BREEDING & GENETICS PIH-39
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Crossbreeding Systems for Commercial Pork Production
Authors:
William T. Ahlschwede, University of Nebraska
Charles J. Christians, University of Minnesota
Rodger K. Johnson, University of Nebraska
O. W. Robison, North Carolina State University
Reviewers:
Russell and Jane Clark, Frankfort, Indiana
Walter A. Gross, University of Rhode Island
James and Shirley Mitchell, Eaton, Ohio
Irvin Omtvedt, University of Nebraska
Years of experience and research show that crossbreeding
pays. The hybrid vigor gained through crossbreeding improves per-
formance of both the breeding herd and individual pigs. Surveys
indicate that more than 90% of market hogs in the U.S.A. are
crossbreds. However, crossbreeding is not sufficient to assure
profitable performance. Rather, specifying which breeds to cross
and how to cross them is needed to describe a crossbreeding sys-
tem. Choices among crossbreeding systems can dramatically affect
profit levels.
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|Table 1. Heterosis advantage for production traits. |
|_________________________________________________________________ |
| First Multiple |
| cross cross |
| purebred crossbred Crossbred |
|Item sow sow boar |
|_________________________________________________________________ |
| Percentage advantage over purebred |
|Reproduction |
| Conception rate 0.0 8.0 10.0 |
| Pigs born alive 0.5 8.0 0.0 |
| Littersize 21 days 9.0 23.0 0.0 |
| Littersize weaned 10.0 24.0 0.0 |
|Production |
| 21-day litter weight 10.0 27.0 0.0 |
| Days to 220 lb. 7.5 7.0 0.0 |
| Feed/gain 2.0 1.0 0.0 |
|Carcass composition |
| Length 0.3 0.5 0.0 |
| Backfat thickness -2.0 -2.0 0.0 |
| Loin muscle area 1.0 2.0 0.0 |
| Marbling score 0.3 1.0 0.0 |
|__________________________________________________________________|
The value of crossbreeding depends upon hybrid vigor. Hybrid
vigor, or heterosis, is the superiority of the crossbred compared
to its parental breeds. In pigs, hybrid vigor appears important
for pig survival and growth, litter size and mothering ability in
sows and gilts and boar breeding performance (Table 1). Differ-
ences in performance among breeds can be utilized by some
crossbreeding systems to take advantage of the best attributes of
breeds while minimizing the impact of their deficiencies.
Crossbreeding became a common practice as a result of
crossbreeding research in the 1930's and 1940's. Crossbred off-
spring of purebred parents were indeed superior. Following the
lead of corn growers, crossbred females became the base of com-
mercial production. However, with pigs, development of inbred
lines did not prove feasible. Rotational crosses, which nicely
fit the most common styles of production in the 1950's and
1960's, were generally adopted. Changes in the way hogs are pro-
duced have led to increased adoption of terminal crosses in the
1980's.
Rotational Crosses
Two general types of crossbreeding systems are described.
Rotational crossbreeding systems utilize replacement gilts from
the market crosses and change breeds of boar each generation. A
three-breed-rotation uses three breeds of boars, rotated in
order, one breed per generation (Figure 1). A rotation of two
breeds is called a criss-cross. Rotations of up to six breeds
have been used to advantage.
Table 2. Heterosis percentage in rotational crosses.
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Generation number Equilib-
__________________________________
Crossbreeding system 1 2 3 4 5 6 rium
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Heterosis
Two breed rotation
``crisscross'' 100.0 50.0 75.0 62.5 68.9 67.2 66.7
Three breed rotation 100.0 100.0 75.0 87.5 87.5 84.4 85.7
Four breed rotation 100.0 100.0 100.0 87.5 93.8 93.8 93.3
Five breed rotation 100.0 100.0 100.0 100.0 93.8 96.9 96.8
Six breed rotation 100.0 100.0 100.0 100.0 100.0 96.9 98.4
Crisscross with F1
boars (four breeds) 100.0 75.0 87.5 81.3 84.4 82.3 83.3
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Rotations using crossbred boars take advantage of hybrid
vigor in boar breeding ability. After the first full round of
breeds in a rotation, some heterosis is lost. To the degree that
genes of the breed of the service boar are present in the sow,
heterosis is reduced. As shown in Table 2, rotations of three or
more breeds retain relatively high levels of heterosis. Serious
losses of heterosis in rotations occur when the planned order of
breed use is not followed. This is likely when generations of
sows are not kept separate or when color is used as an indicator
of sow breed.
