If a deer eats grass what percentage of energy will the deer acquire from the grass?

When a deer eats grass, it typically acquires about 10-20% of the energy stored in the grass. This is due to the inefficiencies in energy transfer between trophic levels, where a significant portion of energy is lost through metabolic processes, heat, and waste. Thus, while the exact percentage can vary based on factors like the type of grass and the deer's metabolic rate, the energy transfer remains relatively low.