When molasses was added during ensilage of three tropical grasses [hamil grass (Panicum maximum cv. Hamil), pangola grass (Digitaria decumbens) and setaria (Setaria sphacelata cv. Kazungula)] the final pH, concentration of fermentation acids (except lactic acid) and NH3-N content were all similar after 100 days of incubation. Pangola grass silage had significantly higher lactic acid content (66 g/kg dry matter) than the other two. Adding either 4 or 8% (w/w) molasses reduced NH3-N, volatile fatty acid content and pH but increased lactic acid content in the final silages. Numbers of lactic acid bacteria remained approximately constant during the course of the fermentation, although large differences were noted in the species composition of the populations. At the time of ensiling, only Pediococcus spp. and Leuconostoc spp. were detected. By 5 days, the homo-fermentative population, notably Lactobacillus plantarum, dominated (43%) and remained dominant. Hetero-fermentative rods were only detected in the 100-day silage, where they represented 29% of the strains isolated. Homo-fermenters were more abundant in pangola (60%) and setaria (47%) silages than hamil (27%) silages. Homo-fermenter populations were lowest in the 12-week forage. Molasses additions increased homo-fermenter populations. Pangola grass gave the best quality silage but, since the water-soluble carbohydrate content in the grasses was insufficient to promote a strong lactic fermentation, the addition of 20 to 30 kg molasses/tonne should achieve satisfactory preservation.

Lactic acid bacteria were isolated from various tropical silages made from either forage sorghum (Sorghum bicolor cv. Sugardrip): three tropical grasses: hamil grass (Panicum maximum cv. Hamil), pangola grass (Digitaria decumbens) and setaria (Setaria anceps cv. Kazungula) either with or without addition of molasses and from mixtures of pangola or setaria grasses with leucaena (Leucaena leucocephala) or gliricidia (Gliricidia sepium). The 311 wild strains isolated and 13 reference strains were examined by 80 biochemical, physiological and morphological tests. A computer‐assisted complete linkage analysis produced 16 clusters and five unclustered strains at 82% S. The largest cluster included 134 wild strains and the reference strain Lactobacillus plantarum. The results showed that Lactobacillus plantarum was the predominant lactic acid bacterium in all of the tropical silages.

S U M M A R YSilages were prepared from the tropical grasses, pangola grass (Digitaria decumbens) and setaria (Setaria sphacelata), with the addition of molasses (4% w/w) and/or leaves (33%) from the leguminous trees leucaena {Leucaena leucocephala) and gliricidia (Gliricidia sepium). All forages were grown at the University of Queensland farm in south eastern Queensland during 1985. These silages, together with hays made from these grasses and sorghum silage (13 diets) were fed to sheep to assess their nutritive value. All silages were well preserved, as indicated by low pH (3-5-4-4), low ammonia N (26-57 g/kg total N) and high lactic acid (73-95 % total acids) contents. The addition of legumes increased both the dry matter (DM) and total N (TN) contents of silages to the same extent as the addition of both legumes and molasses at ensiling. Sheep given silages prepared from pangola grass and legumes ( +molasses) consumed similar DM intakes (22-9-25-4 g/kg 075 per day) as sheep given pangola grass hay (23-9 g/kg 0 ' 75 per day). Silage made from pangola grass + molasses was of low palatability (161 g/kg 075 per day). The digestibilities of silage DM (DMD) and its fibrous components were significantly (P < 005) lower (DMD 53-3-60-6%) than that of pangola hay (DMD 64-7%). Silages and hay made from setaria, and sorghum silage, were of lower nutritive value than those from pangola grass. The addition of leucaena and molasses increased silage DM intakes (211 g/kg 0 ' 75 per day) above those for setaria hay and setaria + molasses silage (16-7 and 190 g/kg" 75 per day respectively). The intakes of silages made from gliricidia (171 g/kg 075 per day) were significantly (P < 005) improved when molasses was included at ensiling (21 -8 g/kg 075 per day). The digestibilities of silage DM were significantly (P < 005) higher (DMD 53-6-60-4%) than that of setaria hay (DMD 40-6). Liveweight change in sheep was significantly (P < 005) correlated with intakes of digestible DM (r 2 = 0-74) and with N intake (r 2 = 0-82). The inclusion of legumes in the silages increased N retention and, for setaria silages, also increased rumen ammonia concentration. It was concluded that tropical grasses can be effectively ensiled by the addition of legumes alone and, with the exception of setaria/gliricidia silages, the resultant silages were of sufficiently high quality to merit their use in tropical animal production systems.

The effects of adding two legumes, Gliricidia sepium and Leucaena leucocephala, cv. Cunningham, and molasses on the fermentation characteristics of silages made from two tropical grasses (Pangola grass, Digitaria decumbens, and Setaria sphacelata cv. Kazungula) were investigated. Pangola grass silages contained significantly higher contents of water-soluble carbohydrates and lactic acid than did setaria silages after 100 days fermentation, but there were no significant differences between the two silages in populations of lactic acid bacteria and contents of total N and NH3-N. Addition of either species of legume had no significant effect on fermentation acids and NH3-N contents, and numbers of lactic acid bacteria. Addition of both legumes reduced NH3-N production in the silages by 59% after 5 days' fermentation. Numbers of lactic acid bacteria were not significantly affected by the different treatments. Enterococcus faecalis represented 60% of the lactic acid bacteria isolated from the treated herbages prior to ensiling. By 100 days of fermentation, only lactobacilli were isolated: 82% homo-fermenters and 18% hetero-fermenters. Lactobacillus mesenteroides subsp. dextranicum was found only in the silage supplemented with 33% (w/w) legume. It was concluded that the low quality of tropical grasses used as feeds for ruminants may be significantly improved by ensiling these grasses with small amounts of molasses and with high-protein tree leaves.

The effects of temperature, aerobic and anaerobic conditions in the silo and plant characteristics [water-soluble carbohydrate (WSC) contents, growing season] on the fermentation characteristics of a tropical forage species, Sorghum bicolor cv. sugar-drip, were investigated. Silages fermented in oxygen-impermeable bags were well preserved and had low pH (3.7), high lactic acid [72 g kg(-1) dry matter (DM) ≡ 80% of total acids], and low butyric acid (0.12 g kg(-1) DM) and ammonia nitrogen (NH3-N) (57 g kg(-1) total nitrogen contents. Conversely, the use of oxygen-permeable bags as silos allowed aerobic decomposition of the ensiled forages. Increasing the incubation temperature lowered the population of lactic acid bacteria, reduced lactic acid production and caused the pH to rise. The heterofermentative Leuconostoc spp. predominated on fresh forages but homofermentative Lactobacillus plantarum began to dominate after 5 and 8 days of fermentation. Heterofermentative lactobacilli, notably Lactobacillus brevis, were dominant among the isolates obtained from 100-day silages. Varying the WSC contents, by crushing and/or chopping the forage, and growing season did not significantly affect the fermentation quality of the resulting silages. It was concluded that the maintenance of anaerobic conditions is essential if good quality silage is to be produced from tropical forage species.