Carcass Traits of Steers Finished on Three Forage Systems

Linda Benedict, McMillin, Kenneth W., Persica III, Manuel Anthony, Gregorie, Cole  |  11/15/2014 4:03:23 AM

Kenneth W. McMillin, Manuel A. Persica III, J.C. Gregorie and James N. Maynard

A market for forage-fed beef exists in the United States. Research has shown that one-third to onehalf of consumers prefer the taste of forage-fed beef to grain-fed beef. Another benefit of forage-fed beef is increased support of locally produced products. Previous research in the LSU AgCenter has shown that forage-finished beef can be produced using forage resources available in Louisiana. The present study was conducted to determine the impact of the three forage production systems on carcass traits and composition. Each year for three years, cattle were obtained by random selection of six steers from each forage system for a total of 54 steers of 3/8 Gelvieh, 3/8 Red Angus and 1/4 Brahman breeding. The forage systems were:

System 1 was primarily bermudagrass during summer, fall and spring and ryegrass in winter.

System 2 was bermudagrass in summer, a dallisgrass-and-clovers mix during fall and spring, and a ryegrass-clovers mix during winter.

System 3 was bermudagrass and sorghum-sudangrass hybrid with forage soybeans during summer, a dallisgrass-clovers mix during fall and spring, and a ryegrass-clovers mix during winter.

Carcass traits of finished cattle are important because they determine the relative value in yield and predicted palatability of the meat. Quality grades estimate the eating properties or palatability of the lean beef, and yield grades estimate the amount of meat, or yield, expected from the carcass after removing bones and trimming excess fat. Quality grades are determined primarily by the relative bone maturity and the marbling in the Longissimus dorsi – ribeye muscle – with consideration to muscle color.

Yield grades are determined by combining the carcass weight; subcutaneous fat thickness at the 12th and 13th ribs; kidney, heart and pelvic fat percentage; and the area of the ribeye muscle at the 12th and 13th rib junction. Yield grades estimate the percentage of the carcass that will produce boneless, closely trimmed retail cuts, often 45 percent to 50 percent of the carcass for feedlot-finished cattle.

Cattle finished in feedlots usually have quality grades of Select or Choice, which are desired by grocery stores and many restaurants because of the level of fat marbling within the muscle, and yield grades of 2, 3 or 4. Carcass grading is typically done at 24 to 48 hours after slaughter before carcasses are divided into primal cuts for shipment as chilled boxed beef. Beef produced on forages usually have lighter carcass weights, less subcutaneous fat, and lower marbling levels when slaughtered at the same age as cattle finished on silage or grain. This results in lower quality grades of Select or Standard and lower yield grades of 1 and 2.

Each year 18 steers were selected after approximately 324 days on their respective forage systems and were randomly assigned to two groups for humane slaughter in a Louisiana state-inspected meat plant. Carcasses were chilled in a 36-degree F cooler overnight before evaluation. After trained meat scientists evaluated the carcass traits based on U.S. Department of Agriculture specifications, primal rib cuts were removed from each carcass side.

The 9-to-11-rib section from one side was divided into ribeye muscle, other lean tissue, fat and bone while the remaining portion of that primal cut and the rib primal cut from the other side were cut into steaks for determining cook yield, tenderness, electrical conductivity and sensory panel palatability. Boneless, closely trimmed retail cuts were calculated from carcass weight, ribeye muscle area, 12th rib fat thickness and percentage of kidney, pelvic and heart fat. These data were analyzed along with the year, forage system and individual steers with each system.

Live weights of the randomly selected steers did not differ among years or forage system, but carcass weights were heavier in 2013 and tended to be heavier for steers finished on forage systems 2 and 3. The heavier carcasses produced higher dressing percentages in the third year and with systems 2 and 3. The ribeye muscle area was not different among years or forage systems; however, carcass fat thickness and percentage of kidney, heart and pelvic fat increased in the second and third years. The yield grades were slightly higher in the second and third years but were not different within year or among forage systems.

The percentage of boneless, closely trimmed retail cuts is predicted by yield grades, with no differences by year or type of forage system. Percentages of ribeye muscle and the other separable lean tissue were higher and bone percentages were lower in the 9-to-11-rib sections in 2011 than for the other two years. This corresponded to the slightly lower yield grades and slightly higher percentage of retail cuts in 2011.

Marbling scores are based upon the visible intramuscular fat in the ribeye muscle at the 12th rib. Carcasses had slightly higher amounts of marbling in 2013 than in 2011 and 2012, which was expected since fat deposition was also higher in the third year. Quality grades based upon the skeletal maturity, lean color and marbling were minimally different, and most carcasses graded Standard, a grade lower than the commercial beef target of Select for retail merchandising. Several producers, however, are successfully marketing forage-finished beef in Louisiana with minimal amounts of marbling.

Although there were some differences in availability of forage mass and nutritive values among the forage systems during the grazing seasons, these did not result in large differences in carcass characteristics of the forage-finished steers. Additional studies may be justified to determine carcass characteristics of cattle finished on other forage systems. 

Kenneth W. McMillin holds the Mr. & Mrs. Herman E. McFatter Endowed Professorship in Animal Science. His co-authors are Manuel A. Persica III, research associate in the School of Animal Sciences; J. Cole Gregorie, research associate at the Sweet Potato Research Station in Chase; and James N. Maynard, graduate assistant in the School of Animal Sciences.

This article was publish in the fall 2014 issue of Louisiana Agriculture.

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