Changes in chemical composition and nutritive value of urea treated whole crop wheat during exposure to air

Abstract

Utilisation of winter wheat for silage production is popular in northern Europe as the crop can be grown in a wide range of climates and soil conditions. However, unacceptable losses of dry matter (DM) and a decline in nutritive value of the ensiled crop can occur during conservation and feed-out. Changes in chemical composition and nutritive value of fermented whole crop wheat during exposure to air was investigated using a range of maturities of wheat (growth stages (GS) 49 (boot), 71 (seed coat water ripe) and 87 (hard dough)) and levels of urea (0, 20 and 40 kg/t DM) in small scale silos. The experiment was a factorial design with initial DM of forage, level of application of urea and period of exposure of silage to air being the factors. The effect of increasing concentration of urea reduced the maximum temperature of the silage on exposure to air ( P<0.001) and increased the time taken to achieve the maximum temperature ( P<0.001). Increasing the initial DM content of forage ensiled depressed the maximum temperature recorded in the silo as well as increased the period of time to reach maximum temperature ( P<0.001 for both effects). Losses in DM from the conserved forages were greatest in crops ensiled at an immature stage of growth not treated with urea. Addition of urea at ensiling reduced the losses in DM ( P<0.001). However, at intermediate stages of growth (GS 71) and low levels of application of urea (20 kg/t DM), the rate of loss of soluble carbohydrates were increased ( P<0.05) compared to untreated forages. Ammonia released as a result of urea treatment at ensiling reduced the rate of loss of DM and of loss of nutritive value (neutral detergent cellulase digestion (NDCD); P<0.001). However, no changes in the concentration of starch during exposure to air were observed for any treatment. Treatment of whole crop wheat with urea is an effective method of preserving forage nutritive value during ensiling and on exposure to air at feed-out.