288 THE BREEDING OF ANIMALS 



come from valuable mutations which have been recognized 

 by the alert breeder. 



But whether the present valuable characteristics of 

 the domestic animals have come through continuous 

 variations or by sudden mutations or in any other way, 

 selection by man has been the one outstanding fact in 

 the development of the many valuable races and breeds 

 of animals. It is conceivable and very probable that 

 similar variations have been induced by similar causes 

 in all wild forms, but wild forms have remained relatively 

 stationery while the domestic races have been greatly 

 improved. 



273. Aids to selection. The breeder has consciously 

 or unconsciously brought to his aid numerous practices 

 which have greatly facilitated his efforts. The manu- 

 facturer who has invented a labor-saving device or a 

 complicated machine to perform certain work puts it to 

 the test by actually applying the machine to the work 

 in hand. Likewise the skillful breeder has found it greatly 

 to his advantage to test his animal creations by actual 

 performances. 



The breeders of trotting horses have no means of deter- 

 mining how successful they are in producing speed except 

 by trial on the track and it is not only necessary to train 

 now and then a horse but every individual in the stud 

 must be tested to be certain that all possess the quality 

 of speed. 



The highly successful breeders of meat animals, cattle, 

 sheep and swine, maintain their breeding animals in a 

 high state of condition. In some cases the meat animals 

 used for breeding purposes by noted breeders are kept 

 so fat as to interfere with the normal reproductive func- 

 tions. But even so, such a practice is essential to the 



