Hampton Veterinary Centre Hampton Veterinary Centre Hampton Veterinary Centre


Gutworms in Cattle

Gutworms are ubiquitous – any pasture that has ever been grazed will be a risk. The most important worms in cattle are Ostertagia and Cooperia.

Their primary effect is poor growth, with or withoutdiarrhoea. Ostertagia lives within the abomasal wall (4thstomach) and their emergence causes a reduction in dry matter intake, even if there are no clinical signs of worms. Although primarily affecting younger stock, there is increasing evidence that an ostertagia burden in adult cows can significantly lower dry matter intake.

Cooperia lives within the small intestines and particularly affects young animals out for their first grazing season.  

Diagnosis can be through faecal sampling of groups of animals to look for worm eggs, however poor growth rates in a herd of youngstock on good grazing can only really be attributable to a parasite burden – even if there is no diarrhoea.

Ideally calves should grow at 0.75 kg per day – if they are not achieving this, worming should be considered.

Other high risk factors to consider when assessing the parasite burden of your animals include:

  • Sward height– less that 4cm is high risk
  • Grazing history– if it has been grazed by youngstock within the last year
  • Previous worming history– most wormers only last 8 weeks 

Acquired immunity to gutworms can be slow to develop. In particular, it can take 2-3 years for animals to become immune to Ostertagia. Immunity often wanes over winter when animals are housed as they are no longer exposed to the worms. This can mean that they are susceptible to reinfection in their second grazing season. This should be considered if this age group are lacking in condition.

Treatment of intestinal worms is pretty straight forward – all wormers should be effective: Choice of wormer really depends on management.

Many people use the Autoworm® pulse-release boluses. These release the wormer every three weeks, allowing the animal to build up its immunity in the gaps between. 

Other worming options include pour-ons, drenches or injections and the choice is really a personal preference. However, make sure you read the data sheet for details of how long each product lasts to ensure your animals are covered.  

Blowfly Strike

Blowflies are the most common external parasites found on sheep with over 80% of flocks affected each year. Flystrike will affect any species of animal if the conditions are right.

The female flies are attracted to decomposing matter on the animal, such as wounds or faeces. Each female lays up to 250 eggs which hatch after 12 hours. The odour from the initial “strike” attracts other flies causing a rapid increase in fly larvae (maggots). When the maggot population become overcrowded, they start to attack the living tissue of the sheep.

The first signs in a sheep are patches of discoloured wool with a foul smell and agitation. This quickly leads to nervous signs, recumbency and toxaemia.

The high risk period for blowfly strike is between May and September. The disease can easily be prevented by applying an anti-ectoparasite product at the start of this period.

The longest acting preventative is CLiK® which lasts for 16 weeks so will cover the whole at risk period. This is sprayed directly on to the fleece.

Good management will also help prevent problems:

  • Daggingto remove faecal soiling
  • Treat scour
  • Dock tails
  • Treat and prevent footrot
  • Dispose of carcasses


The best product to treat blowfly strike is Coopers Spot-on® as this can be directly applied to the wound to kill the maggots. The area should be clipped and cleaned and any maggots removed. The animal may also need treatment with antibiotics depending on the severity of the strike.