Effect of the tropical forage calliandra on microbial protein synthesis and ecology in the rumen

Aims: To determine the effect of condensed tannins in Calliandra calothyrsu s (calliandra) on rumen microbial function. Methods and Results: Microbial populations, ruminal protein synthesis and f ermentation end-products were measured in sheep fed roughage hay supplement ed with calliandra (30%), with and without inclusions of polyethylene glyco l (PEG) to counteract the effect of tannin, Molecular and conventional enum eration techniques were used to quantify rumen bacteria, fungi and protozoa , and protein synthesis was predicted from estimates of urinary purine excr etion, The total number of cellulolytic bacteria, including populations of Fibrobacter succinogenes and Ruminococcus spp., was significantly lower in sheep supplemented with calliandra and these populations increased when ani mals were treated with PEG. By contrast, protozoa and fungi and the microbi al group containing Bacteroides-Porphyromonas-Prevotella bacteria appeared to be less affected. The efficiency of microbial protein synthesis in the r umen was not altered significantly. Conclusions: Calliandra caused significant shifts in rumen microbial popula tions without changing the efficiency of protein synthesis. Significance and Impact of the Study: The effect of calliandra tannins on r umen digestion may result more from complexing with nutrients than direct i nhibition of micro-organisms.