Effect of growth stage on the quality of hay and silage of Amaranthus hypochondriacus

This experiment was conducted to investigate the effects of growth stage on the quality of Amaranthus hypochondriacus hay and silage and thus determine the optimum cutting time for A. hypochondriacus. A. hypochondriacus at the squaring stage, initial bloom stage, full-bloom stage, and mature stage were used as experimental materials to make hay and silage, and to compare the nutrient composition of hay and silage and the fermentation quality of the silage. The results were as follows: 1) with the extension of growth stage, the contents of neutral detergent fiber and acid detergent fiber in A. hypochondriacus hay gradually increased, but the relative feed value decreased; meanwhile, the content of crude protein gradually decreased. 2) The pH was less than 4.2 in all silages except squaring stage silage, and the quality of silage in the squaring stage was poor. Compared with the squaring stage and initial bloom stage, the content of lactic acid in the mature stage was significantly increased (P < 0.05), but it was not significantly different from that of the full-bloom stage (P > 0.05). In addition, the content of acetic acid was lowest, and the ammonia nitrogen: total nitrogen ratio was remarkably lower than that of squaring stage silage. The relative feed value of A. hypochondriacus silage showed a tendency to be gradually reduced with the extension of growth stage, as did the content of crude protein. In contrast, the contents of neutral detergent fiber and acid detergent fiber both had an inverse trend. The contents of water soluble carbohydrates and starch in the mature stage were significantly higher than those in other stages (P < 0.05). It can be concluded that to make hay and silage, it is best to cut A. hypochondriacus during the mature stage.