The level of heterosis in advanced generations of a rota-
tional cross depends upon the number of breeds in the rotation.
As shown in Table 2, initial crosses all express 100% heterosis.
With succeeding generations, the heterosis level modulates (the
first six generations are shown) until an equilibrium is reached.
The heterosis equilibrium, characteristic for each rotation, is
shown in the right hand column of Table 2.
Rotational crosses are general purpose crosses. Offspring of
each generation are used for market production and as replacement
gilts. Since breeds appear first as the sire of the market hogs
and a generation later as the sire of the sows, performance both
as market hogs and as breeding stock is considered in choosing
breeds. There is little opportunity to take advantage of the
differences among the breeds used in the cross. Performance in
rotations would be maximized if there were no breed differences
in performance. We would want them to all be as good as the best
in every trait.
Terminal Crosses
Terminal crosses take their name from the fact that the sys-
tem terminates with the market cross. Replacement gilts are not
saved from the matings designed for market production. A simple
terminal cross would be a Yorkshire sow mated to a Hampshire boar
with all of the offspring marketed. Replacement gilts are pro-
duced by matings other than the market crosses. Because breeds
are used in specialized roles, (in this example, the Hampshire
boar sires market hogs but not replacement gilts) terminal
crosses can take advantage of breed differences.
A more common terminal cross is mating Landrace x Yorkshire
first cross (F1) females to Hampshire x Duroc first cross (F1)
boars (Figure 2). The sow in this case is a cross between two
breeds which have reputations as good sows. The sire is a cross
of two breeds with reputations for efficient lean gain and fast,
efficient gain. In this way, terminal crosses allow breeds to be
used in roles that take advantage of their strengths, while
minimizing their deficiencies. This allows terminal crosses to be
more productive than rotational crosses. In this example, maximum
use of heterosis is realized. The boar and the sow are both
first crosses with 100% heterosis, important for breeding per-
formance, littersize, and maternal performance. Since there are
no common breeds in the parents, the offspring also have 100%
heterosis, important for piglet vigor, survival, and rapid gain.
In terminal crossbreeding systems, replacement gilts are not
selected from the market crosses. They must either be purchased
or produced in special matings. Because of this, terminal crosses
were generally not used by commercial pork producers. Histori-
cally, rotational crosses fit the production systems. However,
production systems have changed. Many intensively managed pork
producing units today are able to program the special gilt pro-
ducing matings into their schedule without difficulty. Terminal
crosses are becoming more popular.
Opportunities exist to combine rotational and terminal
crossbreeding systems. Many producers have used rotational
crosses among breeds that excel in maternal performance to pro-
duce replacement gilts for terminal matings. These systems,
called rotaterminals, combine the ease of operation of a rotation
with the specialization and high productivity of terminal
crosses.
Crossbred Boars
The use of crossbred boars has sparked discussion and con-
troversy in the industry in recent years. In the mid 1970's their
use was sufficient to stimulate stories in the popular press. By
the late 1970's, research trials had been conducted that clari-
fied their attributes. Crossbred boars were found to excel pure-
bred boars in breeding performance as measured by farrowing rate
of sows and gilts to which they were exposed. They were more
vigorous, active breeders. While this advantage may appear small
(Table 1), timely pregnancies are crucial to intensively managed
pork producing operations. In addition to the improved conception
rates identified in research trials, commercial pork producers
report fewer problems and longer useful lives with crossbred
boars.
Crossbred boars can be part of a crossbreeding system. Pure-
bred boars, crossbred boars, and combinations of purebred and
crossbred boars are being used in productive, profitable
crossbreeding systems, which maintain high levels of heterosis.
The availability of both purebred and crossbred boars allows
increased flexibility in planning and operating crossbreeding
systems. In the discussion that follows, both types of boars are
used. Whether purebred or crossbred boars are used, the success
of the breeding systems depends upon following the system.
Evaluating and Choosing
Crossbreeding Systems
One would like to choose the crossbreeding system that would
provide the most favorable economic outcome. However, the many
factors involved in determining the outcome of a system make it
difficult to effectively evaluate. Farm objectives vary, facili-
ties differ, and desired breeds and crosses are not always avail-
able.
Recent studies using computers to model crossbreeding sys-
tems have helped clarify the differences among systems. At least
five separate computer programs which analyze crossbreeding sys-
tems have been utilized in these studies. The computerized
models, some of which are very complex, take into account breed
differences for each of the traits studied, the mode of inheri-
tance for specific traits, relationships among traits, the
economic impact of each of the traits, and market prices of
inputs and production. These studies offer guidance in choosing
among various systems.
