Ensilage from alkali-treated roughages

Abstract

Three experiments examined the chemical properties and digestibility of silage made from ground wheaten straws and a ground mature legume hay treated with alkali, the effects of type and concentration of alkali, heating during the initial alkali-reaction phase, and the effect of a grain supplement on initiation and maintenance of fermentation. All silages opened in good condition. Initial (1 1/2 hour) pH values for alkali-treated silages were high : 5% NaOH, 11.5; 1.25% NaOH, 9.1 ; 1.25% NH4OH, 9.8 c.f. 6.9 for non-alkali control silages. Final (day 41) pH values for the 4% and 5% NaOH treatment ranged from 6.24-4.86. Inclusion of grain at the start of the process generally favoured early decline in pH values at 70 hours, but had no marked effect on the resultant product at 41 days. Inclusion of grain did not appear to be warranted since, in experiment 1, substantial quantities of acetic acid (0.73-2.33 g 100 g-1 silage DM) and of lactic acid (1.08-1.50 g 100 g-1 silage DM) as well as some propionic acid were found in alkali-treated roughage ensiled alone. These values were greater than for control (no alkali) silages not receiving grain, and indicate that alkali solubilization of hemicellulose occurred, with subsequent fermentation. Alkali treatment increased the digestibility of wheat straws by 60 to 80%; but it did not alter that of alkali-treated mature siratro hay. NH4OH was less effective than NaOH in increasing silage dry matter digestibility. It was concluded that potentially useful silage can be formed from alkali-treated roughages despite the initial highly alkaline environment. The results indicate that neither heating during the main alkali reaction phase nor the inclusion of grain are necessary, either for the initiation of useful fermentation or for the formation of a useful product.