Dr Todd See Swine Genetics Specialist

The focus generally is placed on color, intramuscular fat, tenderness, pH, and water-holding capacity. However, consumers also are interested in nutrition, food safety, animal welfare, and environmental issues. Consumer demands are leading to the development of branded pork products that have a specific set of marketable attributes. When these quality products are clearly identified, they can be marketed more easily to the target audiences that want that specific bundle of qualities.

Today, the main areas of emphasis in genetic selection are lean yield, efficiency, growth rate, and reproductive performance. Quality measures get little consideration. But given current consumer attitudes, this is beginning to change. It will still be essential to emphasize more than one trait in pork production, and the potential for selection should not be wasted on unimportant traits. In most cases the economic advantage for satisfying consumers is unknown or not transferable to the pig producer. If we consider genetic selection for consumer traits, we must know if they are truly economically important, are heritable, and are positively or adversely correlated with other important traits. It is also important to know and understand breed differences for quality measures and how different breeds should be utilized in crossbreeding programs. This article will discuss each of these areas and describe how genetic selection could be made, using an index or total score that combines each trait with its economic value and correlates each trait to the other traits in the index.

Breed Differences

Genetic differences in pork quality among swine breeds have been shown in several large industry quality evaluation programs (Table 1), providing the industry an opportunity to design superior pork products for specific markets. The results support the use of Duroc seedstock for the highest quality pork because of its excellent marbling (intramuscular fat or IMF), ultimate pH, and tenderness as measured by the Instron. In general, direct and maternal heterosis effects are negligible on meat quality traits. However, this does not hold true for traits like ultimate pH in certain crosses when the halothane (HAL) or RN- genes are involved.

Major Genes

Part of the breed variation in meat quality can be ascribed to large breed differences in allelic frequencies for major genes affecting pork quality. The halothane-sensitive allele ranges in frequency from near 0.03 in the Duroc to near unity in the Pietrain. "Stress-resistant" breeds include Chester White, Duroc, Hampshire, and most of the Landrace and Large White National varieties. Poland China and certain Landrace populations are intermediate. Belgian Landrace and Pietrain are "stress-sensitive". The HAL gene has been shown to have detrimental effects on pH, color, drip loss, IMF, and tenderness.

Another major gene is the RN- allele, which is responsible for the "Hampshire effect". This has a detrimental effect on ultimate pH, cooking loss, and water-holding capacity but may have a positive effect on tenderness.

Genetic Parameters

Table 2 presents the heritabilities and genetic and phenotypic correlations for growth, carcass, and quality traits. The growth traits - feed conversion ratio (FCR), average daily gain (ADG), days to 250 pounds (D250), pH, tenderness of cooked pork (TEND), Minolta color (COLOR), and drip loss (DRIP) - are all moderately heritable. Backfat depth at the tenth rib (BF10), loin muscle area (LMA), and intramuscular fat (IMF) - carcass traits - are highly heritable. Important correlations to look for when evaluating growth and carcass traits are adverse relationships between growth (ADG and D250) and carcass (BF10 and LMA) traits. A desirable relationship exists between BF10 and the traits FCR and LMA. For the muscle quality traits, IMF has an adverse relationship with BF10 and LMA. However, a desirable relationship has been observed between pH and the traits of DRIP, TEND, and COLOR. COLOR also has a positive relationship with DRIP.

Economic Values

The economic value for each genetic trait is intended to represent the expected change in producer profit for a unit change in the trait. In general, the method of calculating economic value is to estimate the marginal costs that are saved by superior performance. There are ranges of estimates of economic values of traits, and they are likely to vary across regions, markets, and production systems. They also vary from farm to farm.

The results of a consumer preference study (Pork and the U.S. Consumer Conference) provide an indication of the economic value of marginal changes in meat quality traits. Considerable uncertainty remains about how much of a premium pork marketers can collect for differentiated pork products and what volume they can sell at that price. Considerable uncertainty also exists about the costs that marketers will incur to distinguish their products and how much of a premium they will pass through to packers and producers. It is also known that losses occur during slaughter and processing because of poor pork quality. However, the magnitude of these losses is not known. Another loss that can occur is when a consumer, dissatisfied with the pork product, never purchases pork again. This, too, is hard to measure. Ultimately, a producer must make genetic choices based on available incentives.

