On-farm testing programs are designed to assist seedstock producers in evaluating their animals in a systematic manner. The programs described in this chapter will assist breeders in: 1) selecting of boars and gilts for use in their breeding programs; 2) providing procedures for identifying superior individuals within strains, lines, or breeds; 3) supplying high quality performance tested seedstock; and 4) communicating unified terminology and breeding stock selection guidelines to the pork industry.


The objectives of on-farm testing programs are best achieved through whole herd testing. Testing only a selected sample of the herd yields limited and biased information. Expected Progeny Differences (EPD) that describe the genetic merit of each animal as a parent can be estimated most accurately by combining all of the available information on a pig and its relatives.

Accuracy is an extremely important part of any testing program. Since most producers have the ability to adequately conduct performance tests, professional assistance from breed associations, testing organizations, state Cooperative Extension Services, and private commercial concerns is available to aid producers in the mechanics, record processing, and reporting of data from a testing program. Further, the involvement of agents without a vested interest in the results may provide greater assurance of accuracy and serve as motivation for the producer to collect and use the appropriate information.

Pigs should be evaluated within contemporary test groups. A contemporary group is a group of pigs of the same breed or breed-cross, born in a short period of time (no more than six weeks), fed the same diet (see Appendix A for sample diets), and raised in the same facilities under the same management. These test groups should be managed uniformly, and all pigs within the test group should be given an equal opportunity to perform. Contemporary groups should consist of at least 20 pigs from at least five litters and at least two sires. Testing smaller groups will lead to inadequate comparisons and less reliable EPDs.

Breeders who choose to use either within-herd EPD or across-herd EPD programs should follow the recommendation that all pigs be tested. Otherwise, breeders should use a base program rather than the within-herd EPD or across-herd EPD programs. Selection of animals to be tested will lead to misleading and incorrect information on the EPDs being calculated. Each record should be expressed relative to the test group or herd average by the use of deviations from the average, or EPDs.

Base Program

Seedstock on-farm testing programs should encompass whole herd testing of sow productivity and all performance traits (on all intact males and all females). In reporting data, deviations from the average within contemporary groups should be used. Seedstock programs should also include sire and dam litter summaries. When ranking animals, selection indexes (see p. 14) should be used to assign appropriate emphasis to each of the various traits. Participants of the base swine improvement program should meet the following minimum recommendations.

  1. Identification of all pigs in the herd. NSIF recommends the universal ear notching system that identifies the litter in the right ear and the individual pig in the left ear (Appendix B). If another ear notching system is used, the system should be stated and described. Ear tags or tattoos may be used to supplement ear notches.

  2. Birth Record. Within 3 days of birth all pigs must be individually identified and the following recorded in an appropriate recordbook or file kept by the breeder: gender, birth date, identification and breed of parents. These records are essential.

  3. Sow Productivity. The number of pigs farrowed alive and dead should be recorded. The number of pigs born alive should be adjusted to a mature sow equivalent by adding the following numbers to the record based on the parity of the female:

Table 1. Parity adjustment factors for number born alive.
Number born alive (L)

An individual breeder may wean at any time, but litter weight should be recorded before weaning and as near to 21 days of age as possible for the most accurate assessment of sow milking ability. NSIF recommends weighing pigs between 14 and 28 days and adjusting to a 21-day basis. Post-farrowing litter weights may be adjusted to a 21-day basis by using the following multiplicative factors:

Table 2. Factors for adjusting litter weight to a 21-day basis.
Age Weighed
Age Weighed

The following equation was used to compute the tabular values and can be used to directly adjust litter weight to a 21-day basis:

Adjusted 21-day litter weight = wt[2.218 - .0811(age) + .0011(age2)].

Producers using a protocol that involves weaning pigs at an extremely young age (e.g., Segregated Early Weaning) should state how sows are evaluated for productivity. NSIF recommends pigs be weaned no earlier than 10 days of age; using factors in Table 2 will permit sows to be ranked on the Sow Productivity Index (see page 14). The closer to 21 days of age pigs are weaned, the more accurate the adjustment will be. If pigs must be weaned earlier than 10 days of age, use an alternative index (page 14).

