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

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.

The effect of grazing on the fatty acid profile of longissimus thoracis muscle in Galician Blond calves

“…Consequently, total n-3 PUFA were highly significant (P , 0.001) in P compared with PC and C treatments. Calves fed exclusively on pasture grazing were able to synthesise higher amounts of n-3 PUFA than calves finished on concentrate, in accordance with the results of French et al (2000), Varela et al (2004) and Nuernberg et al (2005). It is widely documented that 18:3 n-3 can serve as a substrate for further desaturation and elongation of PUFA (Noci et al, 2005).…”

“…is in parentheses after the parameter estimated for each term of the model. compared with calves finished on concentrate (C and PC) (Table 5), in agreement with French et al (2000), Varela et al (2004) and Nuernberg et al (2005). Thus, a more favourable PUFA : SFA ratio from a dietetic and health point of view was present in beef of grass-based calves (P).…”

“…Other studies showed that effects of feeding on SFA content depended on maturity. French et al (2000) and Moloney et al (2001) found higher concentration of SFA in meat from 18-monthold bulls fed on concentrates than fed on grass, whereas Enser et al (1998) found the opposite in 12-month-old steers.…”

“…Twenty different CLA isomers have been naturally found in food, especially in a variety of ruminant meats (French et al, 2000). The major CLA isomer, rumenic acid cis-9, trans-11 (cis-9, trans-11) 18:2 is produced in the rumen as a result of incomplete biohydrogenation of dietary 18:2n-6 isomer through the action of the enzyme linoleic isomerase from the ruminal bacteria (Harfoot and Hazelwood, 1997) and in tissues is synthesised from trans-11 18:1 (trans-vaccenic acid, VA) by D 9 -desaturase, an enzyme active in the mammary gland and in adipose tissue (Griinari et al, 2000;Mosley et al, 2006).…”

“…According to this, diets rich in these FAs should increase the concentration of CLA in the fat depot of the animal (Pariza et al, 2001). In addition, it has been shown that grazing-based diets offered to steers increased the concentration of CLA and PUFA intramuscular fat when compared with concentrate-based diets (French et al, 2000).…”