Parasite control essential for greater productivity

 

September 2012

In 2005, a survey of New Zealand sheep farmers revealed the problem of drench resistance in parasitic worms was greater than expected. More recent evidence suggests the issue has continued to worsen.

Since the survey, considerable research effort has resulted in the development of a number of recommendations which can help farmers minimise the development of drench resistance, and which do not negatively impact on worm control.

Building on previous research, AgResearch recommends farm management strategies that sheep farmers should adopt to reduce parasite infestation in lambs.

“There is no silver bullet which farmers can use to avoid the effects of parasites altogether,” says AgResearch Science Group Leader for Animal Nutrition and Health, Dr Ian Sutherland. “However they can reduce their losses considerably.

“To reduce selection for resistance we need to kill as many resistant worms as possible. This might seem obvious, but it requires farmers to know the resistance status of the worms on their property. It also needs them to use products with the best chance of killing those resistant worms; this means using combination products containing more than one drench type.

“In a world-first, we have published experimental proof that combination drenches not only provide better worm control, but actually delay the development of resistance.”

A second management strategy farmers should utilise is ‘refugia’. This can be difficult to understand at first as it means allowing stock to graze pastures contaminated with parasites. However, the secret is to make sure these parasites have not all been exposed to drenching and are therefore less likely to have resistance genes.

The result is that any parasites which survive treatment are quickly diluted by susceptible worms picked up from the contaminated pasture. Without this dilution factor, the only worms able to breed are resistant to treatment.

Dr Sutherland stresses that neither of these recommendations be used in isolation.

“Using combination drenches without ensuring adequate ‘refugia’, will eventually result in resistance developing to even the most effective drench. However, used together, they can significantly minimise the development of resistance and ensure the sustainability of worm control.”

Less research has been conducted into drench resistance in cattle parasites. This is despite losses estimated at $400M per annum in productivity losses and cost of control. Dr Sutherland says there are two major issues in the control of cattle worms. One is effectiveness of treatment and the other is resistance – two different but inseparable issues.

Recent AgResearch trials have established that a drench delivered orally was significantly more effective than the same molecule administered as a pour-on or injectible.

“The bottom line is that farmers may be spending considerable sums on treatments which are simply not working effectively,” says Dr Sutherland.

“Our advice is where practicable to use oral drenches, which have been shown to be more effective than the other two options.”

The second issue is drench resistance. The national survey mentioned earlier also measured resistance in cattle parasites, and established it was almost universal. At that time, the problem was largely confined to a worm species regarded as not particularly damaging. Recent research by the AgResearch Parasitology Team has, however, recorded resistance in the Ostertagia worm, a species regarded as extremely serious, and which can cause significant damage and death in cattle.

“The potential significance of this development cannot be underestimated,” says Dr Sutherland. “It is early days and there is much to learn about resistance in cattle parasites. However, we need to address the issue urgently, and hopefully make similar progress in developing recommendations for sustainable parasite control as we have in sheep.”

An estimate of the economic impacts of sheep sector parasite control scenarios proposes that use of strategic combination drenches and high efficacy drench programmes in lambs could decrease the impact of current anthelmintic-resistant parasites and return revenue gains (from prime lamb production) on a per farm annual basis of between $6,900 to $8,600 (this includes some animal health cost savings).

On a national sheep level, this would translate to an additional $73 to $91 million per annum in lamb revenue at farm-gate.

Some 3.3 million young cattle are reared and grown each year (beef and dairy), producing an annual gain in ‘livestock value’ of the animals to yearling age of about $1.5 billion. Even small percentage gains due to effective parasite control would be significant.

In dairy cattle, parasitic impacts on dairy heifers meeting calving target liveweights lead to productivity losses, conservatively estimated at $25 million per annum nationally.

Total project investment from 2007-2012 was $9.4 million from the Ministry of Business, Innovation and Employment, the Ministry of Primary Industries’ Sustainable Farming Fund, Beef + Lamb New Zealand and industry partners.