The effects of grazed grass, grass silage, or concentrates on fatty acid composition and conjugated linoleic acid (cis-9, trans-11-18:2; CLA) concentrations of i.m. fat of steers fed to achieve similar carcass growth rates were investigated. Fifty steers were divided into 10 blocks based on body weight and assigned at random from within blocks to one of five dietary treatments. The experimental rations offered daily for 85 d preceding slaughter were 1) grass silage for ad libitum intake plus 4 kg of concentrate, 2) 8 kg of concentrate plus 1 kg of hay, 3) 6 kg of grazed grass DM plus 5 kg of concentrate, 4) 12 kg of grazed grass DM plus 2.5 kg concentrate, or 5) 22 kg of grazed grass DM. The concentration of polyunsaturated fatty acids (PUFA) in i.m. fat was higher (P < .05) for steers offered ration 5 than for those given any other ration. Decreasing the proportion of concentrate in the diet, which effectively increased grass intake, caused a linear decrease in the concentration of i.m. saturated fatty acids (SFA) (P < .01) and in the n-6:n-3 PUFA ratio (P < .001) and a linear increase in the PUFA:SFA ratio (P < .01) and the conjugated linoleic acid concentration (P < .001). The data indicate that i.m. fatty acid composition of beef can be improved from a human health perspective by inclusion of grass in the diet.

Fatty acid composition, including conjugated linoleic acid, of intramuscular fat from steers offered grazed grass, grass silage, or concentrate-based diets.

Growing consumer interest in grass-fed beef products has raised a number of questions with regard to the perceived differences in nutritional quality between grass-fed and grain-fed cattle. Research spanning three decades suggests that grass-based diets can significantly improve the fatty acid (FA) composition and antioxidant content of beef, albeit with variable impacts on overall palatability. Grass-based diets have been shown to enhance total conjugated linoleic acid (CLA) (C18:2) isomers, trans vaccenic acid (TVA) (C18:1 t11), a precursor to CLA, and omega-3 (n-3) FAs on a g/g fat basis. While the overall concentration of total SFAs is not different between feeding regimens, grass-finished beef tends toward a higher proportion of cholesterol neutral stearic FA (C18:0), and less cholesterol-elevating SFAs such as myristic (C14:0) and palmitic (C16:0) FAs. Several studies suggest that grass-based diets elevate precursors for Vitamin A and E, as well as cancer fighting antioxidants such as glutathione (GT) and superoxide dismutase (SOD) activity as compared to grain-fed contemporaries. Fat conscious consumers will also prefer the overall lower fat content of a grass-fed beef product. However, consumers should be aware that the differences in FA content will also give grass-fed beef a distinct grass flavor and unique cooking qualities that should be considered when making the transition from grain-fed beef. In addition, the fat from grass-finished beef may have a yellowish appearance from the elevated carotenoid content (precursor to Vitamin A). It is also noted that grain-fed beef consumers may achieve similar intakes of both n-3 and CLA through the consumption of higher fat grain-fed portions.

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A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef

Effect of pasture vs. concentrate feeding with or without antioxidants on carcass characteristics, fatty acid composition, and quality of Uruguayan beef

http://ssu.ac.ir/cms/fileadmin/user_upload/Mtahghighat/tfood/ARTICLES/meat/Authentication_of_meat_and_meat_products.pdf

Authentication of meat and meat products

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) 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

Effects of time on feed on beef nutrient composition

Angus x Hereford steers (n = 48) similar in frame size and in muscle thickness were allotted to eight groups (n = 6) of similar mean live weight for serial slaughter at 28-d intervals (0 to 196 d). Except for d-0 steers, which served as grass-fed controls, all steers were fed a high-concentrate diet during the finishing period. Upon slaughter, one side of each carcass was trimmed of subcutaneous fat in the wholesale rib region. Postmortem longissimus muscle (LM) temperature was monitored for each side during the 24-h chilling period. After quality and yield grade data were collected, rib steaks were removed and aged (7 d) and sensory traits of the steaks were evaluated. Most carcass grade traits increased linearly (P less than .01) with days on feed, whereas most sensory panel variables and marbling increased curvilinearly (P less than .05). Generally, after 56 d on feed, carcasses chilled at slower rates (P less than .05) with increased days fed. Taste panel tenderness, amount of perceived connective tissue, and shear force values peaked at 112 d and were slightly less desirable for cattle fed longer than 112 d (quadratic term, P less than .01). Postmortem muscle temperature at 2.5 h was the chilling time most highly correlated with tenderness values among untrimmed sides. Correlations for shear force with 2.5-h LM temperature, marbling score, days fed, fat thickness, and carcass weight were -.63, -.61, -.56, -.55, and -.53, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

S G May

Papers

Effects of time on feed on beef nutrient composition

Effect of days fed, carcass grade traits, and subcutaneous fat removal on postmortem muscle characteristics and beef palatability.