Fact Sheet #11

Purdue University

Cooperative Extension Service

West Lafayette, IN 47907

Utilizing Central Boar Test Stations to Enhance Genetic Progress

C. M. Wood, Virginia Polytechnic Institute and State University
J. W. Mabry, University of Georgia
A. P. Schinkel, Purdue University

Reviewed by:

Dallas Reeve, Denison, IA

Wes Blanchard, West Lafayette, IN

Rodney Goodwin, Iowa State University

Larry Young, MARC

Ron Bates, University of Missouri

Robert Busch, Chico, CA


Central boar test stations have been in operation in the U. S. since 1954, providing uniform environments in which to evaluate genetic merit of boars from different farms. Through the ensuing decades, the central test stations responded to the ups and downs of the swine industry in general. By 1987, 33 test stations were in operation, some testing boars directly for gain, backfat, and feed efficiency, others evaluating market offspring of herd sires.

Currently, central test stations are used to demonstrate performance testing procedures and to evaluate genetic merit of potential herd sires under uniform conditions. Test stations offer accurate, unbiased collection of performance data and a reliable source of healthy breeding stock. However, seedstock producers often use the results more for marketing than for genetic improvement. A common error is to attempt to directly compare boars tested at different stations or at different times. Under the selection index system presently, in use, such comparisons of boars across tests are erroneous because the performance records are not yet analyzed with the most appropriate genetic evaluation procedures.

Other current limitations of the test station system include:

Currently, a majority of the tests compare young boars directly; only a few stations conduct progeny tests. In addition, information gained through the central tests is not being used extensively in other testing programs. With the advent of breeding value estimation programs such as the Swine Testing and Genetic Evaluation System (STAGES), the possibility exists to combine data collected by producers on the farm with the information from stations. Use of all available data can enhance the accuracy of breeding value estimation for performance traits of herd sires already in use, as well as provide estimates of a sire's ability to produce reproductively efficient daughters. In addition, the value of young, unproven boars can more accurately be predicted.

As breeding value estimation procedures are implemented in the swine industry, the role of the central test stations should continue to evolve, and many of the above limitations will be overcome. Central test stations will expand their role beyond that of education to that of complementing and enhancing on-farm genetic improvement programs.


Seedstock producers are in the business of selling breeding value (the worth of an animal as a parent). The greater the genetic improvement in production efficiency, the more valuable superior seedstock should be. As explained in NSIF-FS9, Concepts of Genetic Improvement, genetic progress in a single trait can be predicted on a yearly basis by


                    heritability x
   yearly        selection differential
   genetic   =   ______________________
improvement         genetic interval

Therefore, producers can maximize genetic progress by increasing the selection differential, increasing effective heritability, and decreasing generation interval.

Increasing Selection Differential

The selection differential (sometimes referred to as reach") is the difference between the average performance of the animals being selected and the average performance of the group from which those animals are being drawn. Selecting only the very best boars and gilts will improve selection differential. The selection differential is related to selection intensity, which is a measure of the proportion, or percentage, of animals selected. The smaller the percentage selected from among the top performing animals, the greater the selection differential, because the average performance of the selected animals will be that much better than the average performance of the total group.

If artificial insemination is fully utilized, the top 1 to 2% of boars tested in stations and on farms should be sufficient to meet replacement requirements in seedstock operations, assuming that performance testing becomes the norm. Central stations offer a convenient marketing outlet for merchandising the very best potential herdsires identified from different farms, making such a sale attractive to potential buyers.

Table 1 illustrates the difference that selection intensity can make, To maximize the selection differential, under natural mating conditions, keep only as many replacement sires as absolutely necessary to meet breeding goals. Also, the fewer superior gilts selected as replacements, the larger the selection differential. The proportion will vary depending on a producer's goals, but selections should be made within the top half of a gilt group, even during herd expansion. On the other hand, a herd that consists primarily of sows will make slower genetic progress because of a longer generation interval. A balance between the factors must be sought by each producer.

Table 1. Influence of percent selected (no. replacements/no. tested) on gene progress.a

                            Group            Percent            Possible
Situation                   Size             Selected           Progress
Multiple-breed test        40 total
 Breed A                   10 boars             50%              .04 lb./yr.

National test of
 Breed A                   50 boars             10%              .08 lb./yr.

Sire summary              500 boars              1%              .13 lb./yr.
a In all cases. five boars are required to meet needs, a heritability
of .40 is assumed for average daily gain, and generation interval is
one year.

