Worms in Cattle

Managing cattle worms at the farm level is a complex issue. It requires a sound understanding of the worm life cycle and the interactions between the worm, host, and environment. 

Symptoms of the Disease/Condition. 

There are two broad types of worms that can affect cattle: 

  • Gut worms (gastrointestinal): The three most important are Ostertagia ostertagi, Trichostrongylus axei, and Cooperia oncophora. Ostertagia and T.axei live in the 4th stomach (abomasum) and Cooperia lives in the small intestine. 

  • Lungworm: Dictyocaulus viviparous lives in the lungs and windpipe causing parasitic bronchitis. Very little is known about lungworm in cattle in New Zealand and the mainly pasture based systems which we run cattle in NZ probably accounts for why it is less of a problem compared to overseas where cattle are kept indoors for some or all of the year and lungworm is regarded as a serious parasite. 

The Impact 

The effects of parasitism are likely to be most severe and of greatest long term significance in the first year of life. These young animals have little or no acquired resistance to worms, have minimal reserves to draw on, and should be making maximal skeletal and muscular growth if their lifetime production is not to be impaired. 

There is little published work on the effects of worms in cattle in the second and later years of life. The Ostertagia worm can “hibernate” in the young animal and emerge later on resulting in clinical disease in the older animal (Type 2 Ostertagiosis).  

Mature cattle that have endured a drought can suffer weight loss if exposed to substantial numbers of larvae on pasture. 

The significance of gut worms in young cattle is mainly determined by the level of exposure to infection. If the levels are high, clinical disease will result in: 

  • loss of appetite 

  • listless appearance 

  • intermittent, profuse, watery diarrhoea 

  • rapid weight loss and emaciation 

However the subclinical effects are probably more important economically – reduction in feed intake results in poor weight gain. 

Level of nutrition also affects the ability of the cattle to cope with the effects of parasites and resist their establishment. 

There have been numerous drenching trials in New Zealand that have demonstrated the scale of potential losses from parasitism by gut worms. They average about 15kg liveweight (treated cattle end up 15kg heavier than untreated) but range up to 55kg liveweight and 33% mortalities. 

Replacement heifers may have lower mating performance because of lower mating weights. 

The other impact of worms is the inevitable risk of drench resistance. 


Faecal egg counting (FEC) as a tool to diagnose worm burdens in cattle is less reliable than in sheep and goats. The development of immunity to worms (particularly Ostertagia) by young cattle and the expression of that immunity by suppressing egg production of active gut worms makes the use of FEC in cattle older than 5-6 months unreliable. 

Blood testing for gut damage (measuring pepsinogen concentration in the blood) may be a useful diagnostic test in cattle with large Ostertagia burdens. 

Management and Control 

There is a wide range of anthelmintics and different ways they can be administered in cattle. 

Contact your nearest VetEnt clinic to learn more about how to manage worms in your cattle.