Abstract
Growth rate and feed efficiency of White Leghorn day-old chicks fed 28 soybean meals of various nitrogen solubility index (NSI=% of water soluble nitrogen in total nitrogen) as a main source of dietary protein were studied in 4 experiments to make certain the usefulness of NSI as an index of nutritive value of soybean meal treated at various conditions.
Highly significant negative correlation was observed between chick's performance and NSI of soybean meals prepared from the same raw material at the same time on different condition. However, it was confirmed that NSI of soybean meal changed after the prepation of the meal. Actually no periodical change was observed in moisture and total nitrogen content of the meal, the change in NSI was certainly due to the change in water soluble nitrogen of the meal. Little periodical change was observed in trypsin inhibitor activity of the meal and the change in urease activity was inconsistent.
Furthermore, the direction of the periodical change in NSI seemed to differ in soybean meals prepared by different procceures. In Expt. 506, NSI of soybean meals treated in high temperature without moisture, increased after the preparation. On the other hand, NSI of soybean meals treated with vapour in Expt. 610, decreased significantly within 2 months after the preparation.
Therefore, as an index of nutritive value of soybean meal, in general, prepared from various raw materials with different procedures at different time, NSI only serves as very rough one. From the data obtained in these experiments, nutritive value of soybean meal with NSI of less than 33% may be assumed to be normal but final decision on nutritive value should be made based on other data such as chick's performance.
