Journal of Animal Science, Vol 71, Issue 8 2079-2088, Copyright © 1993 by American Society of Animal Science

JOURNAL ARTICLE

Effects of time on feed on beef nutrient composition

S. K. Duckett, D. G. Wagner, L. D. Yates, H. G. Dolezal and S. G. May
Department of Animal Science, Oklahoma State University, Stillwater 74078-0425.

Forty-eight Angus x Hereford yearling steers were used to assess the effect of time on feed (TOF) on the nutrient composition of beef longissimus muscle (LM). Steers were fed a high-concentrate diet with the exception of the d-0 group, which served as a grass-fed control, and then were serially slaughtered at 28-d intervals during the 196-d feeding period. Steaks were removed from the 10th rib and trimmed of exterior fat and epimysial connective tissue before nutrient analysis. Intramuscular fat content doubled (P < .05) between d 84 and 112 but did not differ (P > .05) from d 0 to 84 or from d 112 to 196. This increase in fat content resulted in decreased (P < .05) concentrations of moisture, protein, and ash in the LM. Concentrations of Mg, K, and Fe in the LM increased (P < .10) with advanced TOF. The increase in the total lipid (TL) content of the LM stemmed from a proportional increase (P < .05) in neutral lipid (NL). Polar lipid (PL) remained constant (P = .33) throughout TOF. The NL and TL became more unsaturated as TOF increased, primarily due to a linear (P < .01) increase in oleic (C18:1) acid concentration. In contrast, the polyunsaturated fatty acid (PUFA) concentration in the PL exhibited a linear (P < .01) decrease across TOF. As a result, advanced TOF increased the monounsaturated fatty acid (MUFA) content by 22% and decreased the PUFA content by 72% in the LM. The ratio of hypercholesterolemic (C14 + C16):hypocholesterolemic (MUFA+PUFA) fatty acids was unaffected by increasing TOF from d 28 to 196; however, this ratio was lower (P < .05) for grass-fed controls (d 0) than for d 28 to 84 and d 196. Cholesterol content (milligrams/100 grams) changed cubically (P = .06) across TOF. Ultimately, by limiting TOF to 112 d, the beef industry could provide consumers a palatable beef product that easily fits into a healthy diet and at the same time diminishes the costs associated with external fat trim.

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