You are correct. If you maximize rumen fermentation and microbial yield, additional starch would be digested in the small intestine (estimated to be about 1 kg for a lactating cow). However, any amount above rumen and small intestine digestion would be lost in the feces or fermented in the large intestine (not as beneficial as in the rumen or small intestine). Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET In my opinion, the degree of processing to be used on any single operation depends on the percentage of corn or nonstructural carbohydrates (NSC) in the ration. If the ration is already very high in NSC, then cracking might be beneficial to tone down the fermentability in the rumen. High fermentability can lead to depressed dry matter intake or increased incidence of subclinical acidosis. When corn prices increase relative to other by-products such as distillers grains, lower NSC diets could achieve more energy from grinding the corn grain. There is a lot of compensation of NSC digestion in the small and large intestines from cracking corn grain, but still, on average, you lose 5 to 10% digestibility in the total tract compared with fine grinding, which could be enough energy for up to 5 lb/day of milk (if feed intake is not changed). Shifting starch digestion to the intestines with coarse processing also could lose energy to support microbial protein production in the rumen; on the other hand, increasing starch fermentability decreases the efficiency of microbial protein production. That is, increasing the percentage of starch being digested in the rumen will increase microbial protein production but at a decreasing rate. The bottom line: with high starch diets (approaching or exceeding 30%), dairy cows might benefit from cracking instead of fine-grinding the grain. With lower starch diets (approaching or being below 25% starch), fine-grinding increases the digestibility and energy supply from the corn grain. In the latter case, I recommend grinding so that the average particle size is below 1 millimeter (1 mm = 1000 micrometers = 1000 microns). Some have found better results with even finer grinding, but that this depends on the type of corn grain (more benefit from very flinty grain types) and other considerations such as dustiness, cost of grinding, or feedbunk management issues. As always, take care to prevent subclinical acidosis or depressed intake with fine grinding. Jeff Firkins, Professor of Dairy Nutrition, Ohio State University

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