Disease Control

Grouse are prone to two particular diseases, Louping Ill and Strongylosis. The latter occurs especially if numbers are high, partly accounting for the grouse's natural "boom-bust" population dynamics.

Louping Ill in Sheep and Grouse

Louping Ill is a particular problem encountered in certain moorland areas. Sheep ticks carry a virus that attacks the nervous system of sheep and red grouse. It has been proven to be 79% fatal in grouse chicks.

Control requires the cooperation of many people, and an initiative on the North York Moors has shown just how successful this can be. In 1995 Moorland Association members, The North York Moors National Park Authority, farmers and shooting tenants were successful in gaining financial assistance from MAFF and European Objective 5b funds to help control the disease through sheep dipping, vaccination for sheep and bracken control. A total of 4000 hectares of bracken within this 44,000 hectare SSSI site were treated and returned to heather. During the first four years of the programme, lamb deaths dropped by 7%, which equated to 2000 lambs saved, and the Game Conservancy Trust reported a substantial year-on-year reduction in ticks found on red grouse.

Trichostrongylus Tenuis

Trichostrongylus Tenuis is a nematode worm that can occur in the gut lining of an adult red grouse and cause strongylosis or "grouse disease". The digestive efficiency of the grouse is reduced and with a high infestation it will die, especially in early spring when food quality is at its worst and the bird is stressed by breeding activities. Grouse suffering from strongylosis also become easier targets for predators.

The eggs of the Trichostrongylus Tenuis worm are ejected into the heather in grouse faeces; there they hatch into larvae, which are subsequently ingested by grouse feeding on the heather. As the grouse population on a moor increases, so does the number of larvae in the heather and hence the number of worms in the grouse; as many as 40,000 have been counted in badly infected old birds. As the population peaks, grouse begin to die from strongylosis, and the 'crash' can be dramatic, with few surviving. The number of larvae in the heather now decreases; surviving grouse and their chicks become more healthy, and numbers begin to build again towards another inevitable 'crash' - such is nature's way. The moor manager can reduce the severity of this cycle by shooting hard when populations build towards a peak. He can also use medication to treat the disease.

Grouse ingest grit to break down food in their crops before digestion, and it is grit coated with a worm killer that is used to treat the disease. This grit (referred to as 'medicated grit') is distributed around the moor in small trays after the end of shooting. It is then replaced by plain grit at least 28 days before start of shooting the following season to ensure that no medication enters the human food chain. In the interim, the grouse will have found the trays and picked up the medicated grit, thus ingesting the chemical, which in turn will have killed the worms in their gut. The practice is now well established and results proven, but research continues to optimise the procedure, for example by varying the concentration of chemical.

Another means of administering medication is by direct dosing, using a syringe. Grouse are caught up at night using a lamping technique; a small dose of chemical is syringed into their beaks and the birds are ringed and released. The operation is swift and causes little apparent distress to the birds. It would normally be reserved for treatment of a high worm infestation in the flock.

For latest research and guidance on Trichostrongylosis Tenuis, the use of medicated grit and direct dosing in the treatment of worm can be found on the Game and Wildlife Conservation Trust's website.