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

The effects of grazed grass, grass silage, or concentrates on fatty acid co mposition and conjugated linoleic acid (cis-9, trans-11-18:2; CLA) concentr ations of i.m. fat of steers fed to achieve similar carcass growth rates we re investigated. Fifty steers were divided into 10 blocks based on body wei ght and assigned at random from within blocks to one of five dietary treatm ents. The experimental rations offered daily for 85 d preceding slaughter w ere 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 c oncentrate, 4) 12 kg of grazed grass DM plus 2.5 kg concentrate, or 5) 22 k g of grazed grass DM. The concentration of polyunsaturated fatty acids (PUF A) in i.m. fat was higher (P < .05) for steers offered ration 5 than for th ose given any other ration. Decreasing the proportion of concentrate in the diet, which effectively increased grass intake, caused a linear decrease i n the concentration of i.m. saturated fatty acids (SFA) (P < .01) and in th e 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 d ata indicate that i.m. fatty acid composition of beef can be improved from a human health perspective by inclusion of grass in the diet.