Forage Quality and Methane Reduction Potentials of Selected Browse Species from Borana Rangeland , Southern Ethiopia

The study was conducted to assess leaf biomass production, chemical composition, in vitro gas and methane production, rumen degradation and tannin biological activities of selected browse species from Borana rangeland of Southern Ethiopia. Twenty three browse species namely, Acacia brevisca, Acacia busei, Acacia drapanolobium, Acacia melifera, Acacia nilotica, Acacia nubica, Acacia , Senegal, Acacia seyal, Acacia toritlis, Acacia oerfota, Angeosis leiocarpa, Asparagus spp, Balanites aegyptica, Boswella neglecta, Cadaba farinose, Carrissa spinarum, Commiphora Africana, Croton macrostachys, Grewia bicolor, Justica odora, Rhus natelensis, Terminalia browini and Ziziphus spina-Christi were selected for this study as they were identified as main browse species for dry season supplementation. Plant density, leaf biomass yield (DMY) and leaf protein yield (CPY), as well as chemical and nutritional composition of the leaf biomass such as y dry matter (DM), ash, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), total phenolics (TP), total tannins (TT), condensed tannin (CT) were determined for the browse species. Plant density from 1343-69 plant/ha and from 39.8-5.6 kg/plant, DMY 1803-391 kg/ha, CPY 267.1-43.5 kg/ha, DM 96.8-89.6% DM, ash 15.76. 8 % DM, CP 28.7-13.8 % DM, NDF 43.2-25.4 % DM, ADF 20.3-11% DM, ADL 14.26. 0% DM, TP 31.4-19.1 % DM, TT 27.5-11.7 % DM, CT19.4-3.2 % DM, Ca 2.15-1.43 % DM and P0.42-0.22 % DM of the leaf biomass. Gas volume after 24 hrs of incubation ranged from 29.4-51.2 ml /200 mg DM while at 48 hrs of it ranged from 39.056. 6 ml/ 200 mg DM. The gas production from the soluble fraction (a) ranged from 13.8-24.3 % DM, gas production from the insoluble but rumen degradable portion (b) 50.0-78.5 % DM, rate of gas production (c) 0.012-0.043 /h and potential gas production (a+b) 67.0-93.7 % DM. Organic matter digestibility (OMD) ranged from 42.2-58.0 % DM, short chain fatty acids (SCFA) 0.33 to 2.01 mmol/liter, metabolisable energy (ME) production 7.2-10.4 MJ/kg , methane production 9.1-15 ml/200mg DM, methane reduction potential (MRP) 12.2-57.5 and Partitioning factor (PF) 1.47-2.36 in the leaf biomass. Tannin bioassay by addition of polyethylene glycol (PEG) was observed to change gas production, OMD, ME and SCFA production from treated leaves while PEG had no effect on the above parameters for blank syringes. Increase in gas production on 24 hrs of incubation ranged from 6.2-70.4%, at 48 hrs of incubation 7.9-72.5%, methane production 3.3-24.8 % , SCFA production 6.1-166% and ME production 1.1-76.6% . The in sacco degradability of the DM of the browse species was also evaluated. The instantly soluble fraction (A) ranged from 19.2-30 DM while degradability of the insoluble but degradable fraction (B) 41.464. 2 % DM, Potential degradability (A+B) 64.285. 3 % DM and effective degradability (ED) 33.263. 4 % DM in the browse species. In sacco degradability experiment ranked the browse species in the following decreasing order: Croton macrostachys>Rhus natelensis>Boswella comiphora>Acacia drapanolobium>Acacia busei>Ziziphus spina –Christi>Terminelia browini>Angeosis leiocarpa>Justica odora>Acacia toritilis>Asparagus spp>Carrisa spanara>Commiphora Africana. The evaluated browse species had medium to high nutritional values and phenolic composition, gas production and tannin biological activities, low to medium methane production and higher DM disappreance values. The authors recommended further evaluation of these browse species to reduce the CT level of the feeds to threshold level as well as animal feeding experiments for effective utilization of these feed resources as dry season supplementation to grazing ruminants.