**4. Protecting environment: green livestock production**

Rapid breakdown of herbage proteins in the rumen and inefficient incorporation of herbage N by the rumen microbial population are major determinants of N (and C) loss and pollution in pasture-based livestock production system. Thus, when livestock are given fresh forages, they can waste 25–40% of the forage protein-N during ruminal fermentation. An increase from 23 to 34% in rumen N use efficiency through feeding higher WSC containing grasses could result in a 30% reduction in N<sup>2</sup> O and NH<sup>3</sup> emissions [91]. Similarly, increasing the digestibility of cell walls in forages has been practiced to lower CH4 losses, but in fresh grass and grass silage, the scope of this approach seems limited. CH4 production in ruminants tends to increase with maturity of forage fed, and CH4 yield from the ruminal fermentation of legume forages is generally lower than the yield from grass forages [92]. Shifting the animals from grass to legume plant species tends to decrease the enteric emission due to lower proportion structural carbohydrates and faster rate of passage which shifts the fermentation pattern towards higher propionate production. Further, enhancing N use efficiency in the rumen may also contribute to a reduction in the amount of C (both as CO<sup>2</sup> and CH4 ) excreted. The concept of mixed or TMR silage may certainly address these concerns and enable eco-friendly livestock production. The impact of the form of C relative to N and the effect at different C:N ratios in terms of rumen function and conversion efficiency is an area of considerable promise that requires further detailed research.
