Cattle infected with parasites can cause serious production losses and at times welfare problems.

Farmers have become accustomed to being able to control worms and other parasites with drenches, so the true significance of these parasites can be forgotten.

With increased stocking densities and intensive grassland management, parasite control can be difficult if not managed correctly.

Drench resistance is already a problem, not just for sheep but it is becoming a problem in cattle. So, what do we need to know to have maximum impact at minimum cost?

The major parasites that cause problems in cattle are the ones that live in the animals' stomach and intestines often called worms or Gastrointestinal (GIT) parasites.

The parasite life cycle commences when the adult female worm, living in the animal, lays an egg which is deposited onto the pasture.

The egg then goes through three stages to the infective larval stage which is eaten by the animal.

Once inside the animal, the larvae then matures to become an adult or in the case of the brown stomach worm development can be inhibited to mature at a latter date.

Usually this cycle takes around thirty six days but it can vary due to climatic conditions at pasture level and the animals own immune system or current worm burden.

The larvae are picked up from the contaminated pasture during grazing and as there is no way of controlling the eggs or larvae on the pasture we need to reduce pasture contamination and availability to the animal.

Drenching should not just be directed to control worm burdens in the animal; more important is the contamination on pasture.

Control it, and a more complete control of gastro intestinal worms in cattle is ensured.

Basic considerations must be directed towards sound animal management with good nutrition of paramount importance.

Knowing your stock; keeping track of their production gains and being alert to seasonal factors that enhance parasite build up on the pasture (temperature, moisture, grazing history, pasture height, stocking rate, etc) will assist with planning an effective parasite control programme, which may change from year to year.

Ways to reduce pasture contamination include rotating pastures, preventing overcrowding and overgrazing and providing good quality pasture, hay and supplements and using an effective drench at the right time.

Weaners and yearlings are the most susceptible to worm burdens and symptoms can include poor growth rates, rough coats, scouring or bottle jaw. These animals should be drenched and placed onto good quality pasture.

Yearly drenching of adult cattle is often not necessary as this class of animal has developed some immunity and the effects of worms on well-fed adult cattle are usually minimal. These animals can be drenched to reduce the amount of pasture contamination but you should also look at the time of year, pasture availability and climate.

Measures to prevent resistance in cattle to drenches used to treat parasites parasite include:

• Treat all incoming cattle with the latest class of drenches (Avermectins/macrocyclic lactones (ML) plus levamisole.

• Keep cattle in yards for 48 hours before turning out onto contaminated pasture.

• Do not try to maximise production by keeping animals 'worm free'.

• Only treat weaners and yearlings, unless it is essential to treat older animals on health grounds.

• Use different pasture each year for calves.

Until the animal matures, worms will cause problems but if you offer good quality pasture to this class of animal drenching requirements will be minimised.

Dr Mike Jeffers is a senior veterinary officer for cattle with the Victorian Department of Primary Industries in Geelong. For further information visit www.dpi.vic.gov.au