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United States Department of Agriculture

Agricultural Research Service


item Riley, David
item Chase, Chadwick

Submitted to: Florida Cattleman
Publication Type: Trade Journal
Publication Acceptance Date: January 12, 2006
Publication Date: February 12, 2006
Citation: Riley, D.G., Chase, C.C., Johnson, D.D., Olson, T.A. 2006. Additional brahman tenderness research results. Florida Cattleman. 70(5):36-37,39.

Technical Abstract: This is the second of two articles that summarizes recent research related to Brahman beef palatability. A progeny test of 27 Brahman bulls was conducted in the late 1990s at Brooksville. This project resulted in collection of carcass grading data and tenderness measurements from 724 purebred Brahman steers and heifers over a seven year period. This experiment is one of the largest studies, if not the very largest, involving such data from purebred cattle. It was essential that we fully investigate the genetic control over tenderness traits in Brahman. We also thought it essential to responsibly use these data to approach the Brahman tenderness issue in a variety of ways. We have an obligation as scientists not only to consider traditional interpretation of the facts, but also new ways of thinking about or approaching those facts. There are three major sources of beef tenderness variability: the contractile state of muscle (as indicated by sarcomere length), protein proteolysis, and connective tissue components. The contractile state of muscle is related to cold-shortening and the resultant tenderness issues; increased contraction that occurs during rigor mortis results in tougher steaks. It can often be effectively controlled by methods of chilling and hanging carcasses. Protein proteolysis is muscle fiber breakdown or tenderization that occurs postmortem. It involves two cellular enzymes called calpains (called mu- and m-calpain). Their activities are restrained by a third enzyme called calpastatin. Higher levels of calpastatin activity are characteristic of beef from Brahman cattle; they appear to be responsible for at least part of the tenderness differences between Brahman and British cattle. Connective tissue surrounds muscles, muscle bundles and fibers. The principal structural protein of connective tissue is collagen; collagen is also the most abundant protein in the animal’s body. Collagen fibers are strengthened by intermolecular cross linkages that increase with age. This is the major reason that meat from older animals is often tougher than that of younger animals. Warner-Bratzler shear force (force in lb required to pull a dull blade through a cooked ½ inch core of meat) was measured at the University of Florida (UF) meat science lab after 7, 14, and 21 days of refrigerated aging. A trained UF sensory panel evaluated different aspects of tenderness after 14 days of aging. Physical measurements of tenderness (fragmentation of muscle fibers) were recorded on a subset of carcasses after 1, 7, 14, and 21 days of aging both at UF and the University of Georgia (UG). The amounts of mu- and m-calpain activities were measured at UG, as well as the inhibitor enzyme calpastatin (which was also measured separately at UF). Collagen levels were measured at UF on samples from 468 of the Brahman carcasses. We obtained and stored DNA from all calves and their parents so that we could participate in future studies that use newly discovered DNA markers. A progeny test is a very good and useful design for detection of DNA marker association with the traits of the cattle we observed. Postmortem Tenderization in Brahman Cattle Steaks from a subset of the overall data (87 calves) were used in the evaluation of postmortem proteolysis by calpain and calpastatin activity at UG. Although this is a very small number of records, results indicated that there were sire differences for mu-calpain and calpastatin activity. Such sire differences are at least suggestive of exploitable genetic control. We also used this subset of data to evaluate the progression of tenderization across aging time. The tenderness trait that we used was a measure of the amount of muscle fiber fragmentation in the steak. Three aspects of physical tenderness were considered: 1) tenderness at the beginning of the aging period, 2) tenderness at the end of the aging period, and 3) the rate of change. Sires appeared to differ greatly in how steaks from their progeny fit into these three components. For example steaks from some sires’ progeny increased in tenderness rapidly, and aging after 10 to 12 days produced no further increase in tenderness. Steaks from the progeny of other sires steadily increased in tenderness throughout the 21-d aging period. At the other extreme, steaks from other sires’ calves started poor and finished poor; in other words, aging was of no benefit. Even though this was a small data set, it isn’t hard to envision a system that directs steaks from different sires’ calves to different product groups that require differential aging. This is a novel combination of genetic and environmental management that should be considered further. What Measurements Best Explain or Predict Tenderness in Brahman Steaks? We conducted a statistical test that is commonly used to choose the most important influences from a large group of possible explanatory variables on a given measurement. Fifteen different carcass attributes were evaluated for their relative influence on seven different measures of tenderness in these data. Three important findings from this work were: 1. The information that is available at the time carcasses are given quality and yield grades poorly accounts for tenderness variation in Brahman beef. For example, the traits that influence USDA quality (marbling score) and yield grade (12th rib fat thickness, ribeye area, carcass weight) had almost no association with measures of tenderness. 2. Although calpastatin activity may effectively explain tenderness differences among breeds or breedtypes of cattle (e.g., Brahman as compared to British or European breeds), it was not effective for explanation of within-Brahman tenderness differences. 3. Perhaps the key result was that collagen content was among the most important (often the most important) explanatory variable for all aspects of tenderness. This appears to be a result unique to the Brahman breed and warrants additional investigation. What is known at the molecular level associated with Brahman tenderness? Are there useful DNA markers? Samples from 502 calves were used in analyses by our ARS collaborators in Nebraska. Tenderness measures were checked for association with molecular markers (SNP) within three known beef quality genes. Initially, our collaborators reported that the markers that appeared to be strongly associated with meat quality in British or European cattle were not associated with similar traits in Brahman cattle. Using these data, they have recently found and published a marker within one gene that was associated with a reduction of almost 1 lb in Warner-Bratzler shear force. Perhaps bulls or cows that possess this ‘good’ gene could be identified and used to produce offspring with more tender steaks. These early results are encouraging; however, caution is appropriate, as we are certainly in the very early stages of DNA marker/trait association efforts. Our knowledge of these associations and maybe the usefulness of such markers for identification of superior parents will increase in years ahead. Australian work has demonstrated an association of poor temperament with poor tenderness in cattle. There are currently several U.S. studies, including our own, evaluating the association of tenderness with temperament traits in purebred and crossbred Brahman cattle. We continue to gather data such as these to address the Brahman tenderness question in our projects at Brooksville. If you would like a copy of any of the published results below, please contact me at 352-796-3385 or Casas, E., S. N. White, D. G. Riley, T. P. L. Smith, R. A. Brenneman, T. A. Olson, D. D. Johnson, S. W. Coleman, G. L. Bennett, and C. C. Chase, Jr. 2005. Assessment of single nucleotide polymorphisms in genes residing on chromosomes 14 and 29 for association with carcass composition traits in Bos indicus cattle. J. Anim. Sci. 83:13–15. Riley,

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