[Resistance of broilers to Marek's disease virus].

Studied was the resistance, resp., susceptibility of the initial broiler lines - 66 and 77 of the Cornish breed, and 88 and 99 of the Plymouth Rhock breed, which are used in this country for the production of the four-line hybrid, - to the virus of the Marek's disease, isolate CT-1. A biologic assay was carried out with a total of 2080 young birds divided into three groups; I groups - infected abdominally; II group - contacts; and III group - controls. Certain breed, line, and sex differences were established in terms of resistance, resp., susceptibility of the investigated birds to the CT-1 isolate of the Marek's disease virus. More resistant were the birds of the Cornish breed as compared to those of the White Plymouth Rhock breed. A rising trend was observed in the resistance of cockerels in comparison with the poults of the respective line. Most susceptible to Marek's disease proved the birds of line 99, especially the poults that were currently used for the production of the mother parental form of the four-line hybrid. The birds with abdominal infection showed death cases as early as the second month of age, mortality rising up to end of the fourth month, while with the contacts and controls most death cases were observed at the fifth month of age. Essential decrease in mortality set in with all three groups after the birds reached six months of age. At a low rate of infections which was experimented with the contact and the control group there were not opportunities to fully discover the resistance of birds to Marek's disease.