Worm Management

Overview

The Australian climate can be broadly classified into three broad zones, namely arid, tropical/sub-tropical and temperate. This sub-division is useful for the purpose of discussing the epidemiology of worm parasites disease of cattle, because the presence of parasite species, their economic importance, cattle management and worm control programs will differ between zones.

Worms

Major parasites in northern Australia include, barbers pole worm (Haemonchus placei), nodular worm (Oesophagostomum radiatum) and small intestinal worm (Cooperia punctata and C. pectinata). In southern Australia the major parasites are small brown stomach worm (Ostertagia ostertagi) and liver fluke (Fasciola hepatica). Other parasites include black scour worm (Trichostrongylus spp.) and small intestinal worm (Cooperia spp.)

Grazing Management

Dung pats can provide shelter for worm larvae for several months, even in very dry conditions. Therefore, paddocks continually grazed by young cattle in autumn and winter can become highly contaminated with worm eggs and larvae. Particularly in higher rainfall areas, it is important to prepare a number of “worm-safe” pastures so that young susceptible cattle can be moved every few months to paddocks with fewer worm larvae. It should be a goal to graze weaners from early August onwards on the least contaminated pastures available.
Monitoring the level of worm burdens and where appropriate the presence of liver fluke with a worm test is good practice. This can help make decisions as to whether a drench is required.

However worm tests are less reliable in adult cattle than sheep. In yearling cattle that appear to be “wormy” but have a low egg count, it is possible to use a “diagnostic drench”, by drenching a sample of the cattle and monitoring their response to the treatment.

Rotational grazing with cattle on a 6 monthly rotation will also help control parasites in both species.

Treatment Program

The ML (macrocyclic lactone) group of drenches are usually the most suitable treatment , especially where it is important to remove the larval stages of Ostertagia in late summer or autumn. As levamisole based drenches are ineffective against the inhibited stages, they are mainly used in northern areas of the country. Although some benzimidazole (BZ) drenches have a label claim for control of “arrested” stages of Ostertagia, the ML drenches are more reliable in this regard, and simpler to administer using the pour-on or injectable route of administration. A routine worm control program is useful, especially in high and medium rainfall areas.

In general calves should be drenched at weaning with an ML or BZ drench. If using a BZ drench, a follow-up drench one month later may be useful on farms with a worm problem. Similarly if egg counts are high and additional drench may be required in late autumn. In some herds two year old/ first calf heifers may also require treatment. In areas where Type II Ostertagiosis may occur a late summer –early autumn treatment is recommended. Additional treatments for liver fluke, usually given in late autumn (April/May) to control immature fluke and again in the spring to control adults and reduce pasture contamination are necessary where this parasite is present.

Adult cattle develop a solid immunity by 2 years of age and under normal circumstances cows do not require treatment. However bulls suffer more from parasitic diseases and a routine summer-autumn treatment is advisable.

A quarantine drench is recommended when new stock are introduced to the farm.