Nutrient digestion in the large intestine as influenced by forage to concentrate ratio and forage physical form.

Digestion in the large intestine was investigated in four growing steers fitted with duodenal and ileal cannulas. Diets assigned within a 4 x 4 Latin square were: 20% long alfalfa hay and 80% grain; 15% pelleted alfalfa, 5% hay, and 80% grain; 80% hay and 20% grain; and 60% pellets, 20% hay, and 20% grain. Intake of DM was not affected by diet. Organic matter digestion in the large intestine averaged 9, 3, 1, and -4% of total tract digestion for the 20% hay, 20% pellet, 80% hay, and 80% pellet diets, respectively, with significant increases due to high grain diets and long hay. Digestion of CP in the large intestine as a percentage of total tract digestion was unaffected by diet but averaged 3, -1, .3, and -6% for the respective diets. Percentage of total tract starch digestion occurring in the large intestine increased with grain feeding and averaged 6, 3, 1, and 1%, respectively. Digestion of ADF and NDF in the large intestine as a percentage of total tract was unaffected by diet; however, the respective means were 16 and 15, 7 and 7, 5 and 15, and 1 and 1%. In a second trail the same animals were fed a more typical dairy cow diet consisting of 50% grain, 25% corn silage, and 25% long alfalfa hay for a single 18-d period. Digestion in the large intestine accounted for 2.1, .2, 3.6, and 6.4% of total tract digestion of organic matter, starch, ADF, and NDF, respectively; however, feed intake was not as great as in the first trail. Although conditions of these studies differed from those commonly experienced by lactating cows, the underlying principals should apply. The large intestine would be expected to make an even greater contribution to total tract digestion in lactating cows consuming proportionally more DM.