Get on top of worms

Worm infection costs the Australian sheep industry an estimated $436 million per year, most of which comes from lost production. One of the predominant sheep health issues of the past few years has been worms.

The life cycle of the worm involves both your pasture and the animal. Whilst an effective drench temporarily fixed the animal problem, the conditions of the past few years has meant worms survived in the environment. In time, paddocks that were clear of worms became scarcer meaning newly drenched animals quickly became reinfested with worms. The forecasted hot, dry summer may provide an opportunity to address this issue.

Strategic summer drenching involves an effective drench at the beginning and end of the season. This is to take advantage of the destruction of worm larvae on pasture by heat and lack of moisture. Drenching is expensive and time consuming therefore pre drench faecal egg counts (FECs) should always be considered as this will put some science and evidence into whether to drench.

Furthermore, ineffective chemicals and/or an inadequate drench procedure can reduce the effectiveness of summer drenching. FECs following drenching can also provide information of how effective treatment has been thus providing information about possible drench resistance. Worm resistance, particularly to the white and clear drenches, is common in Victoria and unnecessary overuse and the incorrect use of drenches just add to the problem.

After drenching, you should try to put your sheep onto low-risk pastures. These may be paddocks previously grazed by cattle, cut for hay or silage, or grazed by low-risk sheep such as older wethers. Large reinfestations of worms can occur in as little as three weeks if your drenching program is ineffective.

WormBoss, is a website which deals with all facets of worm control in sheep and goats in Australia and provides several tools to assist with decision making including a regional Drench Decision Guide. The regional Drench Decision Guide is available both as a step-by-step online tool or as a decision tree, which can be printed. The regional Drench Decision Guide asks questions, and the answers you provide help it produce an advisory report.

The first question relates to whether your sheep are showing clinical signs of worm infection with scouring and/or weight loss being suggestive of the scour worms, and anaemia and lethargy being suggestive of Barber’s pole worm.

The second question relates to whether the sheep are lambs or weaners since weaners are amongst the most susceptible sheep to the effects of worms due to their low immunity, and their worm control needs to be managed strategically at critical times. The third question relates to whether the sheep are rams at the point of joining since the stress of joining lowers immunity and the potential for build-up in worm numbers.

The final question covers all other scenarios and includes ewes at the point of lambing in which worm control is important since pregnant ewes often suffer a breakdown in immunity to worms at around the time of lambing for up to two months after lambing. It also includes the months of November/December and January/February, which are typically the times of the first and second summer drenches respectively. These drenches are important in reducing worm numbers the following winter but also potentially increase the risk of drench resistance.

In each scenario, the regional Drench Decision Guide will give management advice related to that scenario and drench advice based on the results of worm testing. Effective worm control can be a complex subject so in addition to the guides and tools that WormBoss provides it is recommended that you seek advice from your veterinary advisor.