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THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
plant that is equipped with cold storage. One can visualize a
central unit through which many of the marketable food products of the community will be prepared, conditioned, standardized, preserved, and sold. To this unit may also come the
foods needed but not produced locally--a crate of blueberries
from Maine, a hind quarter of a fed yearling from the Cornbelt,
a carload of sweetpotatoes from the South. Market outlets will be
more numerous and the food supply more varied as "cold
storage" is brought closer and closer to the farm and the farm
home.
Local conditions will be the determining factor in the adaptability of freezer lockers and refrigeration to a particular community. New facts and new inventions will influence the extent
to which controlled temperatures will affect our methods of
food storage and distribution. But the practicability of refrigeration and cold storage lockers for preserving the family's food
supply appears to have been proved.
THE MINNESOTA STUDIES OF CROSSBREEDING SWINE 1
L. M. WINTERS, P. S. JORDAN, O. M. K ISE R AND
R. E. COMSTOCK
University of Minnesota
This project was intitiated in the fall of 1928. For six years,
the experiment was carried out independently at the West Central Experiment Station, Morris, Minnesota, by Jordan and at
the Northwest Experiment Station, Crookston, Minnesota, by
Kiser. The back-crossing phase of the project was then conducted
for one more y ear at Crookston and for two more years at Morris.
During this time, 1,589 pigs were farrowed alive, and 962 were fed
out under experimental conditions. Not all the pigs weaned
were fed out under experimental conditions because each year a
n u m b e r were farrowed too late to be inculded very satisfactorily
in the feeding trials.
PROCEDURE
The breeds used were the Poland China, Duroc Jersey, Chester
White, and Yorkshire. The project was so organized that the
same boars that sired the purebred pigs also sired the crossbreds.
In addition, the dams of the first-cross pigs were either half or full
sisters to the dams of the purebred pigs. The crossbred gilts kept
1Published as Paper No. 1556 of the Scientific Journal Series of the Minnesota Agricultural Experiment Station.
THE A M E R I C A N SOCIETY OF A N I M A L P R O D U C T I O N
197
for breeding were in all cases half sisters to the purebred gilts
used for breeding. On the average, they were closer than half
sisters because of relationship through their dams.
Gilts only were used for breeding throughout the experiment,
and all pigs were spring farrowed. All pigs were weaned at 56
days and closed out of the feed lot at 220 pounds. Standard
rations were used through the entire period.
EXPERIMENTAL RESULTS
Detailed results have been published elsewhere (1 and 2);
hence summaries only will be included here.
The main advantages of the crossbreds over the purebreds are
presented in Table 1. Statistical treatment by the "t test" is also
presented. A study of the table will show that in most respects
the differences are significant or at least on the border of significance. In a review of both Tables 1 and 2, it should be borne in
mind that there were 15 lots of first-cross and only eight and six
of three-breed-cross and back-cross, respectively. Both of the
latter groups are, therefore, seriously handicapped from the standpoint of statistical treatment. It should also be borne in mind
that feed lot equipment did not permit all data being gathered
by litters; hence, all analyses are by lots rather than litters. This
method of treatment handicaps the data for statistical analysis.
From Table 1, it can be observed that as regards weight per pig
at weaning, less time to reach 220 pounds and less feed per 100
pounds gain, the differences in favor of the crossbreds are all significant. In daily gain the differences in favor of the first-cross and
three-breed-cross are decidedly significant. The difference in
favor of the back-cross is on the verge of significance.
In litter weight at weaning only the difference in favor of the
three-breed-cross is significant; that of the first-cross is on the
verge of significance. In number weaned and total weight per
litter of live pigs, none of the differences are significant. In number born alive per litter, on]y the data in favor of the first-cross
are significant. Table 2, however, brings out differences here
which are significant. When the three types of crossbreds are put
in one group and contrasted with the purebreds as to number
born alive, the differences are significant to the extent of a 2.90 F
required and 4.26 f o u n d . ~ T h e differences between purebred,
first-cross, and three-breed-cross are on the verge of significance:
a 3.09 F required and 2.99 found. In number weaned and in litter
weight at weaning, the differences between the three groups are
highly significant.
