Age resistance of cattle to the nodular worm Oesophagostomum radiatum.

Two groups of seven castrated male calves, aged three and 13 months respectively, which had been reared worm-free, were infected with 5000 larvae of Oesophagostomun radiatum. At autopsy six weeks later a mean of 403 +/- 398 adult worms were recovered from the older animals and a mean of 1174 +/- 484 from the younger. This significant difference (P less than 0-01) indicates that the resistance of cattle to initial infection with O radiatum increases with age.