Increasing Effective Heritability

All traits measured on pigs are affected by genetics and the environment. Heritability (h2) is a measure of the contribution made by genes. The methods used to measure traits can reduce variation due to environment and increase effective heritability. Effective heritability can be increased in many ways. Some examples include using precise equipment, recording measurements correctly, and testing all animals. Use of central test stations can help increase effective heritability as well. They offer a uniform testing environment for boars from many herds and the opportunity to measure traits (such as feed efficiency or halothane sensitivity) that may be too expensive for individual producers to measure on their farms. Also, as discussed later, entry rules - can influence the makeup of pens and whole tests, allowing maximum exploitation of genetic relationships to increase effective heritability.

Decreasing Generation Interval

Generation interval is defined as the average age of parents when they are replaced by their offspring. This term is in the denominator of the yearly genetic improvement equation, so the longer it takes to replace an animal in the herd, the longer it takes for an improved genetic package to have an impact. In addition, the merits of decreasing generation interval by culling a large proportion of sows must be weighed against the decrease in selection differential if more gilts are saved to replace those sows. However, there is no reason a herd sire a seedstock operation should be kept any longer than a year, since a reasonable number of sons should be available from which to choose a replacement. One strong point in favor of central test stations is that generation interval for boars is minimized if production traits such as average daily gain, backfat, and feed efficiency are of prime concern. By the time a boar is mature enough become a herd sire, his breeding value can be estimated for those traits by measuring him directly.

Applications to Central Test Stations

When programs such as STAGES are fully implemented, the capability will exist to combine on-farm performance data with central test data to allow comparison of animals across stations and herds. By testing in one location young boars that have common ancestors (parents and/or grandparents) and that are from different herds, pedigree (genetic) ties can be used to improve accuracy genetic evaluations of all animals the farms and in the test stations. Direct comparison in central test stations of even unrelated boars out different herds can allow all animals, in those herds to be compared fairly as shown in Figure 1. Boars at Test Station 1 can be directly compare each other because they are in the same place at the same time. Then, through their pedigree ties (common ancestors) with animals in different herds, indirect comparisons can be established. By combining direct and indirect comparisons, a complete network of ties can be constructed, allowing evaluation of all animals. This addresses the problems of limited space and inadequate progeny numbers. With appropriate evaluation procedures, the problem of limited carcass data also may be alleviated, since barrow information can be included as well.

S1, S2, etc. represent offspring of Sires 1, 2, and so forth. With on-farm testing, only the sires within each herd can be compared (eg., S1 vs. S2 vs. S3). Under central test station indexing procedures, the same applies within each station (eg. S2 vs. S5 vs. S7 only). Using a complete evaluation system such as STAGES, progeny information in these three herds and two test stations can be used to fairly compare all 10 sires, because a sire's progeny, placed in herds and test stations, provide genetic ties which interconnect all farms and stations involved.

Figure 1. Use of central test stations to increase the completeness of an across-herd evaluation program.

Adapted from Purdue Cooperative Extension Service Bulletin AS-438.

By utilizing the genetic ties among stations, evaluation of boars within a breed, across stations, will be easier. This should replace the current practice of ranking boars of different breeds that happen to be in the same test. A more accurate analysis would be provided by a national sire evaluation published once or twice a year by each breed association, which would rank herd sires for economically important traits, based on information gathered in central test stations and on the farm. Producers then could use sire expected progeny deviations (EPD's) when deciding which progeny to select and or buy as replacements.

Producers also would have the opportunity to use EPD's of parents to help decide which young boars should be sent to the test stations. By consigning boars from outstanding parents. producers could group the superior progeny together, which should improve merchandising. The effective heritability also would be improved by having access to parents EPD's, since information from relatives contributes knowledge about the animal being evaluated. Finally, generation interval would be decreased, since young animals would be tested and selected as herd sires, rather than the producer having to wait for progeny information.

By using on-farm information, breeding values of traits expressed only in female relatives can be evaluated and included in the off-test information, along with performance traits measured at the test station. This can be an effective merchandising and selection improvement tool, especially for animals from maternal lines or breeds.

Perhaps most importantly, by gathering superior young animals central locations, test stations will continue to serve as a benchmark the industry. Marketing will be enhanced since potential buyers would have access to a larger number of quality boars at a single location, artificial insemination gains further acceptance in the swine industry, highest ranking boars in a breed will be sought out by boar studs. A second group of boars, as determined by EPD, should be attractive to individual seedstock producers who wish to have herd sires on the premises. Finally, a third set of tested boars would be valuable to commercial producers interested in making within herd improvements. The bottom group of animals still must be culled but on a breed-wise basis, rather group or location basis.

