Effects of Genetics vs Management on Beef Tenderness
Michael E. Dikeman, Ronnie D. Green, and Duane M. Wulf
Although consumers eat beef primarily because of its great flavor, tenderness is considered the most variable and most important palatability trait. In general, when consumers have a complaint about the palatability of beef, it is because of unacceptable tenderness. The National Beef Tenderness Study published in 1987 found that, except for the tenderloin, considerable variability occurred in tenderness, and a significant proportion of all beef cuts were unacceptable in tenderness. Although the relationships between the tenderness of the longissimus muscle (the main muscle in rib and striploin cuts) and the tenderness of other muscles is variable and not especially high ( r = -.03 to .68 among 10 muscles), tenderness generally is measured on the longissimus muscle because it is one of the most variable muscles from animal to animal, it has the most total value, and almost always is cooked by dry heat with the expectation that it will be tender, juicy, and flavorful.
Recent market studies have shown that consumers are willing to pay more for beef of known tenderness. Although consumers are the ultimate judges of whether or not beef is desirable or undesirable in tenderness, properly trained sensory panels are more precise and sensitive in detecting tenderness differences and most accurately evaluate the complex nature of tenderness. Warner-Bratzler shear force determinations of tenderness are more repeatable and often are used instead of consumers or trained sensory panels because the cost is about two-thirds less and many more samples can be evaluated in the same amount of time. A committee of meat scientists appointed by the National Cattlemen’s Beef Association recently developed a standardized procedure for conducting Warner-Bratzler shear force on cooked beef to maximize repeatability and to allow for more direct comparisons of results from different studies. Therefore, Warner-Bratzler shear force is the common method of measuring beef tenderness and the method used in this Fact Sheet to discuss the effects of genetics and management on tenderness.
Effects of Genetics on Tenderness
The extensive Germ Plasm Evaluation research project at the U. S. Meat Animal Research Center, Clay Center, Nebraska, demonstrated that significant differences in tenderness of steaks occurred between cattle sired by Bos taurus breeds and those sired by Bos indicus breeds when mated to Hereford and Angus cows. Mean tenderness differences among Bos taurus-sired cattle when mated to Angus or Hereford dams were small, even though there were significant sire breed differences in marbling. However, in the extensive Germ Plasm Utilization research project at the U.S. Meat Animal Research Center involving several pure breeds of cattle, significant tenderness differences occurred among purebred Bos taurus cattle. Average tenderness for some purebreds was considered marginally unacceptable, and marbling score was correlated highly with the tenderness differences among breeds. Yet, when three composite breeds were formed from the purebreds to balance favorable carcass composition and meat palatability, tenderness of longissimus steaks did not differ.
Reviews of published literature on the genetic control of tenderness show that the heritability of Warner-Bratzler shear force is moderately high (29 %). A few studies have shown that the heritability of calpastatin activity, the inhibitor to the calpain enzyme system involved in postmortem tenderization, is quite high (40-70 %). Numerous studies have shown that marbling, one of the factors that affects tenderness, is also high in heritability (38 %). These levels of heritability suggest that progress could be made through selection, if the traits could be measured easily. The advantages of genetic selection are that it is cumulative and permanent as compared to management practices. However, selecting for tenderness and other palatability traits has been difficult because of the coordination, time, and expense required in obtaining steaks from meat processing plants on a routine basis. Furthermore, generally only university or government research labs have the capability to accurately measure tenderness.
Expected Progeny Differences (EPD's) have become "user friendly" tools for cattlemen to use in selecting for numerous production traits, but as of December, 2000, only one cattle breed association had EPD's for Warner-Bratzler shear force and none had EPD's for sensory evaluated tenderness or other palatability traits. In addition, not much economic incentive has existed in the past for seedstock producers to select for tenderness. Therefore, selection for tenderness has not been practiced. Recent surveys have demonstrated that consumers are willing to pay for known or guaranteed tenderness and some producers of branded products are showing interest in marketing beef with guaranteed tenderness. Consequently, the economic incentive to select for tenderness may now exist.
Breed Differences in Tenderness. Considerable research data are available that show some breed differences in longissimus tenderness among purebred Bos taurus cattle, but these differences can be minimized by including at least 25% "British”"breeding in crossbreeding programs. Crosses of most "Continental" with typical "British" breeds produce meat that generally is very acceptable in average tenderness, although variability still exists among animals. Several of the "composite breeds" include at least 25% "British" breeding, and mean tenderness generally is very acceptable in them.
