REPRODUCTION                                      PIH-45


        Reproductive Efficiency in Managing the Breeding Herd

Emmett Stevermer, Iowa State University
Allan Mueller, University of Illinois
Wayne Singleton, Purdue University

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.


     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.*
  Parity             No. born live             Litter weaning wt.
      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
* National Swine Improvement Federation Guidelines, 1987.

Table 2. Percent of farrowings in each parity for various numbers
of maximum parities.*
                             Maximum parities
Parity    2       3      4      5       6      7       8      9
  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
* 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.
parity               9.5                10.5                11.5
  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

     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-

Table 4. Reproductive performance and economic benefits of  vary-
ing maximum parity culling levels.*
                                         Maximum parities permitted
Item                               2     3     4     5     6     7     8
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
*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.

     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-

     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

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.

Cooperative Extension Work in  Agriculture  and  Home  Economics,
State  of Indiana, Purdue University and U.S. Department of Agri-
culture Cooperating. H.A. Wadsworth,  Director,  West  Lafayette,
IN. Issued in furtherance of the Acts of May 8 and June 30, 1914.
It is the policy of the Cooperative Extension Service  of  Purdue
University  that  all  persons  shall  have equal opportunity and
             access to our programs and facilities.