If possible, litters should be standardized to between 8 and 12 pigs per litter within 24, but not later than 48, hours after birth. Pigs selected for transfer should be average in size. Males, rather than females, should be transferred if possible. After standardization, the number of pigs reared in the litter should be recorded B all pigs given to the sow to raise, including foster pigs. Standardization of the post-farrowing weight record will prevent discrimination against a good milking sow or gilt that has a lesser opportunity because of smaller than optimum litter size. The litter weight (already adjusted to a 21-day basis) should be standardized to 10 pigs by adding the appropriate value from the following table:

Table 3. Factors for adjusting 21-day litter weight for number of pigs after transfer (number allowed to nurse).
Number of pigs
after transfer
Adjustment factor for
21-day litter weight (W)

Post-farrowing litter weights should also be adjusted to a mature sow equivalent by adding the following numbers to the record based on the parity of the female:

Table 4. Parity adjustment factors for 21-day litter weight.
Adjustment factor for
21-day litter weight (W)

The adjustment factors in Tables 1-4 were derived for general purpose use from large data sets. NSIF recommends that whenever possible, specific adjustment factors be derived from data sets for specific populations, for use in those populations specifically.

An alternative measurement is loin-muscle depth. Many packers use this measurement, in conjunction with backfat depth, to predict percent lean of carcasses (see page 25).

Growth. Growth rates must be measured on all intact males and/or all gilts by one of two procedures.

A.Age at a constant weight. If pigs are not weighed on test but only a final weight is taken, weights should be taken at or near 250 pounds or some other comparable constant weight. The equation for adjusting days to a constant weight is:

where a = 50 for boars and barrows, and 40 for gilts.

B.On-test gain. Pigs should be weighed on test at an average pig weight consistent with the management program of the operation. Average pig weights of approximately 70 pounds are recommended. Ranges in starting weights among individual pigs should be minimized. Off-test pig weight should average at least 160 pounds more than starting weight. If pigs being tested have undergone segregated early weaning (SEW), the test may be started at an average starting weight of 40 pounds and off-test pig weights should average at least 190 pounds more than starting weight. The protocol for the SEW process is provided in Appendix C.

5.Backfat. All pigs should be measured for backfat thickness at the tenth rib location when they are weighed off-test at 250 " 15 pounds. The average of two measurements, taken 2 inches off the midline on both sides of the pig, should be obtained if a metal probe or A-mode ultrasound machine is used. If a B-mode (real-time) ultrasound machine is used, a single measurement is sufficient. Backfat depth should be measured at the midpoint of the loin, and should include the skin and all fat layers. NSIF recommends that pigs be measured by NSIF certified technicians (see Swine Genetics Factsheet 16). If any other backfat measurements are taken, an explanation should be given. All measurements should be adjusted to a constant basis using the formula below:

where b = -20 for boars, +30 for barrows, and +5 for gilts.

6.Live Evaluation. Any genetic defects should be recorded. Structural soundness and underline soundness are examples of visual traits that affect production and reproduction and should be evaluated. Breeding animals must be structurally correct and mobile to carry out their normal functions and sows must have functional nipples to raise pigs. Recommendations for live evaluations are offered in Appendix D as aids in the selection of replacement animals. The animals should be evaluated at or near the end of test and the date of evaluation recorded.

Additional traits that may be considered in the base program are:

7.Birth weight. Weights should be recorded within 3 days of birth.