Table 3. Expected outcome for crossbreeding sytems.
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Proportion Percent Pigs Conception
Mating matings offspring marketed rate
systemSire Dam in system heterosisper litter %
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Purebred matings
HampshireHampshire 0 5.94 85
Duroc Duroc 0 6.34 85
YorkshireYorkshire 0 7.78 72
Landrace Landrace 0 8.40 69
Chester Chester 0 7.35 85
Purebred average
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1 Three breed rotation
HampshireYxD,H.. 33.3 85.7 8.56 80
Duroc HxY,D.. 33.4 85.7 7.96 83
YorkshireDxH,Y.. 33.3 85.7 8.02 85
System average, weighted by proportion matings in system
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2 Three breed terminal
YorkshireYorkshire 5 0 7.78 72
Duroc Yorkshire 15 100 8.08 72
HampshireDxY 80 100 8.81 81
System average, weighted by proportion matings in system
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3 Four breed terminal
YorkshireYorkshire 5 0 7.78 72
Landrace Yorkshire 15 100 8.08 72
HxD LxY 80 100 9.55 87
System average, weighted by proportion matings in system
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4 Rotaterminal with two breed sow
YorkshireLxY,L.. 7.5 66.7 9.10 72
HxD YxL,Y.. 42.5 100 9.08 87
Landrace YxL,Y.. 7.5 66.7 9.34 72
HxD LxY,L.. 42.5 100 9.11 86
System average, weighted by proportion matings in system
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5 Rotaterminal with three breed sow
YorkshireCW,L,Y.. 5 85.7 9.18 81
HxD Y,CW,L.. 29 100 9.22 89
Landrace Y,CW,L.. 5 85.7 9.55 78
HxD L,CW,Y.. 28 100 9.30 88
Chester L,CW,Y.. 5 85.7 9.32 75
HxD CW,L,Y.. 28 100 9.12 90
System average, weighted by proportion matings in system
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6 Rotaterminal with two-way, three breed sow
YorkshireDL,Y,DL.. 7.5 66.7 8.81 88
HampshireY,DL,Y.. 42.5 100 8.81 76
DxL Y,DL,Y.. 7.5 83.3 8.93 88
HampshireDL,Y,DL.. 42.5 100 8.83 78
System average, weighted by proportion matings in system
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7 Two way rotation with four breeds
HxL DY,HL.. 50 83.3 8.61 90
DxY HL, DY.. 50 83.3 8.41 90
System average, weighted by proportion matings in system
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8 Three-way rotation with four breeds
HxL Y,D,HL.. 33.3 92.9 8.93 89
Duroc HL,Y,D.. 33.4 85.7 8.61 79
YorkshireD,HL,Y.. 33.3 85.7 8.30 83
System average, weighted by proportion matings in system
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Table 3. (Continue..)
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Days Fat Growing- Net
Mating to thick-finishing per
systemSire Dam market ness F/G litter
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Purebred matings
HampshireHampshire 183 1.00 3.30 ($19.62)
Duroc Duroc 172 1.20 3.33 ($16.53)
YorkshireYorkshire 177 1.20 3.35 $23.97
Landrace Landrace 180 1.25 3.40 $33.05
Chester Chester 185 1.30 3.45 ($4.25)
_______
$3.32
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1 Three breed rotation
HampshireYxD,H.. 169 1.10 3.26 $75.94
Duroc HxY,D.. 165 1.16 3.27 $51.29
YorkshireDxH,Y.. 166 1.19 3.28 $50.61
________
$59.27
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2 Three breed terminal
YorkshireYorkshire 177 1.20 3.35 $23.97
Duroc Yorkshire 162 1.22 3.27 $46.35
HampshireDxY 166 1.12 3.25 $86.24
________
$77.14
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3 Four breed terminal
YorkshireYorkshire 177 1.20 3.35 $23.97
Landrace Yorkshire 166 1.25 3.31 $51.58
HxD LxY 166 1.19 3.28 $107.28
________
$94.76
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4 Rotaterminal with two
YorkshireLxY,L.. 170 1.23 3.32 $73.48
HxD YxL,Y.. 165 1.18 3.27 $91.07
Landrace YxL,Y.. 171 1.25 3.34 $78.29
HxD LxY,L.. 166 1.19 3.28 $90.07
________
$88.37
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5 Rotaterminal with thr
YorkshireCW,L,Y.. 169 1.26 3.33 $77.61
HxD Y,CW,L.. 166 1.19 3.28 $94.57
Landrace Y,CW,L.. 169 1.26 3.33 $87.42
HxD L,CW,Y.. 166 1.19 3.29 $96.28
Chester L,CW,Y.. 171 1.29 3.36 $71.28
