Wednesday, 22 February 2017

What’s up with sheep parasites?


Parasitism costs the New Zealand sheep industry $270 million annually, with farmers spending $50 million on drench to try gain control (1).

All grazing animals will be exposed to worms that (if left uncontrolled) result in reduced growth rates, illness, and death. Young stock with little developed immunity are most susceptible to parasites. However, there will be times when even adult stock performance can be impacted by parasites.

For over 40 years drenching has been an incredibly effective control method used for parasites. Today we have a number of different drench actives and formulation types that have given farmers the upper hand in the battle against parasites. The first recording of drench-resistant worms in 1979, signalled a change in the balance of power that continues to move away from the farmers.

A 2006 study on over 80 New Zealand farms, found that 64% of farms had resistance to Albendazole, 25% to Ivermectin, and 24% to Levamisole as a single active (2).

More worryingly, this study also found that 64% of farms tested had resistance to one or more drench actives, currently available in double and triple combinations.

There is no evidence to suggest this situation has improved to date. The arrival of two new drench actives (montepantel and derquantel) will offer some respite, but these products are already under pressure to remain effective. It is clear from these studies that if nothing changes in the way we use drenches, it will be a case of when, not if, drench resistance will develop on every farm.

Farmers need to act to decrease the cost of resistance

The good news is that there are a few simple things farmers can do to better manage existing drenches, to ensure they continue to be an effective option. A good place to start is to take a fresh look at how drenches are being used and whether or not those practises are accelerating or slowing the development of drench resistant worms.

Long term success involves more than just reaching for the drench gun, you need a fully integrated worm management programme, including:

  • Reducing larval challenge on pastures.
  • Understanding worm life cycles, and how the environment affects larval populations.
  • Targeting worm challenges at the correct time with the most effective products.
  • Breeding animals with increased immunity/tolerance to worm infection.
  • Providing refugia to ensure drench susceptible worms remain dominant in worm populations.
  • Using regular faecal egg counts to monitor for changes in worm burdens and efficacy of treatments.
  • Minimising the drenching of adult animals.
  • Use a combination drench like Trio Sheep if drenching is required.

The situation on-farm will constantly be changing, requiring frequent review of your worm management programme to incorporate new technologies and strategies. Ravensdown animal health technical managers can help you develop a sustainable worm programme.

(1) - Beef & Lamb R & D Brief 67: Sustainable Internal Parasite Control for Sheep
(2) - Prevalence of anthelmintic resistance on sheep farms in New Zealand. Waghorn, al: N ZVJ 54: 271-277, 2006.