Avoiding resistance

Use medicated grit wisely to offset resistance build-up

The indiscriminate use of medicated grit will inevitably build resistanceThe majority of estates have been providing medicated grit as a safety precaution irrespective of whether wormers have been necessary to improve grouse health and survival. Historically, this type of over-use in domestic livestock has led to the development of drug resistance in parasitic worms.

Evidence from the livestock industry shows that resistance to current wormers can occur within as little as three to five years of use, with resistance to one benzimidazole product resulting in resistance to others within that group. Over-use of medicated grit may accelerate the onset of resistance within the strongyle worm population infesting red grouse.

Avoiding resistance

Medication is not required every year, with no negative effects on production or survival in years when no medication is used if parasite burdens are low. We recommend careful monitoring of parasitic worm burdens by counting eggs in caecal material in the spring before deciding whether to use medication. By not placing medicated grit out until March and withdrawing it in late June/early July, exposure to the anthelmintic is reduced but strongyle worm control is achieved, thus helping to prevent resistance.

By using medicated grit wisely and only targeting the years when it is required, we should be able to keep medicated grit for longer. Once resistance becomes common, medicated grit in the form we currently use it will be ineffective and we currently have no alternative drugs to use, meaning the grouse cycles we consigned to history will be back.

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✓ History of disease
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✓ Assessing grouse for worms
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