ABSTRACT
Sixty-four Holstein steers (247 ± 4 kg) were used in
a 70-d experiment to evaluate the effects of partial replacement of steam flake
corn (SFC) with extruded corn meal (EC) on growth performance and
dietary net energy. Treatments consisted of a steam flaked corn-based finishing
diet containing 0%, 10%, 20%, or 30% EC, where EC replaced 0%, 15%, 30%, or 45%
of SFC (DM basis). Replacement of SFC with increasing levels of EC did not
affect (P > 0.10) ADG, DMI, and gain efficiency. When EC replaced 15% to 30% of SFC, observed dietary NE was 99%
of expected. Whereas, when EC replaced 45% of SFC, observed dietary NE was 94% of expected. Four
Holstein steers (210 ± 7 kg) with cannulas in the
rumen and proximal duodenum were used in a 4 × 4 Latin square experiment to
evaluate treatment effects on characteristics of digestion. Partial replacement
of SFC with EC did not affect (P >
0.10) flow of undegraded feed N and microbial N and to the small intestine, and ruminal microbial N
efficiency (g microbial N/kg OM fermented). Likewise, there were no treatment
effects (P > 0.10) on ruminal
digestion of OM, NDF, starch and feed N. As expected, total tract digestion of
starch for all treatments exceeded 99%. However, partial replacement of SFC with
EC decreased total tract digestion of DM and OM (linear effect, P = 0.02), and dietary DE (linear
effect, P = 0.03). These effects were
more pronounced where EC replaced 45% of SFC. Partial replacement of SFC with
EC did not affect (P > 0.10)
ruminal pH, total VFA concentration, molar proportions of acetate, propionate,
and butyrate, and estimated methane production. It is concluded that partial
replacement of SFC with EC does not have a beneficial effect on ruminal
microbial efficiency and digestive function. The feeding value of extruded corn
for feedlot cattle is comparable to that of steam flaked corn provided the
inclusion rate does not exceed 20% of diet dry matter.