Ostertagia is transmitted by ingestion only. Adults in the abomasum lay eggs that pass in faeces. Once hatched, larvae undergo two moults to become infective third-stage larvae, which migrate onto herbage and are ingested by grazing cattle. Once ingested, these parasitic larvae grow and moult twice more to become egg-laying adults.
Environmental conditions of cold or excessive dryness may trigger a condition known as hypobiosis, in which larval development is arrested so that maturation may take several months. Prepatent period is 17 to 21 days. Brown stomach worm is a widespread parasite of cattle. Affected cattle not only lose weight but often die of overwhelming clinical ostertagiasis.