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item Riley, David
item Chase, Chadwick - Chad
item JOHNSON, D.
item OLSON, T.

Submitted to: Florida Cattleman
Publication Type: Trade Journal
Publication Acceptance Date: 1/12/2006
Publication Date: 2/12/2006
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.

Interpretive Summary:

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