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Quality Lean Growth Modeling Project

Pork producers have accepted the ambitious goal of making pork the "Meat of Choice." Two factors will determine their success:More pork must be raised more efficiently in the U.S. so pork prices are competitive.The quality of pork produced must be improved for increased consumer and processor acceptance for domestic and international consumers alike.The results of the National Pork Producers Council

Pork producers have accepted the ambitious goal of making pork the "Meat of Choice." Two factors will determine their success:

More pork must be raised more efficiently in the U.S. so pork prices are competitive.

The quality of pork produced must be improved for increased consumer and processor acceptance for domestic and international consumers alike.

The results of the National Pork Producers Council (NPPC) National Genetic Evaluation Program (NGEP), reported in 1995, showed a large variance in efficiency and quality of lean produced. That same year, a Consumer Preference Study (CPS) indicated U.S. consumers can discriminate among quality (juiciness and tenderness) levels of pork. Unfortunately, the NGEP showed the most efficient animals to produce did not always result in the products that consumers preferred.

In an effort to improve production efficiency and product quality, the Quality Lean Growth Modeling (QLGM) project was funded by the National Pork Board and began in 1996.

Lean growth models are computer programs that predict growing pig performance. There are several in use by feed companies and several more in university research laboratories.

Generally, pig growth and fat deposition rates have been researched to market weights at 250 lb. However, packer buying programs are encouraging marketing at heavier weights, even past 300 lb. There is little information about feed intake, conversion, or gain on modern pigs from 250-330 lb.

Recognizing this void, the 1996 Pork Forum Delegate Body passed resolutions to research the economics of heavyweight market pig production.

Through the use of new, electronic feeding equipment in the QLGM project, more accurate daily gain and feed intake information can be captured on an individual pig basis. Also, meat quality parameters have been avoided by modelers because data was lacking and it is expensive to collect. This challenge, too, is addressed in the QLGM project.

The economics of changing diets as pigs are finished to heavier weights was also evaluated in the QLGM project. Four nutritional programs (four diets per program) were fed - all with constant energy, mineral and vitamin levels within respective weight ranges - but diets within each program differed by assigned lysine levels. Changes in growth, carcass composition and quality of loins, hams and bellies due to nutritional program differences are evaluated in the QLGM project.

The highest lysine levels (diet 1) should provide excess protein for all pigs. Likewise, the lowest lysine levels (diet 4) are below National Research Council (NRC) recommendations and should restrict most pigs (see Table 7, page 24).

The six genetic lines used in the QLGM project were selected for their diversity with the intent of representing a cross-section of genetic types in the pork industry. This program was not designed to compare genetic lines, but rather to analyze the response of different genetic types to different nutritional programs and off-test weights. Classification procedures are reviewed below.

The variation in pigs provided by six genetic types also facilitated data collection which will allow Fat-Free Lean Index (FFLI) equations to be updated. The packing plant processing the QLGM pigs installed a Fat-O-Meater and an ultrasound system along with a last rib backfat thickness measure. Every carcass was measured with all three systems. Several on-line pork quality measures were also collected.

Nearly half of the carcasses (698) were broken down into primal and subprimal cuts, fat and bone. These (one-half) carcasses were then ground and samples sent to a laboratory to determine chemical lean content. This is the largest current database on U.S. slaughter hog composition. New FFLI equations will be developed for better producer information.

Loin samples from each pig were evaluated fresh for color, pH, drip loss and intramuscular fat content. Chops were cooked at 70 C (158 F) and tenderness, juiciness and cooking loss were measured.

One ham from each carcass was separated into three muscle groups, fat and bone. Each fresh muscle group was evaluated for color, pH and intramuscular fat. Muscle groups were processed into ham, and cooking yields, sliceability, and sensory data were recorded.

One belly from each carcass was sent to a laboratory for processing into retail or foodservice bacon. Shatter loss, processing yield, lean content and sensory data were collected. This is the largest bacon processing trial on U.S. hogs.

Loin samples resulting from this project were used for another Consumer Preference Study since genetics, age, pig nutrition, health and management has been controlled. The consumer studies were conducted during October 1997.

This program spanned three years (1996-1998) because a portion of each of the three groups of about 550 each were grown to 330 lb. The first group of pigs entered SEW nurseries on March 5, 1996 and the last went to slaughter in November 1997.

Program Design The NPPC Genetic Programs Committee wanted variation in genetic types of pigs so that more information could be provided to producers. All seedstock suppliers were offered a chance to enter 300 terminal-cross market pigs in this trial. No ordered genetic sampling of these populations was done so these QLGM results do not represent a genetic evaluation.

