Review: Strategies for enteric methane mitigation in cattle fed tropical forages.

Methane (CH4) is a greenhouse gas (GHG) produced and released by eructation to the atmosphere in large volumes by ruminants. Enteric CH4 contributes significantly to global GHG emissions arising from animal agriculture. It has been contended that tropical grasses produce higher emissions of enteric CH4 than temperate grasses, when they are fed to ruminants. A number of experiments have been performed in respiration chambers and head-boxes to assess the enteric CH4 mitigation potential of foliage and pods of tropical plants, as well as nitrates (NO3-) and vegetable oils in practical rations for cattle. On the basis of individual determinations of enteric CH4 carried out in respiration chambers, the average CH4 yield for cattle fed low-quality tropical grasses (>70% ration DM) was 17.0 g CH4/kg DM intake. Results showed that when foliage and ground pods of tropical trees and shrubs were incorporated in cattle rations, methane yield (g CH4/kg DM intake) was decreased by 10% to 25%, depending on plant species and level of intake of the ration. Incorporation of nitrates and vegetable oils in the ration decreased enteric CH4 yield by ∼6% to ∼20%, respectively. Condensed tannins, saponins and starch contained in foliages, pods and seeds of tropical trees and shrubs, as well as nitrates and vegetable oils, can be fed to cattle to mitigate enteric CH4 emissions under smallholder conditions. Strategies for enteric CH4 mitigation in cattle grazing low-quality tropical forages can effectively increase productivity while decreasing enteric CH4 emissions in absolute terms and per unit of product (e.g. meat, milk), thus reducing the contribution of ruminants to GHG emissions and therefore to climate change.

Follaje de árboles y arbustos en los sistemas de producción bovina de doble propósito / Foliage of trees and shrubs in livestock systems of dual purpose

El follaje de arbustivas y arbóreas tropicales representan una fuente importante de nutrimentos para el ganado bovino en pastoreo de gramíneas tropicales. La composición química, digestibilidad y consumo del follaje de arbustivas y arbóreas son generalmente satisfactorios para su aprovechamiento por los rumiantes, aportando proteína en el rumen que favorece una rápida disponibilidad de nitrógeno para el crecimiento microbiano. Sin embargo, la disponibilidad de energía en relación a la del nitrógeno en el rumen, parece ser una restricción para el uso eficiente del follaje. La incorporación del follaje de arbustivas y árboles forrajeros en la ración de rumiantes tiene el potencial para aumentar la producción animal en sistemas de doble propósito en los trópicos, ya que son una fuente importante de nutrimentos para el ganado que consume gramíneas bajo pastoreo.

Foliage of tropical trees and shrubs represents an important source of nutrients for cattle grazing tropical grasses. Chemical composition, digestibility and intake of foliage of shrubs and trees are generally satisfactory for their utilization by ruminants, supplying protein to the rumen that promotes a readily available nitrogen for microbial growth. However, energy availability relative to nitrogen in the rumen, seems to be a constraint to the efficient use of foliage Incorporation of foliage of trees and shrubs in ruminant rations has the potential to increase animal production in dual-purpose systems in the tropics, since they are an important source of nutriments for livestock under grazing conditions.