This blog provides a summary of the GWCT's guidelines for best practice use of medicated grit.
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Introduction
Moorland management is a delicate balancing act. Land managers must consider grouse populations, the health of the ecosystem, and the economic viability of their operations.
Medicated grit is a tool used in this balancing act, specifically to control strongyle worms (Trichostrongylus tenuis) in red grouse. These parasitic worms, which reside in the guts of red grouse, can have a significant impact on grouse populations, leading to cyclical fluctuations in numbers.
Red grouse naturally consume grit, small pieces of quartz, which they store in their gizzard to aid in the digestion of tough heather shoots, their primary food source. Taking advantage of this natural behavior, medicated grit is created by coating this quartz grit with fat infused with an anthelmintic drug designed to kill the strongyle worms. By ingesting the medicated grit, the grouse receive a controlled dose of medication that helps to reduce the worm burden.
Managing these parasites through medicated grit helps improve the body condition of adult grouse and reduce their scent emission, which makes them less vulnerable to mammalian predators during the breeding season. Healthy grouse populations are more resilient and productive, contributing to the overall health of the moorland ecosystem.
Why Best Practice Matters
While medicated grit is a valuable tool, its use is not without potential risks. Clear guidelines are essential for the responsible use of medicated grit, balancing effective disease control with the critical need to prevent drug resistance and protect the wider moorland ecosystem. The consequences of overuse or misuse can be significant, leading to the development of resistance in the strongyle worm population, rendering the medication ineffective. This is why a meticulous, evidence-based approach is so important.
Key Best Practice Guidelines
To ensure the responsible and effective use of medicated grit, land managers should adhere to the following key recommendations:
Assess Grouse for Worms:
Before starting any parasite management program, it is essential to accurately assess the worm levels present in the grouse population. This involves counting strongyle worms from a sample of at least 20 adult grouse, randomly selected from those shot, preferably both in August and again at the end of the shooting season.
Alternatively, especially in late winter, worm eggs can be counted in fresh grouse caecal pats. These droppings, produced nightly by roosting grouse, provide a non-invasive way to monitor parasite intensity.
It is important to only collect fresh caecal material and to avoid contamination with fibrous droppings. Samples should be stored in cool conditions and delivered to a qualified lab, such as the GWCT, within 48 hours of collection.
GWCT or a vet can conduct these egg counts and provide an approximate adult worm equivalent.
Monitor Worm Burdens:
If early autumn worm counts exceed 500-750 worms per adult bird, the use of medicated grit may be required through the winter before the next breeding season. However, this decision should not be based solely on these counts.
Consider grouse densities, age structure, recent weather patterns, and moor location, as these factors can influence the survival and pick-up of worm larvae. Mild and wet weather, for example, favors larval survival.
If late-autumn worm counts are not sufficiently high to warrant medication, further sampling in late winter is recommended.
Strategic Deployment of Medicated Grit:
Establish a grid of grit sites across the moor, with the frequency of sites broadly aligned with the grouse pair density in spring. Ideally, there should be a grit station in each territory.
Mark each grit site using sections of alkathene pipe or small posts, or record the grid reference of each site using a hand-held GPS device.
Grouse counts in spring, repeated in July, can provide reliable estimates of pre- and post-breeding densities, aiding in determining the appropriate number of gritting stations required.
Maintain Grit Box Hygiene:
Place grit boxes in areas with short vegetation, at least 5 meters away from running and open water sources. Surround the boxes with stones to make them more visible to grouse.
The siting and maintenance of grit boxes are crucial to prevent the spread of respiratory cryptosporidiosis (bulgy-eye), a disease caused by the protozoan parasite Cryptosporidium baileyi.
Use small (20 x 15 cm), well-drained trays to minimize faecal contamination, and raise boxes slightly off the ground to aid drainage.
Regularly change gritting station positions by only 2-3 meters each year to reduce the accumulation of infected faeces near the tray. This also aligns with changes in vegetation height caused by burning or cutting patterns.
Proper Usage:
Medicated grit can only be placed in gritting sites after shooting has finished on the moor and neighboring moors. It must be withdrawn at least 28 days before shooting starts to comply with regulations.
