The effects of wilting grass before ensiling on silage intake

Herbage, predominantly perennial ryegrass (Lolium perenne) grown in Northern Ireland, was harvested at four dates from June to October 1996 (H1, H2, H3 and H4). At each harvest approximately one-fifth of the grass harvested was artificially dried and pelleted (G). The remainder of the grass was either wilted for 28-52 h (W), depending on the weather conditions, or ensiled directly, i.e. unwilled (UW). Within the W and UW treatments an inoculant or formic acid additive was applied to the herbage before ensiling. After a minimum ensiling period of 10 weeks, sixty steers, mean initial live weight 432 (s.d. 37) kg, were offered the twenty forages in a four-period partially balanced changeover design experiment. Each period was of 2 weeks' duration. Dry-matter (DM) intakes were recorded daily, with intakes in the second week of each period used in the statistical analysis of the data. The digestibility of each of the forages was also determined in vivo using four castrated male sheep per silage. Wilting increased the DM content of the silage and the pH, the largest increase in DM content occurring at the second harvest. On average, wilting proportionally increased silage DM intake by 0.21 compared with the unwilled silage (P < 0.001), but the intake of the wilted silage was not significantly different from that of the artificially dried and pelleted grass (P > 0.05). The intake of the wilted silage was higher than that of the unwilled silage at each harvest, the proportional increases being 0.22 (P < 0.001), 0.41 (P < 0.001), 0.19 (P < 0.001) and 0.05 (P > 0.05) at harvests H1, H2, H3 and H4 respectively. Treatment of the grass with formic acid before ensiling resulted in a proportional increase in silage intake of 0.08 compared with the inoculant-treated silage (P < 0.05). Compared with the inoculant-treated silage, formic acid increased silage intake by 0.08, 0.02, 0.14 and 0.10 at harvests H1 (P > 0.05), H2 (P > 0.05), H3 (P < 0.01) and H4 (P < 0.05). The results of this study indicate that the effect of wilting on silage intake varies across different harvests and additive treatments. The difference in response to wilting across different harvests is mainly a result of the prevailing weather conditions during wilting.