Effectiveness of Long-Acting Drenches

A two-year trial undertaken on 8 commercial sheep and beef farms in the Wairarapa looks at the cost effectiveness of long acting drenches.

Parasites are among the most important animal health issues concerning sheep farmers in New Zealand. Farmers invest considerable money and effort to minimise the losses parasites cause. The use of anthelmintics is an important component of worm control for the majority of sheep farmers, however the sustainability and cost-effectiveness of anthelmintic use is threatened by the development of resistance on the majority of New Zealand sheep farms.

One of the practices shown to increase the development of resistance is the use of long acting drenches to adult ewes around lambing time.

The justification for this use appears to be a widespread perception amongst farmers that use of these products will reliably return significant production benefits to both the ewe and her lambs.

This trial aimed to test that belief and see if there were significant economic benefits.

The project was funded from a range of sources – both local and national – to a total of $650,000. Sustainable Farming Fund chipped in $255,000 and the rest was contributed by host farmers, Beef & Lamb NZ, Landcorp, Ravensdown, AGMardt, local vet Keinzley AGVet, and Baker & Associates.

The main trial looked at capsule use and involved 2300 adult sheep and their lambs on 8 commercial farms over two years. Detailed measurements of production variables were carried out through until mating.

The trials include monitoring of whole-farm management practice on each property throughout the duration of the trial. Farm management software was used to look at background feeding, pasture and stock management and the environment that the trial was conducted under.

The trials looked at the link between faecal nematode egg count, body condition

score, liveweight (LW) and other farm production measurements and responses to anthelmintic. They also looked at the carry-over effects of liveweight advantages at weaning to the pre-tupping stage

A total of fourteen trials were carried out, 8 in 2012 and 6 in 2013 on farms in the Wairarapa.

The farmers did a lot of the on-farm work with assistance from scientists and local vets and consultants. Lambs were tagged at birth, which helped the scientists gather information on lamb survival and total weight of lamb weaned per ewe treated.

The results of the trial showed that there is a high variability in the benefits. Dave Leathwick from AgResearch Grasslands says that is significant because this trial has come closer to representing actual commercial conditions than any other that has been done. He also points out there had been little NZ scientific trial work on this area for the last few decades.

Overall he says there’s little in the trial to give any indication of an economic benefit to farmers who use these drenches. He says the variability of response, and the fact that benefits are often negative, was significant given the high proportion of farmers who routinely use these products and the widespread perception amongst farmers that they consistently deliver worthwhile benefits.

The high degree of variability in response measured in these trials casts a lot of doubt on the certainty of achieving an economic return from any of the treatments studied.

Those involved in analyzing the results say that for a farmer, balancing the increased risk of developing resistance through the use of a long acting ewe treatment is difficult enough when there is an assurance of significant benefit. However, if there is a reasonable likelihood of there being only minimal response from use of a long-acting treatment, then the cost-benefit becomes even more dubious when there’s the potentially very high cost of accelerating drench resistance within the flock.

The published results of the trial conclude with this statement : 

We have still got a lot to learn about how some farms appear to either achieve a lower parasite challenge in their ewe flocks, or manage their flocks in such a way that those sheep are able to exhibit greater resilience in the face of a parasite challenge over the spring. 

We have not been able to correlate management factors such as feed cover and pasture management directly with treatment responses, but we have some valuable leads that will be pursued in a separate piece of research.

Eketahuna farmers Royden and Kate Cooper converted from dairying to sheep and beef in 2003.  Royden used to milk cows but wasn’t enjoying the lifestyle and didn’t have the scale to employ a sharemilker..

When the next door sheep and beef farm came up for sale, they took the plunge, sold their cows and shares and bought the new farm. The lease land has since been added and, with another 80ha they bought in 2007, they now run 3300 ewes and 400 cattle.

Royden was part of a group of farmers that hosted Dave Leathwick at a discussion group about drenches and parasites held in Eketahuna. It was this discussion group that led Dave, Chris Garland from Baker and Associates and a group of other interested parties to seek Sustainable Farming Fund support for the drench project.

Royden was one of the farmers who put their hand up to be part of the trial. He said one of the questions he wanted answers to was “Am I missing out on production by not using these drenches?” He said the trial involved a lot of extra work but he was pleased to be engaged with it.

On the basis of the trial results he’s not planning on changing his management to include controlled release capsules or long acting drenches.