Higher Fatty Acid Composition of Immature Forages as Affected by N Fertilization1

Abstract

AbstractHigh levels of both N and total higher fatty acids (HFA) in forage have been associated with increasing the grass tetany hazard to grazing cattle. The objective of this study was to determine the relationship between forage N, total HFA, and HFA species distribution in several forages.Forage N, HFA, HFA species concentration, and total chlorophyll were determined in immature vegetative growth of Agropyron desertorum (Fisch.) Schult., Cynodon dactylon L., Lolium perenne L., Trifolium repens L., and Triticum aestivum L. established with soil fertility levels up to 500 ppm N in the growth chamber. Forage HFA concentrations were positively and linearly related to forage N levels, but regression coefficients were not the same for all species. The HFA concentrations were as high as 16 mmol COOH/100g DM at 6% total N in first cutting Lolium perenne L. The relative HFA species distribution was the same within a given forage, even though total N concentrations ranged from 2 to 6%. The mean HFA specie concentrations (determined by gas‐liquid‐chromotography relative to mean total HFA concentrations determined by titration) when expressed as percent for the grasses were: C14:0 — 2%, C16:0 — 13%, C16:1 — 1%, C18:0 plus C18:1 — 1%, C18:2 —11%, and C18:3 — 67%. The total HFA concentrations were positively correlated with chlorophyll a + b concentrations which was expected, since the HFA of green plants is largely associated with chloroplast membrane.