8.Feed Efficiency. Feed consumption should be measured on an individual basis if possible. If group fed, pigs should be tested in progeny groups. With group feeding, the number of pigs per pen, sex and relationship among pigs in the pen should be noted. If some pigs are chosen for central testing, all pigs of that sex should be tested in a comparable environment in the test station. Initial weight on test should average near 70 pounds with variation among individuals minimized. Off-test average pen weight should be to a constant weight and at least 160 pounds more than average starting weight. If pigs tested have undergone segregated early weaning (SEW), the test may start at an average weight of 40 pounds and off-test pig weights should average at least 190 pounds more than starting weight. The protocol for the SEW process is provided in Appendix C.

9.Loin-Muscle Area. The loin-muscle area (LMA) should be measured on pigs when they are weighed off-test, within a 30-lb range of the desired weight endpoint (e.g., 250 " 15 lb). Loin-muscle area should be measured over the 10th rib at a location 2 inches off the midline. The equation for adjusting LMA to a constant weight basis is:

10.Predicted Percent Lean. This trait can be used in place of backfat in a selection index. Use the following equation to calculate Predicted Percent Lean (PPL) if pigs are weighed off-test at 250 " 15 lb.

If an endpoint weight different from 250 lb is used, refer to Equations 1A and 1B in Chapter 4 to calculate PPL.

Within-Herd EPD Programs

Calculation of EPDs on all pigs in a herd using all available information is a requirement for these programs. In addition to data on the individual, information should include full-sib, half-sib, parental, and progeny data updated regularly. Computer programs are commercially available for the calculation of within-herd EPDs. Procedures, models and genetic parameters used in within-herd genetic evaluations should be well documented, and preferably be those recommended by NSIF.

Across-Herd EPD Programs

Across-herd breeding value estimation should use multiple trait animal model procedures and genetic parameters derived from the data. An accuracy value that reflects the amount of information used in the genetic evaluation should also be made available. Purebred breeders can participate in across-herd genetic evaluation programs through the National Association of Swine Records (NASR). Procedures, models and genetic parameters used in across-herd genetic evaluations should be well documented and preferably be those recommended by NSIF.

Commercial Program

To make accurate selection decisions, commercial producers who select replacement animals from their own herd should measure the performance level of their animals. Obtainable goals should reflect the changes in performance that the producer considers necessary to develop and maintain a profitable program. The records that commercial producers should keep and the traits chosen for genetic improvement are dependent on the economic value of the traits and the extent to which producers plan to utilize the records in decision making. These essential records should provide the basis for a diagnosis of the program's weaknesses as related to the producer's goals, and serve as an early warning tool to monitor potential program problems. Because each producer's goals may differ, and producers' physical operations vary, the traits chosen and level of performance desired may not be the same for all producers. At a minimum, however, all commercial producers should utilize records on sow productivity and boar performance to evaluate and monitor herd production. The Pork Industry Handbook Factsheet 100 has additional information on types of records and their use.

For commercial farms, maximum hybrid vigor is essential in the female. Therefore, planning and implementing a crossbreeding program and keeping a record of female breed composition are important. A sow productivity program should aid in selecting replacement gilts from the most productive sows in the herd and serve as a basis for culling the least productive females. To achieve high production standards, sows need to be prolific, have good milking ability, and rebreed within 7 days post-weaning. Sows that fail to settle in two estrous cycles following weaning should be culled. Computer programs and sow record cards can help as systematic tools to record production activities and performance records. For producers who select replacement females from within their own herds, performance information on individual gilts and their dams is important, and use of a selection index is recommended. The accurate selection of replacement gilts can be accomplished by following the base on-farm program.

Boars purchased from seedstock producers should come from the top 50% of their test group in test station and on-farm programs. Whenever data are available, commercial producers are strongly encouraged to use EPDs when purchasing animals or semen. Boars selected for use in an A.I. program should meet higher standards and be in the top 10 percent of the population evaluated.

Selection Indexes

Environmental influences make it difficult to compare pigs tested at different locations, at different times, or under different management. Using selection indexes based on contemporary group comparisons will allow comparisons of animals in the same test group. Keep in mind, indexes are not appropriate for comparing different groups of animals.

