Parasites worm their way in

They are divided into nematodes (round worms), cestodes (tapeworms) and trematodes (flukes) and are assigned to one of these groups according to their structure.

Worms in the same group tend to have similar life cycles. The nematodes are the most economically important internal parasite of cattle. Tapeworms play a minor role and flukes can cause significant economic losses in some geographic areas.

Nematodes (round worms)

The small brown stomach worm, Ostertagia ostertagi, penetrates the lining of the abomasum (fourth stomach) causing severe damage and inflammation.

Infected heifers can be anaemic, have scours, are off their feed and lose weight. Cattle up to 18 months old can be affected.

This parasite can enter an ‘arrested phase’ of its life cycle which can then resume three to nine months later. This type of disease can cause significant losses in young heifers as the worm larvae emerge.

The barbers pole worm, Haemonchus placei, thrives in northern NSW and Queensland where there is summer rainfall. This blood sucking parasite also lives in the abomasum and causes severe anaemia and loss of protein.

This results in the characteristic ‘bottle jaw’ appearance with affected cattle being weak and slow to move.

The stomach hair worm, Trichostrongylus axei, is the last of the common abomasal round worms. It also damages the lining of the abomasum causing inflammation and reduced absorption of nutrients. The stomach hair worm is often diagnosed in mixed worm burdens and exacerbates the severity of an infection.

The main species of small intestinal worm affecting cattle is Cooperia spp. These worms are often present in mixed infestations. Affected animals will have diarrhoea, poor weight gain and lack of appetite.

Trematodes (flukes)

Both the liver fluke, Fasciola hepatica, and the stomach fluke, paramphistomes, require a particular type of aquatic snail to complete their complex life cycle. For this reason cattle become infected in only certain regions of Australia where these snails exist.

Liver fluke infection results in significant liver damage which causes irreversible scarring. Signs of liver fluke include poor appetite, weight loss, ‘bottle jaw’, anaemia, jaundice and death. Contact your veterinarian to find out if liver fluke is present in your area.

Cestodes (tapeworms)

These worms are long and segmented, measuring up to 6 metres in length. They commonly live in the small intestine but do not usually have any adverse effect on the animal.

Heavy worm burdens may compete for nutrients and lead to poor weight gain. The main concern with tapeworms in cattle is from a human health perspective as cattle can be an intermediate host in the life cycle of the human tapeworm, Taenia saginata.

This is not commonly diagnosed in humans but remains an important zoonotic disease across the world.

What is the impact of gastrointestinal worms in cattle?

The signs of gastrointestinal worm burdens include weight loss, ill-thrift, diarrhoea and dehydration. Research has shown that even low-level infections can have a negative effect on productivity in dairy replacement heifers.

These heifers may not show overt clinical signs and thus are described as having ‘subclinical’ infestations. They may have a suppressed appetite and reduced productive grazing behaviour, leading to reduced feed intake and growth.

Worm larvae cause a significant immune response which can lead to chronic inflammation and gut hypersensitivity. Young, growing heifers are highly susceptible to gastrointestinal worms and the production losses in this group of animals will be the greatest.

If there has been sustained exposure to worms, adult cattle will generally develop good immunity by 18 to 20 months of age.

This article has been adapted from an original article printed in Dairy News Australia, September 2017.