1148 
Journal of Agricultural Research 
Vol. V, No. 35 
that “Spotted Poland-Chinas” are far more fecund than ordinary strains. 
Swine judges commonly consider long-bodied sows more prolific than 
their chubbier mates. A comparison of 1,000 litters of “large type” 
Poland-Chinas with 1,100 litters of “small type” showed no significant 
differenceinfertility. Themeanfor the “large type” was7.854±0.0456, 
and for the “small type” was 7.896±0.0436. Furthermore, the stand¬ 
ard deviation of the two groups was almost exactly the same, being 
2.142±0.0323 for the former and 2.146^0.0309 for the latter. The 
writers have never seen more than isolated instances brought forward 
to confirm the popular ideas on this subject and feel that the bulk of 
such beliefs have resulted from mere advertising schemes. 
Breed certainly has its influence. Bitting (1) has averaged the litter 
sizes for 400 Berkshires, 1,086 Poland-Chinas, and 600 Chester Whites, 
with the following results: 
Berkshire.. 8. 22 pigs per litter. 
Poland-China. 7.45 pigs per litter. 
Chester Wriite. 8. 96 pigs per litter. 
Surface (26) computed the means and standard deviations in the 54,515 
litters of Poland-Chinas and the 21,652 litters of Duroc-Jerseys studied 
by Rommel (22). His constants follow: 
Mean. Standard deviation. 
Poland-China. 7. 435±o. 01 2. 038^0. 013 
Duroc-Jersey. 9.337± .021 2. 427^ .016 
The large numbers here involved undoubtedly prove that real breed 
differences in fertility exist. 
Pearl (15,16) found the number of mammae to be correlated positively 
with the number at a birth when different species are compared, but the 
coefficient is very low within the species. Parker and Bullard (14) 
correlated the same characters in 1,000 litters of swine and obtained a 
coefficient of 0.0035 ±0.0124. The senior author 1 treated the same 
point in 170 litters of which he had made genetic studies and obtained a 
coefficient of — 0.0059 ± 0.0517. 
These figures certainly demonstrate that the number of mammae in 
swine is not related to fertility; in fact, nothing so far discussed presents 
reliable external characters on which fertility selections can be made. 
Apparently fecundity has as profound a genetic as physiologic basis. 
VALUE OF HERDBOOK DATA 
There is now on record an immense mass of data relating to fertility 
inheritance in swine, in the volumes of the different breed registry asso¬ 
ciations. In addition to the name and number of the animal, its parents, 
breeder, etc., the size of litter in which it was farrowed is usually stated. 
1 Unpublished data. 
