LARYNGOTRACHEITIS VACCINATION 19 



plugged with pseudomembrane just as the larynx and trachea are filled in birds 

 sick or dead of infectious laryngotracheitis. 



Vaccination is a medical treatment and medical treatments have their limita- 

 tions. If the limitations of infectious laryngotracheitis vaccination are appre- 

 ciated, cloacal and bursal inoculation may be successfully accomplished on the 

 poultry farm and serious loss from the disease prevented. 



SUMMARY AND CONCLUSIONS 



1. The success of vaccination against infectious laryngotracheitis depends 

 on the number of takes. The most favorable time for reading takes was found to 

 be the fourth and fifth days after vaccination. Takes may be classified, according 

 to degree of inflammation, as poor, fair, good, or excellent. Occasionally takes 

 occur in the bursa of Fabricius which are not visible at the time of examining 

 the live birds. 



2. It has been determined that 94 percent takes in chickens one to three 

 months of age, 97 percent takes in pullets and cockerels four to seven months 

 old, and 90 percent takes in hens and roosters eight to twelve months of age insure 

 a satisfactory degree of immunity for a flock as a whole. The takes should be 

 good, fair, or excellent, for the immunity tends to wear off in birds showing poor 

 takes. When vaccinating is once started, it should be pushed on to completion 

 with as little delay as possible in order to avoid outbreaks of the disease. 



3. After this laboratory information had been obtained, field vaccination was 

 successfully accomplished in six flocks, or 11,204 birds. 



4. A study of diseases simulating infectious laryngotracheitis was made for 

 differential diagnostic purposes, and it was found that autogenous vaccines were 

 specific for infectious laryngotracheitis, coryza, and rhinosinusitis, but not for 

 each other. Therefore, it cannot be emphasized too strongly that before vaccina- 

 tion is resorted to for the control of infectious laryngotracheitis, a correct diagnosis 

 of the disease or diseases infecting the flock is necessary for success. 



5. Since laboratory vaccines for infectious laryngotracheitis have not been 

 entirely successful in the hands of poultrymen, autogenous vaccines may have 

 some use because of their specificity and availability at the time of greatest need. 

 A method of preparing and using autogenous vaccines in infectious laryngotrach- 

 eitis is outlined. It should be understood that this method of vaccination 

 will save the flock if properly applied, but it cannot be depended upon to eliminate 

 carriers; and for the good of the poultry industry as a whole it should be followed 

 by the complete eradication and sanitary control of the disease. Vaccination for 

 infectious laryngotracheitis merely enables the poultryman to choose the time 

 for disposing of his birds and cleaning and disinfecting the premises occupied 

 by them. When accepted in this light, vaccination is a valuable contribution to 

 the control of infectious laryngotracheitis. 