Place approximately 500g of medicated grit in each tray, which should last a pair of grouse approximately seven months.
Regular Monitoring and Replenishment:
Check grit trays regularly to monitor their usage based on the presence of droppings. Remove faeces if possible.
Replenish used grit as needed, but never mix new grit with old grit. This dilutes the effectiveness of the anthelmintic and increases the risk of cryptosporidia infection.
Seasonal Removal and Disposal:
Remove all unused medicated grit at the end of June/early July.
Dispose of old medicated grit responsibly using a licensed waste disposal contractor.
Clean grit trays thoroughly, ideally by power washing, before re-using them. This helps to reduce the potential spread of cryptosporidia.
Provide Plain Grit:
When medicated grit is not in use, provide plain quartz grit to keep birds habituated to the sites.
Place plain grit in a clean tray situated one to two meters from the previous medicated location to avoid contamination.
Offer a similar quantity (500g) of plain grit at each location, with the expectation that it will be consumed before medicated grit is required again.
Record Keeping:
Maintain comprehensive records of medicated grit use, including:
Date and quantity of medicated grit purchased
Manufacturer
Batch number
Expiry date
Date placed on moor
Location of all grit stations (GPS locations if possible)
Date of withdrawal
Date of first shoot
Date and disposal method of old medicated grit
Supporting Evidence
The best practice guidelines outlined above are supported by extensive research and regulatory requirements.
Research conducted by the Game & Wildlife Conservation Trust (GWCT) has been instrumental in understanding the impact of strongyle worms on grouse populations and in developing effective control strategies. GWCT research has demonstrated that the use of medicated grit can lead to an average reduction of 44% in worm burdens in grouse and an increase of 40% in grouse productivity. This increase in productivity is largely attributed to improved chick survival rates.
It was research started in the 1980s by the Game and Wildlife Conservation Trust (GWCT) that established that infection with strongyle worms can cause 4-6 year cyclical fluctuations in grouse numbers.
Medicated grit is only available under license, and a veterinarian prescription is required before purchasing it from manufacturers. Veterinarians typically require evidence of high strongyle burdens in grouse before dispensing a prescription, ensuring that the medication is used only when necessary.
Regulatory requirements mandate the withdrawal of medicated grit at least 28 days before grouse are harvested for consumption. This is to ensure that the drug does not enter the human food chain.
History of Medicated Grit
Medicated grit was first developed in the 1980s by the Strathclyde Chemical Company. The original drug used in medicated grit was fenbendazole, part of the benzimidazole group of drugs, and was sold under the trade name of Panacur. These drugs are ideal because they don't dissolve in water, don't break down in sunlight, and work well in split doses. In 2007, an improved formulation of medicated grit was developed, changing the drug from fenbendazole to flubendazole, still part of the benzimidazole family but licensed for use in game birds. The fat was also changed to a stable non-slip fat to lengthen drug persistency on the grit.
The Threat of Resistance
One of the most pressing concerns in the management of strongyle worms is the potential development of resistance to the anthelmintic drugs used in medicated grit. Historically, the overuse of benzimidazole worming drugs in domestic livestock has led to resistance within just three to five years of use. Because the grouse world only has one drug it can use, it is important to use it wisely.
Avoiding resistance involves minimizing the exposure of strongyle worms to flubendazole. Medicated grit should only be used when necessary to prevent a population crash. Monitoring adult worms or worm eggs can allow for multiple years without medication, or delaying medication until March, which reduces worm exposure to the anthelmintic while still achieving parasite control.
Conclusion
Responsible implementation of medicated grit is essential for maintaining healthy grouse populations and preserving the ecological integrity of moorland ecosystems. By adhering to these best practice guidelines, land managers can effectively manage parasite-induced population crashes in grouse, minimize the risk of resistance, and ensure the long-term sustainability of driven grouse moors.
For further information and resources, consider the following:
Consult with your veterinarian to develop a tailored parasite management plan for your moor.
Contact the Game & Wildlife Conservation Trust (GWCT) for advice, training courses, and worm counting services.
By working together and embracing a science-based approach, we can ensure that medicated grit remains a valuable tool for moorland management for years to come.