REPRODUCTION PIH-45
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Reproductive Efficiency in Managing the Breeding Herd
Authors:
Emmett Stevermer, Iowa State University
Allan Mueller, University of Illinois
Wayne Singleton, Purdue University
Reviewers:
Robert D. Goodband, Kansas State University
Tony and Laura Holcomb, Yuma, Colorado
Lesa Sterling, University of Delaware
James E. Tilton, North Dakota State University
The purpose of this fact sheet is to help pork producers to
better understand the relationship between productivity and pro-
fitability of their breeding herd. Productivity refers to bio-
logical information such as conception rates, farrowing rates,
pigs per litter, pigs per crate and pigs per sow per year.
Profitability refers to the difference between cost of pro-
duction and product value. It is usually associated with high
productivity but is frequently influenced more by market prices
and costs of production than by production.
In evaluating the efficiency of the breeding herd both meas-
ures of performance are important. The primary purpose of the
breeding herd is to provide a source of feeder pigs, either for
direct marketing, or for rearing to market weights in the same
herd. The profitability of the breeding herd should be measured
by profits produced through the feeder pig production phase of
the enterprise but not the additional profits made on the feeder
pigs when finished to market hog weights in the feeding phase of
the enterprise. The latter portion of the potential profits could
have been earned through the purchase of feeder pigs rather than
from raising them within the same enterprise.
Production costs can be divided into two categories: fixed
and operating or variable costs. Fixed costs are those that
relate to the investment in facilities and equipment used for the
raising of pigs. They include taxes, insurance, depreciation and
interest on the investment. Total annual fixed costs are not
highly correlated to production. Annual operating expenses, on
the other hand, are highly correlated to actual production and
account for the majority of the costs in pig production.
On a per unit of production basis, fixed costs usually
decrease as biological productivity increases. Figure 1 shows the
influence that the number of pigs weaned per crate has on the
fixed cost per pig weaned. Operating or variable costs are gen-
erally not very responsive to increased productivity and, in some
situations, may actually increase. For example, if increased
labor is required to increase the pigs weaned per litter, operat-
ing costs per pig weaned could increase.
Sizing the herd
On most farms the number of farrowing crates available is
the resource that determines the maximum number of weaned pigs
that can be produced. The frequency of use of the crates and the
number of pigs weaned per litter are the remaining factors that
are used to calculate the final number of pigs produced.
Most studies fail to show an advantage in sow productivity
for lactation periods of less than 21 days. Allowing for a few
days variation in breeding dates and gestation lengths, 14 far-
rowings per crate per year could be obtained with three week
weaning. Producers using an all-in all-out system allow some time
for cleaning and probably obtain only 12 or 13 farrowings per
crate per year. This rate of usage will require about 6 sows in
the breeding herd for each farrowing crate. The next determinant
of the total number of pigs produced is the number weaned per
litter. When the unit costs of maintaining a sow through breed-
ing, gestation and lactation are shared by the pigs weaned from
that reproductive cycle, it is readily apparent that the sum of
the fixed and operating costs per weaned pig will be lower when
they are shared by a larger number of pigs. An estimate of the
effect that pigs weaned per litter has on the total cost of pro-
ducing 40-lb. feeder pigs is shown in Figure 2.
Replacement Rate
Additional questions that producers face relate to what por-
tion of the breeding herd should be replaced each year and at
what parity sows should be culled.
Gilts typically do not farrow as many pigs in their first
litter as they do in later litters. In addition, gilts are usu-
ally in the herd more days from the time of selection to weaning
of their pigs, consume more total feed and consequently accumu-
late higher production costs than sows. Offsetting some of these
costs is the value of the extra weight gained. In some herds
second litter sows are also below average in productivity, meas-
ured by pigs weaned per litter, as compared to the third and
later parities.
A percentage of farrowings on all farms is from gilts and in
any one year can range from 0 to 100 percent. In many operations,
gilt litters represent 20 to 40% of the farrowings. All selected
replacement gilts do not produce a litter and therefore 50 to 120
percent of the average number of sows in the herd are added as
replacement gilts each year.
Culling
Replacement decisions are usually based on biological and
economic considerations. There are two types of culling that
occur in breeding herds. Involuntary culling is the removal of
females from the breeding herd for reasons such as death, anes-
trous, sterility, abortion, lameness, farrowing difficulties and
old age. Voluntary culling is the removal of females from the
breeding herd based on performance criteria such as numbers of
pigs farrowed and weaned, weaning weights, days from weaning to
rebreeding, production indices, and size or condition.
Table 1. Parity adjustments for number born live and litter wean-
ing weights.*
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Parity No. born live Litter weaning wt.
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1 1.5 6.5
2 .9 0
3 .3 0
4 0 1.5
5-7 0 4.5
8-10 .4 8.5
>10 1.6 12.0
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* National Swine Improvement Federation Guidelines, 1987.
