Composition and Intestinal Digestibility of Rumen Fermented Feeds and Duodenal Digesta in Cows Using Bag Techniques

¹ Animal and Dairy Science Research Institute, Private Bag X2, Irene, 1675, Republic of South Africa
² Institut Für Tierenährung/FAL, Bundesaliee 50, D-3300 Braunschweig, Germany
³ Department of Livestock Science, University of Pretoria, Pretoria, 0002, Republic of South Africa

Three rumen-cannulated and five duodenal-cannulated lactating Holstein cows were used to compare the chemical composition and undegraded dietary protein digestibility of unfermented feedstuffs isolated in two different ways, from polyester bags (in situ rumen-fermented and in vitro pepsin-digested) or from duodenal-collected digesta, respectively. There was a good resemblance between the chemical composition of unfermented feedstuffs isolated from polyester bags and duodenal digesta, irrespective of whether a complete or hay diet was fed. Using the polyester bag isolated undegraded dietary protein and mobile bag for intestinal digestion, the digestibility of this fraction ranged from 36.6 to 37.9% for the hay diet and from 64.5 to 65.2% for the complete diet. The corresponding values for duodenal-collected digesta were 42.6 to 43.2% and 56.5 to 56.9% for the hay and complete diets, respectively. The results suggest that the factor for undegraded dietary protein digestibility used by some of the new protein evaluation systems is too high.

Key Words: mobile bag technique • undegraded dietary protein • digestibility

Submitted on October 10, 1989
Accepted on May 29, 1990