1146 
journal of Agricultural Research 
Vol. V, No. as 
Rommel and Phillips (24) studied the inheritance only through the 
female line, taking no account of a possible influence of the male. George 
(6) correlated the size of litter with that of the paternal and maternal 
grandams, respectively. Only 296 litters were involved in his popula¬ 
tions; hence, his probable errors were large. But in the dam and 
daughter comparisons he approximated very closely the result obtained 
by Rommel and Phillips. His four coefficients follow: 
Daughter and dam. o. 0615 ±o. 0390 
Dam and grandam. 11471k • 0343 
Daughter and maternal grandam.002 5± . 0392 
Daughter and paternal grandam.05081k • 0392 
None of these correlations are three times as large as their probable 
error; hence, none are really significant. 
Simpson (25) approached the problem from a Mendelian standpoint 
by crossing a wild German Schwarzwald boar to a young Tamworth 
sow. The Schwarzwald normally averages 4 pigs to the litter, the Tam¬ 
worth about 11. The particular sow used was farrowed in a litter of 12 
pigs, and to the stint of the wild boar farrowed 9 pigs. In the Fj genera¬ 
tion three females were bred, one to a litter mate and the other two 
to sires unnamed. The first sow produced 4 pigs, the others 4 and 6, 
respectively, all in their first litters. The sow producing the 6-pig 
brood was later served by a pure Schwarzwald boar and farrowed 7 
pigs, being apparently constant for that degree of fertility. One of the 
sows from the brood of 6 gave birth to 12 pigs when mated to a pure Tam¬ 
worth male. The evidence for a segregation of fecundity factors seems 
fairly clear, although the numbers are small. 
NONGENETIC FACTORS AFFECTING FERTILITY 
External factors play a great part in the realization of the inborn hered¬ 
itary capacity for reproduction. Marshall (12, 13) discusses at length 
the relation between season and productivity, while the sterility of wild 
animals in captivity or of domestic animals transferred to vastly different 
altitudes is proverbial. Marshall and Eward (4, 5) have both studied 
the effect of “flushing” in sheep, and Eward has conducted some very 
exhaustive investigations into the relation of the various compounds of 
nutrition to litter size in swine. Using the rate of gain at breeding time 
in gilts 1 as an indication of the state of nutrition, Eward has found as 
much as an average difference of two pigs per litter in favor of the best 
gainers in each experimental lot, when compared with the poorest gainers. 
Protein added to a nitrogen-deficient ration (com alone) produced a 
marked rise in the fertility of gilts and a medium rise in the fertility of 
older sows. 
Many stockmen believe that overfatness diminishes fecundity. There 
may be both a physical obstruction of the reproductive organs due to 
1 A gilt is a young sow intended for breeding purposes. The term is usually applied only until the first 
litter is produced, although it is sometimes extended throughout the suckling period. 
