The objective of this experiment was to evaluate the additive effect of corn stalk silage (CS), 3 nitrogen sources (pig manure, PM; poultry litter, PL; urea, UR) and 2 energy sources (cane molasses, CM; bakery byproduct, BBP), on a diet (145 g CP/DM). Silages composition (g/kg DM) was: 1) 384.6 CS, 384.6 PL, 230.0 CM or BBP; 2) 294.1 CS, 529.4 p.m., 176.5 CM or BBP; 3) 630.0 CS, 30 UR, 340 CM or BBP. The diet contained (g/kg DM): silage 400:600 supplement (corn grain, soybean meal, wheat bran, fish meal, vitamins and minerals). Each silage and concentrate of each treatment were analyzed separately. A factorial arrangement of 3 N sources (PM, PL, UR) × 2 energy sources (CM, BBP) was used in this experiment. The statistical analysis was performed with 2 methods: 1) Mixed lineal procedure (PROC MIXED) assigning literals of treatments with Macro pdmix800.sas (Tukey, P < 0.05); 2) adjustment of gas production with NLMIXED to the model Y_ij = β₁+µ_i1/1+(β₂+µ_i2) e^-β₃^t + e_i, where: maximum asymptote of accumulated gas (mL/g DM) at 72 h, β₂ = Ymax/2 (h) and β₃ = fractional rate of degradation (g DM/h). Diets PL-CM and PM-CM had greater gas production (P < 0.05) during 72 h, whereas PL-CM concentrate and PL-BBP silage produced more gas (P < 0.05) at 72 h. Regarding β₁, diet (273.65) and concentrate (297.86) of PL-CM were greater than the others (P < 0.05), but silage PL-BBP (222.58) produced more gas. Besides, there was an additive effect of the combination silage plus concentrate of PM-CM, regarding β₁, which agrees with gas production (153.12) during all the fermentation. For gas production adjustment to the model, the concentrate and PL-CM diet as well as PL-BBP silage, showed greater β₁ and a higher limit which was higher than the others; besides, β₂ was constant between treatments and β₃ was lower in silages. Thus, it may be concluded that PL-CM and PM-CM combinations have a larger potential for gas production due to the additive effect of their components.