Effect of steam explosion treatments on nutritional quality of corn–wheat mixed straw

To determine the effects of steam explosions on straw feed processing, corn straw silage residue after feeding and wheat straw (7∶3 mixed) were used as test materials. The nutritional value of straw products was evaluated by measuring the conventional nutrients, CNCPS components, gas production in vitro, and physical structure of straw before a steam explosion and at different times (0, 24, and 120 h) after the explosion. We found that crude fat (EE), acid detergent insoluble protein (ADIP), neutral detergent insoluble protein (NDIP), monosaccharide (ESC), soluble protein (SP), total volatile fatty acid (VFA), and calcium (Ca) of mixed straw at different times after the steam explosion were significantly higher than before the steam explosion (P < 0. 05). In contrast, dry matter (DM), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin (ADL), starch, and phosphorus (P) content were significantly (P < 0. 05) lower than before the steam explosion. The CNCPS component, CHO, starch (CB₁), soluble fiber (CB₃), non-digestible fiber (CC), insoluble true protein (PB₁), and fiber-binding protein (PB₂) in the steam explosion group were significantly lower than those in the control (P < 0.05). However, non-fibrous carbohydrate (NFC), volatile fatty acid (CA₁), lactic acid (CA₂), water-soluble carbohydrate (CA₄), ammonia (PA₁), soluble true protein (PA₂). non-degraded protein (PC), and soluble true protein (PA₂) were significantly higher than those in the control (P < 0. 05). Steam explosions could eliminate some anti-digestion materials in straw, increase the contact unit area for microbial activity, gas production, dry matter digestibility, and the relative feeding value (RFV) of corn-wheat straw (P < 0.05). Scanning electron microscopy (SEM) showed that the fiber bonds in corn stalks and panicle skin were broken, the cell wall of the mesophyll was destroyed, only the filamentous veins and filamentous lignin, which were difficult to break, remained, and fibers and fiber bundles became soft and curled after steam explosion treatments. Thus, steam explosions used could significantly change straw’s physical and chemical properties and improve its nutritional value and feeding quality. It is a very effective way to treat straw so that it can be used as feed.