322 PRINCIPLES OF BREEDING. 



but what it is the surest and quickest method yet known of 

 intensifying certain qualities either desirable or undesirable 

 in the breeding herd. 



So much for the advantages of this method. We will now 

 discuss some of the objectionable features of this practice. 

 One of the first objectionable features noticeable will be a re- 

 duction in the size of the animals. This is very apparent 

 in those herds of cattle or swine in which the sires have 

 been selected from the male offspring of the herd from time 

 to time without regard to family relationships. It is impos- 

 sible to retain the size of the animals when in-breeding is re- 

 sorted to in the herd, stud or flock. 



Another objectionable feature of in-breeding is its influence 

 on the constitutional vigor of the herd. That a weakened con- 

 stitution and greater delicacy of the system follows this sys- 

 tem of breeding is very evident from the fact that tuberculo- 

 sis and other diseases is so much more prevalent in those 

 families where this system of breeding is practiced. As 

 stated in the previous lecture the powers of fecundity may 

 be unfavorably influenced by continued in-breeding. There is 

 no doubt but what it has a tendency in this direction. A study 

 of the closely related families of many of our recognized 

 breeds of stock and the breeding records of the same will re- 

 veal this fact. 



In-and-in-breeding caiiriot be carried on for any considerable 

 length of time without evil results making their appearance. 



They may appear in any one of the ways mentioned, or more 

 likely in all of those mentioned. A decrease in size and a 

 weakened constitution are always noticeable and are very in- 

 jurious from a commercial standpoint. 



Evil results from in-breeding can usually be remedied by the 

 introduction of new blood. In doing so nothing but strong, 

 vigorous animals should be selected, as weak animals would 

 not in any way remedy the trouble. The most obvious objec- 

 tion to in-breeding or close breeding is the difficulty of secur- 

 ing animals that are free from constitutional defects, and the 

 danger arising from the tendency of such defects to become 

 dominant in the offspring. 



Line breeding is often practiced. It differs from in-breeding 

 in that in line breeding those animals of very near relation 

 are not bred together. Those from the same foundation stock 

 which are some three or four generations removed are used. 

 In the formation of new breeds in-breeding is of necessity used 



