Beef Cattle Tenderness Genetics and Their Effects 

  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 tenderness genetics 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 genetics and their effects.

     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.