Inter‐relationships between chemical constituents, rumen dry matter and nitrogen degradability in fresh leaves of multipurpose trees

Abstract

AbstractThis work determined the inter‐relationships between chemical constituents, rumen dry matter (DM) and nitrogen (N) degradabilities of fresh leaves from 20 multipurpose tree (MPTs) accessions belonging to the following genera: Acacia (2), Cajanus (2), Chamaecytisus (2), Erythrina (2), Leucaena (8) and Sesbania (4). Significant differences (P < 0.05) were observed among genera in all assayed chemical attributes except hemicellulose. There was apparently no disappearance of N in A saligna after the initial solubility. All genera had similar DM and N solubility but varied in degradation rate of DM (0.064‐0.137h−1; P < 0.002) and N (0.062‐0.135 h−1; P < 0.001), effective degradability of DM (672‐856 g kg−1; P < .001) and effective degradability of N (NED; 701‐902 g kg−1; P < 0.001). Except for A saligna, synchronization indices of the release of nutrients for each accession ranged from perfect (0.93) to poor (‐0.31) for soluble nutrients and from moderate (0.75) to very poor (‐0.81) for insoluble slowly degradable nutrients because N was in excess. Inter‐relationships among chemical constituents, DM and N degradation constants were established using correlation and regression analyses. Negative correlations occurred between N solubility and proanthocyanidins (PAs; P < 0.05), N degradation rate and hemicellulose (P <0.05), NED and either NDF (P < 0.05) or hemicellulose (P < 0.05) or PAs (P < 0.01), while N degradation rate was positively correlated with N content (P < 0.01). Equations for predicting N degradability characteristics (solubility, insoluble slowly degradable fraction, potential and effective degradability, rate of degradation and lag phase) accounted for 0.44‐0.83 of the variation (using chemical constituents), 0.56‐0.81 of the variation using corresponding DM degradation characteristics and, 0.74‐0.89 of the variation using mixed criteria. Superior models were of the form: ND_P = DM_P(‐β), where ND_P and DM_P are corresponding N and DM degradability characteristics, respectively, and β the regression of the deviations of the ratio ND_P : DM_P from unity on chemical constituents and accounted for 0.75‐0.92 Practical implications of DM degradability and nutrient release synchrony indices in relation to basal roughage intake and microbial protein synthesis were discussed. It was concluded that a mixed model could adequately predict N degradability of fresh forages and alleviate analytical cost. A functional approach of classifying browses is outlined.