1906.] 



FEMALE LINE IN POLAND SOWS. 



253 



TABLE Vn. — Correlation in Size of Litter of Poland China Sows 

 BETWEEN Mother and Daughter. — " American Poland China Record." 



Conclusions. 



From the first work in statistics of fecundity of sows (Rommel, 

 1906), it is evident that in Poland China hogs there has been an 

 increase of .48 in the size of litter in the twenty years between 1882 

 and 1902. This result may be attributed to one of two factors. It 

 is either the result of selection (probably more or less accidental) of 

 sows (and boars) from large litters and a consequent inherited ten- 

 dency toward the production of larger litters, or a gradual improve- 

 ment in the environmental conditions, bringing about the same result 

 by external factors. From the first work it is impossible to do more 

 than theorize as to the true cause, the theories being based, of course, 

 on a knowledge of the usages of breeders. 



The tabulation of the sizes of litters from mothers and daughters 

 and the determination of the coefficient of correlation (r) shows that 

 there is an actual correlation between the size of litters of two 

 successive generations, and we are consequently justified in con- 

 cluding that size of litter is a character transmitted from mother 

 to daughter. The coefficient of correlation for the five years is small 

 (.06), but it is appreciable and consequently it would appear proved 

 that, bv judicious selection for breeding purposes of sows from large 

 litters, the average for the breed may be increased. This, combined 

 with the fact that the average has actually been increased, gives us 

 evidence that may be considered very strong. 



Unfortunately the cards used in this work for litters for 1902 

 of the " American Poland China Record " were not written to include 

 the sire, and we are consequently unable at present to determine 

 from these data the influence of the boar on the size of litter of a 

 sow of his oflfspring. This work is being continued, however, and 

 these additional data are being recorded. 



