More information

For further advice on medicated grit use and monitoring of strongyle worms and worm eggs, please contact:

Game & Wildlife Conservation Trust Upland Research Group,
Eggleston Coach House,
Eggleston Hall,
Barnard Castle,
Co. Durham,
DL12 0AG

Tel: 01833 651936


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A PDF copy of these guidelines is available to download.

Assessing grouse for worms

Performing a worm countBefore commencing parasite management, it is important to know what levels of worms are present in grouse. Strongyle worms should be counted from a sample of 20 adult grouse randomly selected from those shot, preferably in August and again at the end of the shooting season.

Worm counts can either be done by estate staff, once trained by the GWCT, or the guts from those grouse selected can be delivered (or posted using a bio-bottle) to GWCT offices and we will do them for you. As a rough guide, we know from previous research that more than an average of 2,000 worms per adult grouse can severely impact on productivity and survival. It is the spread of individual worm values across the measured sample, guided by the average, that will help steer decisions on whether medicated grit is required to control worm parasites. Importantly, these count results should be discussed with your vet when asking for a medicate grit prescription.

Mean infestations above 500-750 worms per adult bird in early autumn may require the use of medicated grit through the winter before the next breeding season. The relationship between autumn worm counts and those in the following spring can however be highly variable and difficult to accurately predict. Larval pick-up in the intervening period will be strongly influenced by winter weather; mild and wet weather being good for worm larval survival and subsequent pick-up by foraging grouse.

If late-autumn worms counts are still not sufficiently high to merit using medication, then we recommend further sampling. This should be done in late winter, but this time through counting worm eggs in freshly gathered grouse caecal pats. Strongyle eggs are passed out in the chocolate-mouse type caecal droppings, which are produced every night whilst grouse are at roost.

The following criteria are import when collecting caecal samples:

  • Only collect fresh caecal material. Those pats with hard dry skins should not be collected.
  • Ideally 48 hours of frost-free conditions are required before collection of caecal.
  • Only the viscus brown “chocolate mousse” type material should be collected, avoid contamination with fibrous droppings.
  • Store one sample per polythene bag, insert hand into bag, collect caecal, turn bag inside out and tie top of the bag.Try to keep the sample together ideally in the corner of the bag.
  • Label each bag clearly, with date/moor/beat/drive/reference number.
  • Store samples in cool conditions such as in a fridge. Do not keep in heated vehicle or in direct sunlight. Do not freeze them.
  • Deliver samples to the GWCT (or a vet who conducts this service) quickly, either in person during office hours or, prior to collection, ask us for a “Bio bottle” and send to us by overnight postal delivery.
  • Aim for samples to always be delivered to GWCT or a vet within 48 hours of collection.

From the number of eggs counted, the approximate worm burden in the bird can be calculated. We and others have carefully calibrated worm egg counts with those of adult worms from the same grouse at different times of year and different parasite intensities. GWCT or your vet can do these egg counts and let you know the approximate adult worm equivalent.

By using egg counts to monitor parasite intensity frequently, more informed decisions can be made over the necessity of using medicated grit. Ultimately, this may be of critically high importance as repeated over-exposure of worms to flubendazole is likely to cause resistance to the drug amongst the worms.

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✓ History of disease
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