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Chapter 17 Management of the breeding herd.


Several management factors maximize reproduction efficiency, measured as number of pigs produced per sow per yr (PPSY). This chapter provides examples from research and field data to illustrate management practices that lead to high herd performance in terms of increased PPSY. Some production units focus on related measures such as pigs per rate per yr.


The bottom line for the breeding herd is to maximize the number of pigs produced per sow per yr (PPSY). With the sow herd at a constant level, incremental increases in PPSY result in incrementally lower costs of production. Thus, higher profits are generally associated with greater numbers of PPSY.

Production units vary in PPSY. The former industry standard, the Pork Industry Handbook, used a PPSY of 16.0 in the economics section as an average of well-managed farms of the 1970s. By the 2000s, a farm that produced only 16 PPSY was a low-producing farm. A minimum acceptable level for PPSY now is 20.0. Many well-managed farms produce over 22 PPSY, while the best farms of the new millennium produce around 25 pigs per sow per yr.

Two main factors affect PPSY: litters per sow per yr and average litter size weaned. Litters per sow per yr are greater by lowering:

* Lactation length

* Nonproductive days

* Sow deaths

* Wean-to-estrus length

PPSY and litters per sow per yr are increased by improving:

* Estrus detection and mating

* Conception rates

* Parity distribution

* Lactation length

The number of pigs weaned/sow is a function first of the number of total pigs born. Total born includes those born alive (seek a high number), those stillborn (fully formed piglets at birth that did not breathe--seek a low number), and mummies (partially developed, partially decomposed piglets, usually black and shriveled--seek a low number).

After the number of pigs born alive is considered, the only other common measure that impacts number weaned is the number of piglet preweaning deaths (piglet mortality). A good piglet mortality value is less than 10%.

Figure 17-1 shows an example of a well-managed herd with 23 PPSY. This herd average PPSY is composed of 2.3 litters per sow per yr and 10.0 pigs weaned/sow. Of 49 best herds shown in Table 17-1, ranked by PPSY, only four herds weaned more than 10.0 pigs/sow. However, 41 herds listed in Table 17-1 had litters per sow per yr of 2.30 or more. Farms ranged in size from 235 to 3,530 sows. These data confirm that herds reach the top level of PPSY more often by having high litters per sow per yr than by increasing the number of piglets born alive or weaned/sow.


Table 17-1 lists the eight factors that contribute to placing a herd in the best or worst categories. The most significant factors that place a herd in the bottom 20% of herds are nonproductive days and weaning age. Nonproductive days are the days a sow is neither pregnant nor lactating. Normally, the nonproductive days are calculated by the average of the number of days from weaning to expression of estrus/mating multiplied by the numbers of litters per sow per yr. Using an example of 2.3 litters per sow per yr, 7 d from weaning to estrus, and an average of 80% conception/farrowing rate, the number of nonproductive days is 20.1 d (7 x 2.3 divided by 0.80), even under the best of circumstances. Still, the best herds have fewer than 60 nonproductive d. This figure suggests U.S. herds have about a three-fold higher number of nonproductive days than the biological minimum.

Better managers minimize the number of nonproductive days, especially by careful heat detection. A large part of the contribution to nonproductive days is failing to breed sows that could be bred. If estrus is expressed and the sow is not bred, another 21 d is added to the number of nonproductive days. Another significant contribution to nonproductive days is the gilt herd that enters the breeding area and awaits expression of estrus and mating. If the average gilt is bred on her second or later estrus, another 21 to 42 d are added to the nonproductive days measure.

Many newer units attempt to minimize the effect of the gilt herd on nonproductive days by use of a specialized building or area typically called a gilt breeding project. In this area, gilts are checked for estrus, bred on their second or later estrus, and kept until pregnancy check (d 30 to 60 after breeding). When they are confirmed pregnant, they are moved to the gestation barn as bred gilts. In this way, a single gilt breeding project can supply gilts to a number of networked units.

Weaning age is a second factor that is under the control of the production unit, but really not under the control of the workers. The production schedule will dictate the weaning age and the flow of sows through the facility. Most modern units wean pigs at less than 24 d. Common weaning ages in the 1990s and continuing into 2001 are 20 to 21 d, 18 to 19 d, 16 to 17 d, and 7 to 14 d. The earlier weaning age may be for a program of segregated early weaning (SEW) or medicated early weaning (MEW). Other ages, especially the 16 to 21 d weaning age, are common in modern pig units.

Farrowing rate contributes significantly to PPSY. Herds with 80% or greater farrowing rate are more successful. A higher farrowing rate requires fewer sows in the unit to produce the same total number of pigs. A 1,000-sow unit, expecting to produce 22,000 pigs/yr (22 PPSY), would need about 200 more sows if its farrowing rate was reduced by 20%.

