Investigations in Ohio have shown that the major pathogen in this family is Ostertagia. The name applied to internal parasitism with these worms is parasitic gastroenteritis. The term Ostertagiasis is often used in recognition of the predominant significance of ostertagia spp. When suitable warm temperatures are present along with adequate moisture, the egg hatches and undergoes two moults during its growth. Development from egg to infective larva on pasture is also temperature-dependent, requiring three to four months in cool weather to as short a time as one to two weeks in warmer weather.
Infective larvae are relatively resistant to environmental hazards.
They can survive for up to a year under optimum circumstances. They survive freezing and are present on spring pastures. High temperatures of summer are unfavorable to the survival of infective larvae. These facts are worth understanding because they have significance in our attempts to control this disease. Roundworm lifecycle small version large version Adult worms mature in the cavity of the abomasum and begin to produce fertile eggs about three weeks after the cow ingests infective larvae.