PRINCIPLES OF LIVESTOCK BREEDING. 13 



been treated, was likewise feeble. Prof. L. J. Cole, of the University 

 of Wisconsin, has obtained similar results on treating male rabbits 

 with lead. Several other experiments have been made along this 

 general line, some of which confirm the preceding results, while 

 others were negative. It seems clear that it is possible to injure the 

 hereditary qualities of the reproductive cells by means of substances 

 in the blood, but that it is not at all easy to do so. 



INHERITANCE OF ACQUIRED CHARACTERISTICS. 



The question whether a specific change in the sire, due to training, 

 care, or accident, can be transmitted to the young, is quite inde- 

 pendent of the question whether a general loss of vigor can be pro- 

 duced in any such way. As we have seen, the latter can be accom- 

 plished through the use of poisons, such as alcohol or lead, and the 

 possibility exists that extreme malnutrition may sometimes have 

 such an effect. The mechanism is at least easy to understand. 

 This is not the case with a specific characteristic. 



There is a strong negative evidence in certain cases. Weismann 

 cut off the tails of mice for 19 generations without causing any 

 modification of the young. Docking the tail of sheep and many 

 similar practices have no hereditary effect. Thus it can be stated 

 very positively that the effects of mutilation or accidental injuries 

 are not inherited. 



With regard to the functional characteristics in which livestock 

 breeders are most interested, the evidence is not so clear cut but is 

 still negative when of a critical character. F. R. Marshall has shown 

 that the average age of the sires of 2.10 trotters was practically the 

 same as that for all Standardbred horses of the same period, indicating 

 that longer training has no effect on the speed of the progeny. F. S. 

 Putney made an analysis of the records of the Jersey herd at the 

 Missouri Agricultural College and found no relation between age of 

 dam and butterfat record of the daughter. 



The failure of acquired characteristics to be inherited does not 

 mean, of course, that proper care and feeding of livestock can be 

 neglected, even from the standpoint of breeding. It is only by testing 

 the speed of his race horses, the butterfat record of his dairy cows, 

 or the fattening capacity of meat animals that the breeder can deter- 

 mine which are likely to transmit the best heredity and so separate 

 the desirable breeding stock from the culls. Moreover, in such a case 

 as the development of an unsoundness in a horse, due apparently to 

 an accident, there should be much hesitation before breeding. The 

 development of the unsoundness is likely to indicate a hereditary 

 weakness, and such horses will be found in general to have sired 

 unsatisfactory colts before the accident and will continue to do so 

 thereafter. 