The number of sows needed to produce 22,000 pigs from a sow herd of 1,000 sows with a decreasing farrowing rate is shown in the following figure. A 100% farrowing rate is nearly impossible to reach on a commercial unit.

100%                     1,000
90%                      1,111
80%                      1,250
70%                      1,333
60%                      1,667

Litter size contributes importantly to a high number of PPSY, but less so than does nonproductive days. The number of pigs born alive (and related factors of rates of stillborn and mummies) is still a very important determinant of a high number of PPSY.

Herds with a high PPSY tend to have a higher average parity, lower sow mortality, more than two matings/service, and a preweaning mortality of less than 14%. These factors, while important, should not be the focus of efforts toward increasing PPSY unless the farrowing rate and the number of nonproductive days are already well under control.

As a general rule, herds with low and marginal productivity problems should focus attention on the areas given below.

All herds      Lower wean age, increase average parity and

Low PPSY       Breeding techniques:
                   Farrowing rate and nonproductive days

Medium PPSY    Breeding techniques:
                   Farrowing rate and nonproductive days
                   Litter size

High PPSY      Breeding techniques:
                   Farrowing rate and nonproductive days
                   Litter size
               Preweaning mortality


Modern pig production units should wean at least 22 PPSY. Producers have the technology to do better than 22 PPSY, but this level remains a challenge on most farms.

The four main factors that contribute to PPSY are litters per sow per yr, total pigs born, stillborn rate, and preweaning mortality. Reaching 22 PPSY requires 11 pigs born, 2.3 litters per sow per yr, fewer than 0.60 stillbirths, and less than 10% preweaning mortality. If the litters per sow per yr are only 2.1 or total born is 10.0 or less, it is biologically impossible to wean more than 22 PPSY.

Well-managed farms that use quality genetics can produce at least 12 pigs born. With 12 pigs born and at least 11 pigs born alive, it should be possible to wean over 10 pigs/sow. With 12 pigs born and low preweaning mortality and low stillborn rate, the farm can wean over 25 PPSY. In fact, with less than 10% preweaning mortality and fewer than 1.0 stillbirths/sow, the farm will wean over 23 PPSY. The total number of pigs born is a function of activities in the breeding and gestation barns. A farrowing barn worker who has been delivered sows with 12 pigs/litter has the tools to wean a very high number of PPSY.

New research in breeding and genetics has identified breeds and at least one specific gene that codes for a high number of pigs born. With less than 10% preweaning mortality and fewer than 1.0 stillbirths, the farm that has 14 pigs born will wean over 27 PPSY. If a herd has 14 total pigs born and low stillbirths and preweaning mortality, the unit could potentially wean 30 PPSY!


Every pig production unit should have goals, and one of the most important is to set the target number of sows to breed. Three main factors determine the breeding target:

* Number of farrowing crates/huts to be filled

* Farrowing rate

* Crate/hut occupancy rate

The formula to calculate the breeding target is:

(no crates/farrowing rate) x crate occupancy rate = breeding target

In this example, the farrowing rate is a fraction (0.80, not 80%) and crate occupancy is a fraction (1.10, not 110%).

Farrowing barns and pastures have a certain number of crates or huts to fill. This fixed number reveals a lot about the size and production schedule of a farm. The greater the number of farrowing units, the greater the number of sows that need to be bred.

Farrowing rate refers to the number of sows giving birth compared to the number bred. If 100 sows are bred and 70 of those sows farrow, the farrowing rate is 70%. The situation is more complex, however, because a certain number of gilts are bred from a gilt pool and also because some sows fail to conceive and are re-bred in a different group. A higher farrowing rate is desired. The average farrowing rate is about 75% on commercial farms. The minimum target should be to have a farrowing rate over 80%.

Most large commercial farms have a crate occupancy rate well over 100%--that is, more sows farrow than the number of crates on the farm. Accountants like this concept because it means that the crates (an important asset) are fully utilized at all times.

As an example of a crate occupancy over 100%, assume the farrowing room has 30 crates. If 33 sows farrow, the crate occupancy rate is 110%. As a practical matter, when the last three sows are to farrow, the worst three litters (that is, those three with the least number of piglets) are weaned or crossfostered. Piglets are transferred to other sows and the sows return to the breeding area. The three new sows get a crate and farrow. Therefore, if the sows have fewer pigs born alive, the crate occupancy rate tends to increase.

