Sustainable use of anthelmintics in grazing animals.

This research article explores methods for sustainable use of anthelmintics (worm-treating medications) in grazing animals to prevent the development of anthelmintic resistance in worms, which could jeopardize animal health and welfare.

Understanding Anthelmintic Resistance

• The article asserts that the key element in avoiding the development of anthelmintic resistance is the proportion of worms that do not come into contact with anthelmintics, referred to as ‘worms in refugia’. This population of worms maintains susceptibility to the drug, limiting the spread of resistance.
• The number of worms in refugia depends on several factors such as the quantity of larvae on the pasture, the proportion of animals treated, and the presence of any worm stages within the host that can evade the anthelmintic’s effects.

Strategies for Asciertaing Anthelmintic Efficacy

• Efforts to maintain anthelmintic effectiveness must ensure a substantial number of worms remain in refugia. After treatment, these worms can reproduce, maintaining a population of susceptible worms.
• The research suggests that in cattle this can be achieved by only treating first-year animals and rotating the grazing areas for calves yearly. Shifting pastures prevents the accumulation of resistant parasites at a specific location.

Specific Measures for Different Animals

• In sheep, the research recommends that only animals that require treatment are given anthelmintic doses. Overuse of anthelmintics can lead to the emergence of resistant worms, therefore, unnecessary treatments should be avoided.
• The article suggests that clean grazing strategies, which involve the use of anthelmintics, should be avoided as these can also contribute to resistance.
• For horses, the removal of faeces from pastures is important, to limit the build-up of larvae and reduce the need for anthelmintic treatment. Anthelmintics should only be used when the condition of the animal necessitates it.

Consequences of Anthelmintic Overuse

• The paper underscores the potential consequences of improper anthelmintic use. It warns that without modification in current practices, the frequency of resistant worm cases may escalate, making it difficult to manage worm related diseases in animals.
• Anthelmintic resistance poses a risk to animal welfare, as the inability to effectively treat parasitic infections can lead to substantial negative impacts on animal health and productivity.