Chemical composition and in vitro fermentation of silages from different sorghum hybrids cultivated in three pilot farms

This experiment compared silages obtained from ten hybrids of sorghum grown in three farms of the Po Valley, in terms of in vitro degradability, gas production (GP), and energy value. Hybrids were sown on 30 experimental plots (three plots per each hybrid), harvested at late-milk stage of maturity and ensiled for 60 d into 30 mini-silos (3 silos×10 hybrids). After ensiling, silages were analyzed for proximate composition, pH, ammonia N, and fermentation acid profile. Degradability of NDF (NDFd) and of true dry matter (TDMd) was determined after 48 h of incubation using sequentially DaisyII incubator and Ankom220 Fibre Analyzer. Two incubation runs (at 48 h) were carried out to evaluate in vitro GP of silages, and to estimate their energy content. All data were submitted to ANOVA considering “hybrid” and “farm” as sources of variation. The interaction between hybrid and farm was never significant and it was excluded from the statistical model. The contents of dry matter and NDF of silages were influenced by hybrid and farm (P<0.001). In contrast, the percentage of non-structural carbohydrates of silages was affected by hybrid (P<0.001) but not by farm. All chemical parameters were significantly affected by hybrid (P<0.01) and, except NCS, by farm (P<0.05). In vitro parameters (NDFd after 48 h and GP at 24 and 48 h of incubation) were influenced by hybrid and farm (P<0.001 and P<0.01), respectively. Among hybrids and farms, large differences (P<0.001) were also found out as regard to net energy content of sorghum silages. Because of this large variability, sorghum silages can be included successfully in ruminant diets considering the peculiarities of each hybrid with respect to the energy requirements of dairy cows.