Prediction of silage feeding value from the analysis of the herbage at ensiling and effects of nitrogen fertilizer, date of harvest and additive treatment on grass silage composition

The prediction of silage feeding value from the analysis of herbage at ensi ling and the effects of rate of nitrogen (N) fertilizer, date of harvest an d treatment additive at ensiling on fermentation, dry matter (DM) recovery and effluent production were evaluated in a factorial experiment. Herbage w as harvested from 75 plots. laid out in three replicate blocks of 25, from the primary growth of a predominantly perennial ryegrass sward. The plots r eceived 72, 96, 120, 144 or 168 kg N/ha and were harvested on 10, 17, 24 or 31 May or 7 June. Herbage was ensiled for 176 days in laboratory silos (6 kg capacity), either untreated or treated with formic acid or a bacterial i noculant, each applied at 3 ml/kg herbage. Increasing the rate of N fertili zer and delaying harvest date increased herbage DM yield but decreased sila ge digestible organic matter digestibility (D-value) and intake potential ( P < 0001). Increasing the rate of N fertilizer increased crude protein (CP), acid inso luble N (AIN) (P < 0.001) acid detergent fibre (ADF) (P < 0.01) and acid de tergent lignin (ADL) concentrations but had no statistically significant ef fect (P > 0.05) on pH or the concentrations of ammonia N, lactic or volatil e fatty acids. Delaying harvesting date decreased CP, AIN and ADF concentra tions (P < 0001) and effluent DM losses (P < 0.001). Treatment with either formic acid or inoculant decreased silage pH and the concentrations of ammo nia N, acetic acid and propanol and increased AIN, ethanol, neutral deterge nt fibre (NDF), ADF and cellulose concentrations, effluent volume, DM losse s and intake potential. Formic acid treatment decreased D-value (P < 0.001) whereas inoculant treatment was not statistically significant (P < 0.05). For potential silage and metabolizable energy (ME) intakes and D-value. str ong positive correlations (P < 0.001) were identified with herbage pH, buff ering capacity and concentrations of CP, AIN, true protein nitrogen (TP), w hile negative correlations (P < 0.001) were identified with herbage yield a nd concentrations of NDF and hemicellulose. With untreated silages, strong positive correlations (P < 0.001) were identified between silage pH and her bage pH and concentrations of AIN, buffering capacity, ash, TP and negative correlations (P < 0.001) were identified with herbage DM yield and concent rations of DM and WSC. Herbage yield and concentrations of NDF, TP, DM and nitrate N provided the best linear relationship for predicting potential ME intake of the resultant untreated silages (R-2 = 0.94). It is concluded th at delaying harvest date had the most detrimental effect on silage feeding value, although this effect was partially overcome by reducing the rate of fertilizer N and use of either an inoculant or formic acid additive. Silage feed value was also highly correlated with the protein and fibre fractions , ash, buffering capacity and pH of the herbage at ensiling.