Efficacy of Salvia officinalis Shrub as a Sustainable Feed Additive for Reducing Ruminal Methane Production and Enhancing Fermentation in Ruminants.

The objective of this study was to evaluate the effects of the inclusion of dried Salvia officinalis (SO) shrub leaves on nutrient degradability, ruminal in vitro fermentation, gas production (GP), methane (CH 4 ), and carbon dioxide (CO 2 ) productions. Dried and ground SO shrub leaves were included at 0% (control), 0.5%, 1%, 1.5%, and 2% DM of a diet consisting of (per kg DM) 500 g concentrate feed mixture, 400 g berseem hay, and 100 g rice straw. The diet was incubated for 48 h. The asymptotic GP and the rate of GP changed linearly and quadratically ( p < 0.01), with the highest GP observed at 1% inclusion of SO and then decreasing thereafter with greater inclusion (i.e., 1.5% and 2%), while CH 4 production and its rate decreased linearly ( p < 0.01) with all levels of SO inclusion. A linear increase in CO 2 production and its rate was also found with an increasing level of SO inclusion in the diet ( p < 0.05). Furthermore, the degradability of DM, NDF, and the concentration of total short-chain fatty acids and acetate changed linearly and quadratically, with the greatest being found at 1% SO inclusion and then steadily declining after ( p < 0.01) with the 1.5% and 2% inclusion levels. Meanwhile, the propionate, NH 3 -N, and microbial crude protein levels showed similar trends, with the plateau found at 1% inclusion of SO, where there was no change in butyrate concentration. Moreover, the pH, metabolizable energy, and partitioning factor (PF 24 ) also changed linearly and quadratically ( p < 0.05), where the pH and PF 24 were considerably reduced and ME increased with a 1% inclusion of SO ( p < 0.05). In summary, SO at 1% inclusion in the diet showed the potential to improve gas production kinetics, nutrient degradability, and the ruminal fermentation profile, with a more significant reduction in ruminal CH 4 production suggesting that SO at 1% could be included in the ruminant diet to reduce their carbon footprint and increase the production performance.