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Weight Loss

High Cost, High Impact

  • Internal parasites are estimated to cost the Australian cattle industry $93.6 million per year!1
  • There are many different species of gastrointestinal worm that can affect cattle in Australia. 
  • Certain species have a more significant clinical and economic impact than others.

Effects and Worm Cycle

Every region in Australia has a mixture of different worm types infecting cattle – it’s rarely just one species. Not only are mixed infections most common, they do more damage to the animal than single infections. For example, cattle infected with both Cooperia and Ostertagia worms can experience reduced daily weight gains to an even lower level than in cattle infected with either species independently1.

Internal parasites statistics


The impact of parasite infection on weight gain


Roundworms are the most common type of internal parasite for cattle across Australia.

The majority of roundworms live in the gut of the host animal, and it is these gut, or gastrointestinal roundworms that will be the focus of this module.

Gastrointestinal worms follow the same basic life cycle. Under ideal conditions, this life cycle takes between 21-28 days.

The Cycle of a Roundworm

Roundworm Life cycle

Step 1

All roundworms begin as eggs. These eggs are produced by female adult roundworms living in the gut of the animal.

Step 2

These eggs are passed out in the animal’s dung. Once on the ground, the eggs will hatch into larvae, given the right environmental conditions (sufficient moisture levels and a temperature between 10-35 degrees).

Step 3

The larvae develop and become infective.

Step 4

The infective larvae move onto grass in water droplets, where they can be eaten by grazing cattle.

Step 5

Once ingested, the larvae enter the gut of the animal and either develop into adults quickly, or they may stay in an “inhibited” stage until a later time. 

When the external conditions are “right” (i.e. favourable for worm survival) inhibited larvae develop into adults. For certain species of round worm this sudden development of large numbers of larvae into adults can cause acute illness and even death in the host animal.

Introduction to Cattle Worm Monitoring

Parasites can affect multiple organs 

Parasites can affect multiple organs


Trichostrongylus axei

Effects stomach lining and interferes with digestion.
Weight loss, poor digestion and diarrhoea.

Haemonchus placei

Sucks blood from stomach lining.
Weight loss, anaemia and death.

Ostertagia ostertagi

Destroys stomach lining, effects stomach acid production, digestive enzymes and mucus.
Weight loss, poor digestion, scours and feed intake.

Large Intestine


Burrows into intestine lining causing tissue damage and negative immune response.
Low feed intake, diarrhoea, weight loss, anaemia and low blood protein.

Small Intestine


Inflammation of the intestinal wall and stunting of villi impacting on digestion and absorption of nutrients.
Poor digestion, weight loss, diarrhoea and dehydration.

Cattle Internal Parasites & Best Practice Worm Monitoring

Small Intestinal Worm (Cooperia spp.)

Most prevalent worm genus/type across Australia and causes slow growth and lack of appetite. Different species of this worm occur in tropical and temperate regions

Cooperia spp. are the dose-limiting genera (i.e. hardest to kill) for all cattle drenches

Damages the lining of the small intestine, affecting nutrient absorption, fluid loss and mucous secretion

Usually appears as a mixed infection with other worm species, where it can magnify the damaging effects of the other species

Causes most problems in young calves as adults usually develop protective immunity.

Small Intestinal Worm

Small Brown Stomach Worm (Ostertagia ostertagi)

Small Brown Stomach Worm

Thrives in cooler, higher rainfall regions and is the most common cause of low growth rates and low feed conversion in these regions
Damages glands and reduces the animal’s ability to absorb nutrients from food
Known as the worm species that causes the most clinical disease:
    • Type 1 Ostertagiosis: Causes diarrhoea, weight loss, stunted growth
    • Type 2 Ostertagiosis: Causes acute illness and death
Most cattle develop immunity to Ostertagia by 2 years of age

Barber's Pole Worm (Haemonchus placei)

Thrives in warm, summer rainfall regions and is known as the “blood-sucking” parasite
Causes anaemia, protein and blood loss, weakness and death
Cattle carrying a heavy load of Haemonchus end up with swelling under the  lower jaw (bottle jaw)

Barber Pole

Stomach Hair Worm (Trichostrongylus axei)

Stomach Hair Worm

The site of infection is the small intestine
Found in temperate regions of Australia
Damages the lining of the small intestine, causing diarrhoea, fatigue and osteoporosis

Nodule Worm (Oesophagostomum radiatum)

Site of infection is the large intestine
Thrives in tropical and subtropical areas of Australia but still present in temperate regions
Damages the lining of the intestine, resulting in “nodules” in the intestinal wall
Causes loss of appetite, diarrhoea and anaemia

Nodule Worm

Cattle Faecal Egg Count Sampling and Culturing


1. Kloosterman A, Albers G, van den Brink R. Negative interactions between Ostertagia ostertagi and Cooperia oncophora in calves. Veterinary Parasitology. Vet Parasitol 1984; 15: 135–50. (for graph chart).

Further Reading

A Better Way To Buy