HxD CW,L,Y.. 167 1.21 3.30 $87.25
________
$90.63
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6 Rotaterminal with two
YorkshireDL,Y,DL.. 168 1.22 3.31 $68.58
HampshireY,DL,Y.. 167 1.13 3.26 $82.53
DxL Y,DL,Y.. 166 1.24 3.30 $77.77
HampshireDL,Y,DL.. 167 1.13 3.26 $83.31
________
$81.46
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7 Two way rotation with
HxL DY,HL.. 169 1.17 3.29 $69.27
DxY HL, DY.. 167 1.19 3.29 $64.94
________
$67.11
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8 Three-way rotation wi
HxL Y,D,HL.. 167 1.18 3.28 $84.84
Duroc HL,Y,D.. 165 1.20 3.28 $68.96
YorkshireD,HL,Y.. 166 1.21 3.29 $57.63
________
$70.48
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Economic projections based on unit farrowing 100 litters at a
base cost of $300 per litter.
Base conception rate of 80%, herd cost adjusted by $28 per sow
above or below 80%.
Base litter size marketed was 7.5 pigs, litter cost adjusted by
$8 per pig above or below base.
Base age to market at 220 pounds was 180 days. Nonfeed costs of
$14 per pig, adjusted by $0.05 per day above or below base.
Feed for growing-finishing charged at $140 per ton.
Hogs were marketed at 220 pounds at a base price of $45/cwt.
with 1.15 in. last rib fat thickness. Premiums and discount
based on fat thickness were 1% for each 0.1 in. below or above
base value.
Table 4. Performance averages assigned to breeds used in
crossbreeding systems analysis procedures.
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Concep- Litter Piglet Days to Fat Feedlot
Breed tion rate size survival220 lb. thickness feed/gain
_________________________________________________________________
% no. % in.
Hampshire 85 9.0 66 183 1.0 3.30
Duroc 85 9.6 66 172 1.2 3.33
Yorkshire 72 10.8 72 177 1.2 3.35
Landrace 69 10.0 84 180 1.3 3.40
Chester White 85 10.5 70 185 1.3 3.45
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Table values refer to purebred performance.
(Source: NC-103 research project publication and test station
averages.)
Johnson, R.K. 1980. Heterosis and Breed Defects in Swine. North
Central Regional research publication No. 262.
Results from one of the crossbreeding systems analyses pro-
grams mentioned above are shown in Table 3. Matings are grouped
into systems. For each type of mating, projections of performance
for six traits were made using the breed averages shown in Table
4 and the heterosis values given in Table 1. An expected economic
outcome for each mating type was also calculated. The economic
system represents conditions experienced in the early 1980's,
with credit given for faster and more efficient gain, higher con-
ception rates, larger litters weaned, and for leaner hogs at
market. An expected outcome for each system was calculated as a
weighted average of the mating outcomes, weighted by the propor-
tion of the mating in the system. With a $45 per cwt market
price, purebred performance with Hampshires, Durocs, Yorkshires,
Landrace and Chester Whites averaged $3.32 per litter profit when
market hogs were sold at 220 lb. (first section of Table 3).
Credit for leaner pigs at market was based upon the National Pork
Producers Council Lean Value System.
The analysis system assumes that all boars are purchased and
replacement gilts are valued as market hogs. Boars are taken to
be of average genetic merit. By including the gilt producing mat-
ings in the system average, replacement gilt costs are accounted
for.
THREE BREED ROTATION-The three breed rotation using
Hampshire, Duroc, and Yorkshire is shown as System 1 in Table 3.
These projections suggest $63 per litter advantage over the aver-
age of the purebred performance of the three breeds involved in
the cross. The net return as purebreds of Hampshires ($19.62),
Durocs ($16.53), and Yorkshires ($23.97) averaged a $4.06 loss
per litter; the three generations of the rotation averaged a
profit of $59.27. Three generations are shown, representing
advanced generations of the rotation. Gilt offspring from one
generation are used as the sows in the following generation.