Table 2. Percent of farrowings in each parity for various numbers
of maximum parities.*
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Maximum parities
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Parity 2 3 4 5 6 7 8 9
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1 54.1 38.9 31.4 26.9 24.1 22.1 20.6 19.5
2 45.9 33.0 26.6 22.9 20.4 18.7 17.1 16.6
3 28.1 22.7 19.5 17.4 16.0 14.9 14.1
4 19.3 16.6 14.8 13.6 12.7 12.0
5 14.1 12.6 11.5 10.8 10.2
6 10.7 9.8 9.1 8.7
7 8.3 7.8 7.4
8 6.6 6.2
9 5.3
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* Culling level of 15% uniformly distributed over all parities.
Since multiparous sows usually are more productive than
first-litter gilts, biological productivity per sow can be
increased by reducing the percentage of gilt farrowings. On the
other end of the scale, the biological productivity of sows
decreases as they produce beyond their 6th or 7th litter. The
1987 National Swine Improvement Federation Guidelines use the
values in Table 1 for adjusting for parity differences in number
of pigs born live and for litter weaning weight. These adjust-
ments show that sows in 4th to 7th parities can be expected to
wean more pigs per litter than other sows in the herd. If a limit
is placed on the maximum number of litters any one sow can pro-
duce, and if a 15 percent culling level is uniformly distributed
across the parities, Table 2 shows the portion of the farrowings
produced from each parity.
Table 3. Expected number born live with involuntary culling of
15% for maximum parities of 2 to 9.
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parity 9.5 10.5 11.5
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2 8.28 9.28 10.28
3 8.54 9.54 10.54
4 8.72 9.72 10.72
5 8.83 9.83 10.83
6 8.90 9.90 10.90
7 8.95 9.95 10.95
8 8.96 9.96 10.96
9 8.97 9.97 10.97
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With higher culling levels, a higher percentage of the far-
rowings will be from first-litter gilts, which tends to reduce
the average number of pigs weaned from the total breeding herd.
Offsetting that is the fact that the selected older sows will
have slightly higher productivity and the herd productivity
remains good when the maximum number of litters permitted per sow
is from 6 to 10. Using the adjustments for number born live by
parities from Table 1, and the parity distribution of farrowings
from Table 2, the average values for pigs born live under the
different maximum parity culling levels and for three different
mature sow values are calculated and shown in Table 3. In a herd
that has the genetic capability to average 10.5 pigs farrowed
live per litter in 4th to 7th parities, if no sows are kept for
more than 6 litters, 9.9 would be the average number of pigs born
per litter. Similar procedures could be used to determine
expected weaning weights.
By using the value of pigs farrowed live from the appropri-
ate column in Table 3 and a value for pig survival rate to wean-
ing, the number of pigs weaned per litter can be calculated for
various maximum parities.
If additional parameters for sow death losses, weights of
culled sows and feed prices are included, the break-even selling
prices per 40 lb. pig for the various maximum parity culling lev-
els can be calculated. The figures in Table 4 were calculated for
herds producing 200 litters per year but with different limits on
the maximum number of parities. The number farrowed live for 4th
to 7th parity was 10.5. The survival rate to weaning was kept at
85 percent for all parities. Sow weights at culling ranged from
425 to 455 lb. over the range of the seven parity levels. Culled
sow market price was kept constant at $40 per hundredweight. Sow
feeding levels were kept constant on a per head per day basis for
each of two stages of production, 5 lb. during prebreeding and
gestation, and 12 lb. during lactation. Litters per sow per year
ranged from 1.82 to 2.17 over the seven parity culling levels and
the sow herd size was increased as necessary to keep the number
of litters per herd at 200. One hundred thirty gilts were grown
to 230 lb. in each of the seven culling levels to keep the facil-
ity needs approximately equal for each culling level. The market
pigs not needed for replacements were marketed at $43.00 per hun-
dredweight. The feed prices include corn at $2.50 per bushel,
supplement at $300 per ton and pig starter at $20.00 per hundred-
weight.
Table 4. Reproductive performance and economic benefits of vary-
ing maximum parity culling levels.*
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Maximum parities permitted
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Item 2 3 4 5 6 7 8
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Litters farrowed 200 200 200 200 200 200 200
Percent gilt litters 54.1 38.9 31.4 26.9 24.1 22.1 20.6
Replacement gilts needed, no. 127 92 74 63 57 52 48
Average herd size, female yrs. 110 105 100 96 93 92 92
Sow deaths, % of breeding herd 4.0 4.5 5.0 5.5 6.0 6.5 7.0
Sow sale weight, lb. 425 430 435 440 445 450 455
Pigs weaned/litter** 7.88 8.11 8.27 8.36 8.42 8.46 8.47
Litters/female/year 1.82 1.90 2.00 2.08 2.15 2.17 2.17
Pigs weaned/female/year 14.34 15.41 16.54 17.39 18.10 18.36 18.38
Total pigs weaned/year 1578 1618 1654 1669 1684 1689 1691
Turnover rate of the breeding
herd, %/year*** 115.5 87.6 74 65.6 61.3 56.5 52.2
Break-even price, $/40-lb pig $38.64$38.95$38.61$38.46$38.20$38.26$38.43
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*Fifteen percent involuntary culling level at each parity.
