The use of medicinal plants and their extracts has recently attracted the attention of many researchers as a methane (CH4) mitigation strategy. This study evaluated the relationship of agronomic traits of Moringa accessions with in vitro gas production measurements and feed digestibility from ruminants. Twelve Moringa accessions were grown at the Roodeplaat experimental site of the Agricultural Research Council in Pretoria, South Africa. Agronomic traits, such as seedling survival rate, leaf yield, canopy and stem diameter, plant height, number of primary branches, plant vigor, greenness, chlorosis, disease and pest incidences were recorded. The leaves were harvested in the fifth month after transplanting to the field. Freeze-dried leaves were extracted with methanol, and their total phenolic and total flavonoid contents were determined. The extract was applied at a dose of 50 mg/kg of dry matter (DM) feed for in vitro gas production studies. Most of the growth and agronomic traits, i.e., seedling survival rate, leaf yield, canopy diameter, plant height, number of primary branches, the score of plant vigor, and greenness, total phenolics and flavonoids were significantly different among the accessions except for stem diameter and chlorosis score. All accession leaf extracts significantly reduced the total gas and CH4 production compared with the control with equal or higher in vitro organic matter digestibility. Higher CH4 inhibition was obtained in Moringa oleifera (M. oleifera) A3 (28.4%) and A11 (29.1%), whereas a lower inhibition was recorded in A1 (17.9%) and A2 (18.2%). The total phenolic (0.62) and total flavonoid (0.71) contents as well as most agronomic traits of the accessions were positively correlated with the CH4 inhibition potential of the accessions. Moringa oleifera accessions A3, A8 and A11 resulted in higher in vitro CH4 inhibition potential and improved organic matter digestibility of the feed with equal or higher adaptability performances in the field. Thus, there is a possibility of selecting Moringa accessions for higher antimethanogenic activity without compromising the feed digestibility by selecting for higher total phenolics, total flavonoids and agronomic performances traits. There is a need for further study to determine the long-term adaptability of promising accessions in the study area with concurrent antimethanogenesis efficacy when used in the diet of ruminant animals.
Keywords: methane mitigation; organic matter digestibility; ruminants; total flavonoids; total gas; total phenolics.