Constitutional Vigor in Poultry 575 



Experiment III 



For the purpose of comparing two different breeds of poultry as to 

 their constitutional vigor, a number of Barred Plymouth Rock pullets 

 were saved from the same hatch as was used in experiment II. These 

 Barred Plymouth Rock pullets also had apparently overcome their earlier 

 vreakness. The selection, general care, and all conditions surrounding 

 this third lot, to be known later as pens 21 (strong) and 23 (weak), were 

 similar to those in experiment II with White Leghorns. 



The stronger sisters to be used in comparison with these individuals 

 were chosen from the same hatch. They were not selected, however, 

 until the time of housing the flocks in their winter quarters. 



It should be understood that in each lot the pullets chosen for the 

 weak pens were, at the time of their selection, such as would ordinarily 

 be considered strong and active individuals. They were termed the 

 weak flocks because at one stage of their growth they had shown such 

 weakness that, in order to save their lives, a specially digestible and 

 nourishing ration had been given them. Many of the other pullets given 

 this ration did not develop satisfactorily. It is evident, therefore, that 

 the term " weak " as applied to these flocks needs to be interpreted in 

 the light of the foregoing statements. All fowls used in the experiments 

 were pullets that ordinarily would have been retained as healthy stock. 



condition of pullets when put into winter quarters 



Several months elapsed between the time of selecting and the time 

 of housing these pullets. During that period many mdividual changes 

 occurred. This was especially pronounced in experiment I. Here several 

 of the previously weak pullets, faihng to retain their temporary strength 

 acquired under special feeding, again gave signs of low vitality; further- 

 more, several of their stronger sisters selected at the same early date 

 failed to maintain their original vigor: so that the two flocks (78 and 79), 

 when flnally penned up for winter observations, showed to outer appear- 

 ance but slight differences in degree of vigor except in the average weight 

 of the pullets. The pullets in flock 78 (strong) averaged 3.5 pounds, 

 while those in flock 79 (weak) averaged only 3.1 pounds. 



The pullets selected for the weaker flocks in experiments II and III 

 showed similar individual reverses. Consequently, both the White 

 Leghorn and the Barred Plymouth Rock flocks of low vitality included, 

 when the records of feeding and production actually began, some excellent, 

 as well as some unquestionably weak, individuals. 



The two stronger flocks to be compared with the low- vitality flocks 

 of experiments II and III were assembled at this time from the choicest 



