i08 maine agriculiural experiment station. i913. 



Inbreeding. 



The third basic factor which makes for success in practical 

 breeding is inbreeding^' This may seem a radical statement, but 

 a careful study of the history of the best improved strains of 

 live stock of all sorts, including poultry, leaves no room for 

 doubt that the attainment of the highest degree of excellence 

 has always been associated with the practice of a very consid- 

 erable amount of inbreeding, of rather close degree. It is a 

 curious paradox of animal husbandry in general, and of poultry 

 husbandry in particular, that while, as a matter of fact, every 

 successful breeder of high grade stock practices inbreeding to 

 a greater or lesser extent, a great many of these men are vio- 

 lent, even fanatical, opponents to inbreeding in theor3\ Most" 

 of them will deny stoutly that they ever practice inbreeding. 

 They contend that they practice "line breeding," but never, 

 never "inbreeding." 



The distinction here is obviously verbal and not biological, 

 being in its essentials precisely similar to that between Tweedle- 

 dum and Tweedledee. The essential and important biological 

 point is that what is actually done is to purify the stock in 

 respect to all characters to as great a degree as possible. What 

 the successful breeder aims to do is to get his stock into such 

 condition that he has only one kind of "blood" in it. Expressed 

 more precisely, though unfortunately more technically, it may 

 be said that the breeder endeavors to get his stock homozygous 

 with reference to all important characters or qualities. The 

 c[uickest way, indeed the only way, practically to obtain this 

 result is by the practice of some degree of inbreeding. Some- 

 times a great stride towards the desired end may be made by 

 mating brother and sister or parent and offspring together. 



That a mating of such close relatives will surely result in 

 disaster is one of the carefully nursed superstitions of breeding, 

 which has often been exploded, but will doubtless always be 

 with us. It may be said that all the evidence which may be 

 gleaned from the experience of stock breeders indicates that the 

 results which follow inbreeding depend entirely upon the nature 

 of the individuals inbred. If one inbreeds weak animals, lack- 



* The following discussion of inbreeding has already appeared, in 

 slightly altered form, in The Farm and Home Poultry Annual for 1913. 



