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Effects of frame-size and time-on-pasture on carcass and beef traits of grass-fed beef

Posted by Teresa Steckler - Pasture

by Taking Stock Contributor

By Anne Zinn, ASAS Communications

A two-year study appearing in the October issue of the Journal of Animal Science examined the effects of frame size and time-on-pasture (TOP) on carcass composition and tenderness in a forage-based finishing system.

A major challenge in pasture-based beef production systems is the determination of a slaughter endpoint and its impact on beef quality. Traditional slaughter endpoints in feedlot finishing systems utilizing high-concentrate diets are related to external fat thickness, live weights, and established percentages of cattle grading Choice. However, based on comparisons with grain-fed finishing systems, the use of these traditional indicators for slaughter endpoints may not be practical in a grass-fed finishing system.

Research on grain-fed finishing systems has shown important effects of time-on-feed on body weight, carcass quality, and beef composition and tenderness. However, little research has been done to address the effects of TOP in a forage-based finishing system on carcass traits or beef composition and tenderness. Dr. Susan Duckett, corresponding author and Professor at Clemson University, and her colleagues used 96 Angus-cross steers over two years to test their hypothesis that TOP is a key factor determining carcass and meat quality in a grass-fed finishing system.

The researchers found that although body weight, hot carcass weight, and ribeye area were greater in medium- than in small-frame sized steers, no other effects of frame size on carcass traits were observed. By contrast, increasing TOP linearly increased hot carcass weight, fat thickness, ribeye area, quality grade, and yield grade, but decreased tenderness of steaks, measured as Warner-Bratzler shear force, such that longer postmortem aging times were required to achieve similar tenderness values.

These results suggest that TOP, but not frame size, is an important determinant of tenderness of grass-fed beef. Based on their results, the authors concluded that "… tender grass-fed beef should be slaughtered at about 18.3 mo of animal age or before."

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