Age Resistance of Cattle to Nematodes of the Gastrointestinal Tract

Abstract

Four experiments were conducted to study the age resistance of cattle to nematodes of the gastrointestinal tract. The experiments used 31 cattle, including 13 calves from 5 to 81/2 months old and 18 steers from 18 to 25 months old. In 3 experiments, 22 of the cattle were grazed on contaminated pastures and they became infected with 8 species of gastrointestinal nematode parasites. In the final experiment, 9 of the cattle were kept in a barn and artificially infected. In the pasture trials, the calves harbored an average of 2 1/2 to 4 1/2 times more worms than the adult cattle, and clinical symptoms of parasitism were observed only in the young animals. Coincident with the overt signs of parasitism was the manifestation of serological aberrations that included sharp drops in the levels of serum inorganic phosphorus and total protein. In the artificially infected cattle, the calves had an average of 5 1/2 times more worms than the adults at time of post mortem. The results indicate that by virtue of age, per se, adult cattle are generally more resistant to nematode parasites and to their debilitating effects than are calves, but that under natural conditions adult cattle can acquire appreciable numbers of nematode parasites.