S. L. Callison*, J. L. Firkins1*, and B. L. Hull#
*The Ohio State University Department of Animal Sciences
#The Ohio State University Department of Veterinary Clinical Sciences
Five first-lactation cows were cannulated in the rumen, duodenum, and ileum and fed diets containing 50% alfalfa silage and 36.6% coarse, medium, or fine ground corn (CGC, MGC, and FGC, respectively), steam-rolled corn (SRC), or a 50:50 mix of CGC and SRC (SC). The corn had a mean particle size of 4.75, 2.56, or 1.15 mm for CGC, MGC, and FGC, respectively, as evaluated by dry sieving and log-normal transformation procedures. The SC had a density of 41 lb/bu (as-is basis).
Finely grinding corn disrupted the corn kernel, considerably increasing nonstructural carbohydrate (NSC; enzymatic assay) digestibility in the rumen (about 40 percentage units; true basis, i.e., corrected for bacterial NSC flow to the duodenum); however, a relatively small increase in total tract digestibility of NSC was noted. Despite the large effect on starch digestibility, ruminal digestibility of neutral detergent fiber (NDF) was not affected as much, resulting in a small but significant shift in NDF digestion from the rumen to the large intestine. Addition of SRC to CGC linearly increased true NSC digestibility in the rumen (about 18 percentage units) but also had much smaller effects on total tract digestibility. Our results show that, although causing large changes in ruminal NSC digestibility, fine-grinding or steam-processing of corn may have only a modest impact on total tract digestibility. Based on this study and others, corn should be steam-rolled to densities less than 41 lb/bu for maximal effectiveness.
1 For more information, contact at: The Ohio State University, 223 Animal Science Building, 2029 Fyffe Road, Columbus, OH 43210, 614-688-3089, Fax 614-292-1515, e-mail: firkins.1@osu.edu