COEX. AXD HOG CORRELATIONS 39 
Heavy fall breeding withdraws young sows from the current summer 
slaughter (season ending October 31) and thus tends to increase the 
average summer weight. Generally speaking, sows bred in the fall 
will be slaughtered the next summer after weaning their pigs, when, 
as relatively old sows, they raise the average summer weight. Heavy 
spring breeding also tends to increase the average summer weight by 
withdrawing relatively light sows from slaughter at the beginning of 
the season and returning some of them at a heavier weight at the end 
before November 1. Light fall and spring breeding should have the 
opposite effects. 
Thus a heavy summer weight should indicate a period of relatively 
heavy breeding, beginning the preceding fall and lasting through the 
following fall, and, conversely, with light summer weight. The cor- 
relations indicate that summer weight is determined by the hog-corn 
price ratio of the preceding winter to a greater extent than by any 
other combination of preceding factors involved in this study. To 
complete the argument, it must be supposed that a favorable hog-corn 
price ratio initiates a period of heavy breeding which lasts through 
the fall nearly a year after the ratio has begun to fall. In other words, 
it appears that heavy breeding is determined not so much by the 
immediate ratio of hog prices to corn prices as to the memory of 
profits obtained during the past year. 
This close relation between summer weight and the relative amount 
of breeding is brought out even more emphatically by the correlations 
with following events. The correlation between summer weight and 
the winter slaughter a year and a half later ( + 0.78) is one of the 
closest in the tables. It is confirmed by the even higher correlation 
of summer weight with the corresponding winter-pork production 
( + 0.83) . These correlations require that a heavy (or light) summer 
weight be accompanied, with great regularity, by heavy (or light) 
fall breeding. Relatively heavy breeding in the spring and preceding 
fall is indicated by the wave of slaughter (fig. 20) rising from the low 
point of the preceding: winter to the peak in the second following 
winter, referred to above (-0.61, -0.02, -0.06, +0.48, +0.78). 
The reason why summer weight tends to reverse itself every two 
years is now apparent. The heavy (or light) breeding of which it is 
an indicator, reaches its climax nearly a year after the high (or low) 
hog-corn price ratio which justified it. The result is an overpro- 
duction (or underproduction) of hogs, reaching its climax in the 
second winter and causing a reversal of hog prices and hence in the 
hog-corn price ratio, in breeding, and thus finally in suminer weight. 
The same "'vicious circle' ; of successive overproduction and under- 
production is brought out, though less sharply in winter slaughter 
and in both summer and winter hog prices. 
Probably the cycle is revealed most sharply by summer weight 
because the latter is of little importance in itself and no forces tend 
to check extreme fluctuations. Fluctuations in slaughter resulting 
from those in breeding tend to be smoothed out b}~ the delaying of 
slaughter at times of surplus and low prices and advance in time of 
slaughter in times of scarcity and high prices. 
Summing up, summer weight is determined primarily by the relative 
amount of breeding from the preceding through the following fall and 
secondarily by the amount of finish. Since these two factors are 
closely related to each other, summer weight is a very close indicator 
