Assessing grouse for worms

Performing a worm countThe most crucial factor in the control of strongyle worms is knowing what worm burdens are in the birds so that parasite control can be targeted at appropriate times.

Parasitic 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 can be delivered to GWCT offices and we will do them for you as part of our Grouse Technical Services. As a guide, we know from previous research that more than 2,500 worms per adult grouse can impact on productivity and, ultimately, survival.

Levels greater than a mean of 1,000 worms per bird from the autumn worm counts should “trigger” the need to put out medicated grit to control the strongyle worms the following spring. To provide better information on parasite burdens, counts of strongyle worm eggs in spring from live grouse should be considered.

Strongyle eggs are passed out in the caecal droppings produced every night whilst at roost. By collecting this material when it is still fresh (within 24 hours of being voided from the birds) and has not been subjected to freezing temperatures or desiccation, numbers of eggs passed can be counted and an approximation of the worm burden in the bird can be calculated.

This egg-counting technique requires more technical equipment than the much simpler worm counting technique. The GWCT provides a service for counting these worm eggs and calculating these spring worm burdens.

Not only is it important to know when to provide medicated grit from worm counts, it is also equally important to know when not to medicate because over exposure to the worming drug can cause resistance to build-up in the worms, which would quickly reduce the effectiveness of the drug.

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