| UPLANDS - MEDICATED GRIT
Reducing anthelmintic intake by grouse Medicated grit did not have to be put out every year on four of eight study moors where medication was experimentally withdrawn. © Laurie Campbell
BACKGROUND Medicated grit has been used since the mid-1980s, but a revised formulation involving a change in benzimidazole drug from fenbendazole to flubendazole and incorporation of a more temperature-resistant binding fat, together with a new mode of grit delivery (withdrawal using flip-lid trays) occurred in 2007. Medicated grit use is popular with grouse managers who use it as an annual insurance against strongyle-induced grouse crashes rather than when it is strictly needed, causing concern that it could cause a widespread build-up of anthelmintic resistance in parasites.
68 | GAME & WILDLIFE REVIEW 2019
The strongyle worm, a nematode parasite, can limit grouse survival and breeding success causing quasi-cyclical fluctuations in abundance. To control worms in grouse, gamekeepers provide medication, in the form of quartz grit covered with a fat coating containing a benzimidazole-based anthelmintic, in each grouse territory. Grouse consume this grit to help digest heather and by doing so, they obtain a split-dose worming treatment, which has been experimentally shown to kill 95% of worms in gamebirds. Medicated grit has been used since the mid-1980s, but a revised formulation involving a change in benzimidazole drug from fenbendazole to flubendazole and incorporation of a more temperature-resistant binding fat, together with a new mode of grit delivery (withdrawal using flip-lid trays) occurred in 2007. These changes have proved popular and now almost all grouse managers use medicated grit every year. Accordingly, worm burdens in grouse have been uncharacteristically low since 2009, suggesting high levels of control from medicated grit. Despite this, most managers use medicated grit as an annual insurance against strongyle-induced grouse crashes rather than when it is strictly needed. This is despite a veterinary prescription being required for its use. It is evident that decisions on whether to prescribe anthelmintics are seldom based on measured abundances of parasite intensities. Over-reliance and inappropriate use of worming drugs amongst domestic livestock has rapidly resulted in a widespread build-up of anthelmintic resistance in parasites. Although resistance in strongyle worms in grouse to flubendazole has not been found, more frequent and widespread use of medicated grit in the last decade may increase the risk of it happening in grouse as well. To encourage grouse managers to reduce anthelmintic use, we conducted a trial where we experimentally withdrew medication from parts of moors. Few participated, only seven of 25 invitees joining in northern England and only one of 18 in the Scottish Highlands. We invited grouse managers to refrain from using medicated grit over a three-year period (2012-14). However, large and sudden parasite increases in early spring 2012 led to one grouse manager resuming medicating grouse later that spring. Thereafter, we asked managers to decide whether to use medication based on actual parasite data collected from their moor in late winter in each year of the trial.
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