Summer drenching – preparing your winter pasture

Summer drenching is vital in minimising the level of larval pasture contamination responsible for winter worm burdens in southern Australia.

The use of a first summer drench is still recommended best practice in the winter dominant and uniform rainfall regions of Australia^1,2. The aim of summer drenching is to remove the worms in the sheep when the numbers of infective larvae on pasture are low or in decline (due to summer weather conditions). This reduces the number of infective larvae on pasture the following winter, thereby reducing the production cost of worms and number of drenches needed at this time.

The predominant worm species of these winter rainfall regions are the black scour worm (Trichostrongylus spp.) and the small brown stomach worm (Teladorsagia spp.). These typically cause problems over the autumn and winter period when favourable conditions and susceptible livestock allow for a significant buildup of infective larvae on the pasture. Research shows that a significant portion of infective larvae responsible for winter infections are deposited on pasture during summer by adult worms present in the sheep⁴. 

The control of these worms over summer will significantly reduce the pasture larval burdens responsible for winter outbreaks. Effective summer worm control programs also reduce the reliance on long-acting drenches later during the lambing season.

Lambs that have reduced worm larval challenge have greater growth rates than lambs with a high larval challenge, even when drenched regularly. Setting up pastures that enable healthy, productive lambs is a summer job. 

Which drench to use

The summer drench of choice is one that:

• Has an efficacy, as close to 100 per cent as possible – any worms that survive this treatment will result in pasture contamination. A combination of highly effective actives in a triple drench such as TRIGUARD® is recommended best practice^2,3.
• Has a short length of activity - that will apply less selection pressure for resistance at a time when there is less refugia (the proportion of worms not exposed to the drench) on the pasture to dilute contamination from resistant adults. Persistent actives such as moxidectin are recognized for their potential to select more rapidly for resistance1, and this effect can be exacerbated during times when there is less refugia on pasture. 

When to summer drench

The timing of the first summer drench between regions is based on what is most appropriate for worm control and drench resistance management. WormBoss.com.au provides a number of recommendations for various regions regarding the timing of the first drench, but generally it is a few weeks after the pasture has senesced in late November/early December.

Timing of subsequent summer drenches is best indicated by worm egg count tests conducted routinely over summer. In non-endemic barber’s pole worm regions, testing should commence 4 to 6 weeks after the first summer drench and continue over the summer to ensure egg counts remain low. Summer rainfall will likely increase the need for subsequent drenches, but by following the above approach, both outbreaks of barbers pole worm and winter pasture contamination will be minimised.

This summer, prioritise a summer drench program to ensure healthy, productive sheep over summer and reduce the risk associated with severe worm infections in winter. TRIGUARD® is an ideal choice for summer drenching due to its combination of three actives and short length of activity. 

This article was written by Boehringer Ingelheim for Seasons magazine. 

Disclaimer – Important, please read:

The information contained in this article is given for general information purposes only, current at the time of first publication, and does not constitute professional advice.  The article has been independently created by a human author using some degree of creativity through consultation with various third-party sources.  Third party information has been sourced from means which Elders consider to be reliable.  However, Elders has not independently verified the information and cannot guarantee its accuracy.  Links or references to third party sources are provided for convenience only and do not constitute endorsement of material by third parties or any associated product or service offering.  While Elders has exercised reasonable care, skill and diligence in preparation of this article, many factors including environmental/seasonal factors and market conditions can impact its accuracy and currency.  The information should not be relied upon under any circumstances and, to the extent permitted by law, Elders disclaim liability for any loss or damage arising out of any reliance upon the information contained in this article.  If you would like to speak to someone for tailored advice specific to your circumstances relating to any of the matters referred to in this article, please contact Elders.

References:

1. WormBoss 
2. Love (2007) Sheep worm control: summer vs winter drenching in southern NSW. DPI Prime facts 
3. 3Love (2007) Sheep drench combinations, resistance and ‘refugia’. DPI Prime facts
4. Anderson (1983) The availability of Trichostrongylid Larvae to Grazing Sheep after Seasonal Contamination of Pastures.