Detoxifying Signal Grass: Ensiling Brachiaria decumbens Improves Rumen Fermentation and Growth Performance in Sheep

Abstract

Fresh Brachiaria decumbens contains high concentrations of steroidal saponins, which impair rumen degradability and depress growth performance in sheep. This study evaluated whether ensiling B. decumbens improves rumen fermentation and animal performance. The work combined in vitro rumen fermentation analysis with an in vivo growth trial lasting 98 days. Fresh Pennisetum purpureum was used as a control forage to reflect typical smallholder feeding practice, while B. decumbens was offered either fresh or ensiled to assess the effect of saponin reduction. Eighteen healthy six-month-old male Dorper cross sheep were dewormed, acclimatized, and randomly allocated to three dietary treatments, control (P. purpureum), fresh B. decumbens, or ensiled B. decumbens, with six animals per group. Forages were harvested at seven weeks of growth and offered twice daily at 3% of body weight on a dry matter basis. Rumen fluid collected after acclimatization was used to determine gas production, ruminal pH, in vitro organic matter digestibility, ammonia nitrogen, and volatile fatty acid profiles. Feed intake was recorded daily, and body weight was measured weekly. Data were analyzed using one-way ANOVA. Fresh B. decumbens resulted in significantly lower cumulative gas production over 72 hours. Although fermentation kinetics, ruminal pH, and digestibility did not differ among treatments, fresh B. decumbens markedly reduced ammonia nitrogen, total volatile fatty acids, acetate, and propionate concentrations. In contrast, ensiled B. decumbens produced higher fermentation end-products than the control. Sheep fed ensiled B. decumbens achieved the highest final body weight, weight gain, average daily gain, and feed efficiency. Overall, ensiling effectively mitigated the negative effects of saponins, enhanced rumen fermentation, and improved growth performance, supporting the use of ensiled B. decumbens as a viable basal forage for sheep.