LARYNGOTRACHEITIS VACCINATION 9 



moving into the laying houses in September. None of the birds died and the 

 laying, which had just begun, was not noticeably affected. The percentage of 

 takes in this group was 83.43, and as near as could be determined about 10 percent 

 of the birds were affected. Since 10 percent of the vaccinated birds had either 

 poor or no visible takes, it is reasonable to assume that as immunity wore off in 

 this group, the susceptible birds contracted the disease from carriers, thus com- 

 pleting their protection against infectious laryngotracheitis. 



A small flock of White Leghorns which was overlooked at the time of vaccina- 

 tion contracted the disease so^n after being moved into the laying houses and 

 about half of them died as a result of exposure to the vaccinated birds, although 

 the latter showed no symptoms of disease at this time. This indicates that 

 carriers were present in the vaccinated flock, and the White Leghorns contracted 

 the disease from them. 



Flock 3 



This flock consisting of 450 pullets and cockerels was vaccinated in the fore- 

 noon of July 19, 1933. The vaccine was prepared according to the modified 

 Swift method the day before vaccination. The birds in this flock were examined 

 for takes five days after vaccination. The percentage of takes following the first 

 vaccination were so high that second treatment was considered unnecessary by 

 the owner. A cockerel in which no visible take was evident after vaccination 

 died of infectious laryngotracheitis. The rest of the birds came through the 

 year without showing any indications of the disease. 



Flock 4 



This flock consisted of 4,040 birds. Since the laboratory was not equipped to 

 prepare vaccine for so many birds, it was decided to vary the method in order 

 to meet the situation. Only enough vaccine was prepared in the laboratory to 

 vaccinate 50 birds. The only object in preparing vaccine by the modified Swift 

 method is to preserve it for use at a later time and for transportation. The 

 treatment does not add anything to its properties; as a matter of fact such vaccines 

 may be entirely unsatisfactory due to faulty desiccation. Theoretically, fresh 

 vaccines prepared on the farm should be more virulent, insure a higher percentage 

 of takes, and eliminate all possibility of poor vaccine, because if the virulence 

 of the vaccine should prove to be unsatisfactory in the inoculated birds, it would 

 not be used by anybody having practical experience with this method of producing 

 immunity. 



Accordingly 50 pullets and cockerels were culled from Flock 4 and confined 

 in a colony house some distance from all other birds. These birds were inoculated 

 intratracheally with the desiccated virus September 7, 1933. On September 11 

 the owner telephoned that the inoculated birds were coming down with the 

 disease and judging by the severity of the symptoms the virus was satisfactory 

 for vaccine. Hence it was agreed to begin vaccinating the next dav. 



On September 12 a dozen of the most marked clinical cases were selected from 

 the inoculated flock, six in the morning and six in the afternoon, and fresh liquid 

 vaccine prepared in the usual manner from the tracheal exudate. On this day 

 1,021 birds were vaccinated. The next day 1,535 birds were vaccinated using 



