Soy sauce residue in total mixed ration silage: fermentation characteristics, chemical compositions, in vitro digestibility and gas production

The work aimed to evaluate the effect of different levels of soy sauce residue (SSR) replacement on chemical compositions, fermentation quality and in vitro digestibility of total mixed ration (TMR) silages. The experiment followed a completely randomised design, and four treatments were designed according to different mixing ration of SSR, Napier grass and concentrate (based on fresh weight): (1) 65% Napier grass + 35% concentrate (control); (2)15% SSR + 55% Napier grass + 30% concentrate (SS15); (3) 25% SSR + 50% Napier grass + 25% concentrate (SS25); (4) 35% SSR + 45% Napier grass + 20% concentrate (SS35). TMR was ensiled in a laboratory silo (10 L) after mixing. All silos were opened after 60 days of ensiling and then were sampled for chemical compositions, fermentation quality and in vitro digestibility analysis. All TMR silages were preserved well, as indicated by the low butyric acid (BA; <1.60 g/kg dry matter), ammonia nitrogen (NH3-N; <50.0 g/kg total nitrogen) contents, and the high V-Score value (>80.0). However, SS25 and SS35 significantly (P < 0.05) decreased the BA, NH3-N, ethanol contents and yeast counts, and significantly (P < 0.05) increased the V-Score value compared with the control. SS35 significantly (P < 0.05) increased 72 h cumulative gas production (GP72), in vitro dry matter digestibility (IVDMD) and crude protein digestibility (IVCPD) compared with control and SS15. There was no significant (P > 0.05) difference in vitro neutral detergent fibre digestibility (IVNDFD) among all TMR silages. In conclusion, SS35 replacement was recommended for TMR silage making.Highlights Ensiling is an effective method to utilise soy sauce residue. Soy sauce residue replacement had no unfavourable effect on the fermentation quality of the total mixed ration. 35% soy sauce residue replacement improved the in vitro digestibility of total mixed ration silages.