Methane mitigation and energy efficiency in cattle through graded levels of soapnut supplementation in total mix ration

The study evaluated the impact of dietary soapnut powder (Sapindus spp.) supplementation on enteric methane emission, feed intake, and energy utilization in ruminants. Three dietary treatments were formulated: control (T1, no soapnut), 1% soapnut (T2), and 2% soapnut (T3) in total mixed ration (TMR). Enteric methane emissions (g/d) were significantly (p = 0.03) reduced with increasing soapnut inclusion, recording a 10.51% and 16.27% reduction in T2 and T3, respectively, compared to T1. This dose-dependent effect is attributed to saponins that suppress ruminal methanogens and protozoa. Dry matter intake (DMI) remained statistically unaffected (p = 0.57), indicating that the reductions in methane emissions were not due to changes in feed intake. Methane yield (g CH₄/kg DMI) showed a significant decline (p = 0.019), further supporting enhanced fermentation efficiency with soapnut inclusion. Gross energy intake (GEI) showed no significant differences across treatments (p = 0.09), while energy loss as CH₄ (Mcal/d) was significantly lowered (p = 0.03) in T3, confirming improved dietary energy retention. The percentage of GEI lost as methane also showed a declining trend (T1: 11.02%, T2: 9.81%, T3: 9.96%), albeit not statistically significant (p = 0.07). The findings suggest that inclusion of up to 2% soapnut in ruminant diets can effectively reduce enteric methane emissions without compromising feed intake or gross energy intake. This strategy holds potential for improving energy efficiency and reducing the environmental footprint of livestock production through natural, plant-based additives.