Chemical composition, in vitro digestibility and fatty acid profile of Amaranthus caudatus herbage during its growth cycle

The aim of this study was to investigate the effects of plant ageing on the chemical composition, gross energy, in vitro true digestibility, neutral detergent fibre digestibility and fatty acid (FA) profile of amaranth. The herbage was harvested at seven maturity stages, namely early-, mid- and late-vegetative, shooting, budding, early flowering and grain fill. The effects of maturity were analysed by polynomial contrasts. The quality of crop decreased with increasing morphological stages. The chemical composition of amaranth was found closely connected to plant development; while the OM and CP contents decreased (P<0.05), the contents of NDF, ADF, and lignin(sa) increased from the first to the last stage (P<0.05). Consequently, nutritive parameters decreased with increasing growth stage. Even though the lipid content did not differ significantly during plant development, the pattern of FA changed during plant growth. The alpha-linolenic acid content decreased (linear P<0.01; quadratic P<0.05; cubic P<0.01), while linoleic acid content increased (linear P<0.01; quadratic P<0.05) with increasing maturity. As far as other FAs are concerned, palmitic, stearic and oleic acid increased (P<0.01), while stearidonic acid decreased (P<0.05) in later growth stage. A minor FA such as gamma-linolenic acid did not differ significantly during the growth cycle. It is concluded that since its nutritional quality deteriorates and polyunsaturated FA content decreases when cutting is delayed, the first cut of amaranth should be before or at the shooting stage.