GRASS-SILAGE AS A BASIC FEED FOR STORE LAMBS .1. EFFECT OF WILTING, CHOP LENGTH AND STAGE OF MATURITY OF GRASS-SILAGE ON INTAKE AND PERFORMANCE OF STORE LAMBS

Two experiments were carried out with grass silages cut at a leafy (Ex periment 1) and a more mature (Experiment 2) stage of growth to evalua te the effect of wilting and chop length on silage intake and performa nce of store lambs. In each experiment, the herbage was cut with a rot ary mower and was either ensiled within 24 h as unwilted silage (U) or wilted for 1-3 d (W). Each silage type was harvested with either a do uble-chop harvester (D) or a precision-chop harvester (P). All silages were treated with formic acid at 3 1 t(-1) and were well preserved. T he silages were fed ad libitum to Suffolk crossbred store lambs (twent y-four lambs per treatment) without any supplement over a period of 8 or 9 weeks. Wilting of the silages had little effect on silage intake (797 vs. 809g dry matter (DM) d(-1)) or on lamb performance in Experim ent 1. In Experiment 2, wilting of the D silage increased silage DM in take (589 vs. 534 g DM d(-1); +10%) and reduced the extent of liveweig ht losses. Wilting of the P silage reduced silage intake (770 vs. 791g DM d(-1); -3%) and reduced liveweight gains. In Experiment 1 intakes of the D silages were 650-667g DM d(-1) and just maintained lamb live weights. Intakes of the P silages were 39-49% higher than the D silage s (927-968 g DM d(-1)) and increased liveweight gains. In Experiment 2 intakes of the D silages were 534-589 g DM d(-1) and resulted in a lo ss in lamb live weight. Precision-chopping increased silage intakes by 31-48% (770-791 DM d(-1)) in Experiment 2 and improved lamb liveweigh t gains. Lamb performance was higher on the UP silage than on the WP s ilage. The rumen retention time (RRT), estimated from the rumen conten ts of the lambs at slaughter and their silage intake before slaughter, was much shorter for the lambs fed on the P silages (12.6-20.6 h) tha n those fed on the D silages (21.4-29.3 h) in each experiment. Silage intake and liveweight gain were positively related to silage in vivo D M digestibility (DMD), whereas RRT was negatively related to DMD. Howe ver, there were distinct differences between the P and D silages in th e elevation and, to a lesser extent, in the slope of the regression li nes, indicating that intake of D silage was limited by factors other t han the digestibility of the silage. The results of this study show th at the chop length of grass silage had a far greater effect on intake and on lamb performance than silage digestibility, whereas wilting had little or no effect.