Sheep fitted with a PVC cannula in the dorsal rumen, a silastic infusion tube in the abomasum, and single 'T'-shape PVC cannulas in the proximal duodenum @I), distal duodenum (D2), mid-jejunum (J), and terminal ileum (I), were fed on diets varying in crude protein (Nx6.25) and fibre contents. Reducing the environmental burden of livestock production systems is a major objective for current nutrition research. To achieve this objective the first option is to replace the external inputs of concentrate feeds and by-products grown elsewhere by home-grown feeds of a comparable nature. If this is not a viable option, including a larger proportion of home-grown alternative feeds in the diet constitutes a second possibility. Hence, increasing the utilization of home-grown feeds has been identified as one of the keys. For ruminant production, particularly in Western Europe, this implies that a larger part of the diet should be fibrous feeds, such as grass or grass-maize silages. However, for higher levels of production, especially of milk, only part of the nutrients can be derived fiom roughages. Concentrate supplements are needed to meet energy requirements, to optimize m e n conditions and to manipulate the amount and composition of the nutrient mixture rendered available for intermediary metabolism.Livestock production systems geared towards longer-term sustainability aim at the reduction of the environmental burden in terms of nutrient losses, particularly of N and P. In other words, they aim to optimize (1) the conversion of nutrients into product and (2) the

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Intake and digestion and rate of passage kinetics were studied in 6 wether sheep fed on ammoniated wheat straw (AWS) plus pelleted sugarbeet pulp, untreated wheat straw plus sugarbeet pulp, and untreated wheat straw supplemented with urea. Ammonia treatment increased intake and whole tract digestion (rumen + small intestine + large intestine) without significantly affecting rumen pool size and rate of passage. 91% of the increased intake of cell wall material in ammonia-treated straw was due to a higher rate of degradation of cell walls in the rumen. No significant effects of ammonia treatment on concentration, molar composition or rate of absorption of volatile fatty acids were observed. The rate of passage in the large intestine and the contribution of this region to digestion were not significantly affected by ammonia treatment. Rumination and eating time and daily number of rumen contractions did not differ among diets, but AWS showed a lower rumination time/kg NDF ingested than the other 2 diets. After ammonia treatment, whole tract digestion and rumen degradation of hemicellulose increased more than those of cellulose. The effects of ammonia treatment could not be attributed to its nitrogen content since there was no effect on any parameter, except rumen ammonia-N concentration.

Summary Five sheep, fitted with a PVC cannula in the dorsal rumen, a silastic infusion tube in the abomasum, and a single T‐shape PVC cannula in the proximal duodenum (D1), distal duodenum (D2), mid‐jejunum (J) and terminal ileum (I), were fed diets, which varied in crude protein (N × 6.25) and fibre contents. A 15N labelled grass meal‐beer yeast suspension was continuously infused into the abomasum over a period of 1 week. Subsequently, over a period of 4 days, the 15N excess in D1, D2, J and I digesta was related to 15N excess in blood plasma TCA soluble N. The average daily intakes of dry matter and N were 1.02 kg and 25.9 g, respectively. Average daily endogenous N amounted to 4.3 g at D1, 11.1 g at D2, 5.9 g at J and 4.8 g at I. Corresponding percentages of total N flow were: 15.0 (D1), 33.4 (D2), 44.6 (J) and 47.0 (I), respectively. The difference between distal and proximal duodenal endogenous N flow, the jejunal endogenous N flow and the ileal endogenous N flow were positively related to the amount of N, entering the small intestine (R2 = 0.69, 0.81 and 0.63, respectively). The ileal endogenous N flow was also positively related to the small intestinal NDF/DM/non‐protein DM flow and faecal dry matter flow (R2 = 0.81, 0.62, 0.59, 0.91, respectively). The apparent re‐absorption of endogenous protein varied among experimental diets, and was on average between D2 and I 56.0%. Zusammenfassung Die Wirkung von Faser, Trockensubstanz und Protein auf die Passage von endogenem Stickstoff im Dünndarm des Schafes In Experimenten (3 times 3 und 2 times 2) an insgesamt 5 Schafen, die mit einer PVC Kanüle im dorsalen Pansen, einem Labmagenkatheter und mit T‐formigen PVC Kanülen am proximalen Duodenum (D1), distalen Duodenum (D2), mittlerem Jejunum (J) und terminalen Ileum (I) sowie mit einem Katheter in der V. jugularis ausgerüstet waren, wurden Rationen eingesetzt, deren Faser‐ und Rohproteingehalt variierte. In der Tagesration waren 668–1193 g DM, 150–676 g NDF und 22–32 g N enthalten. Die Tiere wurden durch eine 7tägige intraabomasale Infusion einer Mischung von 15N‐Gras und 15N‐Hefe mit 15N markiert. 14 h nach Beendigung der Infusion wurde über eine Periode von 4 Tagen die 15N‐Anreicherung in der Digesta von D1, D2, J und I gemessen und mit der 15N‐Anreicherung in der TCA‐löslichen N‐Fraktion des Blutplasmas in Beziehung gesetzt. Die durchschnittliche tägliche Menge an endogenem N (Ne) belief sich von D1 bis I auf 4.3, 11.1, 5.9 und 4.8g. Das entsprach 15.0, 33.4, 44.6 und 47.0% der Passage an Gesamt‐N. Die Differenz im Fluß an Ne zwischen distalem und proximalem Duodenum sowie der Fluß von Ne am Jejunum und Ileum war positiv mit der N‐Passage an D1 korreliert (R2 = 0.69, 0.81 und 0.63). Der ileale Fluß von Ne war positiv korreliert mit der ilealen Passage von NDF, DM, und Nicht‐Protein‐DM sowie der DM‐Ausscheidung im Kot (R2 = 0.81, 0.62, 0.59 und 0.91). Die scheinbare Re‐Absorption von Ne varierte zwischen den Rationen. Im Durchschnitt wurden zwischen D2 und I 56% des Ne reabsorbiert. Es wird gefolgert, daß erhebl...