Several studies have shown that as the percentage of Bos indicus breeding increases, tenderness decreases almost linearly. Research data suggest that the percentage of Bos taurus "British" breeding should be at least 62.5% (5/8) in Bos indicus x Bos taurus crosses in order to provide an acceptable average level of tenderness. Thus, "composites" that consist of 5/8 British Bos taurus origins x 3/8 Bos indicus breeding generally provide an acceptable level of tenderness. However, considerable variability can still exist, and some cattle will produce meat that is unacceptable in tenderness.
Selecting for Marbling to Improve Tenderness.
Selecting for increased marbling should result in an indirect improvement in tenderness, although the phenotypic relationship between marbling and tenderness is not especially high. Increased marbling results in a dilution effect on the connective tissue (collagen) in meat and provides lubrication in the chewing process, both of which aid in the improvement of tenderness. Increased marbling is most important when meat is cooked to relatively high endpoint temperatures. Several research studies have shown that the risks of having steaks of undesirable tenderness increase significantly as USDA quality grades decrease from Prime to Choice to Select to Standard. Breeders of several purebred breeds have been selecting for increased marbling through progeny testing of sires and(or) ultrasound evaluation of progeny of sires. Some studies have shown that the genetic correlation between marbling and tenderness tends to be higher than the phenotypic correlation.
Because of its high level of heritability (38 %), progress can and has already been made by selecting for increased marbling. Several breed associations are now using ultrasound information obtained by certified technicians and images interpreted by Iowa State University for development of EPDs for marbling as well as ribeye area and fat thickness. Using beef breeds that are noted for high marbling in crossbreeding programs generally results in meat that has a desirable level of marbling. Current pricing systems for carcasses and meat reward higher levels of marbling; therefore, the economic incentive for increased marbling likely will continue to be important in the future.
We should point out the relationship between marbling and percentage of meat yield is antagonistic. In other words, as marbling increases, percentage of meat yield generally decreases, unless both traits are selected for simultaneously. We also should reemphasize that the phenotypic relationship between marbling and tenderness is not especially high, although favorable. Consequently, some cattle with relatively high marbling will produce meat that is unacceptable in tenderness, and some cattle with low levels of marbling will produce meat that is very desirable in tenderness. The ideal situation would be to select directly for tenderness (or against toughness) and simultaneously select for increased marbling and improved percentage of meat yield. However, direct selection for tenderness (or against toughness) has not been feasible because tenderness can be evaluated only on cooked meat obtained from progeny groups of cattle. Even when tenderness information is obtained, it has not been available in “producer friendly” tenderness EPDs.
Michael E. Dikeman, Ronnie D. Green, and Duane M. Wulf
Although consumers eat beef primarily because of its great flavor, tenderness is considered the most variable and most important palatability trait. In general, when consumers have a complaint about the palatability of beef, it is because of unacceptable tenderness. The National Beef Tenderness Study published in 1987 found that, except for the tenderloin, considerable variability occurred in tenderness, and a significant proportion of all beef cuts were unacceptable in tenderness. Although the relationships between the tenderness of the longissimus muscle (the main muscle in rib and striploin cuts) and the tenderness of other muscles is variable and not especially high ( r = -.03 to .68 among 10 muscles), tenderness generally is measured on the longissimus muscle because it is one of the most variable muscles from animal to animal, it has the most total value, and almost always is cooked by dry heat with the expectation that it will be tender, juicy, and flavorful.
Recent market studies have shown that consumers are willing to pay more for beef of known tenderness. Although consumers are the ultimate judges of whether or not beef is desirable or undesirable in tenderness, properly trained sensory panels are more precise and sensitive in detecting tenderness differences and most accurately evaluate the complex nature of tenderness. Warner-Bratzler shear force determinations of tenderness are more repeatable and often are used instead of consumers or trained sensory panels because the cost is about two-thirds less and many more samples can be evaluated in the same amount of time. A committee of meat scientists appointed by the National Cattlemen’s Beef Association recently developed a standardized procedure for conducting Warner-Bratzler shear force on cooked beef to maximize repeatability and to allow for more direct comparisons of results from different studies. Therefore, Warner-Bratzler shear force is the common method of measuring beef tenderness and the method used in this Fact Sheet to discuss the effects of genetics and management on tenderness.
Effects of Genetics on Tenderness
The extensive Germ Plasm Evaluation research project at the U. S. Meat Animal Research Center, Clay Center, Nebraska, demonstrated that significant differences in tenderness of steaks occurred between cattle sired by Bos taurus breeds and those sired by Bos indicus breeds when mated to Hereford and Angus cows. Mean tenderness differences among Bos taurus-sired cattle when mated to Angus or Hereford dams were small, even though there were significant sire breed differences in marbling. However, in the extensive Germ Plasm Utilization research project at the U.S. Meat Animal Research Center involving several pure breeds of cattle, significant tenderness differences occurred among purebred Bos taurus cattle. Average tenderness for some purebreds was considered marginally unacceptable, and marbling score was correlated highly with the tenderness differences among breeds. Yet, when three composite breeds were formed from the purebreds to balance favorable carcass composition and meat palatability, tenderness of longissimus steaks did not differ.
