Ruminal Fermentation and Intestinal Flow of Nutrients by Lactating Cows Consuming Brown Midrib Corn Silages

¹ Department of Animal and Avian Sciences, University of Maryland, College Park, MD 20742
² Animal Manure and Byproducts Laboratory, Livestock and Poultry Sciences Institute, Agricultural Research Service, USDA, Beltsville, MD 20705

Rumen characteristics and digestive kinetics of brown midrib corn silage were evaluated with five late-lactation (221 DIM ± 20 d) multiparous cows fitted with ruminal and duodenal cannula. Dietary treatments were applied by using a single reversal design with two 21-d periods where either brown midrib (BM₃) or isogenic (ISO) corn silage were included in a total mixed ration formulated to be 40% concentrate and 60% corn silage on a dry matter (DM) basis. Rumen and total tract digestibilities of DM, organic matter, neutral detergent fiber, acid detergent fiber, starch, and N were determined and rumen characteristics evaluated. Apparent rumen DM and organic matter digestibilities were greater for the BM₃ corn silage (7.1 and 4.7 percentage units, respectively). Dietary intake and duodenal flow of starch were greater and rumen and total tract starch digestibilities were lower for BM₃ corn silage diets than ISO corn silage diets. However, more starch (1.1 kg/d) was apparently digested and absorbed postruminally in cows fed the BM₃ corn silage diets. Duodenal flow of neutral detergent fiber was 0.9 kg/d lower, and ruminal (15.9 percentage units) and total tract digestibilities (4.4 percentage units) were higher for BM₃ treatment compared with the ISO treatment. Digestive patterns of ADF were similar for the BM₃ and ISO treatments. Ruminal pH was lower in the cows fed the BM₃ corn silage than those fed the ISO corn silage. As a result of a tendency for decreased N excretion in urine and slight increases in N intake due to increased DM intake, N balance tended to be greater for the BM₃ treatment compared with the ISO treatment. These results may partially explain the benefits of feeding BM₃ corn silage to cows during early lactation, as the observed increases in fiber component digestibility and improved N economy may combine to enhance DM intake and better support the nutritional demands of milk production for the high producing dairy cow.

Key Words: Brown midrib corn silage • digestion • rumen • intestine

Submitted on January 29, 2001
Accepted on June 28, 2001

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