Abstract: This research investigated the optimal concentration of sodium diacetate when used as an additive in alfalfa silage production. Such technology is valuable to provide forage of superior nutritive value and enhance economic performance and development of ruminant livestock industries. An alfalfa crop (cv. Golden queen) at early flowering growth stage in the first harvest in early June was divided into eight parts and ensiled in laboratory mini-silos with sodium diacetate added to each at different rates of 0% (Control), 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6% and 0.7% by weight. After 45 days fermentation at room temperature, the silage quality, nutritional properties, and protein molecular structure differences of the eight silages were evaluated. The results were as follows: the pH value, and neutral and acid detergent fiber contents of the sodium diacetate-treated silages were significantly lower than those of the Control treatment (P<0.05), and the sensory score of treated silages was better than that of the Control treatment. Compared with the Control silage and the other silages treated at lower rates, the addition of 0.7% sodium diacetate resulted in the highest protein content, and the lowest contents of propionic acid, butyric acid and ammonia nitrogen. In addition, protein structure evaluation indicated that the peak height and peak areas of the amide Ⅰ and Ⅱ regions were significantly decreased, and the ratio of the α-helical region height to the β-fold region height was significantly increased. This study indicates that the addition of an appropriate amount of sodium diacetate in silage production significantly improves the nutritional quality, fermentation quality and protein molecular structure of alfalfa silage. Balancing silage quality improvement against economic cost considerations, the data indicate that the optimum dosage of sodium diacetate is 0.5%-0.6%.

Key words: alfalfa, silage, sodium diacetate, fermentation quality, molecular structure