Table 2 brings out rather clearly that the crossbreds are superior
to the purebreds through the suckling period. Since the means
198
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for the three-breed-cross are higher than the means for the firstcross, it is apparent that the differences between purebred and
crossbreds have not suffered by the inclusion of the three-breedcross. A comparison of the significance of differences between
purebreds and first-cross through the weaning period shows
significance in most points in Table 1 but fails to do so in Table 2.
The reason for this is that in Table 2, the number of lots has been
reduced to comparable data in the three-breed-cross. In this
connection, it is very significant that when we reduce the numbers (Table 2) the differences between the first-cross and purebreds are barely significant, but with the same numbers, the
differences between the three-breed-cross and the purebreds are
significant in every case through the weaning stage. This shows
very clearly the superiority of the three-breed-cross over firstcross through this period; it emphasizes the superiority of the
crossbred sows as mothers.
The differences between the different crosses and the purebreds
after weaning are about the same (the pigs are then removed
from the environmental influence of the dams). For the factors
considered after weaning as large numbers are required by the
pigs out of crossbred mothers as in the first cross to bring out
significant differences. This also emphasizes the advantageous
influence of the crossbred dam. Through the suckling period,
there are differences b e t w e e n the crossbreds, and these differences
are in favor of the pigs out of corssbred sows. After .weaning, all
three groups of crossbreds show about the same amount of advantage over the purebreds.
CONTINUOUS
C R O S S B R E E D I N G IN P R A C T I C E
Evidence (2) has already been presented showing that both
crisscross and rotation breeding work satisfactorily in practice.
Table 3 is a summary of the past ten years' hog production by
Hiram Johnson. Gilts only have served as brood sows. Up to
1932, Mr. Johnson maintained a herd of high grades, practically
purebreds. In 1932, he made the first cross, this was followed
by a third breed cross, and the rotation system of breeding has
been followed ever since. The data from Mr. Johnson's record
do not prove that the continuous crossbreeding system has been
responsible for the improved performance of his sows after 1932,
but they do prove, beyond all question, that the use of crossbred
sows did not result in a deterioration of his herd for market
production. Mr. Johnson's hogs are mixed in color, but they
bring top price on the market.
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ARE THE RESULTS OF THIS EXPERIMENT OUT OF LINE WITH
OTHER RESEARCH WORK?
In 1922 Wright (3) showed ver y conclusively the advantages
of crossbred females over purified strains for breeding purposes.
In a study of fat lamb production in South Africa, Bonsma (4)
found that crossbred ewes were superior to purebreds for fat lamb
production. As a result of his studies, he advocates a breeding
policy whereby crossbred ewes will be produced systematically
in the range area and then made available to the farming areas
for breeding to a ram of a third breed. Hammond (5) advocates
breeding crossbred ewes to rams of a third breed for fat lamb
production. Hammond ver y aptly points out "Haphazard crossbreeding is useless and ultimately leads to failure, but a properly
organized system will give good results. It should be emphasized
that indiscriminate crossing is a v e r y different thing from a wellthought out system, the one leading to economic failure and the
other to success." In New Zealand, the crossbred pig has commanded enough respect so that half-bred litters are now recorded
by the P i g Breeders' Association (6).
CRITICISMS OF THE EXPERIMENT
During the past year, many pointed criticigms of the experiment
have appeared. We will deal with only one (7), since it was
somewhat the f or e r unner and has served as a base for the others.
Anderson states, "If more than one litter is produced per year per
sow, confusion would soon exist in its application, and a mixture
of breeding stock would soon exist." All the farmer has to do
to avoid confusion is retain the same sows for fall farrowing that
farrowed in the spring, or he may follow the practice of many
farmers and use spring gilts for spring farrowing and fall gilts
for fall farrowing. This practice is especially satisfactory in
northern latitudes where it is advisable to have the spring and fall
pigs farrowed closer together than is permitted by use of the same
SOWS.
