NUTRITIVE VALUE AND GREENHOUSE GAS MITIGATION POTENTIAL OF EIGHT BROWSE PLANTS FROM NORTHERN GHANA

Abstract

Five separate experiments were conducted to assess the nutritive value and greenhouse gas (GHG) mitigation potential of eight browse plants in Northern Ghana. The browse species were Ceiba pentandra, Khaya senegalensis, Senna siamea, Ficus gnaphalocarpa, Pterocarpus erinaceus, Albizia lebbeck, Azadirachta indica and Gmelina arborea. The nutrient compositions of the browse plants were determined before the various experiments were conducted. The crude protein was highest (229.2 g/kgDM) in A. lebbeck and lowest (92.3 g/kgDM) in K. senegalensis. The highest NDF was obtained in P. erinaceus with the least in F. gnaphalocarpa. The ADF ranged between 163.4 and 291.8 g/kgDM in G.arborea and C. pentandra respectively. The concentration of condensed tannin was highest (114.5 g/kgDM) in F. gnaphalocarpa but below measurable limits in A. lebbeck. In experiment I, the in vitro batch culture was used to evaluate the DM digestibility of the browse plants incubated in nitrogen sufficient and nitrogen deficient media. The experiment was designed as a completely randomised block design in 8×2 factorial arrangement. The interaction between media and browse plants was not significant (P≥0.480) for all the parameters measured. However, in vitro DM digestibility (IVDMD) and ammonia nitrogen (NH3N) concentration were higher (P<0.05) in Albizia lebbeck than the other browse plants. The N-sufficient media had higher (P<0.05) NH3N than the N-defficient media, but the IVDMD was similar (P>0.05). In vitro DM digestibility did not also differ between A.lebbeck and the high CT-browse plants (C. pentandra and F. gnaphalocarpa). In experiment II, the in sacco technique was used to evaluate the extent of protein degradation in the rumen using the completely randomised design. The CP degradability parameters all differed (P<0.05) among the browse plants. The high CT-browse plants (C. pentandra and F. gnaphalocarpa) had a lower (P<0.05) effective CP degradability compared with the low CT-browse plants. In experiment III, the in vitro continuous culture technique was used to investigate the effect of three of the browse plants (C. pentandra, S. siamea and G. arborea) on enteric methane emission in a 4×4 Latin square design. Methane gas was reduced (P>0.05) by 38%, 19% and 19% when wheat straw was supplemented with C. pentandra, G. arborea and S. siamea, respectively. In experiment IV, nitrogen metabolism and fiber digestibility of the browse were assessed in a cross-over design. Four browse plants (C. pentandra, S. siamea, G. arborea and A. lebbeck) were each used as partial replacements for rice straw in a completely randomised block design. Differences (P<0.001) in daily DM intake, daily CP intake, nitrogen balance and CP digestibility were recorded. The effect of supplementing Djallonké sheep grazing on natural pastures with four browse plants on growth and carcass characteristics were assessed in experiment V. A total of 25 intact rams were randomly assigned to four browse plants (C. pentandra, S. siamea, G. arborea and A. lebbeck) and a control. The highest daily DM intake of the supplement was reported in lambs fed the G. arborea. Daily liveweight gain of the supplemented animals improved (P<0.05) when compared to the control animals. Testicular weight increased (P<0.05) in rams that were fed A. lebbeck diet. It can be concluded that, the browse plants had potential to reduce enteric methane emission and improve growth performance of Djallonke sheep when used as dietary supplement.