122 POULTRY PRODUCTION 



be mated back to the original female B with correspond- 

 ing results. 



While Felch's system is commonly spoken of as line breed- 

 ing, it is only with reference to the individuals shown in the 

 outside lines of Fig. 58 that true line breeding takes place. 

 The mating of the two extreme lines to produce the groups 

 at / and M averaging half the blood of the sire A and half 

 the blood of the dam B simply represents other methods of 

 getting the results of the first cross, or of a brother and sister 

 mating from group C shown at R without, however, having 

 them directly connected genetically. 



t)anger of Line Breeding. — ^As in grading, danger lies in 

 the temptation to use as a breeder a grade male that " looks 

 good", so in line breeding the danger lies in trusting in the 

 efficacy of line breeding, in and of itself, and in continuing 

 to mate relatives after they have ceased to "look good." 

 Inbreeding in any form offers opportunity for the segre- 

 gation of characters, thereby not infrequently disclosing 

 recessive poor qualities as well as tending to render pure 

 dominant desirable qualities. This increases directly with 

 the closeness of inbreeding, the closest possible being that 

 of a brother and sister mating as shown at C and R in 

 Fig. 58. 



Few fowls are fully fertile and fewer still are both fertile 

 and vigorous. Selecting relatives both of which approach 

 perfection in physique is difficult. Many weaknesses are hid- 

 den, only to be discovered by disappointing experience. It is 

 easy to mate individuals of a greater or less relationship 

 where an unsuspected mutual tendency toward infertility 

 will be disclosed. It is all too common to mate fowls with a 

 more or less common ancestry, that already show the warn- 

 ing earmarks of a weakened constitution. The result can 

 hardly be other than a progeny that is weaker than eitlier 

 parent. 



The difficulty in such cases is not in, line breeding as a 

 practice, but in the skill and judgment in selection. As 

 Marshall' puts it, "We may say of the cases (of line breeding) 



I Breeding Farm Animals. 



