| dc.description.abstract | Many smallholder farmers in sub-Saharan Africa are using herbaceous
and shrub legumes for livestock feeding and as green manures. Besides their
beneficial high nitrogen contents, these legumes also contain a variety of antinutritive
compounds, such as tannins, alkaloids and saponins. The objectives
of this study were: i) to investigate the roles of anti-nutritive plant compounds
in tropical forage legumes on nutrient utilization by ruminants and the
consequences of their interactions, ii) to explore the effects of tannins and
alkaloids and their interactions on decomposition and mineralization patterns
of animal and compost manures in acidic tropical soils, and iii) to investigate
the role of micro- and meso-fauna on decomposition of soil amendments
containing tannins and alkaloids. In vitro, purified condensed tannins (CT)
and sparteine (quinolizidine alkaloid) significantly (P < 0.05) depressed
neutral detergent fiber degradability. However, only CT significantly reduced
cumulative gas volume and the rate of gas production. A significant negative
interaction (P < 0.01) between tannins and alkaloids on rate of gas production
was observed. Simulations with the Cornell Net Carbohydrate and Protein
System (CNCPS) showed that reduction of the degradation rate of the B2
carbohydrate fraction (digestible fiber) by CT reduced energy allowable milk
by 1.0 kg! d when the rate changed from 0.067 h-l to 0.051 h-l. Microbial
protein synthesis from fermentation of forages with alkaloids and tannins was
responsive to the level and quality of available energy in a feed and the
inhibitory effects of the secondary compounds were most evident under
conditions of limited nutrient availability. Tannins, but not alkaloids, reduced
N digestibility by animals, but there were no significant effects on intake and
dry matter digestibility. Feces from animals fed legumes containing tannins
and alkaloids and compost from these same plants decomposed significantly
faster (P < 0.05) than feeds when incubated in the soil. Decomposition and
release of nutrients from soil amendments placed in 2000 11mpore size
litterbags were higher (P < 0.001) than those placed in 53 Jlffi mesh size bags.
These studies indicate that presence of anti-nutritive compounds in ruminant
feeds, especially tannins, can reduce nutrient availability but may not
necessarily affect animal performance. These studies also suggest that
presence of meso-fauna is critical in litter and manure decomposition in the
soil. | en |
