Genetic Parameters of Pork Quality Traits

 

Dr. Rodney Goodwin

National Pork Board

 

The goal of swine breeders must be to produce wholesome, lean, tasty pork for consumers.  Breeders have traditionally selected seedstock for production efficiency traits such as growth, carcass backfat, number of pigs weaned per litter and loin muscle area and ignored meat quality characteristics that may be genetically correlated.

Traits of ham and loin meat quality, nutritional composition and eating quality were included with growth and carcass traits in this evaluation.  The growth and carcass traits evaluated are leg soundness score, average daily gain, dressing percentage, carcass loin (longissimus dorsi) muscle area at tenth rib, carcass off midline backfat at tenth rib, carcass midline backfat at last rib, carcass midline backfat at last lumbar, inside ham muscle (semimembranosus) weight, outside ham muscle (biceps femoris and semitendinosis) weight, knuckle muscle group (quadriceps group) weight, and carcass length.

Meat quality, composition, and eating quality traits of the longissimus dorsi taken from the tenth to twelfth rib section are marbling score, color score, firmness score, Minolta L reflectance, ultimate pH, protein solubility, pigment, tenderness, juiciness, chewiness, flavor, Instron tenderness, cooking loss, cooked moisture content, raw and cooked total lipid percent, raw and cooked cholesterol content, myoglobin content and seven fatty acids (myristic, palmitic, palmitoleic, stearic, oleic, linoleic and arachidonic).

Inside ham, outside ham and ham knuckle traits of Minolta L reflectance, drip loss, Hunter L color score, ultimate pH, cooking yield, cooked ham Hunter L color score, and cooked ham slice yield were evaluated.

The effects and interactions of eight breeds, two sexes (barrow and gilt) and two HAL genotypes (NN, Nn) are reported for all traits.  All test pigs were evaluated for HAL-1843 genotype and the 1999-2001 test pigs have also been evaluated for Rendement Napole, H-FABP and A-FABP genotype. A tissue sample from each test pig has been frozen to supply DNA for evaluation of new gene markers.

Heritabilities, economic values and genetic correlations among these traits give swine breeders a guide to weighting traits for a selection goal.

The National Barrow Show is a trademarked event of Hormel Foods Inc. The Co-sponsor of this event is the National Association of Swine Registries (NASR), which represents eight purebred swine registries. In 1991 a Sire Progeny Test was added to the annual breeding stock shows and sales. This test is open to all breeders of pure lines or breeds. The National Pork Producers Council/National Pork Board funded the meat quality evaluation for nine years and continues to fund gene marker evaluation. There have been twelve tests conducted since 1991.

A sire group consists of eight purebred progeny representing at least three litters. There is no restriction on genetic relationship of dams. Pigs can be barrows or gilts. Each progeny pig has a three generation pedigree from the appropriate registry.

Pigs are entered into a central test station on one day in late March or early April. Pig entry weight is 10-30 kg. After at least seven days acclimation sire groups with average weight of 32 kg or more are started on test. Leg soundness scores were done by the University of Minnesota after pigs weighed 90 kg. Pigs were removed from test only when the attending veterinarian and station manager agreed that illness or injury had compromised a pig’s performance. Any pig removed from growth evaluation was also excluded from other evaluations.

Pigs were marketed weekly. Off test weight was 111 kg or more, resulting in an average off test weight of 113 kg. All pigs were slaughtered at the Austin, MN Quality Pork Processors plant. Carcass measurements were taken in the coolers twenty four hours post mortem. Loin samples were taken to Iowa State University for quality trait evaluation. Ham samples were taken to Texas A&M University for composition and quality evaluation.

 

Distribution of pigs by breed is shown in Table 1.

 

Table 1. NBS test pigs by breed.

 

 

Genetic values (EPD) of sires for growth, carcass, and meat quality have been calculated by Iowa State University and provided to breeders. Growth trait evaluation results by breed are shown in Table 2.

 

Table 2. Growth traits by breed, 1991-2001. Least squares means and standard errors.

 

 

Carcass trait evaluation results by breed are shown in Table 3.

 

Table 3. Carcass traits by breed, 1991-2001. Least squares means and standard errors.

 

 

Table 4. Fresh loin quality traits by breed, 1991-2001. Least squares means and standard errors.

 

 

Table 5. Cooked loin traits by breed, 1991-2001. Least squares means and standard errors.

 

 

Table 6. Ham composition traits by breed, 1996-1997. Least squares means and standard errors.

 

 

Table 7. Ham muscle differences by breed, 1996-1997. Least squares means and standard errors.

 

 

A tissue sample from each test pig has been frozen and stored for future evaluation of gene effects. As gene tests become available DNA will be extracted for evaluation. The variety of breeds and broad sampling of breeds provides a unique resource for swine breeding research.  The National Pork Board owns this tissue-DNA-performance databank. Researchers can apply to the NPB Genetics Program Committee for access to the database.