The respiratory take was apparent in the \oiinger chicks on the third 

 or fourth dav, l)eing quite mild until the fifth day. The 4-week-old birds 

 showed a take on the second day. The length of respiratory take in all 

 groups was about 15 days. Xn mortality appeared in the older birds during 

 this time while one chick was lost in the younger group. 



All birds were challenged 4 weeks later. One half were challenged by 

 the intratracheal route with 1000 infective chick doses of a field strain of in- 

 fectious bronchitis virus. 'Vhe second half were challenged with the Boney 

 challenge strain of Newcastle virus as previously described. Two birds died 

 as a result of the Newcastle challenge and one showed paralysis. Three birds 

 showed mild respirator)- symptoms for two days when challenged with in- 

 fectious bronchitis. 



Following this trial a further laboratorv test was conducted on some 

 600 chick divided into 6 pens. The parent stock was vaccinated with a field 

 strain of infectious bronchitis virus and with wing web vaccine for New- 

 castle disease just as they came into production. Random blood samples 

 were taken from all groups of chicks and it was apparent that parental im- 

 munitv existed for Newcastle disease and infectious bronchitis. 



The birds were vaccinated with combination Newcastle and infectious 

 bronchitis vaccine by the spvay technique. The take was mild on the second 

 and third days. About the fifth day the take was quite apparent. Respiratory 

 take had disappeared from all groups by the 17th day. 



At 8 weeks random blood samples were drawn for serological test. On 

 Hemagglutination Inhibition test 63.3 per cent showed positive H. I. titres. 

 while on serum neutralization test for infectious bronchitis 76.8 per cent 

 showed positive titres. 



At 16 weeks onlv 55.1 per cent showed positive H. I. titres for New- 

 castle disease; 68.8 per cent were capable of neutralizing better than 100 

 embryo lethal doses of infectious bronchitis virus. 



Experimental Results 



Spraying with UNH Newcastle Vaccine 



During a three-month period. 25 flocks involving 67.280 birds were 

 inoculated in the field at 2 to 3 days of age with the Bi strain of Newcastle 

 virus. The spray technique, utilizing the Z & W type sprayer, as well as 

 others, was used in the administration of this vaccine. The size of the flocks 

 ranged from 550 to 10.000 chicks. Brooding systems of all types were en- 

 countered. 



In all cases, respiratory symptoms were observed around the fifth or 

 sixth day post inoculation. The average length of response was 6.5 days. The 

 mortality from all causes averaged 1.8 per cent for the first two weeks fol- 

 lowing vaccination. Blood samples, taken at random, were withdrawn at 4. 

 8, 12, and 16 weeks, respectively. Geometric mean titres are shown in Table 

 1. (In the compilation of geometric mean titres for this bulletin, serum 

 samples in the H. I. test were diluted no higher than 1 :128. This explains 

 the relatively low figure obtained. It must be remembered here that the geo- 

 metric mean titre is merely a value obtained for the use of comparison 

 purposes.) 



9 



