Drench resistant parasites are a concern - Elders Rural Services
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Drench resistant parasites are a concern

When it comes to cattle, most producers are unaware that anthelmintic resistance in cattle is now a real concern.

Anthelmintic resistance is a genetic trait of resistant worms that allows them to survive drench treatments which were previously shown to be effective.

Dr Matthew Playford, a veterinary parasitologist with over 30 years of experience in this field, and the owner of Dawbuts, an independent parasitology laboratory, said we are now seeing drench resistant parasites impacting the productivity of cattle in different production systems all over Australia

Research conducted in Australia over the last couple of years has confirmed all major production limiting species of worms (Cooperia, Haemonchus and Ostertagia) have demonstrated resistance to our most heavily relied upon drenches – the macrocyclic lactones (the ‘mectins’) – plus other classes of drench. These findings are not limited to one geographical region or climatic zone.

Drench administration matters

The way we administer a drench also impacts the rate of resistance development. The use of pour-on products results in variable dosing of animals. Some of the pour on product is absorbed across the skin while some is absorbed by licking the product off themselves and other cattle as this can result in underdosing, it should ideally be reserved for scenarios when facilities for cattle handling are poor and human safety is a concern.

Injectable or oral drenches are the most effective way to deliver consistent dosing to cattle.

How to manage resistance

To manage anthelmintic resistance, Dr Playford advises that producers should be performing, routine faecal worm egg count (WEC) as a monitoring tool to assess the need for drenching.

Worm egg counts are correlated with the total number of worms in the animal, and this in turn is correlated with the product losses which occur. Low worm burdens produce little impact on cattle, whereas high burdens rob cattle of daily weight gain, feed conversion efficiency and milk production. In the worst-case scenario can kill cattle.

Efficacy of at least 95 per cent is important

Additional to WEC monitoring, farmers should be keeping track of drench efficacy with simple ‘before and after’ drench tests (Drench checks).

The WEC obtained can then be used to estimate the percentage of each type of worms killed by a treatment. A benchmark of 95 per cent efficacy is used to indicate whether a drench is performing at an appropriate level of efficacy and to identify resistance.

Key considerations

  • When drenching on your property, you should be considering the points below from our industry experts at Paraboss.
  • Young stock, and cattle under nutritional stress or metabolic stress are more susceptible to worms. Most, if not all cattle will require a drench at weaning.
  • High stocking rates, especially in wet and cool conditions will favour larval survival and hence increase the exposure of cattle to worm populations.
  • Drench only when necessary, so perform routine WEC to assess need, especially in adult cattle.
  • Ask for sensitive tests – those with a sensitivity of 20epg or below.
  • Use an appropriate drench – a drench with at least 95 per cent efficacy on your farm.
  • Combination products, such as Dectomax V, containing actives from different chemical classes that target the same parasites will have greater efficacy (unless the worms present are 100 per cent susceptible to the drench) as the two actives will have different modes of actions to maximise effect. Combination products also delay the onset of resistance as fewer resistant worms can survive treatment.
  • Oral and injectable anthelmintics are considered best practice as they provide higher and less variable blood levels of the chemical than pour-ons. Oral products, however, are less likely to achieve high concentrations in the tissues such as the intestinal wall and skin compared to injectable products.
  • Long-acting products should be used with care, as they are likely to increase the levels of resistance (as they have with sheep).
  • When treating external parasites like ticks and lice, consider products specific for this purpose if worm control is not required at the same time.
  • Always use a quarantine drench, i.e., combination products, when purchasing cattle, to minimise the introduction of resistant worms onto your property.

Article written by Dr Matt Playford, Zoetis, for Seasons magazine. 

Dr Matt Playford is the Managing Director of Dawbuts. He is a highly skilled and experienced livestock veterinary parasitologist. Dawbuts is focused on providing parasitology diagnostic services; contract research for pharmaceutical companies both in Australia and overseas; training in animal health, production and biosecurity to pharmaceutical and rural store merchandise employees and producers; and on-farm advisory and consultancy to producers.

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Drench resistant parasites are a concern