This experiment compared silages obtained from 3 hybrids of sorghum grown on 2 farms of the Po Valley (one irrigated and one not), in terms of in vitro degradability, gas production (GP), and energy value. Hybrids (forage, sweet or grain genotypes) were sown in experimental plots (3 plots × 3 hybrids), harvested at late-milk stage of maturity, and ensiled into mini-silos (3 silos × 3 hybrids) for 60 d. After ensiling, silages were analyzed for composition and fermentation profile. Two incubations (at 48 h) were carried out to measure NDF degradability (NDFd), GP, and the metabolizable energy (ME) content of silages. Data of silage composition were submitted to ANOVA, considering farm (F), hybrid (H), and F × H interaction as variation sources. Incubation (run) was also considered as a fixed effect in the statistical model for the parameters obtained by in vitro incubation (NDFd, GP, and energy content). On the irrigated farm (Farm 2), the DM contents of silages were higher than those of the non-irrigated one (P<0.001) and the fermentation profile was more favorable. Values of GP at 24 and 48 h and ME content were higher (P<0.05) for silages of Farm 2 in comparison with Farm 1. Within hybrids, the grain sorghum revealed the greatest DM content whereas the forage sorghum, as expected, was the richest in fibrous fraction content, followed by the sweet and grain genotypes (P<0.001). Consequently, values of GP were significantly (P<0.01) influenced by hybrid (167, 200, 215 ml/g DM and 229, 257, 267 ml/g DM for forage, sweet and grain genotypes after 24 and 48 h of incubation, respectively). The F × H interaction was significant for all considered parameters excluding DM, lignin, ash, pH, and in vitro parameters. On the two farms, in general, forage and grain genotypes were largely different, whereas the sweet sorghum was quite similar to the forage in one case or grain in the other. Results of this experiment highlight the large variability of the nutritional values of sorghum hybrids grown in different conditions.
