The effect of pre-wilting and incorporation of maize meal on the fermentation of Bana grass silage

Abstract

An experiment was conducted to investigate the effects of pre-wilting Bana grass (Pennisetum purpureum x P. americanum) herbage under sunny conditions for 0, 6, 18, 24, 32 and 48 h and ensiling it with maize meal. Four levels of maize meal (viz., 0, 5, 10 and 15% on fresh weight (Fw) basis) were tested. The experiment had a split-plot design. Wilting increased the concentration of water soluble carbohydrates (WSC) significantly (p<0.001) on a Fw basis, although there were no significant changes on DM basis. Unwilted grass contained 36.1 g·WSC·kg-1·Fw (127.6 g·kg-1·DM) and this increased to 64.1 g·WSC·kg-1·Fw (116.7 g·kg-1·DM) after 48 h of pre-wilting. Wilting also increased the DM content of herbage significantly (p>0.001) from 250 to 620 g·kg-1, between 0 and 48 h respectively. The concentration of fermentation end-products decreased (except butyric acid) and pH increased when the period of wilting increased, indicating that fermentation was restricted. In particular, lactic acid content declined from 50.8 to 26.2 g·kg-1·DM (p<0.01) and the residual WSC contents of silage increased from 2.7 with fresh herbage to 18.1 g·kg-1·DM with 48 h of wilting (p<0.001). Rapid wilting for 24 h, to a DM of 450 g·kg-1 was optimum since important increases in pH, residual WSC and DMD occurred at this level of wilting. Acetic acid, butyric acid and ammoniacal-N contents were lowest with 24 h of wilting. There were no significant interactions between length of wilting and the incorporation of maize meal. Wilting had a greater influence on fermentation than the incorporation of maize meal. Addition of maize meal facilitated fermentation by increasing forage DM content and reducing effluent production. In addition, the maize meal increased DMD. It was concluded that maize meal should generally be incorporated at a level of 5% on fresh weight basis.