With rotational crosses, the breed composition changes each
generation. After several generations, 57% of the genes come
from the last sire breed used, 29% from the grandsire and 14%
from the great grandsire. If the breeds in the rotation are dif-
ferent for important traits, wide swings in performance and
profit can be expected from generation to generation. This is
apparent in Table 3. Littersize raised is considerably higher in
the Hampshire sired generation because of the Yorkshire influence
in the sow, and the pigs are leaner. These differences led to an
expected economic advantage of $25 more profit per litter for
this generation. Swings in performance and profit of this magni-
tude are expected with rotational crosses.
TERMINAL CROSSES-System 2 in Table 3 is a three-breed termi-
nal cross, with Duroc-Yorkshire F1 sows mated to Hampshire boars
to produce the market hogs. These matings are on the third line
of the system. The second line is the matings that produce
replacement gilts, Yorkshire sows bred to Duroc boars. The first
line in the system shows the matings that produce the Yorkshire
gilts used as sows in the second line. The average for the system
is calculated on 5% purebred Yorkshire matings (line 1), 15%
Duroc x Yorkshire matings (line 2) and 80% terminal matings (line
3). This system projects an advantage of about $18 per litter
over the rotational cross in System 1. The same breeds are used
in both systems. The advantage is due to higher levels of
heterosis in both sows and pigs, the beneficial effect on litter-
size of a high percentage of Yorkshire in the sows of all matings
and the improved carcass value due to the Hampshire sire in the
terminal crosses.
System 3 in Table 3 is a four breed terminal using both F1
sows and F1 boars to produce the market crosses. The system is
similar to System 2, except that Landrace-Yorkshire F1 sows are
used and F1 Hampshire-Duroc boars sire the terminal crosses. This
system combines two good maternal breeds in the sow producing
most of the pigs and takes advantage of the heterosis in boar
breeding ability in the terminal matings. This system projects a
$35 per litter advantage over the rotation in System 1. The addi-
tional $17 per litter advantage over the three breed terminal is
due to the inclusion of a second superior maternal breed in the
sow and the improved conception rate because of the crossbred
boar.
ROTATERMINAL SYSTEMS-Rotaterminal systems are shown as Sys-
tem 4, 5, and 6 in Table 3. In these systems, replacement gilts
are produced with rotational crosses. These females are then
mated to terminal boars for market production. These systems are
run similarly to rotations, except that most of the matings pro-
duce only market crosses. Depending upon the choice of service
sire, any sow can produce either replacement gilts or market
hogs. Production in the terminal matings of the rotaterminal are
generally not as profitable as in the analogous terminal matings
in System 3 primarily because maternal heterosis is lower. For
the system, some of this difference is made up because gilt pro-
duction is less expensive, being based on crossbred sows.
System 4 is a rotaterminal based on a Yorkshire-Landrace
crisscross. The first line in the system shows the matings pro-
ducing Yorkshire sired replacement gilts. The gilts produced in
this mating appear in the second line as the sow producing termi-
nal crosses by a Hampshire-Duroc F1 boar, and in the third line
of the system mated to Landrace boars to produce replacement
gilts. The Landrace sired gilts are used as the sow for terminal
matings in line 4 of this system and as the mothers of Yorkshire
sired gilts in line 1. This system projects a $30 a litter advan-
tage over the three breed rotation. While the breed composition
of System 4 is similar to System 3, the reduced level of maternal
heterosis in terminal matings (66.7% vs. 100%) accounts for the
$6 per litter disadvantage for the system.
System 5 and System 6 are rotaterminals that use three
breeds in the sow. System 5 is based on a three breed rotation
of Yorkshire, Landrace and Chester White. The increased maternal
heterosis and individual heterosis in gilt producing matings
accounts for the $2.26 per litter advantage over System 4. How-
ever, an additional breed of boar and type of mating is required.
System 6 also uses three breeds in the sow but relies on only two
types of boars to produce replacement gilts. Sows are produced by
a crisscross between the Yorkshire and the Landrace-Duroc F1.
Compared to System 4, this gives a sow with less Landrace and
increases maternal heterosis in half of the matings. The reduced
littersize of the Duroc and the lower conception rate of the
purebred terminal sire reduce the expected net income of this
System. Since the Duroc is reputed to be better adapted to exten-
sive production conditions than the Landrace, the sow in System 5
would be classified as a hardier sow than those in System 4, and
might be better adapted to extensive production systems.
