All indications are that we’ll likely experience a drier summer this year. This will greatly assist us in our management of worms, keeping in mind that the worms in the animals are still producing eggs and these will hatch when conditions such as moisture and heat are right.
It is important to keep monitoring the sheep’s worm burdens by doing regular worm egg counts (WECs) and treating them when required.
The summer drench is a strategic drench which aims to reduce the worm population using the dry summer heat. Summer drenching is a common practice in regions which have uniform or winter rainfall – such as Victoria, Tasmania, much of New South Wales, and the southern parts of South Australia and Western Australia. The goal is to lower the number of worms that are present in the following autumn and winter, as the dry hot weather reduces the amount of viable worm eggs and larvae on the pasture.
If not done correctly, one of the dangers associated with this practice is the selection for drench resistant worms. Any worms that survive the summer drench, can be carried by the sheep over the summer period into autumn, where they contaminate the pasture with drench resistant worm eggs that then develop into infective larvae. It is really important then to use an effective drench (ideally greater than 98 per cent effective). In many cases this would be a combination drench like Tridectin, containing three broad spectrum actives and the only three-way drench that contains moxidectin. Its export slaughter interval (ESI) of only 17 days provides flexibility if destocking is required. Always consider doing a worm egg count 10 to 14 days after drenching (Drench check) to monitor the efficacy of the drench used.
The timing of the summer drench is not a set date or management event like other strategic drenches such as the pre-lambing drench and the weaning drench. Drenching occurs when the weather conditions are no longer suitable for worm egg development and larvae survival. This is when the days become consistently hotter, the humidity drops and the pasture begins to hay off. For many areas, this can start as early as the first week of November.
Nature doesn’t closely follow a script though. Should conditions favour the development of infective larvae (rain and heat) the flocks should be monitored by doing worm egg counts (WECs), starting about two weeks after the rain event. Should a second summer drench be required, consider a different combination drench to the one used as the first summer drench.
To ensure continued profitability over the next few seasons, the summer drench is a critical consideration for any sheep producer.