Fatty acids in forages. I. Factors affecting concentrations

Boufaied, H., Chouinard, P. Y., Tremblay, G. R, Petit, H. V., Michaud, R. and Belanger, G. 2003. Fatty acids in forages. I. Factors affecting concentrations. Can. J. Anim. Sci. 83: 501-511. When forages represent a high proportion of ruminant diets they provide a significant quantity of fatty acids (FA). Effects of growth stage, fertilization, conservation method, growth period, species, and cultivar on forage FA were determined in four experiments. Concentrations of C 16:0, C 18:2, C 18:3, and total FA (TFA) in timothy (Phleum pratense L.) decreased (P < 0.01), respectively, by 15, 16,31, and 23% between stem elongation and early flowering. Nitrogen fertilization (120 vs. 0 kg N ha^-1) caused an increase (P < 0.01) of 18% of C16:0, 12% of C18:2, 40% of C 18:3, and 26% of TFA concentrations. Phosphorus was not deficient and P fertilization (45 vs. 0 kg P ha^-1) had no significant effect on timothy FA concentrations. Wilting and drying decreased (P < 0.01) timothy C18:2, C 18:3, and TFA concentrations. Concentrations of C18:2, C18:3, and TFA were higher in summer regrowth than in spring growth, primarily in orchardgrass (Dactylis glomerata L.) and timothy (P < 0.01). Significant variation for all FA concentrations was observed among 12 species (P < 0.05); on average, the C18:3, C18:2, and C16:0 accounted for 88% of TFA in studied species. Timothy was the only species in which the difference among cultivars was simultaneously significant (P < 0.05) for concentrations of C18:2, C18:3, and TFA. Among the grasses, an annual ryegrass (Lolium multiflorum Lam.) cultivar had the highest C18:3 concentration (20.6 mg g^-1 DM) whereas a timothy cultivar had the lowest (7.3 mg g^-1 DM) (P < 0.05). Among legumes, a white clover (Trifolium repens L.) cultivar had the highest C18:3 concentration (16.5 mg g^-1 DM) whereas an alfalfa (Medicago sativa L.) cultivar had the lowest (6.0 mg g^ DM) (P < 0.05). Polyunsaturated FA concentrations in forages can be increased by harvesting timothy at an early stage of development and as fresh grass, by increasing N fertilization of timothy, and by choosing species with higher FA concentrations such as white clover and annual ryegrass.