The efficiency of digestate as inoculum for in vitro digestibility of feeds

Rumen fluid is the most widely used inoculum for in vitro feed digestibility trials. The digestate from animal manure is widely studied but there are no data on its use as an alternative inoculum; its use would be greatly beneficial thanks to its availability, easiness in sampling and possibility to store it for long times. In this study we perform a preliminary test on the potential efficacy of the digestate as inoculum for in vitro digestibility of feeds using rumen fluid as control. The parameter used to assess the efficacy of the digestate was the Neutral Detergent Fiber Digestibility of nine Total Mixed Rations for dairy cows classed into three groups according to their Neutral Detergent Fiber amount (low; medium; high). Four incubation times (48 h, 60 h, 72 h and 96 h) were tested; the data were compared with those measured with the rumen fluid after 48 h of incubation. The results showed that no significant differences were observed among the four incubation times. The digestibility using digestate as inoculum was lower than rumen fluid with low fiber diets at 48 h of incubation. For medium fiber diets, the digestibility values were similar with only one exception; for high fiber diets no differences were observed between rumen fluid and digestate at all incubation times. According to these results, digestate proved to be an efficient substitute of the rumen fluid with high or medium fiber diets, with low fiber diets incubation time need to be of 60h to have similar values to rumen fluid. Further trials with digestates of different origin and chemical and microbiological composition are needed to confirm its efficacy to determine the in vitro digestibility of a wider range of feeds.