448 Pork Production 



mating of individuals descending from the great Long- 

 fellow 16835. 



It would be a mistake, however, not to set down the 

 observation that practically every one of these breeders 

 recognized and experienced the possible evils which lay 

 hidden in the system. Practically every one who success- 

 fully used in-breeding to fix type and establish uniformity 

 came to the point in his experience where he clearly saw 

 the necessity of introducing fresh blood, or, in other 

 words, of making an out-cross. This was apparent in a 

 tendency towards sterility and a lack of vigor and con- 

 stitution. Further, the observations of everyday experi- 

 ence furnished some pertinent facts in this connection. 

 A gilt produces a litter of pigs by her own sire and 

 the usual result is a large proportion of runts, with 

 possibly one or two of them half male and half female 

 (hermaphrodites). Some of the pigs, on the other hand, 

 may have escaped apparent injury and are unusually 

 thrifty and vigorous. Such extremely close breeding 

 almost invariably has the effect of greatly reducing the 

 vigor of pigs. 



If the experiences of the early constructive breeders 

 are put together, the general observations of present-day 

 breeders, and the results of scientifically planned breeding 

 experiments with small animals like rats, mice, guinea 

 pigs, and insects, the result will support the following 

 conclusions : 



1. In-breeding has the effect of simplifying and puri- 

 fying the hereditary or breeding qualities of an individual, 

 whether good or bad. This it does by bringing into 

 expression characters which were once latent or hidden, 

 thus enabling the breeder to eliminate from the herd 

 those animals which show undesirable reversions. It is 



