Characteristics and in situ degradability of whole crop faba bean, pea, and soybean silages

Abstract

The objective of this study was to determine the ensiling characteristics and ruminal nutrient degradabilities of faba bean (FS, Vicia faba L.), soybean (SS, Glycine max (L.) Merr.) and pea (PS, Pisum sativum L.) silages. Forages were harvested between the beginning- and full-seed stages and ensiled in mini-silos for 0, 2, 4, 16, and 45 d. Two lactating Holstein cows fitted with ruminal fistulae were used to determine ruminal nutrient degradabilities. Results showed that all silages went through a rapid fermentation as indicated by rapid decline in pH and sharp increase in lactic acid concentration within the first 2 d of ensiling. Extensive proteolysis took place between day 0 and day 4 post-ensiling as indicated by a significant reduction in true protein (TP) and a significant increase in non-protein nitrogen (NPN). During the 45 d of ensiling, TP decreased (P < 0.05) by 26, 31, and 45% while NPN increased (P < 0.05) by 82, 54, and 47% for FS, SS, and PS, respectively. Chemical analysis showed that the three 45-d silages contained a similar level of neutral detergent fiber (NDF, average 421 g kg-1). Crude protein (CP) was highest (P < 0.05) for FS, intermediate for SS, and lowest for PS. Distribution of protein fractions showed that soluble protein and NPN were highest (P < 0.05) for PS, intermediate for SS, and lowest for FS. Neutral (NDICP) and acid (ADICP) detergent insoluble protein levels followed an opposite order to that observed for soluble crude protein (SCP) and NPN. Results of the in situ study showed that SS and PS had a similar ruminal degradability of dry matter (average 68.8%) and CP (82.9%), which were higher (P < 0.05) than those of FS (66.2 and 79.4%, respectively). However, no differences in ruminal degradability of NDF (average 34.7%) were observed between the three legume silages. Key words: Silage, ensiling, forage quality, nutrient degradability