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I . A new in vitro method using the intestinal fluid of the pig for predicting the digestibility of diets was proposed.2. A 0.5 g sample of pig diet was placed in a IOO ml Erlenmeyer flask, 20 mg pepsin (EC 3 . 4 . 4 . I ) in 10 rnlo.075 M-hydrochloric acid was added, and the mixture was incubated for 4 h at 37". Then, after neutralization with 0.2 M-sodium hydroxide, 10 ml of intestinal fluid was added and incubated for an additional 4 h at 37". This fluid was obtained from a pig fitted with a simple cannula in the upper jejunum.After the two-stage incubations, the contents of the flask was centrifuged for 10 min at 1250 g and the residue transferred to preweighed filter paper for dry matter (DM) and crude protein (nitrogen x 6 2 5 ; CP) determinations. The in vitro DM and CP digestibility was calculated on the basis of the original DM and CP content of the diet respectively.3. The intestinal fluid could be stored at -zoo for 60 d without losing its activity on DM and CP digestion.4. A high correlation was found between this in vitro method and the standard in vivo procedures, for seven diets commonly used for growing or adult pigs, when diets were ground to pass through a I mm screen for the in vitro experiment, but there was an obvious dissimilarity between the two methods, especially where Y and X are in vivo and in vitro digestibility respectively.5 . This method is rapid and reproducible and particularly suited for the evaluation of a large number of samples. Since this method assesses only stomach and small intestinal digestion, it therefore may require further modification when used for diets which include large amounts of crude fibre. Also, depending on the needs of the investigator, the addition of a correction factor for endogenous faecal nitrogen loss may be required.

The effects of level of feed intake (0.8, 1.2 and 1.6 kg/d) and body-weight of the pig (49 and 92 kg) in Expt 1, and dietary neutral-detergent fibre (NDF; 30, 60, 90, 120 and 150g/kg) in Expt 2 on the endogenous ileal flow of amino acids (AA) and nitrogen were studied with protein-free diets into which purified wood cellulose was incorporated at the expense of maize starch. In Expt 1, one of the proteinfree diets containing 90 g NDF/kg was used. Female pigs were fitted with a simple 'T' cannula a t the terminal ileum. In Expt 1, the endogenous ileal AA and N flow, expressed as g/kg dry matter (DM) intake, decreased significantly (P < 0.05) with increasing DM intake, except for proline. By contrast, the values expressed as g/d remained constant. There was no significant difference in endogenous ileal flow ( P > 0.05) between initial body-weights of 45 and 90 kg except for histidide, isoleucine, phenylalanine, threonine, valine and serine, in which the ileal flow determined at the higher body-weight was significantly higher (P < 0.05). In Expt 2, the effects of dietary cellulose levels on the endogenous ileal flow of AA and N were not significant (P > 0.05), although the values tended to increase as dietary cellulose levels increased for most AA and for N. It is concluded that the daily endogenous ileal flow of AA and N remains relatively similar at different D M intake and cellulose levels. Therefore, correction of apparent ileal digestibility of AA and N to the true ileal digestibility should be made with the endogenous ileal flow values expressed on a daily amount basis, not the values expressed on a D M intake basis. Amino acids: Endogenous ileal flowThe determination of true ileal amino acid (AA) digestibility is important to the improvement of feed formulation in pigs (Furuya & Kaji, 1991). When determining true digestibility it is necessary to know the endogenous ileal AA flow. Dry matter (DM) intake is the most commonly used reference base for the endogenous ileal AA. This base assumes that the amounts of endogenous ileal AA are directly related to DM intake; but there have been no studies specifically designed to evaluate the influence of feed intake levels on endogenous ileal AA output and the basis for the endogenous connection is doubtful. Green et a/. (1987) found a decrease in apparent ileal AA digestibility with decreasing feed intake and suggested that the endogenous flow remained relatively similar at different DM intakes. An increase in endogenous ileal AA flow with higher levels of fibre in the diets has been demonstrated (Sauer et al. 1977;Taverner et al. 1981). By contrast, Drake (1990) found no effect of increased dietary fibre intake on endogenous ileal N flow. Additionally, an increasing intake of indigestible DM apparently caused no increase in the losses of endogenous protein (Taverner et al.

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