Managing Internal Parasites in Cattle

Internal parasites pose a significant challenge to any cattle operation by affecting production and animal welfare outcomes. The annual cost of internal parasites to the Australian cattle industry is estimated at $19.7M in northern Australia and $99.9M in southern Australia, based on prevention and production costs1.  

The first step toward effectively controlling these parasites begins with understanding what parasites your herd might be at risk from.  

Understanding the Common Internal Parasites in Cattle

The types of internal parasites present are largely influenced by climatic zone and rainfall. The major parasites of concern in northern Australia include Barbers Pole worm (Haemonchus placei), Nodule worm (Oesophagostomum radiatum) and Small Intestinal worm (Cooperia punctata and C. pectinata). In southern Australia, the common internal parasites affecting cattle include the Small Brown Stomach worm (Ostertagia ostertagi) and Liver Fluke (Fasciola hepatica), along with Black Scour worm (Trichostrongylus axei) and Small Intestinal worm (Cooperia oncophora). 

The small brown stomach worm (Ostertagia ostertagi) in one of the most important roundworms and can significantly impact production efficiency in young and young adult cattle2. If present in mixed infections with small intestinal worms (Cooperia species) and nodule worm (Oesophagostomum radiatum), the impact of this worm is increased. Ostertagia is common in temperate, high rainfall and winter rainfall areas of southern Australia2 and can compete their lifecycle in as little as 21–28 days under ideal conditions. The severity of infection is increased if infective larvae arrest and become ‘inhibited’ in small nodules in the stomach wall, often during late spring and summer. The inhibited larvae resume development when environmental conditions for egg hatching and larval survival on pasture are more favourable, typically in the following autumn. Mass re-emergence of inhibited larvae causes type II ostertagiasis, which is severe and can result in weight loss, diarrhoea and death3.  

Liver fluke (Fasciola hepatica) is an important parasite of cattle grazing in wet areas, where the intermediate host is present. This environment suits the hatching of fluke eggs into free-swimming larvae and provides a suitable habitat for the intermediate host, an aquatic snail. For this reason, liver fluke infections are prevalent in higher rainfall (>600 mm per annum) areas or irrigated areas of NSW, Victoria and Tasmania, as well as some regions in south-east Queensland and South Australia2. It does not occur in Western Australia and quarantine requirements are in place to prevent its introduction. Liver fluke can cause both acute (sudden onset) and chronic (long-term) disease3. Chronic disease is more common in cattle and is associated with fibrotic damage to the bile ducts of the liver where the adult flukes live. This can result in a gradual loss in condition and compromised weight gain, anaemia and decreased milk production, as well as downgrading of infected livers at slaughter2.  

We recommend visiting the MLA Cattle Parasite Atlas for further information on the most important parasites in your region. 

Prevalence of Internal Parasites 

The prevalence of internal parasites is influenced not only by temperature and moisture, but grazing system and paddock management. Higher worm levels are promoted under high stocking rates, especially in high rainfall areas where larval survival is favoured, and particularly on ‘cattle only’ properties. 

Susceptibility of Cattle to Internal Parasites 

The susceptibility of the cattle host is largely influenced by its immunity and genetic factors. For gastrointestinal worms, young cattle are particularly susceptible, including weaners, yearlings and those under two years of age. Of these animals, most of the impact from worms is likely to occur in the first six months post-weaning when immunity is not fully developed.   

In adult stock, cattle are more susceptible when immunity breaks down due to periods of stress or hormonal changes. This includes nutritional or metabolic stress during pregnancy or lactation, particularly for first-calf heifers. Bulls tend to be more susceptible to infection as well. Generally adult cows maintained in good body condition will develop and maintain immunity to worm infections.2  

On the contrary, cattle do not tend to develop immunity to liver fluke2. As such, any cattle grazing pastures where the intermediate snail host could inhabit are at risk of fluke infection. 

Managing Internal Parasites in Cattle 

An integrated approach is important in managing internal parasite infections to ensure effective control. Good grazing management can decrease the reliance on chemical controls and include rotational grazing, spelling of paddocks, reducing stock intensity, alternating grazing by stock of differing susceptibility i.e. adult cattle or sheep, and improving the nutritional status of your herd. Preparing a number of safe, low worm-risk pastures for more susceptible cattle is also recommended4. For liver fluke, fencing off high-risk wet areas and improving drainage in paddocks are also good practices. 

Producers have a large array of anthelmintic treatments available to them to assist in controlling internal parasites. The choice will be governed by which parasites you need to target, the resistance status of the parasites on your property, and preferred application mode – be it an oral (e.g. Fasimec™ Cattle Oral), backline pour-on (e.g. Baymec™ Pour-On) or injectable (e.g. Bomectin™ Injection) formulation. It’s recommended these treatments are used strategically, rather than reactively, for effective parasite control. For a best practice strategic treatment program in your area, refer to

Monitoring the level of worm burdens and where appropriate the presence of liver fluke through diagnostic testing, is also good practice for guidance on the requirement for drenching. The timing of drenching around high-risk periods and management events, such as weaning, should also be considered. 

Drench resistance is present in some herds, so it is recommended producers check the effectiveness of their drenches by conducting a faecal worm egg count reduction trial. This will determine the drench resistance status of worms on your property and provide guidance on the drench classes (e.g. macrocyclic lactones (ML), benzimidazoles (BZ), levamisole) and actives within each class that may be able to be used effectively on your property. In southern Australia, resistance to ivermectin and other single active drenches is increasingly recognised, so understanding your drench resistance status is even more important when selecting your drench. The use of combination products is considered best practice in delaying the development of drench resistance. 

It's also important to prevent the introduction of new or resistant worms onto a property by treating all incoming stock with a quarantine drench and confining them to a quarantine paddock to allow time for treated worms to die and to ensure eggs from resistant worms are not spread around your property. A quarantine drench should be a multiple active treatment, containing two or more unrelated actives4

For further advice on Elanco’s cattle parasite solutions, contact your local Elanco representative to get started.  

1 Shephard et al. (2022) B.AHE.0327: Priority list of endemic diseases for the red meat industry — 2022 update. MLA.  

2 Paraboss – Wormboss (2022) Accessed August 2022.  

3 MLA (2005). The Cattle Parasite Atlas. 

4 DPI, NSW (2017). Cattle worm control in NSW. Primefact 419, 2nd edition.