Deworming your herd

Worms present a significant production threat to grazing cattle with infection costing the industry a lot of money every year. The main worms affecting cattle are stomach, gut worms and lungworms commonly termed roundworms (nematodes) and tapeworms (cestodes).


Types of worms that can affect your herd

  • Roundworms: Roundworms are cylindrical and vary in length from a few millimetres to several centimetres. They parasitise the small intestine, large intestine, stomach and lungs. Generally they are host specific, i.e. sheep nematodes do not infect cattle. Exceptions are the Barbers Pole Worm and the gut worm Nematodirus battus which can affect either.
  • Stomach worm: In cattle, brown stomach worm (Ostertagia ostertagi) is by far the most important worm. Disease only occurs in first and sometimes second season grazing stock as immunity is developed over this period. Two types of disease occur; Type I during the summer, as larvae are picked up from the pasture and Type II in early spring when arrested larvae re-emerge from their dormant state in the abomasal wall. Symptoms of the two types of disease are very similar.
  • Lungworm: Lungworm is more serious in cattle than in sheep. In endemic areas, first season cattle can be vaccinated prior to turnout.
  • Tapeworms: adult worms and live in the small intestine with the head attached to the intestine wall. Segments are shed in the faeces thirty days after infection in quite long chains. Immunity develops rapidly and, although diarrhoea and unthriftiness can be associated with tapeworm, generally clinical and economic losses are minimal.

Life cycle of worms

Factors affecting infection levels on pasture

  • Worms present: Some roundworms produce thousands of eggs daily, others only a few hundred.
  • Stock management: Higher stocking rates produce greater contamination, especially in the right conditions for egg or larval development, such as the spring and summer.
  • Immune status of animals: The influence of stocking density will be greatest if all the stock are fully susceptible, or if the ratio of susceptible to immune stock is high.

Symptoms of animals with worms

As a cattle owner, you need to recognize the symptoms of worms in your cattle so that you can alert your vet to medicate your herd and prevent serious worm problems from developing. A regular worming schedule can protect your cows from developing a significant

  • Low Productivity: Worms are parasites that feed off of your cows’ bodies, draining nutrients out of your animals. Because your animals with worms are not getting the full benefit of the nutrients that you give them, they will grow more slowly and produce less milk and smaller calves.
  • Poor Body Condition: Animals that have worms tend to be in poor physical condition. Cows may be thin, have ribs showing and have a generally poor appearance. Their coats often appear dull and unhealthy. Cows with worms often continue to look poor even when you provide them with additional nutrition because the additional feed is going to the worms rather than actually benefiting the cow.
  • Assorted Physical Symptoms of Worms: Animals with worms often have diarrhea. They may be dehydrated as well as experience problems consuming and digesting their feed. Animals with severe worm infestations may become significantly lethargic (drowsiness) or even die as a result of their poor physical condition.
  • Anemia and Bottle jaw: Anemia is a common problem caused by parasites (Barbers pole worm) that drink the animal’s blood, including worms and ticks. Over time, the animal can lose enough blood that it becomes anemic.
  • Lung worms cause coughing and unthriftiness

Controlling worms

The aim of any worm control strategy is to prevent the exposure of young susceptible animals to high levels of infestation on pasture in the second half of the grazing season. This can be done using:

  • Immunity and nutrition: Well-fed animals develop immunity faster and are better able to expel parasites and to withstand the effects of those that remain. Young cattle are most susceptible to worms, but usually develop useful immunity by around 20–24 months.
  • Use of low risk pasture/clean grazing: Dung pats can provide shelter for worm larvae for several months, even in very dry conditions. Therefore, paddocks continually grazed by young cattle in autumn and winter can become very wormy.
  • Wormer treatments
  • Integrated systems incorporating strategies 1 and 2

NB: However control of roundworms by clean grazing alone is impractical on many farms, due to lack of available clean grazing. Wormer [anthelmintic] treatment is often necessary.

When to dose cattle

Mature cattle may be relatively immune to worm infections, although there has been work to show that worming adult cattle at certain times of the year can be beneficial for production. Discuss with your vet or prescriber how this may affect your farm.