**Values are from the middle column of Table 3 using a survival
rate to weaning of 85%.
***Turnover rate is the portion of the breeding herd that is sold
or dies during a year and is the replacement rate needed to main-
tain the average herd size.
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With sow salvage values deducted from the total costs, the
differences in the break-even price needed to cover all costs per
feeder pig produced were small and insignificant. The numbers in
Table 4 are based on 15 percent involuntary culling at each par-
ity. With higher culling levels, higher replacement rates would
be needed and a higher percentage of gilt litters would be pro-
duced.
Many producers cull first and second parity females on the
basis of performance criteria. This practice increases the need
for more gilt litters and often doesn't result in much improve-
ment in total herd performance because the ``accuracy'' or repea-
tability for numbers born live is low. Accuracy is defined as the
relationship or correlation between the estimated breeding value
and the animal's true breeding value. The animal's true breeding
value is usually never known. The accuracy of the estimated
breeding value is dependent upon the heritability of the trait
and the number of records on the individual or its relatives used
in the evaluation procedure. If only a single record is used to
estimate genetic merit, the accuracy of the estimate is the
square root of the heritability of the trait. For a trait, such
as pigs born per litter, with a heritability of 0.10, the accu-
racy for that trait based on one record would be 0.32. Even with
three records, it would only be 0.45.
Purchased or Homegrown Replacements
Purchased replacement gilts usually cost more than home
raised replacements, but offer producers an opportunity to make
dramatic changes in their herd's health level and genetic compo-
sition. This system also often simplifies the selection and
breeding programs for producers. The extra cost of purchased
replacement gilts might be recovered with improved productivity.
Three areas that offer significant opportunities for improvement
in productivity from changing genetics would be: carcass quality,
feed efficiency and pigs weaned per litter. Additional parame-
ters, such as heavier pigs at weaning, faster growth rates and
higher conception rates, might also be obtained, but their influ-
ence on production costs will be less noticeable.
Figure 3 shows the amount of improvement a feeder pig pro-
ducer would need to achieve in either feeder pig market price, or
pigs weaned per litter to justify various replacement gilt premi-
ums. Figure 4 shows the amount of improvement a producer would
need to achieve in either pigs marketed per litter, market price
or feed efficiency of the finishing pigs if the gilt premiums are
to be recovered by that phase of the enterprise. These values
were determined from base values of $43.00 per hundredweight
market price, 3.6 feed efficiency of the growing-finishing pigs,
8 pigs weaned per litter, 2.0 litters per sow per year and 50
percent annual replacement rate of the sow herd. A 50 percent
replacement rate is equivalent to 7th to 8th parity culling.
When productivity and cost evaluations of purchased replace-
ment gilts are considered, voluntary culling should be kept to a
minimum. The extra cost of the purchased replacement should be
offset with pigs weaned over the herd life of the purchased
replacement. From a practical standpoint that extra cost should
be spread over as many pigs as possible. The more culling that is
practiced, the more first-litter females one needs and the fewer
litters a sow produces while in the breeding herd. The goal
should be to reduce the number of first-litter gilts in the herd
by reducing culling. For many herds, this is an area that affords
considerable opportunity. Practices which reduce sow deaths,
lameness and infertility are all helpful in reducing the number
of replacement gilts that a herd will need.
Additional fact sheets on these areas are:
PIH-8 Managing sows and gilts during breeding and gestation for
efficient reproduction
PIH-27 Guidelines for choosing replacement females
PIH-39 Crossbreeding programs for commercial pork production
PIH-46 Care of the sow during farrowing and lactation
PIH-89 Managing the gilt pool
PIH-96 Troubleshooting swine reproductive failure
PIH-106 Genetic principles and their applications
REV 12/89 (5M)
Figure 1. Effect of pigs weaned per crate on fixed cost per pig
weaned.
Figure 2. Effect of number of pigs weaned per litter on the cost
of producing a 40-pound pig.
Figure 3. Percentage improvement required to recover purchased
replacement gilt premiums in a feeder pig producing program.
Figure 4. Percent improvement required to recover purchased
replacement gilt premiums in a farrow-finish program.
% Figures are available in hard copy.
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