Published online by Cambridge University Press: 02 September 2010
Four silages were prepared from a sward of perennial ryegrass (Lolium perenne cv. Melle). Two were ensiled directly either without (UWN) or with formic acid at 31 1/t fresh material (UWA). The remaining herbage was left undisturbed in the swath for 43 h (WL) or was spread and harvested after 19 h (WS). The dry matter (DM) concentrations at harvest for the unwilted herbage were 229 (UWN) and 238 g DM per kg (UWA) and wilting increased DM concentration to a similar extent for both treatments (WS, 339 v. WL, 346 g DM per kg).
Forty British Friesian steers initially 3·5 months of age and 105 kg live weight were used for the trial. Eight steers were allocated to an initial slaughter group and the remainder were offered the four silages at a restricted level to give 940 kJ digestible energy per kg M0·75. These animals were slaughtered after 112 days to estimate the incremental increases in the components of the body.
Loss of DM in the field by respiration increased from 22·2 to 40·6 g/kg DM cut with increased length of wilting. In silo losses were greater with unwilted (UWN, 222, UWA 183 g/kg DM ensiled) than with wilted silage (WS, 133 WL, 122 g/kg DM ensiled). All silages were well preserved. Wilting was more effective than formic acid in reducing total fermentation acids but a lower proportion of these acids was in the form of lactic acid.
Live-weight gain was lower for the steers given the control (UWN) silage (398 g/day) than for those given silages UWA (463 g/day), WS (476 g/day) and WL (470 g/day). However, a lower proportion of the gain by steers given UWN was in the form of gut contents so that gains in fat, protein and energy were not significantly affected by treatment. In conclusion, when steers were given similar amounts of digestible energy and unwilted silage was well preserved, neither the use of formic acid nor wilting influenced gains in protein and energy. Further, the duration of wilting, in the absence of any differences in DM content, had no effect on animal performance.