Density of steam-flaked sorghum grain, roughage level, and feeding regimen for feedlot steers.

Two hundred fifty-two steers (366 kg) were assigned to a 3 x 2 x 2 factorial arrangement of three densities of steam-flaked sorghum grain (bulk [flake] density of 437, 360, and 283 g/liter, B34, B28, and B22, respectively), two roughage levels (9 [R9] and 18% [R18]) and two feeding strategies (ad libitum [AD] or multiple of maintenance [MM], 2.3, 2.5, and 2.7 MM for wk 1, 2, and 3, and 2.9 MM thereafter). Steers fed R18-AD gained faster than steers fed R18-MM (1.59 vs 1.52 kg/d, P = .10); for R9 diets, no difference (P greater than .25) was found between steers fed AD and MM (interaction, P = .07). Flake density did not affect ADG (1.53 kg, P greater than .2). Dry matter intake decreased (9.8, 9.3, and 9.0 kg/d, linear, P less than .001) and gain efficiency (G/DMI, kg of gain/100 kg of DMI) increased (15.7, 16.5, and 16.9, linear, P less than .001; quadratic, P = .19) as processing degree increased (B34 to B22). Percentage of choice carcasses for B34 (67.0%) was higher (linear, P = .05) than for B28 (51.9%) and B22 (52.3%). Fecal starch and pH were 10.8, 5.7, and 4.0%, and 6.11, 6.23, and 6.37 for B34, B28, and B22, respectively (linear, P less than .001). The correlation between fecal starch and pH was -.51 (P less than .001, n = 252). Enzymatic glucose release, in vitro 6-h gas production, microbial protein synthesis, and protein degradability were 375, 483, and 559 mg/g; 24.7, 28.2, and 31.1 ml/.2 g; 6.15, 6.88, and 7.84 g/100g; and 61.4, 56.6, and 42.2% for B34, B28, and B22, respectively (linear, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)