ROTATIONS WITH CROSSBRED BOARS-The last section of Table 3
shows two rotations using crossbred boars. System 7 is a
crisscross among four breeds using two types of F1 boars. This
gives the breed balance found in the four breed terminal. The
heterosis level in the sow and pig is similar to a three breed
rotation. This system projects nearly $8 per litter advantage
over the three breed rotation. The maternal contribution of the
Landrace and improved conception rate of crossbred boars account
for the difference.
System 8 is a three way rotation, using purebred Yorkshire
and Duroc boars along with an F1 Hampshire-Landrace boar. This
system attempts to balance white and colored breed influences,
while reducing some of the generation to generation fluctuations
in performance characteristics of rotational crosses. The
increased level of heterosis accounts for the $3.37 per litter
advantage over System 7.
Large differences in performance and profit potential among
the crossbreeding systems are indicated in Table 3. While the
numbers in Table 3 are produced by computer simulation, the cal-
culations are based upon results of real breeding experiments.
The budget used was based on costs reported by pork producers who
keep records. Further, the results reported here seem to closely
follow the experiences of producers who use the various systems.
Large differences in projected profits should not be
translated directly into a recommendation that all producers use
the mating system with the largest estimated profit reported
here. The projections shown are for a small number of possible
crossbreeding systems. The systems shown were chosen to illus-
trate differences and represent the most common applications.
However, it appears that the advantages of the terminal systems
can be realized by most pork producers.
Rotation crosses have generally been recommended for commer-
cial production since the advantages of crossbred pigs were
demonstrated in the 1940's. The attributes of terminal crosses
were known, but production methods favored the use of rotations.
Seasonal farrowing coupled with replacement of the whole breeding
herd at one time made rotations easy to use. Extensive production
systems minimized the advantage of specialized maternal breeds.
Small production units did not allow subdivision for replacement
gilt production. And health programs were not sufficiently
strong to encourage purchasing replacement gilts. All of these
factors are different today. Terminal crossbreeding systems more
closely fit the production systems being used for commercial pro-
duction than do the rotations.
Operating rotational crosses properly has become difficult
on most pork producing farms. Rotational crosses save replacement
gilts from the market crosses, changing the breed of boar each
generation in a prescribed order. With multiple farrowing in
modern facilities, it is desirable to replace cull sows with
gilts after each farrowing. The gilt, being of the new genera-
tion, is to be bred to the next breed of boar in the rotation.
Many producers lack the breeding pens, sow identification, and
personnel necessary to assure that sows are bred to the correct
breed of boar. Too often the replacement gilt is bred to the same
breed of boar used to breed the group of sows she will join, the
breed of boar of her sire. These mistakes (the mating of sows and
gilts to boars of the breed of their sire) are common and costly.
In a rotational system using purebred boars, backcross matings
cut heterosis in half. In a three breed rotation, heterosis is
cut from 85.6% to 42.8%, with accumulated production losses which
average $40 per backcross mating.
The breeding management required to operate rotational
crosses on intensively managed pork producing farms will support
terminal crossbreeding systems as well. With a three breed rota-
tion, the sows must be identified according to their breed of
sire and provision made, either through adequate breeding pens or
hand mating, to breed with three breeds of boars simultaneously.
The same is required of the terminal and rotaterminal systems
described in Table 3. The operational advantage of the rotations
observed in the 1940's is generally absent today. In addition,
production systems are in place which can take advantage of breed
differences, particularly in sow productivity.
The key to the operation of terminal crossbreeding systems
is the acquisition of sows. Unlike rotations, replacement gilts
are not kept from matings designed to produce market hogs.
Replacement gilts are produced in special matings. The high lev-
els of productivity experience with gilts and sows from these
special gilt producing matings give the terminal crossbreeding
systems their advantage. Operationally, the production of
replacement gilts is the key to the terminal crosses.
A second determiner of the success of the terminal
crossbreeding systems is the ability to meet the nutritional and
environmental needs of the more productive sow herd. Feeding pro-
grams and housing systems that supported rotational crosses might
not sustain performance with terminal crosses, which wean 1 or 2
pigs more per litter. Adjustments in the care and management of
the breeding herd are in order.
If the pork producing industry followed the lead of the
poultry industry, replacement females would be purchased. The
practice of buying replacement gilts has expanded during the last
decade. Buying gilts is functional for every farm that farrows.
However, questions of health risk and cost must be answered
before judgments of feasibility can be made. Generally, the mat-
ings that produce replacement gilts for terminal crosses are not
as productive as the terminal crosses. Hence, the purchase price
represents, in part, the lost productivity in the breeder's herd.
