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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Sixty ribeye steaks were used to determine the effects of anabolic implants on i.m. lipid composition of beef steers. Steaks were obtained from carcasses (346 kg) of steers assigned to four treatment groups (C = nonimplanted control; ET = 28 mg of estradiol benzoate plus 200 mg of trenbolone acetate on d 0; ET/ET = ET on d 0 and d 61; and S/ET = 20 mg of estradiol benzoate plus 200 mg of progesterone on d 0 and ET on d 61) and fed a high-concentrate diet for 127 d. Total fatty acid content of the longissimus was less (P < .05) for implanted steers. Implanting increased (P < .05) stearic and linolenic acid percentages and reduced (P < .05) oleic acid percentage but did not alter (P > .05) percentages of other fatty acids. These changes translated into increased (P < .05) percentages of saturated fatty acids and reduced (P < .05) monounsaturated fatty acids in the longissimus of implanted steers. However, on a per-steak weight basis, implanting did not alter (P > .05) the amounts of any of the individual fatty acids, but it increased (P < .05) the total cholesterol amount. Implanting with an estrogenic compound first reduced (P < .05) the percentage and total amounts of linoleic and polyunsaturated fatty acids. On a percentage basis, implanting alters fatty acid amounts; however, when the increase in ribeye size with implanting is accounted for and fatty acids are evaluated on a per-steak basis, these differences are not significant.

Hetero-yellow (HY), red (RED) and brown (BR, high tannin) sorghums were fed dry-rolled or reconstituted (RED and BR only) to evaluate the effect of variety and reconstitution on the site and extent of starch and protein digestion in steers fitted with ruminal, duodenal and ileal cannulae. Processed grains were incorporated into 88% sorghum (DM basis) diets fed at 2% of body weight in a 5 X 5 Latin square. Ruminal fermentation of organic matter, starch and protein tended to be lower for the dry-rolled RED than for either the dry-rolled HY or BR sorghum. Digestion of organic matter (OM) and starch in the small intestine was very low for dry-rolled sorghums. Total tract starch digestibility was lower for the dry-rolled RED sorghum (86.9%) than the BR (90.8%) and HY (91.4%). Nitrogen (N) digestibility ranged from 53.1% for the dry-rolled BR to 64.5% for the HY. Tannins were extensively (95.2%) degraded in the rumen, which may have enhanced fermentation of the BR sorghum. Reconstitution increased (P less than .05) total-tract starch digestion of the RED and tended to increase starch digestion of the BR as well. Total N flow to the duodenum tended to increase with reconstitution, with most of the increase being due to greater (P less than .05) microbial-N. Reconstitution also increased (P less than .05) total-tract N digestibility of the RED. The response to reconstitution for the RED sorghum appeared to be due primarily to an increase (P less than .10) in the extent of fermentation of organic matter and starch in the rumen. Reconstitution of BR, however, enhanced disappearance of starch from the small intestine. In both cases, most (97.3%) of the digestible starch of the reconstituted sorghums had disappeared before the terminal ileum. In contrast, 14.5% (621 g) of the digestible starch of dry-rolled RED disappeared in the large intestine. Sorghum grain variety and reconstitution appear to alter site and extent of starch and protein digestion, which may result in variable performance of cattle fed sorghum grain diets.

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