed to doing it well. Do the weighing on time, stay abreast of your feed supply and demand; anticipating and correcting feed shortages before they occur so that untreated animals don’t suffer the triple whammy of no drench, grazing lower (high larval intake), and insufficient feed.

There may be one or more times in the year (pre-winter Ostertagia clean-out is a good example) where all animals should get a blanket treatment regardless of the TST results. If liver fluke is an issue on your property there may be a case for a blanket treatment for this parasite.

If you’re thinking of designing a TST system for your own young cattle, spend some time discussing it with us before you start.

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