Lipid content and fatty acid composition of grasses sampled on different dates through the early part of the growing season

Mir, P. S., Bittman, S., Hunt, D., Entz, T. and Yip, B. 2006. Lipid content and fatty acid composition of grasses sampled on different dates through the early part of the growing season. Can. J. Anim. Sci. 86: 279–290. In order to explore the value of herbage for the production of ruminant products with a high content of conjugated linoleic acid (CLA), a study was undertaken to determine the content of fatty acids that can be hydrogenated [hydrogenatable fatty acids (HFA)] in herbage of three cool-season forage grasses, orchardgrass (OG), perennial ryegrass (PRG) and tall fescue (TF). Dry matter (DM) yield, lipid content (ether extract) and fatty acid concentration (weight percent of detected fatty acids) on five sampling dates in the spring of 2004 were determined. HFA is the available substrate for the production and deposition of fatty acid bioconversion products in ruminants that consume the grass. Fatty acid content of the grasses was estimated as the product of fatty acids concentration (weight percent) and lipid content (ether extract), while HFA was estimated as the sum of the content of C18:1, C18:2 and C18:3. The DM yield of the three species of grasses increased (P < 0.05) between Mar. 29 and Apr. 28, after which the increase was observed for TF followed by PRG. However, the lipid content decreased in all the grasses over the 140 d of sampling. Although concentration of the saturated fatty acids and C18:1 and C18:2 increased over the sampling period, the content did not alter substantially. In OG samples, C18:2 concentrations were higher (P < 0.05) than those in PRG or TF in all samples. The concentration and content of C18:3 was highest (P < 0.05) in all the forages, but declined progressively. Results indicate that the availability of HFA is greatest in OG and PRG, especially in the early samples, but DM yields are low; however, later in the season TF produces more DM but with substantially reduced lipid and HFA content.