Genetic Improvement of carcass quality:
bringing home the bacon

J. Chesnais
Canadian Centre for Swine Improvement Inc.

Introduction

The Ontario Carcass Appraisal Project has produced a wealth of information, on growth performance carcass and meat quality, and relationships between live, grading and carcass measurements. This information has already been used to complete a number of tasks:

However, OPCAP has not been the only meat and carcass quality research and development project undertaken in Canada. During the last few years, there has been several other projects:

It is important to understand the relationships between these various projects or programs. Some activities are undertaken primarily for research, while others aim to monitor meat and carcass quality, and others to provide data for selection. The purpose of this paper is to review the strengths and weaknesses of the tools available for research, selection or monitoring of meat and carcass quality and examine how they can be used together to advance the industry.

Why is carcass and meat quality important?

The industry produces only one product and pork meat. Making sure this product is of good quality is essential to preserve or extend markets for Canadian pork. In addition, the development of value-added products is key to the future of the industry. In order to produce specialized, ready to market products that seek premium prices in Canada or abroad, we must be able to control product quality.

Meat and carcass quality can be controlled or improved in several ways: they are affected by genetics, management and feeding, health, transportation and handling, packing and processing. In this paper, we will focus primarily on genetic improvement and the monitoring of its impact in breeding herds, commercial herds, and slaughtering plants. There is a good reason for paying special attention to the genetic improvement of meat and carcass quality: it responds well to selection. Table 1 shows that the heritabilities of most carcass traits are in the 30% to 50% range, i.e. between one-third and one-half of the total variation in these traits is of genetic origin. For meat quality (Table 2), the heritabilities are generally in the 30% range, with some in the 60% range (e.g. marbling).

Swine test stations

One of the tools that has been used very early in the genetic improvement of meat and carcass quality is the test station. It consists of bringing together, in one location, animals from several sources evaluating their growth performance and collecting slaughter data. Recent examples are OPCAP, the Commercial Product Test in Quebec, the NPPC terminal lines trial or the Shur-Gain study in Ontario. The main advantage of the test station is that it offers a controlled environment, where many traits can be measured, including traits that would be difficult to measure elsewhere. Its main drawback is its cost. Consequently, it generally applies to relatively small numbers of animals.

For the above reasons, test stations are a very good tool for research. They can also be used to monitor the meat and carcass quality of a population, or to compare genetic sources (e.g. comparison of breed crosses in Quebec commercial product test, or comparison of terminal lines in the NPPC trial). These comparisons, however, are generally done on an occasional basis because of the cost.

Test stations can also be used to test the siblings of boars that have been preselected based on the genetic values of their parents. Some genetic progress for meat and carcass quality can then be achieved if the best boars are widely used through AI (Kennedy, 1992). However, the use of test stations for this type of selection is declining, because other options are available to genetically improve meat and carcass quality traits at a lower cost.

On-farm testing

Selecting breeding animals on the basis of live measurements at the farm is an effective way to improve carcass quality. Current measurements include backfat thickness, loin depth and loin eye area. Biopsies could provide a way to obtain meat quality data on the live animal, if the process can be carried out without creating controversy. The cost of on-farm testing is relatively small, and its accuracy can be fairly high (lean yield predictions are more accurate from live than from grading measurements). In addition, testing can be carried out directly on the candidates for selection. For these reasons, on-farm testing programs are a key selection tool for meat and carcass quality in breeding herds. When applied systematically, they can generate relatively rapid genetic gain. Examples in Canada include the backfat thickness, halothane gene probe and loin-depth programs.

On-farm testing programs can also be used for monitoring of breeding herd performance or for comparing genetic lines for traits that can be measured in the field. The main limitation of on-farm testing is that it applies to only a relatively small number of traits. Selection or monitoring for the other traits therefore require different approaches.

