Feed intake, methane yield, and efficiency of utilization of energy and nitrogen by sheep fed tropical grasses

Forage allowance impacts dry matter (DM) intake and the use of nutrients by ruminants. The efficient use of protein and energy from pasture is related to better livestock performance and lower environmental impacts. The aims of this study were to evaluate the effect of forage allowance levels on intake, digestibility, nitrogen (N) and energy balance, and methane (CH₄) emissions by lambs fed fresh pearl millet [Pennisetum americanum (L.) Leeke]. An indoor trial was performed using lambs in a completely randomized design with four treatments [forage allowance at 1.5, 2.0, 2.5 kg DM/100 kg of live weight (LW), and ad libitum allowing 20% of refusals] and four replicates (lambs). Forage intake, digestibility, total urine and feces excretion, and CH₄ emission were measured to calculate N and energy balances. An increase in forage allowance resulted in a linear increase in lamb forage intake, N retention, and metabolizable energy intake. Moreover, lamb CH₄ emission (g/day) also increased with greater forage allowance, while CH₄ yield decreased linearly as forage allowance increased. Our results indicate that maximizing forage intake improves N and energy use efficiency and mitigates CH₄ yield and decreases CH₄ conversion factor (Ym) by lambs fed pearl millet forage. Thus, management strategies that optimize intake of tropical forages by ruminants improve the use of nutrients ingested and mitigates negative impacts to the environment.