Effects of ensiling, exogenous protease addition and inoculation on ruminal in vitro starch digestibility in rehydrated corn

Abstract Text: Three experiments were simultaneously performed to evaluate the impact of: 1) rehydration and ensiling of dry ground corn on starch digestibility; 2) exogenous protease addition to rehydrated unensiled and ensiled corn on starch digestibility; and 3) exogenous protease addition or inoculation on fermentation profile and starch digestibility of rehydrated ensiled corn. To achieve these objectives, seven treatments (n = 3) were performed: dry ground corn (DRY), DRY + water addition to achieve DM content of 70% (WAT), WAT + exogenous protease addition (WATP), WAT ensiled for 30 d (ENS), WATP ensiled for 30 d (ENSP), ENS + inoculation (ENSI) and ENSP + inoculation (ENSPI). Vacuum-sealed bags were used for ensiled treatments. Exogenous protease (DSM Nutritional Products, Basel, Switzerland / Novozymes, Bagsvaerd, Denmark) was added at a rate of 1,825 mg of protease per kg of corn DM. The recommended dose (4.5 g per ton of rehydrated corn) of a microbial inoculant containing lactic acid bacteria (1 x 10⁹ CFU/g; Silo Charger “D”, NU-AG Bosko, Inc., Oskaloosa, IA) was applied to inoculant treatments. Experiment 1 compared DRY, WAT and ENS in a completely randomized designed. Data were analyzed using Proc Mixed of SAS with treatment as a Fixed effect. Experiment 2 compared WAT and ENS without or with exogenous protease addition (WATP and ENSP, respectively) in a completely randomized designed in a 2 x 2 factorial arrangements of treatments. Data were analyzed using Proc Mixed of SAS with ensiling, protease addition and their interaction as Fixed effects. Experiment 3 compared the effects of exogenous protease addition and inoculation in ENS corn (ENS, ENSP, ENSI, and ENSPI). In experiment 1, starch digestibility was greater for ENS (64.9%) than DRY and WAT (51.7% on average). In experiment 2, ensiling and exogenous protease addition increased (P < 0.05) starch digestibility, but exogenous protease addition was more effective in ENS than WAT (6.4-% vs. 2.6% units increase). In experiment 3, starch digestibility was increased by the addition of protease (P = 0.02) but not inoculant (P = 0.38). Inoculation resulted in lower (P < 0.05) pH, acetate, propionate and ethanol concentrations, but greater lactate (P = 0.001) and total acid (P = 0.09) concentrations. Ensiling and protease addition increased starch digestibility in rehydrated corn. 

Keywords: ensiling, protease, starch digestibility