Effective worm control may sometimes require pre-emptive (‘strategic’) treatments to prevent the contamination of pasture with worm eggs in the dung, ahead of times of the year when worm populations begin to increase rapidly. Preventing the development of large worm populations reduces the need for more frequent treatment at other times of year, reducing both the cost and effort of worm control and the development of drench resistance.
An example is in winter rainfall regions, where worm populations are at their lowest during the hot and dry summer period, and increase after seasonal rains in autumn. Ensuring that few worm eggs are deposited onto the pasture from early autumn onward has been shown to limit winter worm burdens in young stock, thus preventing the signs of disease and significantly reducing production loss.
Strategic programs have been developed for most cattle-grazing regions of Australia and are based on research to define the seasonal patterns of worm development, and the relative benefits of strategic treatments. Click on this link to go to the WormBoss annual program guide.
However, strategic drench treatments have a strong potential to increase the level of drench resistance, as any resistant worms that survive these treatments are the source of populations in the next few months. Treatments should therefore be kept to the minimum necessary, and only to the classes of cattle which will benefit most. In general, strategic treatments to cattle (as opposed to in sheep) are usually necessary only in younger age groups, as the strong immunity to worms seen in adult cattle, especially cows, reduces the likelihood of significant worm disease or production loss.