Ohio State University Extension Bulletin

Research and Reviews: Poultry and Swine

Special Circular 164-99

Frequency and Effects of the Napole Gene in the U.S. Pork Industry

D. L. Meeker1
S. J. Moeller
K. M. Irvin
D. M. Wulf
C. L. Knipe
R. C. Emnett
The Ohio State University
Department of Animal Sciences

Other Cooperators: National Swine Registry, National Pork Producers Council, Ohio Pork Producers Council, University of Illinois, Iowa State University

1 For more information, contact at: The Ohio State University, 122A Animal Science Building, 2029 Fyffe Rd., Columbus, OH 43210; 614-292-1351; Fax: 614-292-3513; e-mail: meeker.40@osu.edu.

Abstract

The Napole gene is associated with several factors that could influence fresh and processed pork quality. These factors could be either positive or negative, depending on environmental factors, interactions with other genes, and processing techniques. Meat from animals with the gene loses approximately 7% more moisture in the form of drip than normal animals and has a lower ultimate pH that can diminish fresh meat quality. However, both French and American researchers have noted a trend for animals with the RN gene to have meat that is more tender. There is no doubt that the U.S. pig population has a significant incidence of the RN gene, especially the Hampshire breed. It is likely the RN gene is also in other breeds, but the extent is not yet known. The primary objective of the Napole gene research at The Ohio State University is to learn important information about the role of genetics in meat quality.

Background

The Napole gene (noted as RN- in the mutant form and rn+ in the normal form) is reported to be a major dominant gene influencing meat quality, particularly drip loss, and cooking loss during processing of pork. The highest frequency of the gene is reported to be in the Hampshire breed, although it is probable that other breeds also have some incidence as well.

Only curing of post-mortem muscle or the glycolytic potential (GP) test from muscle biopsy or meat can determine whether animals carry the RN- allele (Milan et al., 1996). Biopsies are expensive and invasive to breeding animals, and tests of meat are not useful to select breeding stock except with time-consuming progeny tests. The RN- allele is fully dominant so tests on muscle tissue cannot distinguish between homozygous (RN- RN-) and heterozygous (RN- rn+) animals. Identification of a closely linked marker could result in a quick DNA test using a small amount of blood or tissue.

Recently, University of Illinois meat scientists have used the GP test to identify Napole genotypes and develop Napole gene positive and negative lines of pigs. The estimated cost of the test is $25-$30 per sample plus technician time and expense of collecting the sample. The Meat Laboratory at The Ohio State University now has the capability to do this test.

Results of the University of Illinois research indicate a significant economic loss to packers-processors due to increased drip and cooking loss of pork from pigs with the Napole gene. This loss is increased when the stress or HAL gene is also present. Since the Hampshire breed is a major sire breed and forms the genetic base of many breeding-company sire lines, the influence of the Napole gene may be large in the United States. Some breeding companies are choosing to remove Hampshire genetics from their genetic lines. However, the superior leanness and carcass lean yield of the Hampshire as an asset the U.S. pork industry should not discarded. The industry needs to determine the contribution of the Napole gene to the leanness and eating quality of pork to decide the most appropriate strategy for selection.

These things need to occur for a selection program to be effective:

  1. The frequency of the gene in the Hampshire breed needs to be estimated. Hampshires free of the RN- allele could be identified and multiplied.

  2. A test for Napole genotype must be developed and made available. Several U.S. and European geneticists are trying to map the gene and develop a test using molecular biology. Success may come in one year, or five years, or never. The field test that has been developed is the GP evaluation that can classify animals into two groups: positive or carrier (RN- RN- or RN- rn+), and negative (rn+ rn+). Several environmental variables need to be standardized to make the test more reliable in various field situations, but researchers have been successful in classifying genotypes.

  3. Genetic correlations with other traits must also be measured. If there are significant correlations to other economically important traits, removing the RN- allele from a population may hinder progress in other areas.

Ohio State University Activities

The Ohio State University is part of a research consortium to investigate these parameters to help the pork industry deal with quality problems.

The objectives of these projects are to:

  1. Develop the ability to efficiently conduct GP tests at The Ohio State University.

  2. Establish the presence of the RN gene in the Ohio State University swine population.

  3. Establish linkage relationships between available pig DNA microsatellites and the RN locus in the Ohio State University swine population.

  4. Identify classes of genetically similar lean pigs with differences in selected genetic markers, specifically markers that predict the presence of the RN-.

  5. Search for a connection between the genetic markers and post-mortem carcass measurements that predict muscle quality and processing characteristics of pork.

  6. Provide information linking economically significant traits of pigs to identified genetic markers.

  7. Assist breeders and producers in genetic and processing strategies to improve pork quality.

Pigs representing the major families in the Ohio State University swine population at The Ohio State University's Ohio Agriculture Research and Development Center (OARDC) Western Branch research station will be sampled by biopsy or slaughtered at the OSU Meat Laboratory and tested for glycolytic potential to verify presence or absence of the RN gene. Tissue will be extracted from the OSU pigs and from the NPPC sponsored National Barrow Show Progeny Test. DNA samples will be stored for possible later projects when a more complete pig genome map is available and the new markers have been discovered. Measurements on hams and loins from each slaughtered pig will include initial pH, pH at 45 minutes, ultimate pH, lipid content, water holding capacity, objective measures of color, PSE, and other possible quality predictive measurements. GP tests and pH measurements can be used to verify the accuracy of any RN gene classification resulting from DNA tests that become available. Further testing at the OSU Meat Laboratory may include bacon and ham processing, and palatability and tenderness tests. All available information from the pigs used in this experiment on DNA haplotype, meat quality and quantity traits, and growth performance traits will be analyzed. While much information may be available on some of these traits (especially production traits), relationships to genetic haplotypes with respect to the RN gene and to meat processing traits are not well known.

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