Nutritive value and fatty acid content of soybean plant [Glycine max (L.) Merr.] during its growth cycle

Soybean [Glycine max (L.) Merr.] is mostly cultivated for grain in Asia, South and North America and it may be grown to be used as high-protein forage for grazing, haying or ensiling. Field trials with the soybean cultivar Eiko were conducted in North-West Italy to determine its chemical composition, gross energy, in vitro true digestibility (IVTD), neutral detergent fibre digestibility (NDFD) and fatty acid (FA) profile during growth. Herbage samples of cultivar Eiko were collected at seven progressive morphological stages, from the early vegetative to the seed-pod stage, during the 2014 growing season. The effect of plant growth was analysed by polynomial contrasts. Crude protein and ash decreased with increasing stage, whereas neutral detergent fibre, acid detergent fibre and lignin increased with progressive growth stage. No differences in lipid content during growth cycle were observed. IVTD decreased, whereas NDFD did not change with advancing growth stage. The most abundant FA during growth was a-linolenic (C18:3n-3), which accounted for 464-538 g/kg of total FA. It decreased with advancing growth until the late vegetative stage when it increased. Significant differences were also found for c-linolenic acid (C18:3n-6) and stearidonic acid (C18:4n-3), while no differences in the content of minor and unknown FAs were noted during growth.