Effetto del medium e della proporzione di inoculo ruminale sulla fermentazione di sottoprodotti agroalimentari.

The energy content of feeds for ruminants is traditionally estimated using in vivo and in situ methods that evaluate the feed digestibility. These traditional methods use the rumen environment to measure feed degradation and are the standard against which the in vitro methods are often compared. At the same time, these techniques are criticized i) for problems related to animal welfare; ii) for the high costs iii) for the poor reproducibility and iv) because they measure the degree of disappearance and not the actual amount of fermented substrate. Therefore, in vitro methods, that reproduce in laboratory the conditions found in the rumen of the animals, are becoming more popular. The objective of this test was to reduce the complexity of in vitro methods for feed assessment simplifying the composition of fermentation medium and reducing the dosage of rumen fluid as inoculum of fermentation. Another goal was to reuse residual fluids of fermentation as microbial inoculum for feeds incubation. The test was carried out using as substrate of fermentation 2 by‐products (tomato peels and citrus pulp) and a roughage (Silybum marianum ‐ milk thistle) incubated with two different mediums (the conventional Menke medium and a “simplified” medium) and two different ratios between inoculums and medium (inoculum/medium = 5/55 ml or 30/30 ml). Three subsequent incubations were carried out: each lasted 12 h, for a total incubation time of 36 h. In the second and in the third incubation the residual fluid of fermentation of the previous incubation was reused as inoculum. The results suggest that a simplified medium can be used as alternative to the conventional Menke medium, providing that the pH of the inoculum does not fall below 5.5, and a high dose of microbial rumen fluid is used as inoculum. Moreover, the dose of rumen fluid used as inoculum of fermentation can be reduced without adverse effects on gas production. The residual fluids of fermentation residues can be re‐used as microbial inoculum at the condition that a complex medium (such as Menke) is used and the dose of microbial inoculum is reduced from conventional 30 ml to about 5 ml. The results also showed that the citrus pulp and tomato peels are characterized by high fermentability and their complete degradation requires the use of a medium dose higher than that 10 used in this research. Differently, the roughage is characterized by the ability to buffer the pH and stimulate rumen microbial activity, especially, when the pH of the medium falls below values of 6. For this reason, the combined incubation of by‐products and roughage increased the gas production compared to the single incubation of by‐products.