PRINCIPLES OF SWINE BREEDING 27 



Reversion, or atavism. — Breeders frequently have 

 animals appear in their herds that are unlike their parents 

 or any near ancestor, but they seem to resemble some of 

 the older types of animals from which the breed origi- 

 nated. These variations are referred to as reversions, 

 and the tendency to revert is spoken of as atavism. The 

 tendency to revert is constant, and it seems that the 

 higher bred and more specialized our types become, the 

 more subject they are to reversion. It seems that even 

 through most extensive breeding we cannot escape the 

 influences of atavism. Especially does atavism manifest 

 itself when two different strains are crossed, or when the 

 animals are placed under different or adverse conditions. 

 Usually these reversions are undesirable in breeding, but 

 those reversions resulting from changed environmental 

 conditions can be controlled to some extent. Those 

 atavisms that are congenital are beyond our control and 

 use. Therefore, the further we advance in our swine 

 breeding the greater will be the efforts required to main- 

 tain what we have produced up to the attained standard. 



Superfoetation and superfecundation. — This is an ab- 

 normal condition resulting from a pregnant sow con- 

 ceiving during a pregnancy. They sometimes will come 

 in heat while pregnant, and if served may conceive. 

 This condition is rare, however. It also may happen 

 that during a period of heat a sow may be served by more 

 than one boar, with the result that she may have pigs in 

 the same litter by both. Such a condition is referred to 

 as superfecundation. It will occur often where the 

 opportunity is presented. 



Fecundity. — Fecundity of swine refers to their pro- 

 lificacy, or their ability to produce young in abundance. 



