The effect of sample drying conditions on estimates of condensed tannin and ®bre content, dry matter digestibility, nitrogen digestibility and PEG binding of Calliandra calothyrsus

Leaf samples of the browse shrub Calliandra calothyrsus were used to study the effect of temperature of drying (25, 45, 65, 85 and 1058C), and method of drying, either in dry air (aerobic) or in dry nitrogen (anaerobic), on estimates of ®bre, condensed tannin (CT), digestibility and PEG binding. These estimates were also made on freeze-dried samples. Correlations were made between these variables. In general, there was much less change with increasing temperature for samples dried anaerobically than for samples dried aerobically for all measures. For the condensed tannin measures (using the butanol±HCl with tannins isolated from C. calothyrsus as a standard), there was an interaction of method temperature of drying … p < 0:01 to p < 0:0001†. At higher temperatures there was more bound tannin (proteinand ®bre-bound) with aerobic drying. Free tannin under anaerobic conditions increased slightly with increasing temperature whereas there was a large linear decrease under aerobic drying. A similar response was obtained by the protein precipitation method though the mean level of free tannin using this method was much lower than by the butanol±HCl method (11% vs 21%). Total CT (TCT) increased slightly with temperature under anaerobic drying, but decreased by a similar magnitude (about 10%) with aerobic drying. The freeze-dried samples had values similar to samples dried at the lower temperatures (25 and 458C) for all measures. The mean TCT for C. calothyrsus in this study of 29% is far higher than those reported in other studies using unrelated tannin standards. Acid detergent ®bre (ADF) was higher for the aerobically dried samples, and levels for both drying methods increased slightly with temperature. For neutral detergent ®bre (NDF), levels rose at temperatures above 458C; the rise with aerobic drying was much greater and gave a signi®cant interaction … p < 0:01†. Both the N% in NDF and the total N in NDF were higher in the aerobically Animal Feed Science and Technology