Effect of finishing system (feedlot or pasture), high-oil maize, and copper on conjugated linoleic acid and other fatty acids in muscle of finishing steers

Sixty Angus steers (413 +/- 8.0 kg) were used to determine the effects of copper (Cu), maize type, and finishing system ( confinement v. pasture) on performance, carcass characteristics, and fatty acid composition of longissimus muscle in steers. Steers in confinement were given individually high concentrate diets containing either typical or high-oil maize, using Calan gate feeders. Steers grazing pasture ( tall fescue) were maintained in four pastures with each pasture containing five steers. Salt was used to limit concentrate intake in pasture steers to approximately 0.6 of that observed in confinement steers. One half of the steers in each treatment received a CuO needle bolus at the initiation of the study while the remaining steers received no supplemental Cu. Equal numbers of steers per treatment were harvested after 91, 112 or 133 days on food. Rate of gain was lower (P < 0.01; 1.2 v. 1.6 kg/day) for pasture-fed steers compared with steers receiving typical maize. Cu supplementation increased (P < 0.05) ADG in steers given typical maize (1.8 v. 1.5 kg/day) and those on pasture (1.3 v. 1.1 kg/day) but not in steers given high-oil maize diets (1.5 v. 1.5 kg/day). Gain, dry-matter intake and gain/food did not differ between steers given typical or high-oil maize. Plasma cholesterol concentrations were lower (P < 0.01) in steers given typical maize relative to steers given high-oil maize. Steers receiving a Cu bolus had higher plasma (P < 0.05) and liver (P < 0.01) Cu concentrations than steers not receiving a Cu bolus. Steers receiving typical maize had lower (P < 0.05) liver Cu concentrations than steers receiving high-oil maize. Steers finished on pasture with limited concentrate had conjugated linoleic acid (CLA) concentrations in longissimus muscle that were approximately three times higher (P < 0.01) than steers given typical maize. Cu supplementation tended (P < 0.10) to increase muscle CLA. Longissimus muscle from pasture-fed steers was lower (P < 0.01) in C16:0 and higher (P < 0.05) in C10:0, C17 : 0, C18 : 3, C20 : 3 and total polyunsaturated fatty acids than steers given typical maize. Muscle C18 : 1 trans and C17 : 0 tended to be reduced (P < 0.10) by Cu supplementation. These results indicate that finishing cattle on pasture with limited grain increases CLA in longissimus muscle and that Cu supplementation also alters the fatty acid composition of muscle.