Reviews of published literature on the genetic control of tenderness show that the heritability of Warner-Bratzler shear force is moderately high (29 %). A few studies have shown that the heritability of calpastatin activity, the inhibitor to the calpain enzyme system involved in postmortem tenderization, is quite high (40-70 %). Numerous studies have shown that marbling, one of the factors that affects tenderness, is also high in heritability (38 %). These levels of heritability suggest that progress could be made through selection, if the traits could be measured easily. The advantages of genetic selection are that it is cumulative and permanent as compared to management practices. However, selecting for tenderness and other palatability traits has been difficult because of the coordination, time, and expense required in obtaining steaks from meat processing plants on a routine basis. Furthermore, generally only university or government research labs have the capability to accurately measure tenderness.
Expected Progeny Differences (EPD's) have become "user friendly" tools for cattlemen to use in selecting for numerous production traits, but as of December, 2000, only one cattle breed association had EPD's for Warner-Bratzler shear force and none had EPD's for sensory evaluated tenderness or other palatability traits. In addition, not much economic incentive has existed in the past for seedstock producers to select for tenderness. Therefore, selection for tenderness has not been practiced. Recent surveys have demonstrated that consumers are willing to pay for known or guaranteed tenderness and some producers of branded products are showing interest in marketing beef with guaranteed tenderness. Consequently, the economic incentive to select for tenderness may now exist.
Breed Differences in Tenderness. Considerable research data are available that show some breed differences in longissimus tenderness among purebred Bos taurus cattle, but these differences can be minimized by including at least 25% "British”"breeding in crossbreeding programs. Crosses of most "Continental" with typical "British" breeds produce meat that generally is very acceptable in average tenderness, although variability still exists among animals. Several of the "composite breeds" include at least 25% "British" breeding, and mean tenderness generally is very acceptable in them.
Several studies have shown that as the percentage of Bos indicus breeding increases, tenderness decreases almost linearly. Research data suggest that the percentage of Bos taurus "British" breeding should be at least 62.5% (5/8) in Bos indicus x Bos taurus crosses in order to provide an acceptable average level of tenderness. Thus, "composites" that consist of 5/8 British Bos taurus origins x 3/8 Bos indicus breeding generally provide an acceptable level of tenderness. However, considerable variability can still exist, and some cattle will produce meat that is unacceptable in tenderness.
Selecting for Marbling to Improve Tenderness.
Selecting for increased marbling should result in an indirect improvement in tenderness, although the phenotypic relationship between marbling and tenderness is not especially high. Increased marbling results in a dilution effect on the connective tissue (collagen) in meat and provides lubrication in the chewing process, both of which aid in the improvement of tenderness. Increased marbling is most important when meat is cooked to relatively high endpoint temperatures. Several research studies have shown that the risks of having steaks of undesirable tenderness increase significantly as USDA quality grades decrease from Prime to Choice to Select to Standard. Breeders of several purebred breeds have been selecting for increased marbling through progeny testing of sires and(or) ultrasound evaluation of progeny of sires. Some studies have shown that the genetic correlation between marbling and tenderness tends to be higher than the phenotypic correlation.
Because of its high level of heritability (38 %), progress can and has already been made by selecting for increased marbling. Several breed associations are now using ultrasound information obtained by certified technicians and images interpreted by Iowa State University for development of EPDs for marbling as well as ribeye area and fat thickness. Using beef breeds that are noted for high marbling in crossbreeding programs generally results in meat that has a desirable level of marbling. Current pricing systems for carcasses and meat reward higher levels of marbling; therefore, the economic incentive for increased marbling likely will continue to be important in the future.
We should point out the relationship between marbling and percentage of meat yield is antagonistic. In other words, as marbling increases, percentage of meat yield generally decreases, unless both traits are selected for simultaneously. We also should reemphasize that the phenotypic relationship between marbling and tenderness is not especially high, although favorable. Consequently, some cattle with relatively high marbling will produce meat that is unacceptable in tenderness, and some cattle with low levels of marbling will produce meat that is very desirable in tenderness. The ideal situation would be to select directly for tenderness (or against toughness) and simultaneously select for increased marbling and improved percentage of meat yield. However, direct selection for tenderness (or against toughness) has not been feasible because tenderness can be evaluated only on cooked meat obtained from progeny groups of cattle. Even when tenderness information is obtained, it has not been available in “producer friendly” tenderness EPDs.
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