ANNUAL REPORT, 1936 87 



respectively for the high and low mortality lines. The mean annual egg records 

 of the two lines were 209 and 257. 



Breeding for High and Low Resistance to Fowl Paralysis. (F. A. 



Hays, W. C. Sanctuary and J. H. Vondell.) The studies to date indicate that 

 different degrees of resistance to fowl paralysis exist. Since the mode of trans- 

 mission is little understood, progress has been slow. Recurrent waves of the 

 disease are difficult to explain in stocks of birds bred under uniform conditions 

 from year to year. Specific phases of this disease are now being investigated. 



DEPARTMENT OF VETERINARY SCIENCE 

 J. B. Lentz in Charge 



Poultry Disease Control Service. (H. Van Roekel, K. L. Bullis, O. S. 

 Flint, and M. K. Clarke.) 



1. Pullorum Disease Eradication. During the 1935-36 testing season a total 

 of 255 flocks (including three flocks of poultry other than chickens) representing 

 344,233 samples (including 152 from fowl other than chickens) was tested. The 

 testing results of the chicken flocks showed increases in tested flocks (8), tested 

 birds (48,535), tests (42,194), and non-reacting flocks (17) over the previous 

 season. The average percentage of positive tests was 0.30, which is the lowest 

 attained during the sixteen-year testing period. Of the total birds tested, 95.6 

 percent were in 230 non-reacting flocks, a definite increase over the percentage 

 (89.5) for the 1934-35 season. Furthermore, among the 315,215 birds in the 

 negative flocks, 90.9 percent were in the 100 percent tested flocks. 



The merit of annual testing is emphasized by the following data presented 

 on 151 flocks which were tested for three or more consecutive years. Among 

 271,410 blood samples collected from 263,400 birds only 0.10 percent gave a 

 positive test. The number of birds in flocks tested for three or more consecutive 

 years represented 79.9 percent of the total birds tested. 



The results for the 1935-36 testing season show steady progress in pullorum 

 disease eradication. The data prove that poultrymen who follow a conscientious 

 testing and disease-prevention program are able to maintain a pullorum clean 

 flock. 



2. Pullorum Disease Investigations. 



(a) Antigenicity Studies of S. pullorum Strains. The purpose of this inves- 

 tigation was to determine whether or not the agglutinative sensitivity of certain 

 selected strains of Salmonella pullorum could be increased by serial passage 

 through day-old chicks. Duplicate sets of three strains employed in the antigen 

 for routine pullorum disease testing were selected. Day-old chicks were inocu- 

 lated subcutaneously with viable fresh antigen and held for a short observa- 

 tion period. Each lot of chicks was inoculated with antigens prepared from 

 cultures recovered from the preceding lot of chicks. The organisms were 

 properly identified after each isolation. Antigens were prepared from the 

 isolated strains and tested with known positive and negative sera. A standard 

 stock antigen composed of the three strains was tested simultaneously with 

 the same sera. Following the serial passage of the six strains of S. pullorum 

 through twelve lots of chicks, no change was noted in the agglutinative sensi- 

 tivity of the strains. 



