Assessment of the nutritive value of Calliandra calothyrsus: its chemical composition and the influence of tannins, pipecolic acid and polyethylene glycol on in vitro organic matter digestibility

Calliandra leaves and stem samples were harvested from a site near Harare, Zimbabwe from 3-year-old shoots. Ground samples were analysed for their chemical composition, tannin content and lectin activity. Calliandra leaf was richer in crude protein than the stems (253 and 182 g/kg, respectively) and lower in crude fibre (191 and 364 g/kg, respectively). The tannin content of Calliandra leaves was higher than that of stems (127 and 97 g/kg, respectively) when determined by the vanillin-HCl method. The protein precipitating capacity and lectin activity were, however, higher in the stems than the leaves. Calliandra has a balanced amino acid profile, with the stems having a higher methionine content than the leaves but the sum of the sulphur amino acid content in both leaves and stems was relatively low (1.4 and 1.9 g/100 g protein, respectively). Although the crude protein (N × 6.25) content of leaves and stems was reasonably high, only 625 and 527 g/kg of the crude protein, respectively, for the leaves and stems could be accounted for by the summation of the amino acids. Gas production and calculated organic matter digestibility (OMD) in vitro using rumen microbes was very poor for both the leaf and stem in comparison with a standard ryegrass hay. The in vitro degradability of the leaves was poorer than that of the stems but extraction of both leaves and stems with either acetone or methanol improved their degradability. The residual leaf material after solvent extraction had a higher degradability than the stems, indicating the removal of compounds that may have inhibited digestion. Addition of polyethylene glycol (PEG) at a tannin to PEG ratio of 1:2 abolished the depression associated with the methanol extract in the stems, but hardly improved the digestibility of the leaves. At about the level found in the plant, pipecolic acid did not affect gas production or OMD of grass hay by rumen microbes in vitro.