The EU is the largest producer of milk products in the world and dairy farming is traditionally one of the most profitable sectors in EU agriculture.
Of the many infectious diseases that affect dairy cattle, worm infections are among those with greatest impact on productivity. All herds with grass-based production systems are infected. With a total of around 88 million EU cattle, economic losses caused by gastrointestinal (GI) roundworms constitute a huge problem for the industry. The major economic impact is due to sub-clinical infections causing reduced growth and milk production.
For the whole EU, losses of 1.7-2.7 BN€ have been estimated in dairy cattle alone. The roundworms Ostertagia ostertagi and Cooperia oncophora (shown below) are among the most common parasites infecting the GI tract of cattle in the EU and other temperate regions.
O. ostertagi (brown stomach worm) infects the stomach, while C. oncophora infects the small intestine. Both have direct life cycles with free-living stages on pasture and parasitic stages in the host. Female worms produce eggs that pass in faeces. Within faeces, infective larvae develop. Infective larvae spread from faeces to the surrounding vegetation. Cattle are infected when they ingest larvae from contaminated pasture. In the stomach or intestines larvae mature to adult worms. Female worms start producing eggs after ~3 weeks.
Grazing calves are generally exposed to Ostertagia and Cooperia mixed infections.
Infection causes watery diarrhoea, thirst, loss of appetite, reduced weight, dull hair coat, loss of condition and eventually death.
The disease (parasitic gastro-enteritis) mainly occurs in young stock during the first grazing season when pasture contamination is high and calves have not developed protective immunity. Some degree of immunity develops during the first grazing season, and second season grazing heifers and adult cattle are protected against clinical disease. Subclinical infections mainly occur in older cattle. In adult dairy cows, O. ostertagi can cause a significant decrease in milk production in heavily infested herds.
Stomach lining of a calf infected with O. ostertagi (right) compared to that of an uninfected animal (left)
Calf with diarrhoea due to GI roundworm infection
Control is mainly based on preventive treatment with anthelmintic drugs.
The intensive use of these drugs can interfere with the development of natural immunity.
Concerns have been raised regarding chemical residues in consumer products and the environment.
The most important consequence is the increasing incidence of drug-resistant parasites. This has been reported for O. ostertagi and C. oncophora.
These factors have stimulated the search for other control options such as vaccination.