In vitro screening of plant extracts to enhance the efficiency of utilization of energy and nitrogen in ruminant diets

This study was completed to identify plant extracts that modulate partitioning of degraded organic matter (OM) towards microbial protein synthesis, at the expense of gas production, and decrease protein degradation in the rumen. In the preliminary study, effects of aqueous extracts of picrorhiza kurroa root, Plumbago zeylanica root, Terminalia bellerica fruit and Zingiber officinale rhizome and aqueous methanol extract of M oleifera seed on rumen fermentation end products were examined in vitro at 2.0 mg/ml of incubation medium using while clover hay (Trifolium repens) as substrate. Another study was conducted to evaluate the ability of two promising extracts, selected based on their ability to decrease ammonia N concentration, on in vitro degradable crude protein (IVDCP) and protozoal populations using the same substrate at a lower dose (1 mg/ml). Finally, the extract which did not affect IVDCP, but decreased ammonia concentration, was further investigated to assess its effect on substrate degradability, microbial mass and a partitioning factor (PF; ratio of substrate truly degraded to gas volume produced at 24 h of incubation) at two different doses (0.75 and 1.0 mg/ml) using a mixed diet (700 g local grass hay and 300 g concentrate mixture/kg) as substrate. In the preliminary study, M. oleifera aqueous methanol extract decreased total gas, total volatile fatty acids (VFA) production. acetate propionate ratio and ammonia concentration and increased microbial purines (44%) and efficiency of microbial CP synthesis (EMPS). P. kurroa aqueous extract decreased total gas production and ammonia concentration (35%) and increased propionate production but did not affect total VFA production, microbial purines and EMPS. The decrease of ammonia in the presence of P. kurroa extract was mainly mediated through a decrease in in vitro CP degradability (28%). M. oleifera extract had activity against rumen protozoa, but did not influence CP degradability. Even at a lower concentration (i.e., 0.75 mg/ml) with a forage based mixed diet as substrate, M. oleifera extract decreased gas production, without affecting true organic matter or neutral detergent fibre degradability. and increased microbial purines and PF Results suggest that aqueous methanol extract of M. oleifera seed and aqueous extract of P kurroa root may have potential as feed additives to increase the efficiency of utilization of energy and N in ruminant diets. (C) 2007 Elsevier B.V. All rights reserved.