Farmers drenching too often say experts
Farmers could be drenching their sheep too often and need to act smarter to reduce the risk of parasite resistance and declining productivity, a veterinary parasitologist warns.
‘‘New Zealand farmers have become adept at regular fourweek drench programmes but my concern is this is too much,’’ said Abigail Chase of Boehringer Ingelheim Animal Health.
‘‘There may be a need there to just think a bit harder and smarter about whether drenching this time around is really such a good idea.’’
Wormwise trainer and sheep veterinarian Rochelle Smith said managing internal parasites was one of the biggest challenges farmers faced.
With drench resistance increasing in stock, farmers have to be conscious of how they are using drenches, she said.
‘‘Farmers need to ask themselves before drenching if they need to do it and think about the nearness of stock to their kill date if they are going on to uncontaminated feed.’’
Research showed that there was widespread resistance to several drench families across both sheep and cattle.
Smith referred to the 2013 McKenna study on 125 North Island farms, which found there was a 47 per cent resistance to white or clear drenches, a 31 per cent resistance to a combination drench of white and clear and a 4 per cent resistance to triple drench.
‘‘Even by drenching every 20 to 21 days you’re still dealing with larvae and reduced growth rates.
‘‘You’re still getting production losses,’’ she said.
Northland sheep breeder Gordon Levet is a leader in breeding worm-resistant sheep.
‘‘With the world demanding fewer chemicals in the food chain, a national flock needing only occasional chemical intervention would ensure a greater marketing advantage,’’ he said.
‘‘The beauty of using nature’s own defence mechanism is that internal parasites have no defence against a genetically enhanced immune system.’’
Levet said that after 30 years of breeding for the worm resistant trait, which had resulted in a high percentage of lambs that can thrive without drenching, he was convinced that his results could be replicated in the national flock.
‘‘First the national flock is becoming more susceptible to worm challenges.
‘‘With the climate warming and more humid conditions, worm populations have not only increased but the danger period has been extended,’’ he said.
‘‘And secondly the national flock is becoming more susceptible to internal parasites because drenching programmes with very efficient drenches, ensure the development of more resilient worms.’’
Chase believed on the whole New Zealand farmers have picked up well on drenching practice that came out of research done through the 1980s.