The data presented in this hnlletin was gathered entirely from the 

 State of New Hampshire, a state on the eastern seal)oard, in which consid- 

 erable poultry population exists at the present time. 



Birds raised on some farms, according to random samples, possess im- 

 munity to infectious bronchitis at all times. This situation exists because of 

 a constant exposure to the virus. The majority of breeding farms do not 

 find this situation to exist, and as a result, a field strain of bronchitis is 

 given to the birds prior to coming into egg production. The general picture 

 of breeding flocks in Xew Hampshire is that practically all flocks have been 

 exposed to bronchitis either by artificial means or by naturally occurring 

 field strains. Consequently, with very few exceptions, chicks hatched from 

 these breeding flocks possess a high parental immunity during the first week 

 of age. Furthermore, it must be kept in mind that such immunity has been 

 stimulated by an unmodified strain. Luginbuhl demonstrated immunity to 

 infectious bronchitis at 5 weeks when the chicks were vaccinated at day-old 

 intranasally with modified infectious bronchitis. 



As may be seen from the tal)le. the majority of chicks hatched from 

 Xew Hampshire breeders possess high parental immunity to Newcastle 

 disease. The practice of applying Newcastle vaccine by the wing web 

 method has been a favorite of the breeders of this state. In the presence of 

 this high parental immunity, however, it has been shown to be possible to 

 infect chicks with the Bj strain. Hitchner (5) showed that it was possible 

 to do so at an early age. and Markham and Bottorff (TO) proved that it was 

 possible to immunize chicks by use of the intranasal or intraocular route in 

 tlie presence of parental immunity. 



Another important factor to be mentioned in connection with the pre- 

 vious results is that of chronic resi)iratory disease. It has l)een determined 

 by the oljservation and study of pipped embryos which showed enlarged 

 hocks and caseous material in the air sacs, also by isolation of CRD agents 

 from day-old chicks, that the incidence of CRD in the chicks hatched in 

 X"ew Hampshire is exceedingly high. In those instances in which high mor- 

 tality was encountered in the field trials, CRD was found to be present in 

 over 90 per cent of the cases. 



While it was originally felt that the chicks to be spray vaccinated must 

 possess parental immimity to infectious bronchitis, results of field trials and 

 laboratory trials on susceptible chicks would seem to indicate that parental 

 immunity, while desirable, is not necessary. From all observations, the in- 

 dications are that the CRD complex presents the biggest problem in af- 

 fecting the results of any mass immunization or other vaccination pro- 

 cedures todav. 



IS 



