Ensiling of whole crop wheat with cellulase–hemicellulase based enzymes: 3. Comparing effects of urea or enzyme treatment on forage composition and stability

Abstract

This work compared the effect of ensiling technique and application of urea or a cellulase–hemicellulase enzyme mixture (FSO2) on the conservation of whole crop wheat. A wheat crop harvested at 600 g dry matter (DM) kg −1 was conserved with or without the application of urea (40 g kg −1 DM) and four levels of FSO2 (0, 1750, 3500 and 15 503 ml t −1 DM). Each forage (5 kg DM) was conserved in polythene-bag silos that were evacuated and sealed immediately, sealed immediately but not evacuated or evacuated and sealed after 24 h. After at least 42 days of conservation, the silos were opened and analysed for chemical composition, rumen fluid-pepsin in vitro digestibility and aerobic stability. In non-urea-treated forages, increasing enzyme application rate did not affect in vitro digestibility, but increased water soluble carbohydrate and lactic acid contents, and reduced pH, neutral detergent fibre, acid detergent fibre and cellulose contents. Compared to the FSO2 only treatments, urea treatment increased pH and N content and reduced ensiling DM loss, neutral detergent fibre, acid detergent fibre, acid detergent lignin and cellulose contents. Application of FSO2 and urea (FSO2 + U) produced forages with higher in vitro digestibility and lower cell wall contents than in FSO2 only forages. NDF and ADF contents were also 5–10% lower in FSO2 + U forages than in those conserved with only urea. Immediate evacuation of silos did not enhance fermentation quality. Delaying silo sealing by 24 h increased lactic acid content and aerobic stability relative to either of the immediate seal treatments. Urea treatment alone and the high enzyme level alone also enhanced aerobic stability. However, increasing the enzyme application rate in the FSO2 + U treatments did not enhance stability. These findings indicate that in whole crop wheat, the medium (3500 ml t −1 DM) and high (15 503 ml t −1 DM) levels of FSO2 application are as effective as urea in degrading cell walls and maintaining aerobic stability. However, nutritive value is optimised when whole crop wheat is conserved using a mixture of urea and the low level (1750 ml t −1 DM) of FSO2.