Slaughter plant data

Collecting data in the slaughter plant and returning it to the producer is the simplest way to provide data for selection and monitoring of meat and carcass quality traits. Two types of programs can be developed to carry this out:

directed programs

These are programs whereby special arrangements are made at the plant to collect meat and carcass quality information on samples of animals. Examples include the OSI Home Test Carcass Appraisal Program, private sampling by plants and/or breeding companies and the national carcass cut-out.

The approach can apply to a large number of traits; the data can often be related to specific parents or lines; and the information can be associated to growth performance if the animals were tested on the farm. However, cost can be high (special carcass cut-outs, need to slow down the kill line).

Directed programs are used primarily to monitor the performance of a population or to compare genetic sources, lines or management approaches for meat and carcass quality on a periodic basis. The information can also be used for "within herd" research. Because of the cost involved, relatively small numbers of animals are involved, which limits the use of these programs for continuous selection.

systematic collection

Another approach is to develop programs whereby slaughter plant data is systematically collected and reported back to producers, and possibly to selection herds. Some information (carcass grading index, backfat and loin depth, health monitoring information) is already available through programs such as APHIN (PEI, Ontario). There is a potential to expand these programs to include additional meat and carcass quality traits. Swine quality assurance programs (Alberta) could also evolve to include this type of information.

The systematic collection of meat and carcass quality data in the plant requires a sizable investment, particularly for the development of systems to identify carcasses from groups of animals or from individual animals. However, once this is done, the cost is moderate. Only traits that are relatively easy to measure in the plant are ususally considered. However, the number of such traits is continually increasing with the development of new technologies. Systematic data collection at the slaughter plant has the potential to provide considerable amounts of meat and carcass quality information on a routine basis. This information would be ideal for monitoring commercial herds. If links can be established between the producer information and that of the breeder (for example through the identification of animals or of groups of animals), systematic collection of meat and carcass quality data at the plant could also form the basis for the continuous selection of these traits in breeding herds, and for the comparison of different genetic sources or lines at all levels of the pork chain.

Strategies for improvement of meat and carcass quality

Each of the genetic improvement and/or monitoring programs described above has its place and can be used to complement the others. Test stations, for example, are particularly useful for research. On-farm testing is an effective means of selection for the traits that can be measured in the field. However, selection for meat and carcass quality would be greatly enhanced by the implementation of systematic data collection at the plant level, and the linking of this data back to breeding herds.

Evaluating different lines or different genetic sources can be achieved in different ways, depending on the objectives of the evaluation: the directed collection of slaughter data will generally produce information on more traits than on-farm testing or the systematic collection of slaughter data, but for smaller numbers of animals because of the inherent cost.

The choice of selection and/or monitoring programs that can be developed to improve meat and carcass quality therefore depends on several factors. Selection goals and a selection strategy must be developed first. Then the objectives of the program must be clarified:

Genetic improvement and monitoring activities can be carried out through concerted action or as a result of private initiatives. Both are needed. Privates initiative, involving packers, producers, breeders or breeding companies can be aimed, for example, at the evaluation of different genetic sources based on the market needs of a particular packing plant, or at the monitoring of contract specifications between a producer and a packer. Concerted action generally involves national, provincial or state organizations. Its goal is often research or the development of standards or information systems that benefit the industry as a whole (e.g. OPCAP, PEPC in Quebec, National Carcass Cut-out, APHIN).

The collection of meat and carcass quality data is only one step among the many that are required to have an effective selection program. Other steps include the development of genetic evaluation systems that use all available data (station, farm, plant). Separate economic indices may have to be developed for different markets objectives, each giving meat and carcass quality an appropriate weight in relations to other traits. Economic incentives for meat and carcass quality must also be part of the system so as to provide a stimulus for the selection effort.

Conclusions

OPCAP, as well as other projects in Canada, have provided a considerable amount of research data on which to build the foundation of a genetic improvement program for meat and carcass quality. What is required next is the development of tools for continuous monitoring and selection of swine for product quality. A key aspect of that development will be building information links across the various industry segments. Although these links are generally easier to establish within integrated enterprises, it would be beneficial for the Canadian swine industry to develop them at a level where they are available to most stakeholders.