The relationship between the number and size of nematodes in the abomasum and the concentration of pepsinogen in ovine plasma

Six-month-old lambs that had been naturally infected with predominantly Tel adorsagia (Ostertagia) circumcincta were tested for plasma pepsinogen conce ntrations because pepsinogen concentrations may reflect the extent of damag e to the abomasum. The distribution of pepsinogen concentrations among thes e lambs was positively skewed with most individuals having relatively low c oncentrations. Pepsinogen concentrations were more strongly associated with variation in the mean length of the adult female worms than with variation in the number of nematodes present. Previous trials have suggested that ge netic variation in the growth of lambs is strongly influenced by genetic va riation in worm length. Together these results imply that variation among l ambs in the pathogenic effects of T. circumcincta depends upon the mean siz e of the worms as well as the number of worms present.