The traits used in the calculation of NSIF selection indexes are defined as follows:

L =the adjusted number born alive record on the dam minus the average of the adjusted number born alive records of her contemporary group.
W =the adjusted 21-day litter weight record on the dam minus the average of the adjusted 21-day litter weight records of her contemporary group.
D =adjusted days to 250 pounds measured on the individual minus the average of the adjusted days to 250 pounds of the test group.
B =backfat measured on the individual, adjusted to 250 pounds, minus the average of the adjusted backfat of the test group.
M =predicted percent lean calculated for the individual minus the average predicted percent lean of the test group.


SPI = 100 +6.5(L) + W
EWSPI = 100 + 10(L)
MI = 100 + 6(L) + .4(W) - 1.6(D) - 81(B)
TIA = 100 -1.7(D) - 168(B)
TIB = 100 - 1.4(D) -106(B)
TIM = 100 - 1.4(D) +12(M)

a Details about the indexes are given in Appexdix E

  1. Sow Productivity Index (SPI). This index provides a measure of sow productivity and is especially useful when culling sows. Prolificacy is measured by the adjusted number of pigs born alive in a litter. Milking ability is measured by the adjusted weight of the litter at 21 days of age.

  2. Early Weaning Sow Productivity Index (EWSPI). This index is designed for use in culling sows when 21-day litter weights are not available. Litter weight at 21 days is used as a correlated trait when the index is constructed, allowing some selection emphasis to be placed on milking ability even when weights are not collected.

  3. Maternal Index (MI). The maternal index is intended to put emphasis on maternal characteristics and is useful for selecting boars to produce replacement gilts and in selecting replacement gilts. Because barrows, and gilts that are unacceptable for replacements, are residuals of this type of mating, there is some emphasis on growth rate, backfat and feed efficiency. Feed efficiency is included as a correlated trait, although it is not measured directly. NSIF recommends that potential replacements not be weaned before 10 days of age so that litter weight can be used to select for milking ability.

  4. Terminal Indexes (TI). The terminal indexes put emphasis on growth, efficiency, and backfat. The terminal indexes should be used for selecting animals to be used in terminal crosses. If backfat is measured using A-mode ultrasound, the TIA should be used. If backfat is measured with B-mode ultrasound or metal probe, the TIB is the appropriate index. The TIM is for use if PPL has been calculated.

These indexes will average 100 for each test group and should have a standard deviation of about 25. A test group should have approximately the following distribution of index values:

Index Value Percent of Animals
More than 150
125 to 150
100 to 125
75 to 100
50 to 75
Less than 50

If EPDs are reported, animals may be evaluated with similar indexes. The simplest index consists of all the EPDs added together. For example, if a producer is interested in litter size, growth and backfat, the index would be:

I = 100 + EPDL + EPDD + EPDB

Use of economic values for each trait will weight the genetic information for the relative economic importance of each trait. Using the economic values in Table 8 (Appendix E) for the same traits would give this index:

I = 100 + 13.5 *EPDL - .17 * EPDD - 15 * EPDB

For more information on indexes, see Appendix E.

Health Program

The following items are herd health recommendations for on-farm testing programs for seedstock producers.

  1. All seedstock producer herds should be validated and certified brucellosis and pseudorabies free.

  2. All pigs offered for sale should be vaccinated against erysipelas and the six strains of leptospirosis, should be free of external and internal parasites.

  3. All pigs offered for sale should be eligible for an interstate shipment permit.

  4. Strict biosecurity measures should be followed for all incoming traffic, such as scanning equipment, feed truck, stock truck, boar buyers, etc. Each farm should have its own scales.


Effective merchandising depends on the integrity of the breeder, coupled with the use of accurate, complete performance information explained by well-defined terms relating to the product to be sold. The use of misleading statements that may be deceptive, impossible claims, or use of selected portions of the total record in the merchandising of performance-tested swine is strongly discouraged. Every possible effort should be made to inform and educate swine producers on the use and interpretation of performance records.

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