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

P. French*†, C. Stanton‡, F. Lawless‡, E. G. O'Riordan*, F. J. Monahan†, P. J. Caffrey†, and A. P. Moloney*
*Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland; †Faculty of Agriculture, University College Dublin, Belfield, Dublin 4, Ireland; ‡Teagasc, Dairy Products Research Centre, Moorepark, Fermoy, Co. Cork, Ireland

ABSTRACT 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.

Implications

The data obtained from this study demonstrate that high grass intake resulted in a higher polyunsaturated fatty acid (PUFA):saturated fatty acid ratio and a lower n-6:n-3 PUFA ratio in intramuscular fat of steers than in that of similar steers fed concentrates. Moreover, a higher concentration of conjugated linoleic acid was observed for grass-fed steers than for steers fed silage and(or) concentrates, when grown at similar carcass growth rates. These data imply that the fatty acid profile of intramuscular fat in beef can be improved from a human nutrition perspective by the inclusion of grass in the diet.

Key Words: Conjugated Linoleic Acid, Fatty Acids, Grasses, Steers

© 2000, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 2000. 78:2849-2855


 Search PubMed
Search for:
MEDLINE and PubMed are registered trademarks of the U.S. National Library of Medicine.