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Studies on N-metabolism in different gastrointestinal sections of sheep using the digesta exchange technique. 2. Passage of endogenous nitrogen

A. Sandek 1,  
J. Kowalczyk 3,  
M. Gabel 1,  
T. Żebrowska 3,  
Institute for Ecological-Compatible Animal Husbandry, University of Rostock, Justus-von-Liebig-Weg 8, 18059 Rostock, Germany
Institute for Applied Agroecology, Justus-von-Liebig-Weg 8, 18059 Rostock, Germany
The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, 05-110 Jabłonna, Poland
Research Institute for the Biology of Farm Animals, Research Unit Nutritional Physiology "Oskar Kellner", Wilhelm-Stahl-Allee 2,18196 Dummerstorf, Germany
J. Anim. Feed Sci. 2001;10(4):605–618
Publish date: 2001-11-06
Using a combination of fistulation and the 15N isotope technique, the flow rates of endogenous N secreted postruminal into different sections of the digestive tract were estimated in growing sheep by digesta exchange between 15N-labelled and unlabelled animals. To investigate the influence of fibre (CF) on these flow rates the estimations were made on two groups that received approximately isonitrogenous diets (16% CP in DM) differing in crude fibre content (Group 1: 14.7%, Group 2: 24.9% CF in DM). The passage rates of total N and 15N at the duodenum and ileum and the excretion in faeces were measured directly. These data were used to calculate the passage of postruminal N secreted in the different intestinal sections. The microbial N passage at the proximal duodenum and distal ileum was calculated as the product of RNA passage at the duodenum and ileum, and the N:RNA ratio of bacteria isolated from rumen fluid. The flow rates of endogenous N into the duodenum and through the ileum and the excretion rate in faeces were estimated by measuring the appearance and disappearance rates of 15N in appropriate intestinal sections of the unlabelled animals receiving 15N-labelled digesta or in the labelled animals getting unlabelled digesta by digesta exchange. The microbial flow rate through the duodenum was in average 5.8 g N/d in Group 1 and 5.1 g N/d in Group 2 (50 and 46% of NAN flux), and 0.9 g N/d (Group 1) to 1.3 g N/d (Group 2) through the ileum (19 and 22 % of NAN flux). The portion of rumen undegraded protein-N of NAN flow was in Group 1 47% both in the duodenum and in the ileum. In Group 2 it was 42% . The endogenous NAN entering the duodenum was low for Group 1 (0.40 g N/d = 3.4% of NAN) and approximately three-fold higher for Group 2 (1.3 g N/d = 12% of NAN). The corresponding values for endogenous N at the ileum were 1.6 g/d (34% of NAN) and 2.2 g/d (36% of NAN) , indicating that in relative terms, endogenous N secretion in this section of the digestive tract was independent of the feeding regime. The excretion rate of endogenous N in faeces varied between the individual experiments (1.84 to 2.39 g N/d for Group 1; 1.54 to 2.00 g N/d for Group 2). In relation to total faecal N excretion the endogenous fraction was higher for Group 1 (56%) than for Group 2 (40%). During all of the experiments, endogenous N as a proportion of total N increased from the duodenum to the rectum. Despite some reservations about the 15N dilution method, its use together with the technique of digesta exchange between labelled and unlabelled animals is a potentially useful way to quantify the passage of postruminal secreted N in dependence of nutritional factors. Further studies are needed to refine the methodology.
J. Voigt
Research Institute for the Biology of Farm Animals, Research Unit Nutritional Physiology "Oskar Kellner", Wilhelm-Stahl-Allee 2,18196 Dummerstorf, Germany
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