The pork industry has incurred tremendous change
in recent years, not only in the manner of production, but also
in the type of commodity produced. This rapid amount and rate
of change has put added pressure on the seedstock industry to
provide the genetic tools to produce an acceptable end product.
Because genetic improvements made towards more efficient pork
production are made first at the seedstock level, the producers
of breeding animals have been very innovative in utilizing the
most current technology.
Before 1985, genetic evaluation of swine in the United States
was conducted on a very limited basis. Because of the biology
of swine and the continuous methods of production, genetic evaluation
had to include the ability to account for multiple records and
large numbers of relatives in order to achieve high accuracy,
features that were for the most part, unavailable up to this time.
The development of a Swine Testing and Genetic Evaluation
System (STAGES) was initiated as a joint venture between Purdue
University, U.S.D.A. Agricultural Research Service, U.S.D.A. Extension
Service, National Association of Swine Records, individual purebred
associations, and the National Pork Producers Council in 1985.
The following year, the first within-herd genetic evaluations
were conducted, with across-herd evaluations available in 1990.
The STAGES program, supervised by Purdue University, has since
been in use for the Yorkshire and Landrace breeds, while PAGE
1, a similar genetic evaluation program conducted by the University
of Georgia, has generated EPD's for the Duroc and Hampshire breeds
In 1998, the National Swine Registry, the registry
for these four breeds, released a new version of STAGES, a combination
of the original STAGES and PAGE 1. This genetic evaluation program
utilizes breed specific adjustments and variance components to
generate Expected Progeny Differences (EPD's) and bio-economic
indexes for the swine industry.
Industry demands for genetic evaluation places certain requirements on any program that is to be successful. EPD's must be accurate, easy to understand and use, accessible and dynamic. The National Swine Registry has strived to address each of these concerns with the new STAGES.
The across-herd genetic analysis for each breed runs
in-house and nightly. NSR members recently submitted the one
millionth performance into the STAGES program, with each record
representing either a maternal litter record or an individual
growth record. Table 1 shows the breakdown by breed performance
records, and the time required to run the evaluation each night.
It was necessary to keep total computer time under 12 hours in
order to run nightly, and currently total run time is slightly
over 9 hours.
|Table 1. Number of performance records in NSR database and run timea|
|aData as of October 5, 1998|
Change in Genetic Base Year
Genetic base is the original population of animals
at the initiation of selection and selection. The average EPD
of this population will be zero, and this genetic base will be
a point of reference for future generations. With the previous
program, the genetic base year for each breed was 1992 or 1993.
A rolling or moving base year is currently in place, utilizing
a four year prior base for maternal traits and a three year base
for terminal traits. This base changes nightly, truly reflecting
a dynamic population. The base year today, December 4, 1998,
for maternal traits would be December 4, 1994 plus and minus 6
months, or include all animals born from June 4, 1994 to June
3, 1995. Terminal traits would then have a three year prior window
of June 4, 1995 to June 3, 1996. The individuals born within
these windows would have average EPD's of zero and average indexes
of 100. The duration of the prior years account for a complete
generation interval, allowing young animals to become parents
with sufficient progeny for accurate evaluation.
STAGES has always calculated bio-economic indexes based on EPD's of traits relative to their economic merit, when used in commercial crossbreeding programs. These indexes were developed so that each index point had a value of $.10 per index point per offspring produced. For Terminal Sire Index (TSI), a unit represents approximately $1 for every 10 pigs marketed, and for Sow Productivity Index (SPI) and Maternal Line Index (MLI), a unit is $1 per litter produced by every daughter of the sire or dam. In the past, the terminal sire index weighted the EPD's for days to 230 lbs., backfat thickness and feed conversion, while the maternal line index included EPD's for number born alive, number weaned adjusted for number after transfer, 21-day litter weight and post-weaning performance.
In order to better serve the users of STAGES, the
230-lb. standard has been raised to 250 lbs., more closely following
the existing pork industry. Growth is now reported as days to
250 lbs., backfat is adjusted to a 250 lb. live weight and an
EPD is now calculated for loin muscle at 250 lbs. The EPD for
loin muscle is not reported; however it is used along with the
EPD for backfat to develop an EPD for pounds of lean adjusted
to 250 pounds liveweight or a 185-pound carcass.
The equation used for this EPD is:
LBLEAN EPD = (-20.3 x Backfat EPD) + (3.41 x Loin
where backfat EPD is in inches, and loin muscle area
EPD is in square inches.
The economic value assigned for backfat has also
changed within our industry. Previously the value used was $10.86
per inch, or a $1.09 change in value per .1 inch change in backfat
depth, while in 1996, NSIF estimated the economic value of backfat
as $15.00 per inch, or $1.50 per .1 inch. This value was utilized
in the development of a curvilinear economic relationship between
carcass value and measurements associated with leanness. This
relationship was developed recognizing the fact that extremely
lean carcasses, those greater than 52 to 53% lean, have an increased
incidence of pork quality problems. Representatives of four major
pork processors, when polled as to their current and future carcass
merit buying systems, identified the ideal backfat range as .65
to .80 inches, while discounting carcasses with 1.1 in. or greater
at an increasing rate. When these carcass merit systems were
scaled to a common value ratio, the maximum carcass value index
(1.00) was attained at 94 LBLEAN.
