38 BULLETIN 1300, U. S. DEPARTMENT OF AGRICULTURE 
di|ately preceding price. Finally, summer slaughter shows a high 
correlation with the preceding summer weight. 
Summer weight can be of very little direct importance as a factor, 
since, as has been shown, it plays only an insignificant direct part in 
determining even summer pork production. It is evident, however, 
that it must be a close indicator of some factor, relatively independent 
of the corn situation, which plays a predominant part with respect 
to hogs. 
SUMMER WEIGHT AND BREEDING 
The five highest correlations between summer weight and preceding 
conditions, as shown in Table 8, indicate that variation in summer 
weight shows a remarkably strong tendency to reversal after a period 
of two years ( — 0.61). Some important factor back of summer 
weight must tend to oscillate in a 4-year period. The other high 
correlations show that a heavy summer weight tends to follow a year 
of light slaughter (summer —0.38, winter —0.61), of cheap corn 
( — 0.51), and to some extent a big corn crop ( + 0.37). 
The first suggestion is that the average weight depends merely on 
the quantity of corn available in the country and the number of 
hogs to which it is to be fed. A big corn crop coupled with a light 
winter slaughter should mean an abundance of corn for summer 
feeding. There is, however, only 42 per cent determination by this 
combination of factors. Moreover, the absence of correlation with 
the slaughter of the summer in question ( — 0.02) raises doubt as to 
whether the number of hogs in the country is an important factor. 
The fact that the price of corn has a distinctly greater effect than 
the size of the crop (which is not true in the case of winter weight) 
indicates that something other than mere quantity of corn is involved. 
In fact, no combination of preceding factors which does not include 
the price of corn has been found to give higher than 47 per cent deter- 
mination. Price of corn and winter slaughter give 55 per cent deter- 
mination. Still higher is that given by price of corn and winter price 
of hogs (60 per cent). By taking into account winter slaughter in 
addition to these two factors the percentage determination is raised 
to 63, which is the highest figure that has been found. Thus it is not 
so much the quantity of corn per head of hogs as the ratio of hog 
to corn prices during the preceding winter that determines summer 
weight. 
The hog-corn price ratio is the factor which measures the profits in 
hog raising and hence may be expected to have a rather close influence 
on the amount of breeding. It is probably largely through this effect 
that it controls summer weight. 
Average live weight must, of course, be determined by the type of 
hog, the average age at slaughter, and the average degree of finish. 
The last factor should be determined by the ratio of corn supply to 
the number of hogs, which, as has been shown, is not of first impor- 
tance. The average age at slaughter depends on a number of things — 
the type of hog, the market demand, and the number of sows bred. 
A change in type and in market demand were undoubtedly responsible 
for the great decline in average live weight between 1870 and 1915. 
This long-period change, however, was eliminated from consideration 
by measuring the fluctuations from a falling trend instead of using 
the absolute live weight. Type and market demand can have little 
to do with the fluctuations from year to year. 