A full range of performance for growth, carcass composition, and meat quality was desired for this project. Previous results reported from the National Genetic Evaluation Program (NGEP) provided good direction but several unknown genetic types were also offered. One (DeKalb Swine Breeders) was chosen for this QLGM project.

The QLGM pre-trial classification parameters used by the NPPC genetics committee are shown in Table 1. The committee relied on NGEP results for Berkshire, Duroc, Hampshire, Newsham Hybrids and Danbred to classify genetic type of entries. DeKalb entries were unknown except for supplier information that indicated good growth, good lean and unknown meat quality. Table 2 shows the pre-test classification of each genetic type based on the NGEP results.

Actual QLGM project results of a genetic type may differ from these due to sampling of pigs, but differences should be consistent between classes.

The actual QLGM project results (Table 3) were used to build Tables 4 and 5 to provide a guide for producers to use in classifying their genetic lines and matching them to the QLGM results. Those post-test classifications appear throughout this publication to provide an easy reference. More accurate lean growth curves, such as those outlined by de Lange in Table 2, page 10, will help producers more precisely classify their market hogs.

The final results of the QLGM project show general agreement with the pre-test classifications and reveal success in measuring large variation for all traits.

The QLGM project evaluated 1,590 pigs in three test groups. The genetic types included high, medium or low classifications for backfat thickness, growth, feed intake and meat quality. Crossbred pigs representing Berkshire, Duroc, Danbred, Newsham Hybrids, Hampshire and DeKalb genetics were evaluated. All program pigs were tested for HAL genotype. And, because this test was not designed for genetic comparison, each genetic type was randomly assigned a letter, A through F, to ensure anonymity.

Other sampling and procedural parameters included:

Three pigs per litter (barrows and gilts) were entered whenever possible (see Table 5). The test pigs were assigned to slaughter weights of 250 lb., 290 lb., and 330 lb. when placed in the SEW nurseries. However, due to slow growth and the protocol of selling the last pig in a pen, a few pigs did not reach their 330 lb. assigned weight (Table 6). Sex of pig was balanced among the three slaughter weights. Sampling of genetic populations was determined by the NPPC Genetic Programs Committee.

All pigs were commingled in SEW nurseries at between 8 and 19 days of age. SEW programs of NGEP were followed. That protocol included Ivomec treatment on day 1, Naxcel on days 1 and 2, Mecadox in the feed, and Denagard in the water from day 2 through 10. Pigs were penned by genetic type and size in nurseries.

Pigs were removed from the nurseries at 40 lb. and moved to a grower building.

At 80 days of age, pigs were moved to a building equipped with electronic feeding and pig weighing equipment (FIRE system) until desired market weight was achieved.

Each pig was evaluated bi- or tri-weekly for backfat depth and loin muscle area by a National Swine Improvement Federation (NSIF) certified real time ultrasound technician. This resulted in up to 10 measurements on the heaviest off-test weight pigs. Scan measurements for intramuscular loin fat or other locations of interest (ham, belly) were also recorded. These serial scan measures are used to estimate growth and lean deposition rates for each pig. The rates of backfat and loin muscle change in the Robison (page 26) article are based on the serial scan data.

The electronic feeding system monitored daily feed intake for each individual pig. Pigs were weighed at each scanning.

At slaughter, a five-rib loin section was taken from one side of the carcass. One section of three ribs was used for meat and eating quality traits evaluation and the other section of two ribs frozen for consumer preference studies (CPS). The CPS loin samples were individually vacuum sealed in plastic bags and deep frozen until needed.

A sample of half carcasses was physically separated into lean, fat and bone to provide data for refining the Fat-Free Lean Index equations.

Boneless primal cut weights were taken during carcass separation.

Ham and belly quality measures were collected and evaluated at meat laboratories.

Four nutrition programs of four diets each had constant energy, minerals and vitamins within a weight range of pigs, but offer different levels of lysine (see Table 7). Tylan was included in all diets. Lysine was supplied by corn and soybean meal in all diets. Feed was fed in ground form at smaller than 750 microns particle size. Added fat was choice white grease.

Pens of pigs were randomly assigned to a nutrition program. Feed was delivered in an electronic feeding system (FIRE) that weighs daily feed intake by means of an electronic ID in a pig eartag. All feed delivered to the FIRE system was weighed by scale cart as a check against the FIRE data.

This project was completed at the Minnesota Swine Testing Station since SEW nursery, grower building and finishing buildings were available. Air temperature and humidity, pig health and other management data were also completed for future model testing.

Presentation of Results There is a very large amount of data resulting from this project and several possible ways to do statistical analysis to answer questions.

The succeeding articles by Robison, Johnson, and McKissick have tried to be as consistent as possible in their reporting.