For example, a farm is a 1,200-sow unit that has 54 farrowing crates that are used each week (actually two rooms of 27 crates each). How many sows should be bred for this unit? If the farrowing rate is 80% and if the crate occupancy rate is set at 110%, 74 sows should be bred each wk. The consequences of breeding 74 sows are in two directions. First, if the farrowing rate turns out to be 90%, the crate occupancy rate would have to be pushed over 115% to accommodate the added sows. Under the target (average) conditions, a producer expects to wean 10% of the sows early (five to six sows). If farrowing rate is 90%, the producer would have to wean 12 to 13 sows early. This could put a strain on the ability of the sows to nurse so many pigs, but they could probably handle it--this is about their biological limit. Estimating 10.8 pigs born alive and 10.0 piglets at 3 d on 54 sows, adding 120 pigs would add an average of two to three pigs/sow. This would leave each sow with 12 or 13 piglets.

In the other direction, the farrowing rate could be 65% (or even lower). With 74 sows bred and a 65% farrowing rate, the crate occupancy rate would be close to 100%. Considering the potential swings from very good to very poor farrowing rates, shooting for the 110% crate occupancy is a healthy target that does not over-tax the sows and fully utilizes the assets (the crates or huts).


The pig is generally considered to be neither photo-sensitive nor a seasonal breeder, in contrast to some breeds of sheep and most birds. Some have said the sow expresses "normal" sexual behavior and reproductive function year-round. However, this is not entirely true. Sows do express a depression in return-to-estrus and conception rates in the late summer and early fall. The seasonal, reduced fertility is thought to be due to a combination of the effects of summertime heat stress, changing grain, and the changing photoperiods (as well as other seasonal cues).

* Decreased farrowing rate

* Increased days from weaning to estrus

Young sows are especially influenced by summer infertility. In one study, parity one sows had an 18% decline in farrowing rate while older sows had only a 5% decline in farrowing rate during the late summer months (Love, 1981). The number of days from weaning until estrus increases in the late summer and fall as well.

To account for the less-than-perfect farrowing rates during the year, Levis calculated a seasonal coefficient to aid in setting breeding targets. A range of 11% to 35% more sows should be bred depending upon the time of the year. The most sows are bred in late summer to accommodate seasonal infertility.


Reproductive efficiency is crucial to obtain profitable pork production. An accepted measure of reproduction efficiency is the number of pigs produced per sow per yr (PPSY).This chapter discussed the two main factors contributing to PPSY: litters per sow per yr and average number of pigs weaned/litter. Number of litters per sow per yr is increased by minimizing nonproductive days, lactation length, days from weaning to post-weaning estrus, and sow deaths, and by improving estrus detection and conception rates. Realistic goals for attaining high PPSY records in a herd are: nonproductive days, <60; weaning age, <24 d; farrowing rate, >80%; litter size, >10.0 pigs born alive; pre-weaning mortality, <14%; mating/service, >2.0; and sow mortality, <8%.

* Weaning to estrus length, days

* Estrus detection

* Breeding

* Pregnancy check

* Return to estrus

* Moving and handling

* Farrowing rate

* Total number of pigs born

* Total number of pigs born alive

* Stillbirth rate

* Rate of mummies


1. Considering two farms, could it be possible to produce less total PPSY on one farm, but actually make more profit than the other farm? How?

2. If a plant needed 16,000 pigs/d, and it processed pigs 250 days/yr, how many sows would be required if the farrowing rate was 90%, 80%, or 70%? Assume the other factors are at a set level (give assumptions).

3. If you have 100 farrowing crates in your facility/wk of production, how many matings should you make? What assumptions did you use to establish the number of sows mated?

4. For the previous question, how many sows would you breed in August to accommodate seasonal infertility?


Love, R. J. 1981. Seasonal infertility in pigs. Vet Rec. 109:407-409.


A swine business web site:

A breeding stock company with records:

A list of software sites for livestock: ANRSI_L2V0007.html

A pig-specific record-keeping program:

For current hog and pig inventories in the USA: briefing/hogs/
TABLE 17-1

Productivity Measures That, If Not Met, Result in the Herd Being in
the Bottom 20% Rather than the Top 20% of the Rankings of Sow Herds.
All Eight Productivity Measures Are Important Determinants of a
Successful Sow Herd. Rank Refers to Relative Economic Importance
(1 = largest economic impact).

                                   SUGGESTED    RELATIVE

Nonproductive days                   < 60          61         1
Weaning age, days                    < 24          55         2
Farrowing rate, %                    > 80          12         3
Litter size, number born alive       > 10.0        11         4
Average sow parity                   > 4.0          3         5
Prewean mortality, %                 < 14.0         1.6       6
Matings/service                      > 2.0          1.2       7
Sow mortality, %                     < 8.0          1         8
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Title Annotation:SECTION V Pig Production Applications That Make Business Sense
Publication:Pig Production, Biological Principles and Applications
Geographic Code:1USA
Date:Jan 1, 2003
Previous Article:Chapter 16 Waste and nutrient management.
Next Article:Chapter 18 Management of sows and piglets: before, during, and after farrowing.

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