Most pork producers who farrow have preferred to produce
their own replacement gilts. With rotational crosses, that was
built into the system. With terminal crosses, special matings
are required. As an example, if Landrace-Yorkshire F1 gilts are
desired, purebred Yorkshire sows and a Landrace boar are
required. Both the number and timing of these matings are coordi-
nated with the production schedule so that gilts are available
when needed. Yorkshire gilt replacements for these matings can
either be purchased or produced. If they are produced, an addi-
tional type of mating is required. Yorkshire sows mated to a
Yorkshire boar are needed. While it is possible to perform these
matings, the small breeding groups, the need to schedule matings,
and the performance differences experienced with purebred sows
and F1 animals complicate management of the system.
The rotaterminal systems attempt to make the job of produc-
ing home raised gilts easier. In the case of the Yorkshire-
Landrace crisscross for replacement gilts, both Yorkshire and
Landrace boars are needed to sire replacement gilts. The advan-
tage of this system is that all of the sows in the herd are simi-
lar. They are all Yorkshire-Landrace crosses with similar levels
of heterosis and performance characteristics. All sows in the
herd are potential mothers of replacement gilts. For replacement
gilts, Yorkshire sired sows are bred to a Landrace boar, or Land-
race sired sows are bred to a Yorkshire boar. Most sows are bred
to a terminal boar for market production. This system allows an
easier flow of replacement gilts into the system, because sows to
produce them are always available. And, because all of the sows
are similar crossbreds, matings producing replacement gilts are
nearly as productive as market crosses. The disadvantage is that
the sow herd expresses only 66.7% of the available heterosis.
This accounts for the difference in profit projected between the
two systems.
The competitiveness of the terminal crossbreeding systems
depends in part upon the proportion of matings committed to the
production of replacement gilts. The number of matings required
to produce replacements depends upon the litter size in the
gilt-producing litters, the number of gilts needed (controlled by
culling in the sow herd), and the proportion of replacement gilt
candidates selected. The proportion of each type of mating in
each of the crossbreeding systems in Table 3 was assigned to pro-
vide ample replacement gilts. In System 3, reducing the propor-
tion of nonterminal matings to 10% would increase the expected
net for the system by $5 per litter. In the rotaterminal systems,
where the gilt producing litters are more productive, the propor-
tion of replacement gilt producing matings is not as critical.
The proportion of litters producing replacement gilts for a
terminal system is an operational characteristic of a farm. It is
suggested that initial proportion of litters producing replace-
ment gilts be chosen to supply an excess of gilts. As the opera-
tion becomes familiar with the attributes of the sows and deter-
mines a functional culling rate, the proportion of gilt producing
matings can be reduced. Since the cost of too many home raised
replacement gilts is generally less than the cost of too few,
starting with plenty is suggested.
Breed Evaluation
The genetic merit of the breeds used in crossbreeding
represents the foundation upon which performance is based.
Heterosis effects and the breeding values of parents are addi-
tions to this base in determining final performance. Hence,
choice of breed can have a marked effect on profitability. As
demonstrated in Table 3, placement of the breed in the
crossbreeding system is also important. Knowledge of breed per-
formance is essential in planning crossbreeding systems and
predicting performance.
Notions and estimates of breed performance come from many
places. The most reliable estimates come from crossbreeding
experiments where several breeds and crosses are tested together.
In these experiments, attempts are usually made to include pigs
from many sources and lines within the breeds. Table 4 is a sum-
mary of the performance of five breeds adapted from the evalua-
tion compiled by project NC-103, a committee of the swine breed-
ing researchers in the U.S.A. A more general summary of the find-
ings of the NC-103 committee is in Table 5.
____________________________________________________________________
| |
|Table 5. Relative performance of breeds. |
|_________________________________________________________________ |
| Concep- Litter size 21-day Age at Back- |
|Breed tion rate raised weight 220 lb. fat |
|_________________________________________________________________ |
|Berkshire + - - |
|Chester White + ++ - -- A |
|Duroc A A - + - |
|Hampshire A - A - ++ |
|Landrace -- ++ ++ A -- |
|Poland A + |
|Spotted -- -- + - |
|Yorkshire - ++ + + - |
|_________________________________________________________________ |
| |
|Based on NC-103 review. |
|Blank cell indicates data unavailable. |
|A indicates performance near average of breeds studied. |
|+ indicates performance superior to average. |
|++ indicates performance substantially superior to average. |
|- indicates performance inferior to average. |
|-- indicates performance substantially inferior to average. |
|__________________________________________________________________|
Table 6. Breed averages of purebred barrows tested at the 1985
and 1986 National Barrow Show.
