The objective of this trial was to evaluate the partial replacement of ground corn with soybean hulls or corn germ meal on ruminal microbial protein synthesis and efficiency and ruminal dilution and passage rates. Three crossbreed steers fitted with ruminal and duodenal cannulas were assigned to two 3 x 3 Latin squares. The experimental diets contained: corn silage (60%), sunflower meal and ground corn (GC diet) that was partially replaced with soybean hulls (SBH diet) or corn germ meal (CGM diet). Ruminal fluid was collected at 3, 6, 9, and 12 hours after feeding for isolation of ruminal microbes. RNA was used as the microbial marker while sodium dicromate and Co-EDTA were used as passage and dilution rate markers, respectively. Ruminal microbial composition was not affected by diets and time after feeding in the present trial. Moreover, duodenal flows of organic matter, total carbohydrates, nitrogen (N), and microbial N as well as microbial efficiency were all not significantly changed across diets. Fluid dilution rate also did not differ and averaged 13.4%/h among diets. Ruminal passage rate of mordant corn silage was lower and a trend for lower passage rate of sunflower meal on GC diet also was observed. Soybean hulls and corn germ meal can partially replace ground corn on diets for confined steers because they provided adequate ruminal environment for microbial growth and microbial protein synthesis.
corn germ meal; dilution rate; ruminal microbial; passage rate; soybean hulls
