SYSTEMS OF BREEDING 613 



other lines is likely to be followed by the pains and penalties of 

 hybridization ; for a departure from line breeding is a kind of 

 crossing in a small degree, and so rapidly do blood lines become 

 intensified that line-bred animals assume all the attributes of 

 distinct strains, as they in truth are, and they will be likely to 

 behave as such ever after. 



In saying that line-bred animals tend to behave like pure 

 strains, and that their progeny from union with other strains 

 behave like hybrids, it is not meant that such unions should 

 never be made, or that such behavior is as persistent as with 

 real crosses. In truth, many lines are so stubborn as never to 

 blend with others afterward (behaving like the most strongly 

 established races), but, on the other hand, most of them will 

 yield to well-directed and persistent effort ; that is to say, a 

 line-bred herd can be modified, and in time made to assume the 

 characters of another family, but the process is attended with a 

 struggle and not a few failures. It has been fashionable at 

 times to decry line breeding, but the fact remains that a few 

 generations of good breeding soon bring the herd and its career 

 to a point where line breeding must be practiced or a worse 

 alternative must be accepted, for with well-selected strains all 

 outbreeding is mixed breeding. 



SECTION V INBREEDING 



Line breeding carried to its limits involves the breeding 

 together of individuals closely related. When it involves the 

 breeding together of sire and offspring or of dam and offspring 

 or of brother and sister, it becomes inbreeding, or " breeding in 

 and in." It is line breeding carried to its limits, and of course 

 possesses. all the advantages and disadvantages of that form of 

 breeding carried to their utmost attainable degree. 



Forms of inbreeding. Three forms of inbreeding are possible 

 among animals, namely : 



i. Breeding the sire upon his daughter, giving rise to off- 

 spring three fourths of whose blood lines are those of the sire, 

 a practice which, if followed up, soon results in offspring with 

 but one line of ancestry, thus practically eliminating the blood 



