8 MASS. EXPERIMENT STATION BULLETIN 442 



SUMMARY 



Records on mortality were secured on three generations of Rhode Island Reds 

 including two inbred lines: one selectively bred for high mortality rate, and the 

 other for low mortality rate. Stock bred for high fecundity, without inbreeding, 

 was used as controls. Samples of morbid and dead birds were examined by 

 pathologists. From these data the following deductions were made: 



L Selective breeding using half-brother and sister matings produced two 

 lines that differed significantly in mortality rate. 



2. Selective breeding failed to give a line that had a lower mortality rate than 

 was observed in the controls. 



3. Although the avian leukosis complex appeared in all lines, it was not a 

 major disorder in the two inbred lines. This disease was the major cause of 

 death in the controls from eight weeks to six months but not between the ages of 

 six and eighteen months. 



4. The incidence of the avian leukosis complex was higher in females than 

 in males. 



5. Cannibalism was more prevalent in the two inbred lines than in the controls. 



6. Injury from fighting was an important cause of death of males in all lines. 



7. High-mortality line females were very inferior egg producers; low-mortality 

 line females were mediocre egg producers; and the control line females were 

 superior layers. 



8. In general, the data indicate that heredity does play an important part in 

 mortality rate. 



