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RésuméLes effets du remplacement du lait écrémé de l'aliment d'allaitement par des concentrés protéiques de

(fig. 1). The apparent digestibility of each diet decreased when that diet was infused into the duodenum at the gastric emptying rate of its protein (slow infusion of the control diet, quick infusion of the fish diet) (table 2) ; infusion at a higher rate (quick infusion of the control diet) increased this effect, while infusion at a lower rate (slow infusion of the fish diet) suppressed it. This decrease in apparent digestibility was more marked for lipid and minerals than for protein.The slow infusion of the fish diet had little effect on faecal amino acid composition (table 4). On the other hand, rapid infusion of the control diet seemed to cause a decrease in the relative proportion of microbial protein in favour of some milk protein fractions (serine and glutamic acid-rich phosphopeptides of 1X' 1' ag 2 and caseins).Blood free amino acid levels, measured during simulation of the gastric emptying of each diet, were similar to those observed during ingestion (table 5). These levels were higher when both diets were infused quickly than when they were infused slowly.In conclusion, the digestion of protein, and especially that of lipid and minerals, as well as the metabolic utilization of amino acids, is highly influenced by the time spent in the abomasum and by the rate of arrival in the duodenum.Introduction.

Summary. The aim of this trial was to study the balance of the amino acid digestion of milk and of methanol-grown bacteria in the terminal small intestine and the hindgut of the preruminant calf. Two diets (control and bacteria) were used. The protein of the control diet was furnished exclusively by skim-milk powder ; 50.5 p. 100 of the protein of the bacteria diet was supplied by methanol-grown bacteria, and the rest by skim-milk powder and synthetic amino acids.Except for methionine, the apparent digestibility of all the amino acids assayed was lower in the terminal small intestine than in the whole digestive tract but the differences were usually less than for total nitrogen (table 5). The largest difference concerned cystine whose apparent digestibility increased from 76 p. 100 in the terminal ileum to 87 p. 100 in the faeces for the control diet, the corresponding values for the bacteria diet being 64 and 79 p. 100. The diaminopimelic acid of dietary bacteria did not seem to be absorbed in the small intestine but large quantities disappeared in the large intestine (table 7). Amino acid digestibility was higher for the milk than for the dietary bacteria, except for threonine and glycine in the terminal ileum and glycine and alanine in the faeces (table 5).The ileal digesta were richer than the faeces in threonine, serine, proline and cystine and were poorer in methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine and arginine (tables 2 and 3). These differences might result from a larger proportion of endogenous protein and a lower amount of gut bacteria protein in the digesta, which also contained more dietary protein than the faeces, at least with the bacteria diet, as shown by the quantities of diaminopimelic acid found with that diet. The respective proportions of dietary, endogenous and gut microbial proteins estimated in the terminal ileum were 16, 71 and 13 p. 100, respectively, with the control diet.The lower digestibility of nitrogen from methanol-grown bacteria seemed due mostly to bacterial wall protein (especially peptidoglycan) resistance to digestion in the small intestine (table 3). However, the differences as compared to milk protein were small ; they did not permit us to show the unavailability of any particular amino acid (except for diaminopimelic acid) at the digestive or the metabolic level.Introduction.

Résumé ― Trois laits de remplacement (témoin, pois et soja) sont distribués à 6 veaux préruminants munis d'une canule réentrante à la fin de l'iléon. Dans l'aliment témoin, les protéines sont fournies presque exclusivement par de la poudre de lait écrémé. Dans l'aliment pois, 33 (Table I). In the control diet, protein was almost entirely provided by skim-milk powder. In the pea diet, a pregelatinized dehulled pea flour provided 33.5% of the protein, the remainder being supplied by skim-milk powder. In the soya-bean diet 73.2% of the protein were provided by a soya-bean isolate and the remainder by whey powder. The apparent digestibility of total nitrogen was significantly lower with the pea and soya-bean diets than with the control diet (0.92, 0.91 and 0.95 at the end of the ileum, 0.92, 0.94 and 0.97 at the end of the whole digestive tract, respectively). Also the ileal digestibility of most amino acids decreased with the pea and soya-bean diets; the differences were greatest for cystine (-0,06; non significant) with the pea diet and for threonine (-0.07; P < 0.01) with the soya-bean diet. Irrespective of the diet the protein escaping digestion in the small intestine appeared to be mainly from endogenous and bacterial origin. Although small amounts of partially degraded dietary protein could be present in ileal digesta with the pea and soya-bean diets, their true digestibility was probably very high.proteins -digestion -ileum -preruminant calf