Do tree leaves promote digestion of grass by cattle?

Abstract

The degree of fermentation of leaves from 14 trees was ranked by relative gas pressures attained in an in vitro system, and four were selected for further study. Progress of fermentation with rumen microbes of fallen leaves of siris (Albizia lebbeck), yemane (Gmelina arborea), tipuana (Tipuana tipu), and bauhinia (Bauhinia carronii), by themselves or in mixtures with angleton grass (Dichanthium aristatum), was monitored by changes in gas pressure and recovery of cell wall as neutral detergent fibre. With the addition of N to N-poor media, responses in fibre digestion ranged from large and positive with yemane by itself or in mixtures with grass, to negative for bauhinia mixtures in which formation of artifact cell wall was observed. Positive associative (non-additive) effects on fibre digestion were recorded for 5 of the 6 leaf/media combinations for siris, yemane, and tipuana, but negative effects were seen for bauhinia mixtures. Following extraction of leaf cell solubles and fermentation of extracted leaf with grass, an increased associative effect was achieved for bauhinia when compared to the unextracted leaf:grass mixture, but no difference was observed for the other leaf types. This study indicated leaf fall from dry-season deciduous trees may provide supplementary nutrition for cattle in northern Australia, but the benefits are highly species dependent.