Clinical pathology of ostertagiasis in calves during prolonged experimental infection

Calves were infected daily for six months with Ostertagia ostertagi at five dose levels, ranging from 200 to 1,600 third-stage larvae. Groups of animals were destroyed at monthly intervals. The haematological and biochemical changes prior to autopsy are described and related to body weight increase, the larval population and abomasal pH at autopsy. From the third month onwards increased activity of plasma pepsinogen was related to the number of larvae maturing within the abomasum. The increase in the pepsinogen and glycoprotein values bore no constant relationship to the number of L3 larvae being ingested at a particular time. The increased pepsinogen activity was, however, correlated with the raised serum glycoprotein concentration and both alterations related to the active tissue damage associated with the adult worm as indicated by increased abomasal pH. Symptoms typical of clinical disease appeared only in the group receiving the highest dose of 1,600 larvae daily.