Iv. Nsahlai et al., INTERRELATIONSHIPS BETWEEN CHEMICAL-CONSTITUENTS, RUMEN DRY-MATTER AND NITROGEN DEGRADABILITY IN FRESH LEAVES OF MULTIPURPOSE TREES, Journal of the Science of Food and Agriculture, 69(2), 1995, pp. 235-246
This work determined the inter-relationships between chemical constitu
ents, rumen dry matter (DM) and nitrogen (N) degradabilities of fresh
leaves from 20 multipurpose tree (MPTs) accessions belonging to the fo
llowing 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 solubil
ity but varied in degradation rate of DM (0.064-0.137 h(-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; 70
1-902 g kg(-1); P < 0.001). Except for A saligna, synchronization indi
ces 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 becaus
e N was in excess. Inter-relationships among chemical constituents, DM
and N degradation constants were established using correlation and re
gression analyses. Negative correlations occurred between N solubility
and proanthocyanidins (PAs; P < 0.05), N degradation rate and hemicel
lulose (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 correl
ated with N content (P < 0.01). Equations for predicting N degradabili
ty characteristics (solubility, insoluble slowly degradable fraction,
potential and effective degradability, rate of degradation and lag pha
se) accounted for 0.44-0.83 of the variation (using chemical constitue
nts), 0.56-0.81 of the variation using corresponding DM degradation ch
aracteristics and, 0.74-0.89 of the variation using mixed criteria. Su
perior models were of the form: ND_P = DM_P(-beta), where ND_P and DM_
P are corresponding N and DM degradability characteristics, respective
ly, and beta the regression of the deviations of the ratio ND_P : DM_P
from unity on chemical constituents and accounted for 0.75-0.92 Pract
ical implications of DM degradability and nutrient release synchrony i
ndices in relation to basal roughage intake and microbial protein synt
hesis were discussed. It was concluded that a mixed model could adequa
tely predict N degradability of fresh forages and alleviate analytical
cost. A functional approach of classifying browses is outlined.