The above applications assume that accurate across-herd evaluations are possible. Under selection index testing procedures currently in use most stations, genetic differences among herds and even herd sires, not be evaluated: only those boars within a breed that are tested at the same station at the same time can compared. Also, while test station evaluations are expensive, low-ranking boars must be called if the swine industry is to make appreciable genetic progress. Under index selection, this means the bottom of each test group. One thing remains constant in the genetic valuation of breeding stock: all values- index or EPD- are related to the average, and animals below a certain level must be called if the average is to improve the following generation. Use of information from across-herd evaluations can actually decrease the number boars culled due to performance in test stations, since boars would be compared within breed, rather than within breed within station.

Producer Involvement

All seedstock operations large, medium, and small can and should be involved in a comprehensive genetic evaluation program and should consider consigning boars to central test stations. In addition, central test station consignors should collect on-farm performance data and use the data when selecting replacement boars and gilts. Over time, this will improve the average genetic merit of the breed.

Central test stations must measure economically important traits in a consistent, uniform manner. The National Swine Improvement Federation Guidelines provide such a system. With no access to on-farm data, a regional or national test consisting of a minimum of 20 boars from at least five different genetic lines or families will provide the best assurance that top-ranked boars within the breed group are truly superior genetically. As the number of boars within a test increases past 20, the number of lines within breed represented by each set of 3 to 4 related boars also must increase to ensure a good genetic comparison, as demonstrated by research conducted at Iowa State University. Finally, the top-ranked boars (indexing over 125 on the NSIF index) must return to seedstock herds and or boar studs so their genetic superiority can be multiplied.

With across-herd comparisons, herd size is no longer a limiting factor, because producers have equal opportunity, to utilize the information generated in central test stations, and individual producers cat determine how they rank relative to their peers. Such information will enhance marketing possibilities for outstanding producers and provide incentive for breeders who wish to improve.

Purebred boars must be evaluated within their breeds, since the goal of performance testing is to improve the genetic merit of each breed, not to compare a boar of breed A with a comparisons make selection of such animals as accurate as possible.

The first step in evaluation of breeding stock is to make sure performance records are kept on all animals in the herd and are used. This means that a scale and some type of backfat probe must be available along with labor to use them, and permanent identification of indi-boar of breed B. Crossbreds make up 95% of the commercial hog population, and all breeds need not have the same goals: each should concentrate on improving strong points and combining ability with other breeds. In order for breed improvement to occur, however, producers must use the information to continue genetic improvement in their individual herds. For example, outside replacements maybe required in order to minimize inbreeding, and use of across-herd individual animals is necessary. Once records are available, consistent selection must be practiced. Consigning just a few registered boars to the nearest test station and ignoring records on the rest of the animals is self-defeating. As shown in Table 2, the cost in time, equipment, and labor is minimal relative to the benefits of keeping records. Second, producers must expand their understanding of genetic principles and applications in order to make the best decisions for their operations. This series of fact sheets is a good source of information, and university researchers and extension specialists are available to help design performance programs. Seedstock producers must be willing to invest in performance testing, utilizing genetic information, in order to remain competitive in today changing swine industry.

Table 2. A comparison of cost of testing versus savings resulting from improvement in days to market.a

Contemporary  No.           Cost of    Cumulative         Cumulative  Net
 Group        Tested  Days  Testingb  Cost      Savingsc  Savings   Change
July 85        48     186    $35.04                                 $-35.04
Sept. 85       10     180      7.30    $42.34    $23.32    $23.32    -19.02
Nov. 85        39     187     28.47     70.81    -15.16      8.16    -62.65
Jan. 86        22     175     16.06     86.87     94.07    102.23     15.36
April 86       37     172     27.01    113.88    201.35    303.58    189.70
July 86        35     173     25.55    139.43    176.86    480.44    341.01
Oct. 86        43     173     31.39    170.82    217.28    697.72    526.90
Jan. 87        55     179     40.15    210.97    149.65    847.37    636.40
May 87         24     169     17.52    228.49    158.59   1005.96    777.47
aImprovement is the actual decrease in days to market in the
University of Georgia Yorkshire Teaching Herd, and includes
environmental effects.
bCalculated as $.73 per pig for labor and processing. Does not
include equipment cost.
cSavings come from $.15 per pig per day fixed costs + an estimated
3.41 lb per day reduction @ $.07 lb feed, using 186 days as the base.

New 8/89

Cooperative Extension work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture cooperating: H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an equal opportunity/equal access institution.