Balancing forage quality and quantity for silvopastoral systems: ruminal degradation kinetics of Tanzania grass associated with the shrub legume Desmanthus virgatus

The objective of this study was to evaluate the effect of different grass:legume proportions on ruminal fermentation kinetics. A completely randomized design with repeated measures over time was used. Treatments consisted of the following combinations: 100% Tanzania grass, 100% Jureminha, 80% Tanzania grass + 20% Jureminha, 70% Tanzania grass + 30% Jureminha, 60% Tanzania grass + 40% Jureminha, and 50% Tanzania grass + 50% Jureminha, with incubation times of 0, 6, 24, 48, 72 and 96 h. In situ degradability of dry matter, crude protein and neutral detergent fiber of the grass-legume mixtures was determined using one rumen-fistulated adult bovine. For dry matter, the 80% grass + 20% legume proportion showed a soluble fraction ( a ) similar to that of the grass monoculture; beyond this proportion, both the a and b fractions decreased, and effective degradability remained numerically higher for the grass, at 53.11, 41.56 and 35.68% at passage rates of 2, 5 and 8%/h, respectively. For crude protein, in contrast, legume inclusion at different proportions positively influenced degradation, with the numerically highest soluble fraction observed at the 70:30 proportion (32.43%). Neutral detergent fiber degradation kinetics were also numerically greater at this same proportion, which showed the numerically highest potentially degradable fraction and the numerically lowest undegradable fraction. Overall, the results indicate that replacing 20 to 30% of Tanzania grass with Desmanthus virgatus was associated with numerically greater degradability of crude protein and neutral detergent fiber in the mixtures. In practical terms, including 20–30% of D. virgatus in Tanzania grass-based forage is a promising strategy to increase the protein value and ruminal fiber utilization of the diet without a marked loss in dry matter degradability, supporting the use of this shrub legume as a protein source in mixed pastures and silvopastoral systems in the tropics.