Fatty acid profile and intramuscular fat concentration of Musculus longissimus thoracis in bulls fed grass silage harvested at one of three maturity stages, either with or without concentrate supplementation

The study investigated the effect of plant maturity of grass silage on intramuscular fat (IMF) concentration and fatty acid profile in M. longissimus thoracis of bulls. From 7 to 8 months of age until slaughter, 36 bulls of Norwegian Red were offered grass silage harvested at three maturity stages ad libitum, with or without concentrate supplement. Increasing plant maturity decreased the proportion of alpha-linolenic acid in IMF (P = 0.04). Concentrate supplementation increased the proportions in IMF of linoleic acid (P < 0.001) and C20:3n-6 (P < 0.008), decreased all analysed n-3 polyunsaturated fatty acids (P <= 0.02), conjugated linoleic acid (P < 0.01) and trans vaccenic acid (P < 0.001). Polyunsaturated fatty acids n-6/n-3 ratios were in the range 1.0-2.1 and increased with plant maturity and concentrate supplementation. Results suggest that 'grass-fed beef' also may be produced indoors with grass silages in regions with short grazing season.