Anderson states, "If the herd is changed for each pig crop and
all the sows sold as soon as the first litter is weaned, a mistake
in selection o~ a sire would be v e r y costly." How can all the
sows be sold as soon as the first litter is weaned? The sows will
not be sold until some time after the last litter is weaned. By that
time the farmer will know if his boar has been a failure. He will
then deal with it the same as he would with purebred or grade
SOWS.
Anderson states further, " T h e efficiency of this system is yet
unproven experimentally and in'practice." Evidence has already
THE AMERICAN SOCIETY OF ANIMAL PRODUCTION
203
b e e n p u b l i s h e d showing t h a t the s y s t e m did w o r k e x p e r i m e n t a l l y .
F u r t h e r evidence has b e e n p r e s e n t e d in this paper.
F o r the p u r p o s e of theoretical analysis we will a s s u m e that o u r
critics are correct a n d t h a t the a b o v e data a n d conclusions a r e
all wrong. We will t h e n see to w h a t conclusion this leads us.
F r o m the e x t e n s i v e e x p e r i m e n t s in corn breeding, we a r e justified in generalizing to the e x t e n t t h a t w h e n two strains are crossed
the h y b r i d vigor resulting is in a b o u t direct p r o p o r t i o n to the
genetic differences b e t w e e n the two strains for the factors affecting vigor. If t h e n we a r e to concede to the critics that t h e r e is no
g r e a t e r or m o r e consistent vigor w h e n two b r e e d s of swine a r e
crossed t h a n w h e n two bloodlines within a b r e e d are crossed, we
h a v e d e s t r o y e d all a r g u m e n t for the recognition of s e p a r a t e b r e e d
organizations. T h e n the only differences b e t w e e n o u r b r e e d s a r e
superficial differences such as color, set of ears, etc. This w o u l d
indeed be a v e r y p o o r t r i b u t e to p a y the m e n w h o h a v e built o u r
b r e e d s of livestock. A n d w h e n we t h e n stress the p u r i t y of the
breeds, it places us in the class with the poultry, rabbit, a n d m o u s e
fancier w h o f r a n k l y admits that he is breediIlg his pets as a fancy.
We, the authors, refuse to concede that the w o r k of o u r constructive b r e e d e r s has b e e n t h a t futile.
On the o t h e r hand, t h e r e is a second g r o u p of critics w h o concede t h a t the first cross carries h y b r i d vigor b u t t h a t the crossbred
females do not m a k e satisfactory mothers. This critic t h e n refuses
to concede t h a t the p r o d u c t i o n of y o u n g and lactation a r e physiological functions c o m p a r a b l e to r a t e of g r o w t h a n d e c o n o m y of
gains. H e c o m p l e t e l y ignores W r i g h t ' s studies of crosses in guinea
pigs which stands as a classic in a n i m a l genetic research. T h r o u g h
his v e r y a r g u m e n t s the critic w o u l d d e s t r o y all sound a r g u m e n t
for the existence of o u r p r e s e n t b r e e d s of swine.
REFERENCES
1. Winters, L. M., O. M. Kiser, P. S. Jordan, and W. H. Peters (1935) A six
years' study of crossbreeding swine. Minn. Bul. 320.
2.
(1936) Crossbred swine. Minn. Special Bul. 180.
3. Wright, Sewall (1922) The effects of inbreeding and crossbreeding on
guinea pigs. U . S . D . A . Bul. 1121.
4. Bonsma, F. M. (1936) Fat lamb production in relation to Merino sheep
farming in South Africa. University of Pretoria, Series No. 1, 32.
5. Hammond, John (1936) Crosses and breeds of sheep for wool and meat
production. La Res. No. 67.
6. Minutes of monthly meeting of the executive. Jan. 20, 1937. The Manawatu-Oroua Pig Development Recording Club.
7. Anderson, Arthur L. (1936) Shall we cross-breed? Breeder's Gazette,
CI: 6.