In Vitro assessment of the nutritive value of expanded soybean meal for dairy cattle

Soybean meal (SBM), a good source of lysine, is widely used as a protein supplement for ruminants [1]. Due to extensive ruminal degradation of protein in SBM, research has focused on treating SBM to increase the ruminally undegraded protein (RUP) content [2].During solvent extraction of soybeans, the whole soybean is cracked and heated to approximately 60 to 74°C, then flaked and exposed to hexane solvent to extract the oil [3,4]. After the hexane is volatilized, SBM is heated to destroy anti-trypsin factors. For production of expanded SBM, the soybeans are heated by friction during passage through the expander; steam injection may also be employed. Upon exit through the expander die at temperatures typically near 120°C, the sudden drop in pressure expands the product, which destroys cell structure and improves oil extraction and lecithin recovery while reducing the amount of solvent needed [5,6]. After cooling, the expanded product is extracted with hexane, which is similar to solvent extraction of soybeans [5].The production of expanded SBM is increasingly popular in People's Republic of China, and this has led to a need for information related to its nutritive value, particularly for dairy cattle that could benefit from products with greater concentrations of RUP. Because expanded SBM is subjected to additional heat, it was expected to have greater RUP than solvent-extracted SBM. Processing of soybeans with heat during oil extraction could increase the availability of lysine by increasing RUP or could decrease lysine availability by impairing intestinal digestion. No research is available on the effect of expanded SBM processing on ruminal protein degradability. Douglas and Parsons [7] evaluated the nutritive value of expanded SBM for poultry by measuring its amino acid (AA) content and the protein solubility and also studied the effect of feeding expanded SBM to broiler chicks. They found that the nutritive value of the expanded SBM was similar to standard solve