8 MASS. EXPERIMENT STATION BULLETIN 311 



Since our knowledge on this point is so meager, it was decided to set up one 

 more experiment before attempting field work. In this investigation 30 pullets 

 and cockerels three months of age were vaccinated in the usual manner and most 

 of the takes appeared on the fourth and fifth days as shown in Table 5. The 

 virus was present in the cloaca and bursa of Fabricius of all the birds the first 

 four days, after which it began to disappear in some of the birds. At the end 

 of the eleventh day, the virus had entirely disappeared from the cloaca and bursa 

 of Fabricius of all of the birds. Two of the birds, however, developed natural 

 attacks of the disease, the virus appearing in the respiratory tract on the third 

 day and remaining in one case for five days, while the other became a chronic 

 carrier for at least two months. No evidence was produced by this experiment 

 to indicate that cloacal or bursal carriers are produced by vaccination against 

 infectious laryngotracheitis, but laryngotracheal carriers may result from natural 

 attacks of the disease. None of the vaccinated birds died, while four of the five 

 controls inoculated intratracheallv with the same virus died. 



FIELD EXPERIMENTS 



After the completion of the laboratory studies, which showed that vaccination 

 against infectious laryngotracheitis is a possibility and that it may have some use 

 on the poultry farm as a preventive, the following field experiments were carried 

 out to determine its value under range conditions. Results are shown in Table 6. 



Flock 1 



This mixed flock of 1,402 birds was vaccinated on July 3, 1933, in seven and 

 one-half hours. The birds were confined in the colony houses the night before. 

 There were four helpers, two of whom caught the birds and passed them out while 

 the other two held them for vaccination. 



The vaccine was prepared by the modified Swift method eight months before 

 use and stored in a Frigidaire. Immediately before vaccination the vaccine was 

 ground up into a thin paste, using glycerine and saline as a diluent, in an unglazed 

 mortar with an unglazed pestle. 



Four days after vaccination the birds were examined for takes. At this time 

 those birds showing poor takes or none were revaccinated from those presenting 

 good and excellent takes. 



This flock passed through the winter of 1933-1934 without infectious laryn- 

 gotracheitis. This is the first time in four years that this disease has not appeared 

 on this farm in the late fall or early winter and been responsible for considerable 

 mortality and loss in egg production. 



Flock 2 



This (lock consisted of 912 birds. The vaccine was prepared by the modified 

 Swift method six months before vaccination, sealed in test tubes, and stored in a 

 Frigidaire until carried to the farm. Vaccination commenced at noon, July 

 10, 1933, but had to be discontinued at 2:00 p. m. on account of rain. The job 

 was finished at noon the next day, making a six-hour task. Four days after 

 vaccination the birds were examined for takes. 



('■roup 1 passed through the waiter without incident. The percentage of takes 

 in this group was 93.1 5. Group 2 had a slight outbreak of the disease soon after 



