.12 MASS. EXPERIMENT STATION BULLETIN 420 



Necropsy Records for Birds from Eight Weeks to Six Montiis of Age 



A relatively small percentage of sick and dead birds was sent in for necropsy. 

 During the growing season of 1936 fire and accidents disturbed the normal mor- 

 tality rate so that the data for that year are omitted. In table 2 the necropsy 

 records secured on the dead birds examined are presented. It is thought that 

 these records give a fairly representative cross section of diseases and disorders 

 in the flock. It should be noted here that birds in all four lines were hatched, 

 reared, and housed together so that environmental conditions cannot be held 

 responsible for the differences between the several lines. 



The avian leukosis complex (paralysis complex) includes neurol)mphomatosis, 

 visceral lymphomatosis, ocular lymphomatosis, osteopetrosis, erythroblastosis, 

 granuloblastosis, and mj-elocytomatosis. The most prevalent forms of the 

 complex were neural and visceral lymphomatosis. It will be noted that the 

 incidence of this complex varied widely from >'ear to year. In the generation 

 hatched in 1935 a single case occurred in the miscellaneous group of experimental 

 birds and in 1937 only one case was observed and this was in the control group. 

 The generation hatched in 1938 showed a very high incidence of the complex in 

 the miscellaneous group. The complete freedom of the high mortality line and 

 the low incidence in the low mortality line are worth}' of note. In the control 

 group the disease showed an incidence of 17.65 percent, while in the miscellaneous 

 group 60 percent of the birds showed evidence of the complex. In the 1939 

 generation, a low incidence of the avian leukosis complex was evident, and in 

 the large control line no case was discovered. In fact, there were but two cases 

 in the entire population. The death rate from the complex was high in 1940 and 

 in 1941. In the last generation reported in the table the incidence was relatively 

 high in the control line but had declined to a low level in the miscellaneous line. 

 In the last two generations there was no evidence of the disease in either the 

 high or the low mortality lines. 



These data tend to support the idea of a cyclic behavior of the avian leukosis 

 complex through a period of years. Both the high and the low mortality lines 

 were so nearly free of the complex that it played a minor role in their mortality 

 rates. There is very good evidence of a close parallelism between the incidence 

 of the avian leukosis complex and the incidence of other diseases and disorders. 

 In other words, in the generations where the total mortality rate was high, there 

 was a high incidence of the complex. 



Miscellaneous tumors not considered to be associated with the avian leukosis 

 complex did not appear frequently in the different lines. Digestive disorders 

 ranked high in importance in these young birds. Kidney disorders occurred 

 much less frequently. Reproductive disorders and staphylococcosis were ex- 

 tremely unimportant. Other disorders were relatively unimportant, but can- 

 nibalism was of sporadic occurrence. The number of cases where no diagnosis 

 was made on necropsy was significant. 



The last two columns of the table set forth the number and percentage of dead 

 birds that were examined in the laboratory'. In many instances the number of 

 birds examined was too small to give a representative sample. The fact should 

 be noted, however, that there have been no serious outbreaks of contagious or 

 infectious diseases in the flock aside from the avian leukosis complex. 



In general, the data suggest that a generation of birds showing a high incidence 

 of the avian leukosis complex before the age of 6 months is likely to be attacked 

 by a large number of pathological conditions and disorders to bring the total 

 mortality rate to a high level. 