____________________________________________________________________
ADG Age at 10th rib Loin muscle
Breed No. lb./day 220 lb. backfat area
____________________________________________________________________
days in. sq. in.
Berkshire 47 1.66 176.40 1.15 4.53
Chester White 66 1.64 175.94 1.26 4.50
Duroc 161 1.73 171.89 1.22 4.72
Hampshire 75 1.60 177.53 0.91 5.22
Landrace 34 1.65 172.00 1.22 4.49
Poland 47 1.64 173.47 1.12 5.17
Spotted 65 1.68 171.98 1.20 4.72
Yorkshire 93 1.61 178.24 1.15 4.51
____________________________________________________________________
____________________________________________________________________
| |
|Table 7. Performance of boars in central test stations during |
|1984, 1985, and 1986. |
|_________________________________________________________________ |
| ADG Feed/ Backfat |
|Breed No. lb./day gain in. |
|_________________________________________________________________ |
|Berkshire 349 2.10 2.68 0.83 |
|Chester White 326 2.08 2.59 0.82 |
|Duroc 4294 2.27 2.49 0.81 |
|Hampshire 1587 2.17 2.49 0.74 |
|Landrace 685 2.20 2.53 0.78 |
|Poland China 219 2.11 2.68 0.80 |
|Spotted 801 2.09 2.63 0.79 |
|Yorkshire 4028 2.22 2.49 0.79 |
|__________________________________________________________________|
Another source of comparative information is test stations,
including barrow tests. Since breeders choose the pigs tested,
these results are less reliable. Table 6 is a summary of breed
performance based upon results of the National Barrow Show per-
formance test of market hogs. Table 7 is based upon results from
boar testing stations. Word of mouth reports of how a certain
kind of pig performed are also abundant. Since these reports sel-
dom are based upon comparative information, they are of little
value.
Breed averages as presented in these tables have the appear-
ance of accuracy and stability. However, there are limitations to
the usefulness of the numbers. The NC-103 estimates are based
upon studies completed during the 1970's. While it is difficult
for a breed to change rapidly, more current estimates would be
desirable. The data from test stations and the National Barrow
Show are current but selected. If all breeders are equally skill-
ful in selecting pigs to put on test and those who test at sta-
tions are a random sample of breeders in a breed, the data might
be quite reliable. However, these assumptions are not met, and
the data are not very useful.
The breed evaluation data presented here are intended to
give guidance in making decisions. Other factors deserve con-
sideration as well.
o Source of stock: An increasing proportion of commercial
pork producers buy breeding stock from breeding com-
panies. The companies have private breeds and private
lines from the breeds. The performance evaluations
listed here might not apply.
Within a breed, differences in breeding value
exist. While these differences in breeding value are
additions to the breed average, and usually not large,
in regional situations they can be important.
o Changes in breed average: Rapid changes in a national
breed average are unlikely. Basically, such changes
come about in two ways. The first is through selection.
For this to be a factor, selection must be based upon
the same performance criteria and followed uniformly by
all breeders. The second is gene migration. An example
of this is the importation of European Large White
breeding stock into the Yorkshire breed. If the Large
White and Yorkshire are different genetically, this
migration could substantially change the Yorkshire
breed average. A similar situation can be found in the
Landrace breed. Importations during the last decade
from several European and Canadian Landrace breeds
could have changed the Landrace breed average.
o Regional Availability: Although a national market
exists for breeding stock, some breeds are less avail-
able in some areas. When health status and breeding
value are considered, further restrictions on breed
availability in the area of production are to be
expected.
Summary
Large differences among crossbreeding systems in levels of
performance and profitability are due primarily to differences
among breeds, the beneficial effects of heterosis, and the place-
ment of breeds in systems. Generally, the use of one of the ter-
minal crossbreeding systems with superior sow performance is
recommended. Success with any crossbreeding system depends upon
carefully following the system and adopting production practices
that enhance the chosen system. With all crossbreeding systems,
performance can be improved by purchasing breeding stock with
superior genetic merit.
REV 12/87 (5M)
Figure 1. Three breed rotation crossbreeding system.
Figure 2. Four breed terminal crossbreeding system.
% Figures are available in hard copy
______________________________________________
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