Effects of purified condensed tannins extracted from Calliandra, Flemingia and Leucaena on ruminal and postruminal degradation of soybean meal as estimated in vitro

Purified condensed tannins (CT) extracted from the legumes Calliandra calothyrsus (var. San Ramón CIAT 22310 and var. Patulul CIAT 22316), Flemingia macrophylla (CIAT 17403) and Leucaena leucocephala (CIAT 734) were added to soybean meal in proportions of 0 (control), 300, 600 or 900 mg/g of the incubated crude protein (CP). Effects on degradation in ruminal fluid and ruminal fluid followed by incubation in HCl/pepsin were evaluated using a modified two-step in vitro method. When CT were added, dry matter (DM) and CP degradation in ruminal fluid were reduced (P<0.001). With the highest concentration of CT (i.e., 900 mg/g CP), ruminal DM degradation was reduced to 30% of the CT-free control. There was a 25–63% reduction in CP degradation in the rumen due to the addition of CT. The extent of the effect was dependent on the CT source (P<0.001). Depending on CT source, an increase in CT concentration also reduced (P<0.001) total DM and CP degradation (ruminal fluid+HCl/pepsin) by 24–73% and 16–55%, respectively. The proportion of incubated CP which was not degraded in ruminal fluid (estimated rumen escape CP) but degraded in HCl/pepsin increased by 18 and 412% depending on CT source and CT concentration (P<0.001). The highest increase was observed with CT from C. calothyrsus and the lowest with CT from L. leucocephala. HCl/pepsin degradability of rumen escape CP was also reduced with CT addition by 10 and 82% depending on CT concentration and source (P<0.001). In ruminal fluid, CT from L. leucocephala seemed to have less effect on degradation of soybean meal than CT from F. macrophylla and C. calothyrsus. In contrast, when HCl/pepsin was added to soybean meal, the complexes formed between CP and CT from L. leucocephala were more resistant to degradation than those formed with the other CT. This suggests that CT from L. leucocephala were less effective in increasing degradable rumen escape CP than CT from either C. calothyrsus or F. macrophylla.