238 PRODUCTIVE FARMING 



this law were an absolute one, man would find it impossible 

 to make any improvements in his animals by careful selection. 

 Variation among farm animals is a natural tendency for 

 them to differ from each other and from their parents. No 

 two calves in the barn are alike. The pigs in a litter may look 

 alike when young, but the attendant can soon point out 

 differences. This tendency to vary allows stockmen to select 

 the desired types and produce, in time, the animals desired 

 for special purposes. 



Exercise. — Variation Among Animals. — Let pupils tell 

 of variations in color or other marked characters among 

 pure-bred stock such as cattle, poultry, or swine. Care 

 should be used to bring out the law of variation. 



Reversion is the tendency for young animals to exhibit 

 characters of distant ancestors, which their own parents 

 did not possess. 



Sometimes there are characters present in certain indi- 

 vidual animals which are not like any of the animals of the 

 breed. Such cases are called mutations or sports. Such very 

 odd or different characters are not always transmitted by 

 animals to their offspring. When such new characters are 

 given to the offspring they may become fixed and give rise 

 to a new line or strain of animals in a breed. The hornless 

 or polled Shorthorn cattle and the polled Hereford cattle 

 were first started from sports. Now the hornless character 

 of those strains has become fixed. The groups may even be 

 considered as distinct breeds. 



Pure=Bred Animals. — These are animals which have been 

 bred along a certain line or within the bounds of the breed 

 for many generations. The vulgar term full-blood should 

 not be used to express purity of blood in an animal. The 

 term thoroughbred is also incorrectly used in this connection. 

 This name belongs to a breed of race-horses which originated 

 in England. 



Grades are animals which are not pure bred but are part 



