Abstract:
Methane (CH₄) emissions from ruminant livestock contribute
significantly to global greenhouse gas accumulation and represent a
loss of dietary energy. The use of plant-based feed additives rich in
secondary metabolites has gained attention as a sustainable strategy for
methane mitigation. This study evaluated the in vitro effect of Tribulus
terrestris seed powder, a saponin-rich natural additive, on methane
production, protozoal population, and feed digestibility using rumen
fluid collected from local cattle breeds of Sri Lanka. A basal substrate
composed of rice bran and paddy straw was supplemented with T.
terrestris seed powder at graded inclusion levels (10%, 30%, and
50%), alongside an unsupplemented control. In vitro fermentation was
conducted under anaerobic conditions, and methane production was
measured at 6-hour intervals for 24 hours, while in vitro dry matter
digestibility (IVDMD) and protozoa counts were determined after
incubation. Results demonstrated a significant (p < 0.05) reduction in
methane production with increasing levels of T. terrestris
supplementation compared to the control. The methane-reducing effect
was accompanied by a marked decline in rumen protozoa populations,
indicating a possible saponin mediated inhibition of protozoa-
associated methanogenesis. Moderate inclusion levels of T. terrestris maintained acceptable digestibility, whereas higher levels tended to
reduce IVDMD. Overall, the findings suggest that T. terrestris seed
powder has strong potential as a natural methane-mitigating feed
additive for climate-smart livestock systems, provided that optimal
inclusion levels are used to balance methane reduction and nutrient
utilization in local cattle production systems of Sri Lanka.
