Grasses, Vol. 4, Pages 37: Effect of Acacia melanoxylon R. Br. Inclusion on the Chemical Composition, Fermentation Dynamics, and In Vitro Digestibility of Medicago sativa L. Silage

Grasses doi: 10.3390/grasses4030037

Authors:
Cristiana Maduro Dias
Vanessa Melo
Helder Nunes
Alfredo Borba

This study evaluated the effect of Acacia melanoxylon inclusion in Medicago sativa silage on chemical composition, fermentation quality, in vitro digestibility, gas production, and energy value. Due to its high moisture content, M. sativa presents challenges for ensiling. A. melanoxylon, a woody legume with high dry matter (DM) content, was tested as a structural additive. Five treatments were prepared—control (100% M. sativa) and mixtures with 6, 12, 24, and 48% A. melanoxylon (fresh basis)—and ensiled for 45 days under vacuum. Silages were analyzed for DM, crude protein, fiber fractions, pH, ammonia nitrogen, in vitro digestibility, gas production kinetics, and estimated energy values (ME and NEL). Increasing Acacia raised DM (17.75 ± 0.04 → 28.45 ± 0.11%) and reduced pH (5.86 ± 0.01 → 4.53 ± 0.01) and NH3-N/Total N (11.38 ± 0.10% → 8.05 ± 0.10%), indicating improved fermentation quality. Conversely, crude protein, digestibility (IVDMD 62.61 ± 0.05% → 48.02 ± 0.16%), and cumulative gas at 96 h decreased, as did energy values (ME 5.91 → 4.45 MJ/kg DM; NEL 3.13 → 2.02 MJ/kg DM) at higher inclusion levels; gas-kinetic parameters reflected the same trend (lower b and c). Overall, A. melanoxylon acts as a structural co-ensiling option that increases DM and supports fermentation quality while clearly delineating nutritional and fermentability trade-offs; low-to-moderate inclusion (6–12%) appears advisable to balance process benefits against acceptable nutritional penalties.

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Cristiana Maduro Dias www.mdpi.com