Studies on resistance in calves to experimental infection with the nodular worm, Oesophagostomum radiatum (Rudolphi 1803). II. The role of the respective stages of the parasitic life cycle in the stimulation of resistance

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Abstract
Investigations are reported which attempted to define the role of the respective stages of the parasitic life cycle ofOesophagostomum radiatum in the stimulation of resistance in calves to reinfection with this parasite. In one series of experiments with calves reared worm-free, infection was restricted to known stages by treatment with an anthelmintic, and in another series by surgical implants of worms. Subsequent reinfection showed that the early development stages of the parasite up to the early fourth stage larva in the gut lumen, and the exsheathing fluid released at the third and fourth ecdyses, were not essential for the stimulation of resistance. The results also suggest that ability to stimulate resistance increases as the worms mature.