B. Palmer

Microbial interactions with tannins: nutritional consequences for ruminants

Polyphenolics are widely distributed in the plant kingdom and are often present in the diet of herbivores. The two major groups of plant polyphenolic compounds other than lignin are condensed and hydrolysable tannins. These compounds can have toxic and/or antinutritional effects on the animal. It is well established that tannins complex with dietary proteins can reduce nitrogen supply to the animal, but the ability of gastrointestinal microorganisms to metabolise these compounds and their effects on microbial populations have received little attention. In this paper, we review recent literature on the topic as well as present research from our laboratories on the effect of condensed tannins on rumen microbial ecology and rumen metabolism. Interactions of tannins with dietary components and endogenous protein in the rumen and post-ruminally, and their impact on the nutrition of the animal are considered

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

C.S. MCSWEENEY, B. PALMER, R. BUNCH AND D.O. KRAUSE. 2001.

In vitro quality assessment of tannin-containing tropical shrub legumes: protein and fibre digestion

In vitro techniques were evaluated to determine the nutritive value of a selection of tanniniferous tree and shrub legumes (Calliandra calothyrsus, Leucaena leucocephala L. diversifolia and L. pallida) compared with lucerne (Medicago sativa). Polyethylene glycol (PEG) was also added to some in vitro fermentations (10 mg PEG/50 mg plant substrate) to assess the effects of tannins on digestion of dry matter (DM), neutral detergent fibre (NDF) and nitrogen (N). Total tannin content was poorly correlated with digestibility of dry matter and nitrogen. Apparent digestibility of dry matter and N were significantly different between plants and ranked in the following order; lucerne > L. leucocephala > L. diversifolia > L. pallida > C. calothyrsus. Ammonia was not produced (net accumulation) during 72 h fermentation of C. calothyrsus, L. diversifolia and L. pallida although apparent nitrogen digestion in these plants ranged from 36.9 to 44.3%. Acid-pepsin digestion resulted in a further 17‐22% of dry matter digestion in the shrub legumes compared with 8% in lucerne following 72 h fermentation. The amount of acid-pepsin digestible N available was lowest for lucerne (8.4%) and highest for L. pallida (38.9%) with the other legumes ranging from 26.5 to 36.8%. The PEG addition caused a significant increase in rate and extent of DM and NDF digestibility and ammonia production for all the tannin containing shrub legumes but not for lucerne. However, DM loss and fermentability of these plants appeared to be poorly correlated because PEG addition resulted in an increase in volatile fatty acid production ranging from 3.7 to 202% compared with an increase in apparent DM digestibility of 9.1‐30%. It is concluded that in vitro evaluation of apparent DM and N digestibility of tannin containing plants provides a poor indication of true digestion (fermentability) and thus measurements of

The effect of sample drying conditions on estimates of condensed tannin and fibre 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 fibre, 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 dryingO p < 0:01 to p < 0:0001U. At higher temperatures there was more bound tannin (protein- and fibre-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 fibre (ADF) was higher for the aerobically dried samples, and levels for both drying methods increased slightly with temperature. For neutral detergent fibre (NDF), levels rose at temperatures above 458C; the rise with aerobic drying was much greater and gave a significant interactionO p < 0:01U. Both the N% in NDF and the total N in NDF were higher in the aerobically

In vitro digestion studies using 14C -labelled polyethylene glycol (PEG): the effect of sample pretreatment on dry matter and nitrogen digestibility as well as PEG binding of Calliandra calothyrsus

Abstract The effect of sample preparation on measures of in vitro digestibility was studied using leaves of Calliandra calothyrsus . They were chopped fresh (FrCh), chopped and oven-dried at 65°C (ChOD), chopped and freeze-dried (ChFD), oven-dried and ground (ODGr) or freeze-dried and ground (FDGr). Samples were analysed for in vitro dry matter and nitrogen digestibility with or without PEG addition to bind tannins. Ground samples gave higher dry matter digestibilities (IVDMD) than chopped samples, freeze-dried samples had higher IVDMD than oven-dried samples, and fresh leaves were intermediate. The IVDMD values for FrCh, ChOD, ChFD, ODGr and FDGr were 45.3, 34.5, 40.5, 48.4 and 50.1%, respectively. Overall, PEG increased IVDMD from 42.1 to 45.4 ( P P r 2 =0.96), indicating that pretreatment influenced the ability of PEG to penetrate and bind to tannins. Results emphasise the importance of standardisation of sample pretreatment for PEG binding studies and again show that IVDMD studies with tanniniferous forage and browse species using PEG will give unreliable results because of the PEG-tannin complexes in the residue.