Effect of maceration at mowing on silage conservation, voluntary intake, digestibility and growth rate of steers fed precision chopped or round bale silages

Four silages were made from the primary growth of an orchardgrass (Dactylis glomerata)/white clover (Trifolium repens) sward in mid-June. Precision ch opped (PC) and round bale (RB) silages were made from wilted forage that ha d been cut either with a regular mower conditioner (CON) or a mower macerat or (MAC). Silages were fed to growing steers in a 10-wk feeding trial using a 2 x 2 factorial design. To determine apparent digestibility, silages wer e fed to wether sheep and ruminally incubated in nylon bags using two canul ated cows. The DM concentration of silages ranged between 273 and 362 g kg( -1) and was higher in RE than PC silage. Maceration increased fibre concent ration in RE silage but had little influence on PC silage. Nitrogen and its fractions were not influenced by treatment. Maceration increased total aci d concentration in PC silages but lowered it in RE silage. Lactic acid acco unted for a higher proportion of total acids in macerated silages than in c ontrol silages. Steers fed RE silage consumed 35% more DM than those fed PC silage (P < 0.001). Maceration reduced intake of PC silage by 18% but did not affect intake of RE silage (interaction; P < 0.05). Maceration had no e ffect on BW gain in steers fed PC silage, but in RE silage gains were incre ased from 0.87 kg d(-1) to 1.09 kg d(-1) (interaction; P < 0.05). Feed util ization efficiency was poorer for RE than PC silage (P < 0.001) and macerat ion improved feed utilization (P < 0.001). The DM, OM and NDF digestibility coefficients were reduced by maceration in RE but not in PC silage (intera ction; P < 0.05); a similar trend was observed for ADF (interaction; P < 0. 10). Apparent N digestibility was less in MAC than CON silage (P < 0.01). D ry matter disappearance from nylon bags was not influenced by maceration in PC silage but was higher in RE-MAC than RE-CON silage. It is concluded tha t influences of maceration on intake and gain is dependent upon the physica l form of the silage.