Sample economic values based on the results of the consumer preference study are presented for each trait in Table 3. In this table the economic value is the marginal savings in cost due to superior performance. The economic value is then divided by the standard deviation (SD) for the trait to put all value in the same units of measure. Finally, the relative economic value is calculated by setting one trait as the basis by which all comparisons will be made. In this example, BF10 is the base trait and therefore has a relative economic value of $1.00. The relative economic values indicate how much additional profit can be earned by making an improvement of one SD in one trait versus another trait. Relative economic values also indicate what profit is possible by genetic selection for each trait.

At this time, producers should use caution in interpreting the muscle carcass and muscle quality economic values. Producers now selling hogs through a carcass merit program can use their discounts for BF10 and LMA to calculate economic values for those traits. The relative economic values and the relatively high heritability of BF10 and LMA make them important traits in evaluating terminal sires. No incentives are currently available to producers for muscle quality traits such as IMF, pH, and TEND. The Consumer Preference Study indicates that pork marketers have an opportunity to earn considerable profits by creating differentiated products with specified pH, IMF, and TEND. In order to assure consistent quality in these products, packers and processors will need to establish inexpensive measurements of these traits. In order to procure a reliable supply of pork with desired traits, packers will have to offer premiums for them. However, it is important to realize that what consumers prefer to eat is not necessarily the same product they select, based on visual appearance. In addition, some "quality" measures have different values for eating and processing.

Evaluating Multiple Traits

Overall profitability is influenced by many factors. Several traits need to receive emphasis in a well-designed breeding program. The difficulty is determining the appropriate emphasis to place on each trait. Traits are measured in different units (number of pigs, pounds per day, inches, etc.). They are not of equal economic importance and are not genetically influenced to the same degree (different heritabilities). These factors make it difficult to determine the appropriate emphasis to apply to each trait in a breeding or selection program. Selection indexes are used to assign emphasis to each trait and provide a single value to use when comparing animals. The weights assigned to traits included in selection indexes represent the expected change in producer profit for a unit change in each trait. The index weights differ from economic values since they include the heritability of each trait, correlations with traits excluded from the index, and the economic values of traits excluded from the index.

Pigs are commonly ranked on a combination of growth and carcass traits: feed:gain (F/G), D250, BF10, and LMA. The information presented in Tables 2 and 3 was used to construct the weights presented for the various indexes in Table 4. The rIH is an estimate of the accuracy level by which phenotypic measurements of the traits included in the index predict the true genetic merit of the individual. Common selection procedures measure ADG and BF10 and utilize their relationship with FCR in structuring the index. This allows animals to be ranked on FCR without the costly measurement and at virtually no loss in accuracy in selecting animals.

Table 4 describes possible indexes for ranking animals on a combination of eight traits incorporating growth, carcass, and muscle quality measures. In each index, the final ranking is based on all traits, but only traits with coefficients are actually measured on individual animals. Using the accuracy value as a guide, this table suggests that the index to best predict genetic merit for this set of eight traits is Index 2. Index 2 includes the phenotypic measures of D250, BF10, LMA, pH, and IMF.


A fundamental problem facing the industry now is that current carcass merit programs create incentives for selecting for less BF10. The positive correlation between BF10 and IMF means that selection for less BF10 alone will result in less IMF. The positive correlation between BF10 and FCR provides a further incentive to select against IMF. The Consumer Preference Study indicates that consumers prefer to eat pork with IMF greater than 4 percent. To maintain a desirable level of IMF, sufficient incentives are required to offset the costs of higher FCR and the discounts for higher BF10. Producers may wish to collect information on IMF, pH, and tenderness for terminal boars and their market hogs. Producers of hogs with poor muscle quality traits may wish to begin selecting for improvement in these traits.

Bottom Line

Swine producers must select the genetic stock that maximizes their profits. Genetic selections will affect profits for hogs sold one year later (in the case of terminal sires) and two or more years later (in the case of maternal line sires). Producers should select stock using the economic values that are currently available to them, but attention should be paid to the muscle quality traits as well. However, selecting for quality still holds many unknown variables; and until there are price premiums or discounts for differing pork quality, there will be no rush to select genetics based on quality. On a positive note, it is likely that premiums and discounts for muscle quality traits will be introduced in the immediate future, for many markets.

Number born alive and feed conversion remain important variables in reducing production costs. Carcass quality traits such as BF10, LMA, and yield are important for producers selling through carcass merit programs. Meat quality traits, including IMF and pH, will be important in determining hog prices and profits in the near future and perhaps in maintaining a market or establishing new branded markets.


Source: North Carolina State University Swine Extension - April 2002