No. 6. DEPARTMENT OF AGRICULTURE. 427 



the progeny shall not always be like the parents, though apparently 

 antagonistic to the first law, it may be simply a part of the same. 

 The differences being the result of modifying factors in transmission 

 as yet not well understood, and until understood, beyond the control 

 of man. In breeding pure blood animals these differences are not 

 usually very well marked, though they are constantly present. Some- 

 times they are very great, as when, for instance, the progeny of 

 horned parents are hornless, but such variations are of infrequent 

 occurrence. Some have claimed that in transmission variations are 

 more constant and greater than resemblances, in other words, the 

 second law of breeding operates more strongly than the first law. 

 In breeding pure bred animals, this is not true. If it were so. the 

 breeder would be on an uncertain sea, without sail or rudder. The 

 only improvement that he could make would be through selection. 



The presence of the law of variation is by no means inherently 

 adverse to improvement in breeding. The result depends first, on the 

 character of the variation, and second, on the disposition made of 

 the animals which thus vary. Variations are sometimes downward, 

 in other instances they are upward. When downward the animals 

 should be eliminated. When upward they should be retained for 

 breeding. Were it not for variations in the direction of improvement, 

 advance in breeding would be impossible. Viewed from this stand- 

 point the law of variation is a blessing rather than the thorn which 

 it sometimes proves to be. 



The law of atavism is the law which, in transmission, determines 

 that the progeny shall be like some remote ancestor. It is probably 

 a branch of the first law of breeding acting in a erratic way. Like the 

 law of variation, it is a disturbing factor in breeding. But it is more 

 disturbing than the former in that it introduces variations that are 

 undesirable. It resurrects from out the dead past what the breeders 

 have been trying to eliminate. The frequent occurrence of a white 

 calf in the breeding of Shorthorns, which the breeders have been 

 trying to avoid for generations, illustrates the disturbing character 

 of this law. It may be that its existence is intended to compel the 

 breeder to give careful attention to purity in blood lines, since its 

 power wanes in proportion to the increase in the duration of the 

 period covered by pure breeding. 



Having thus briefly outlined these laws, the effort will be made to 

 enlarge on some feature of their practical application to the opera- 

 tions of the breeder and also of every farmer who breeds even one 

 animal on his farm. The points that will be more particularly dwelt 

 upon are those which relate to the evidences of prepotency in sires, 

 to the improvement of live stock through up-grading, and to the 

 futility of promiscuous breeding in so far as it relates to the improve- 

 ment of live stock. 



PREPOTENCY IN THE SIRE. 



Prepotency means the power possessed by a parent to transmit 

 individual and breed properties to the progeny. The measure of its 

 strength, however, is more evidenced in the former than the latter. 

 Thus it is that prepotent sires produce uniformity in the stud, herd 

 or flock. The uniformity thus produced is proportionate to the pre- 

 potency of the sire and the excellence of the uniformity is at least 

 measurably proportionate to the excellence of the individuality in the 



