Results and Discussion
Performance data are presented in Table 2. In Period 1, ADG was greatest (P < 0.01) for steers in the AL feeding regimen and was greater (P < 0.02) for steers fed the CS versus PI diet. Daily DMI was similar (P = 0.15) between steers in the AL and CS feeding regimens, and both were greater (P < 0.01) than that for steers in the PI feeding regimen. Feed efficiency in Period 1 was similar (P > 0.26) for steers fed the CS and PI diets. Similar feed efficiencies between steers consuming corn silage-based versus corn-based diets do not agree with previous research (Glimp et al., 1989; Loerch, 1990; DiCostanza et al., 1998). Loerch (1990) observed superior feed efficiency by steers fed a high moisture corn-based diet compared with those fed a corn silage-based diet. In Period 2, ADG was not affected (P = 0.22) by diet. Similar ADG between steers fed the AL diet and those fed the PI diet in this period does not agree with similar experiments in which ADG was greater for steers in the PI versus AL feeding regimen (Knoblich et al., 1997; Loerch and Fluharty, 1998; Rossi et al., 2000). Daily DMI was greater (P < 0.01) for steers in the CS feeding regimen compared with steers in the AL and PI feeding regimens. Animals can compensate for lower energy intake of roughage-based versus concentrate-based diets by increasing DMI of the roughage-based diets (Smith et al., 1984; Glimp et al., 1989; Hill et al., 1996). However, when compared with steers in the AL feeding regimen, steers in the CS feeding regimen did not increase DMI to compensate for lower energy intake in Period 1, but appeared to compensate in Period 2 by consuming more DM than steers in the AL regimen. DiCostanza et al. (1998) did not observe a difference in DMI among diets consisting of 12, 24, or 36% corn silage. In the current experiment, feed efficiency was increased (P < 0.02) 9.3 and 14.9% in Period 2 for steers in the PI feeding regimen compared with steers in the AL or CS feeding regimens, respectively. Consistent with Period 1, feed efficiency was not different (P > 0.26) between steers consuming the AL or CS diets. In Period 3, ADG was not affected by feeding regimen (P = 0.16), although there was a trend for higher ADG for steers in the PI regimen. In Period 3, daily DMI was much greater (P < 0.02) for steers in the PI feeding regimen vs steers in the AL and CS regimens. Steers in the PI feeding regimen were offered feed ad libitum in Period 3. Feed efficiency was similar among feeding regimens (P = 0.80), which is inconsistent with results of previous prescription intake studies (Knoblich et al., 1997; Rossi et al., 2000). Overall ADG was not affected (P = 0.41) by feeding regimen. Overall feed efficiency was reduced by approximately 9% (P < 0.10) for steers in the CS feeding regimen compared with steers in the PI and AL regimens. Total DMI was approximately 14% greater (P < 0.02) for steers in the CS feeding regimen compared with those in the Al and PI regimens. Corn silage would have to be priced approximately 22% lower than corn to offset the costs of additional feed consumed by steers in the CS feeding regimen compared with steers in the AL and PI regimens (assuming costs per lb of feed on an as-fed basis = $0.035, $0.013, and $0.11 for corn, corn silage, and supplement, respectively). Feeding roughage-based diets in the early finishing period may allow the flexibility of using more roughage when grain prices are high relative to forage.
Carcass characteristics are presented in Table 3. Steers in the PI feeding regimen had a lower (P = 0.06) average hot carcass weight compared with steers in the AL and CS feeding regimens. Likewise, steers in the PI feeding regimen had a lower (P < 0.03) average dressing percentage compared with steers in the AL and CS feeding regimens. Similar differences in carcass characteristics between steers fed using an AL versus a PI feeding regimen have been observed in other experiments (Rossi et al., 2000). Varying the proportion of dietary corn silage has resulted in few differences in carcass characteristics (Loerch, 1990; DiCostanza et al., 1998).