Secretion and reabsorption of endogenous protein along the small intestine of sheep: estimates derived from¹⁵N dilution of plasma non-protein-N

Abstract

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

Studies on N-metabolism in different gastrointestinal sections of sheep using the digesta exchange technique. 3. N secretion and reabsorption

“…The above reabsorption values are considerably higher than those observed by Voigt et al (1996) and Van Bruchem et al (1997) for protein N in the intestinal section between the duodenum and the ileum. These authors found average values of 50%).…”

“…Kay (1969) also determined a similar N secretion (7 g/d) using isolated intestinal loops of sheep. In mul-tiply fistulated nearly adult sheep Voigt et al (1996) and Van Bruchem et al (1997) found higher secretion of protein-N (14 and 17 g/d). As to the metabolic weight the mean value of our study (0.67 g N/kg BM°7 5 ) was identical with that reported by Voigt et al (1996) and only somewhat lower than the results of Van Bruchem et al (1997) (0.83 g N/kg BW 0 75 ).…”

“…LammersWienhoven et al(1998) also found an enhanced N secretion by increase of fibre passage through the small intestine too. Voigt et al (1996) and Van Bruchem et al (1997) demonstrated a high correlation between the passage rate of ileal NDF and that of ileal endogenous protein N in sheep. Furthermore, Van Bruchem et al (1989) reported that the passage of non-protein dry matter through the small intestine strongly influenced endogenous protein release in the small intestine.…”

“…Combination of the ,5 N dilution technique with multiple fistulation of animals also enables the determination of N secretion. Van Bruchem et al (1997) measured the entry of 15 N into the intestinal lumen at different positions after labelling the metabolic pool of sheep with 15 N amino acids. Other authors substituted digesta of 15 N labelled animals with pre-collected unlabelled digesta and studied the level of its labelling (Bergner etal, 1985;Siddonsetal, 1985;Sommeretal., 1986).…”

Modelling endogenous leucine flows at the jejunum and ileum in lambs exposed to the intestinal parasite <i>Trichostrongylus colubriformis</i>

“…Endogenous protein secretions, plus associated losses, are an important feature of digestive tract metabolism in both ruminants (e.g., van Bruchem et al, 1997;Ouellet et al, 2002) and non-ruminants (e.g., de Lange et al, 1990;Hess et al, 1998). Various methodological and conceptual approaches have been used to quantify such secretions but the majority have considered the digestive tract as a single unit (e.g., de Lange et al, 1990), rather than a series of linked and interacting units (e.g., van Bruchem et al, 1997;Ouellet et al, 2002).…”