Figure 1 shows the relationship between carcass value
and LBLEAN. The slope of the dollar value at a specific value
for pounds of lean is the marginal value of the next incremental
pound of lean. Table 2 shows the incremental values per LBLEAN
EPD or per .1 inch change of backfat EPD. The marginal values
become smaller as the pigs become leaner, and go to zero at 94
lb. of lean.
The new STAGES indexes utilize this curvilinear relationship
between carcass value and the EPD for pounds of lean. The Terminal
Sire Index uses a base LBLEAN value of 86 pound, so the economic
value for backfat at 0 EPD for backfat will be $11.44 per inch,
similar to the $10.86 used previously. A base value of 91 lb.
LBLEAN will be used for the Maternal Line Index (value of $5.43),
which will reduce the economic value of backfat to about 50% of
the old MLI. As the pigs become leaner, the EPD's for LBLEAN
will increase as the component EPD's for backfat and loin muscle
area change. As the EPD's for LBLEAN increase, the additional
economic value of each one pound incremental in LBLEAN will become
smaller. Because the maternal line index uses a higher base value
(91 vs 86 pounds), the very leanest animals will be given decreased
economic value and emphasis in MLI.
The new STAGES indexes are similar to the old indexes,
in that they remain bio-economic indexes specifying a dollar value
on a per pig or per litter basis. However the changes made should
result in a better balance of leanness and growth, because the
extremely lean animals will get decreased credit for leanness,
favoring an animal with balanced numbers.
Figure 1. Relationship of carcass value to pounds
of fat-free lean adjusted to 250-lb. live weight.
|Table 2. Incremental increase in carcass value per one pound increase in fat-free lean EPD or one-tenth increase in backfat thickness EPD|
One of the keys to genetic evaluation is proper contemporary
group design. Animals are evaluated on their relative merit within
a contemporary group. A properly designed contemporary group
includes animals that are: 1) the same breed or breed composition,
2) the same gender, 3) of similar age, 4) have had similar care
consisting of the same housing, nutrition and health status.
Tables 3 and 4 identify the optimum and minimum characteristics
of a properly designed contemporary group for STAGES. Submitted
performance information is monitored for inappropriate contemporary
groups at input, and necessary changes in the structure of the
group are made.
|Table 3. Contemporary groups for maternal traitsa|
|Sires of sows|
|a Adapted from Bates, 1998.|
|Table 4. Contemporary groups for growth traitsa|
|a Adapted from Bates, 1998.|
Breed Specific Adjustments
Swine producers need to accurately measure performance
in order to estimate genetic merit. Historically, adjustment
factors have been used to standardize performance records and
allow isolation of the genetic component of observed variation.
The National Swine Improvement Federation provides litter adjustment
factors common to all breeds; however these factors have been
found to differ between breeds, as well as to deviate from NSIF
guidelines. Litter size can be affected by contemporary group,
parity, age at farrowing, previous lactation length and weaning
to conception interval. The development of these adjustment factors
included these factors as well as the genetic merit of the female
in order to more accurately assess reproductive performance.
Tables 5, 6, 7 and 8 show the breed specific adjustment factors
used in the development of the maternal EPD's and indexes.
|Table 5. Breed specific adjustments for number born alivea|
|a Adapted from Mabry et al., 1997.|
|Table 6. Breed specific adjustments for number weaneda|
|a Adapted from Mabry et al., 1997.|
|Table 7. Breed specific adjustment for weaning age (multiplicative)a|
|a Adapted from Mabry et al., 1997|
|Table 8. Breed specific adjustments for 21-day litter weighta|
|a Adapted from Mabry et al. 1997.|
In the competitive industry of producing food for our nation, pork producers must utilize all available tools in order to remain a viable enterprise. Performance testing and the subsequent genetic evaluation and development of Expected Progeny Differences allow breeders to take a hands-on role in cutting edge technology. The new STAGES program was implemented in September 1998 and provides the most dynamic genetic evaluations available in the swine industry. A rolling genetic base year, nightly runs, breed specific adjustments and variance components, proper monitoring of contemporary groups and a curvilinear relationship between carcass value and pounds of lean in the indexes combine for accurate assessment of genetic merit of animals. The program allows the strengths and weaknesses of each breed to be accounted for, and gives us an extremely powerful tool to help produce the meat of the future.
Bates, R.O. 1998. Designating contemporary groups.
Presented at Ninth Annual STAGES Roundtable, March 23, 1998. West
Culbertson, M.S., and J.W. Mabry. 1995. Effect of
age at first parity and lifetime sow performance.
Mabry, J.W., M.S. Culbertson, J.K. Bertrand and A.H.
Nelson. 1997. Effect of age at first mating on SPI. NSIF Proceedings
NSIF. 1997. Guidelines for uniform swine improvement
Schinckel, A.P., D.L. Lofgren, and M.E. Einstein.
1998. Recent STAGES changes. Proceedings of Purdue Swine Day.
Stewart, T.S., D.L. Lofgren, D.L. Harris, M.E. Einstein
and A.P. Schinckel. 1991. Genetic improvement programs in livestock:
swine testing and genetic evaluation system (STAGES). J. Anim.
Stewart, T.S., D.L. Lofgren, D.L. Harris, M.E. Einstein
and A.P. Schinckel. 1993. Using STAGES: a guide to interpreting
STAGES reports for breeders and their clients. Purdue University
and U.S. Meat Animal Research Center.
Venner, J.J. 1998. STAGES: National Genetic Evaluation
Trait Leader List, May, 1998.