Compositae species are applied as whole or part of the feed stock for animals and poultry. However, rabbits display varied preferences in their consumption of these plants, following the order of: Melanthera scandens (MS) > Synedrella nodiflora (SN) > Aspilia africana (AA) > Ageratum conyzoides (AC). This preference profile may be due to variation in chemical composition, flavor or toxicity of the plants. The rabbits in our farm feed on 100% MS or SN with excellent performance. This study, therefore, is set to: obtain the methanol extract of these plants, screen them for their antibacterial activity, determine their toxicity and investigate the chemical composition of their n-hexane fraction (volatile constituents).
Crushed leaves of MS, AC, AA and SN were extracted with methanol using soxhlet extraction technique to obtain the methanol extract of each plant. Phytochemical examination, antibacterial activity determination (using the agar-well diffusion technique) and toxicity studies (using experimental white albino mice) were carried out on the methanol extracts. Vacuum liquid chromatography (VLC) fractionation of each extract was carried out. The n-hexane fractions obtained from the VLC fractionation were subjected to gas chromatography-mass spectroscopy (GC-MS) analysis and the chemical constituents were identified.
Phytochemical screening showed the presence of alkaloids, steroids and tannins in all the extracts. The extracts exhibited varying degrees of antibacterial activities against bacterial strains used for this study. AC showed activity against tested microbes, having zones of inhibition ranging from 10 mm and 22 mm, with the exception of Bacillus stearothermophilus and Pseudomonas fluorescens. MS inhibited the growth of the microbes, having zones of inhibition ranging from 12 mm and 20 mm, with the exception of Bacillus anthracis, Bacillus stearothermophilus, Clostridium sporogens and Enterococcus faecalis. AA did not show activity against four of the tested microbes: Bacillus anthracis, Klebsiella pneumonia, Pseudomonas fluorescens and Enterococcus faecalis. SN however, inhibited the growth of all the bacterial strains tested, with the exception of Escherichia coli only. On the other hand, when streptomycin was used as a positive control, the growth of all the bacterial strains was inhibited, having zones of inhibition ranging from 15 mm and 22 mm. Toxicity study showed that the extracts were not toxic at the concentrations of 10 mg/kg through 1,000 mg/kg; however, at higher concentrations of 1,600 mg/kg through 2,500 mg/kg, the extracts became toxic. The LD50 was determined to be 1,275 mg/kg for all the extracts. GC-MS analysis showed the presence of 4-tetradecene in all of the extracts, except AC.
The varied preferences observed in rabbit consumption of these plants definitely have nothing to do with toxicity. The presence of various fatty acids and unsaturated hydrocarbons in the volatile components of the extracts, which influence the flavor, may be responsible for the wellness of rabbits and their relative preferences in consumption.
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