I 



Examining a laboratory control test on experimental vaccine. 



at 5 weeks with a virulent Newcastle virus, all survived except one bird. 

 Serological tests closely paralleled challenge results in both trials. 



From the results of these trials, it is evident that there may be consid- 

 erable question as to the advisability of vaccinating chicks at 7 days of age, 

 particularly from the standpoint of mortality following vaccination and the 

 apparent lack of resistance to Newcastle disease at 5 weeks of age. How- 

 ever, when chicks are vaccinated by the wing web method at 14 days, the 

 mortality is low and the iriimunity at 5 weeks is good. 



W. R. DUNLOP 



No Detrimental Effect to Chickens from Nitrophenide 

 Fed during Their Entire Period of Growth 



From time to time it has been suggested that the feeding of drugs for 

 the control of coccidiosis may interfere with the stimulation of resistance to 

 the disease. It is also suggested that the drugs may have a toxic effect when 

 fed over long periods of time. Some have even suggested that hatchability 

 and fertility may be affected by the prolonged use of drugs. 



During the past year an attempt was made to critically evaluate the 

 continuous medication with nitrophenide for 22 weeks versus medication 

 over a 12 week period when subjected to natural exposure of coccidosis. 

 The results of the trials indicate that birds getting a prophylactic level of 

 the drug either for 12 weeks or 22 weeks were not prevented from picking 

 up a sufficient amount of exposure to develop immunity. Furthermore, ad- 



41 



