86 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



number of counties, and, in a few cases, sections of a State, includ- 

 ing several counties, have adopted one particular breed of poultry 

 in a standardization scheme. The work has been largely carried 

 on through the parents and older people in States where boys' and 

 girls' poultry club agents are assigned. One Barred Plymouth 

 Rock association in Virginia has developed a cooperative selling 

 association requiring a manager to handle the business. Reports 

 from 4 States show 48 breeding associations with almost 2,500 mem- 

 bers. In Kentucky 22 counties are organized for distributing' 

 hatching eggs of one breed of poultry in each county to the members. 



ANIMAL GENETICS 



Experiments on the effects of inbreeding in guinea-pigs, begun in 

 1906, have now been carried to the eighteenth generation, wholly by 

 matin^s of brother with sister. The mere fact that the closest 

 possible inbreeding can be carried on through so many generations 

 without any very obvious degeneration is noteworthy, especially as 

 the mere following of a rigid system of mating has prevented any 

 effective selection. There has, however, been a slow but progressive 

 decline in all characters connected with vigor. The principal char- 

 acters which have been studied are fecundity (size and frequency of 

 litters), birth weight and later growth, and vitality as measured by 

 the percentage of the young born alive and the percentage of these 

 raised to weaning. 



Another definite result is the pronounced differentiation of the 

 various inbred lines which arose from the same original stock. This 

 is most obvious in the case of color. The original matings produced 

 as a rule a great variety of colors. Now each family has a character- 

 istic color and pattern to which it breeds true and by which it can be 

 identified. 



Different inbred families have been crossed together very exten- 

 sively. The ^oung have shown a very distinct improvement in 

 vitality and size and have produced larger litters than the parental 

 stocks raised simultaneously. It appears that each family supplies 

 much of what the other lacks, and more vigorous offspring results. 



From these and other results it appears that the primary effect of 

 inbreeding is simply the fixation of hereditary factors. The results 

 of the crosses between different inbred families indicate that factors 

 favorable to vigor are in general dominant over unfavorable ones. If 

 one does not tie oneself to too rigid a system of breeding and uses from 

 the first the greatest care in the selection of breeding stock, there 

 appears to be no reason why a high degree of vigor can not be com- 

 bined with the homogeneity and prepotency only to be secured by 



inbreeding. 



ANIMAL HUSBANDRY EXPERIMENT FARM. 



The work at the experiment farm of the bureau used by the Animal 

 Husbandry Division, at Beltsville, Md., has been continued as here- 

 tofore. During the year a tile-ditching machine was purchased. The 

 building erected to replace the sheep barn which was destroyed by 

 fire three vears ago has been completed and equipped. The incu- 

 bator cellar and laboratory also has been completed. 



