Traditional thinking around post-dosing animal management was to move to new fields immediately. The theory was that our animal was worm-free and going to an environment with a low burden, so populations would be slow to build up again and thus performance would be maintained.
However, if there are resistant worms in the animal that aren’t killed by the product, moving to a new pasture will give these reproductive advantage – they will only have resistant worms to mate with – for a long period. Now, best practice is to return animals to where they came for 4-7 days and allow re-infection with susceptible worms. These will mate with the resistant worms left behind in the animal at treatment and dilute down the overall resistant population.
However, using a product with residual activity (Moxodex being an example), any susceptible worms ingested will be killed in the system for a period post-treatment, so there is nothing to gain by returning to dirty pastures. In this case, best practice is to leave a random 10% of animals in the group untreated. Avoid leaving very poor- or very well-performing animals untreated, as the former could be at risk of performance/welfare problems and the latter may not be harbouring a high enough burden to have any positive effect.
If it isn’t possible to return to dirty pasture and we are moving animals immediately post-treatment with non-residual activity products (Albex being an example), we would also ideally leave around 10% untreated. These will infect the new pasture with susceptible worms and help dilute the resistant population.
Traditional thinking around post-dosing animal management was to move to new fields immediately. The theory was that our animal was worm-free and going to an environment with a low burden, so populations would be slow to build up again and thus performance would be maintained.
However, if there are resistant worms in the animal that aren’t killed by the product, moving to a new pasture will give these reproductive advantage – they will only have resistant worms to mate with – for a long period. Now, best practice is to return animals to where they came for 4-7 days and allow re-infection with susceptible worms. These will mate with the resistant worms left behind in the animal at treatment and dilute down the overall resistant population.
However, using a product with residual activity (Moxodex being an example), any susceptible worms ingested will be killed in the system for a period post-treatment, so there is nothing to gain by returning to dirty pastures. In this case, best practice is to leave a random 10% of animals in the group untreated. Avoid leaving very poor- or very well-performing animals untreated, as the former could be at risk of performance/welfare problems and the latter may not be harbouring a high enough burden to have any positive effect.
If it isn’t possible to return to dirty pasture and we are moving animals immediately post-treatment with non-residual activity products (Albex being an example), we would also ideally leave around 10% untreated. These will infect the new pasture with susceptible worms and help dilute the resistant population.
