Effect of dl-malate on mixed ruminal microorganism fermentation using the rumen simulation technique (RUSITEC)

The objective of this study was to investigate the effects of dl-malate on the in vitro fermentation of a 50 : 50 forage : concentrate diet using the rumen simulation technique (RUSITEC) and to compare these effects with those induced by the addition of propionate. The RUSITEC system consisted of eight vessels: three of them received daily 5.62 mmol of dl-malate, three vessels received daily 5.62 mmol of propionate and two vessels received no additives (control). After an adaptation period of 11 days the main fermentation parameters were determined for five consecutive days. There were no significant differences between treatments either in pH or in the daily production of NH3–N. Compared to control diet, the addition of dl-malate resulted in an increase (p < 0.05) of hemicellulose disappearance and a trend (p < 0.10) towards a greater disappearance of dry matter, organic matter and neutral detergent fibre. Differences between dl-malate and propionate in diet degradation were not significant. dl-malate treatment resulted in an increase (p < 0.01) of daily propionate production, and a decrease (p < 0.05) in the amount of both methane (mmol/g DM fermented) and l-lactate (mg/day). Compared to propionate, dl-malate produced an increase (p < 0.05) of acetate production and tended to produce a lower amount of propionate (p < 0.10). In conclusion, these results seem to indicate that dl-malate enhanced the in vitro fermentation by increasing production of propionate and digestibility of hemicellulose.