The effect of drying treatment on the fodder quality and tannin content of two provenances of Calliandra calothyrsus Meissner

Abstract

The effects of freeze drying and of air drying at 30 °C on the nutritive value of Calliandra calothyrsus leaves were evaluated, using material from two provenances grown together under controlled greenhouse conditions. Freshly harvested leaf of each provenance was compared with the dried treatments in terms of in vitro digestibility, content of extractable, protein-bound and fibre-bound proanthocyanidin (condensed tannin) and protein precipitation activity of the extractable fraction, as well as crude protein and fibre content. The effect of long-term (12 months) storage of fresh-frozen and dried leaf was also evaluated. Provenance was found to have a major effect on most of the traits, and large differences between the provenances in proanthocyanidin structure were found by high-performance liquid chromatography, with the tannins of one provenance consisting mainly of catechin/epicatechin subunits (producing cyanidin on treatment with butanol/HCl), and those of the other mainly gallocatechin/epigallocatechin subunits (producing delphinidin with butanol/HCl). This also resulted in large differences in colour yield in the butanol/HCl assay for proanthocyanidins, necessitating separate standards for each provenance. Both drying treatments tended to increase digestibility, though the effect was only significant for one provenance. Air drying, but not freeze drying, increased proanthocyanidin binding to protein, but not to fibre, in both provenances. Long-term freezing reduced proanthocyanidin content by about half and should be avoided in tannin research. The study suggests that careful air drying, without excessive heating, may not reduce the nutritive value of C calothyrsus, though this needs validation through feeding studies with ruminants