Abstract: This experiment was conducted to establish the effects of two types of microalgae [Chlorella vulgaris (AI), C. variahilis (AII) and their combination (AI+AII)] with two substrates (wheat and corn silages) on rumen fermentation, gas and methane production. To each substrate, one of 3 algae treatment was supplemented at 0% and 25% of the total incubated dry matter. A series of 5 measurement points (3, 6, 12, 24 and 48 h) were completed and the gas production was monitored. The proximate and mineral composition of microalgae and substrates were examined. At 48 h incubation rumen fermentation variables and CH4 production were also assessed. When compared with wheat silage, corn silage caused an increase in gas production (P<0.05). Ruminal gas production decreased in the algae groups when compared to the controls (0% algae, wheat and corn silages, P<0.05). Among algae, C. vulgaris had the strongest effect, decreasing gas production by 34%. Among algae, the total volatile fatty acids (VFA) and CH4 production were found to be lower in C. variabilis (P<0.001). Ammonia-N increased with the algae inclusion (P<0.05). But, the ruminal gas production, pH, acetate, the total VFA, CH4 and rumen fermentation efficiency were not affected by the substrate and algae interaction (P>0.05). The prop' ate was the highest (P<0.05) for corn silage when incubated with C. vulgaris. Ruminal butyrate was the lowest for the wheat silage when incubated with the mixture of algae (P<0.05). The NH3-N was the highest in corn silage when incubated with all algae types (P<0.05). Careful selection and combination of substrate and algae may positively manipulate rumen fermentation and may inhibit CH4 production. Further research is needed to validate these results in viva.
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