Apparent ileal digestibility (AID) of energy, dry matter (DM), nitrogen (N) and amino acids and standardized ileal digestibility (SID) of amino acids in low quality soybean meals with different CP concentration (SBM 44% CP and SBM 48% CP) with or without 400 U β-mannanase/kg supplementation were evaluated in 20 cannulated barrows ((Landrace×Yorkshire)×Duroc) with an average BW of 25.08±3.42 kg. A N-free diet was used to determine basal endogenous losses of amino acids. The supplementation of β-mannanase improved (P<0.05) AID of DM compared with non-supplemented diet. However, enzyme supplementation did not improve (P>0.05) AID of N and energy. The type of SBM (SBM 44% CP v. SBM 48% CP) had no effect on AID of DM, N and energy. β-mannanase improved (P<0.05) AID of sum of essential amino acids, arginine, histidine, lysine, valine and glycine. The SID of lysine was higher (P<0.05) in enzyme supplemented than in non-supplemented diets. Larger AID and SID of threonine and proline (P<0.05) were observed in SBM 48% CP than in SBM 44% CP. In conclusion, the supplementation of enzyme improved AID of arginine, histidine, lysine, valine and glycine, but it did not cause marked difference in SID of these amino acids except for lysine. The low nutrient digestibility of the SBM sources used in the present experiment might have favoured the positive effect of β-mannanase supplementation.

The effects of inclusion in the diet of different sources of soya bean meal (SBM) on growth performance, total tract apparent digestibility (TTAD) and apparent ileal digestibility (AID) of major dietary components and mucosal ileum morphology were studied in Iberian pigs weaned at 30 days of age. From 30 to 51 days of age (phase I), there was a control diet based on regular soya bean meal (R-SBM; 44% CP) of Argentina (ARG) origin and five extra diets in which a high-protein soya bean meal (HP-SBM; 49% CP) of the USA or ARG origin, either ground (990 μm) or micronized (60 μm), or a soya protein concentrate (SPC; 65% CP) substituted the R-SBM. From 51 to 61 days of age (phase II), all pigs were fed a common commercial diet in mash form. The following pre-planned orthogonal contrasts were conducted: (1) R-SBM v. all the other diets, (2) SPC v. all the HP-SBM diets, (3) micronized HP-SBM v. ground HP-SBM, (4) HP-SBM of ARG origin v. HP-SBM of US origin and (5) interaction between source and the degree of grinding of the HP-SBM. Dietary treatment did not affect growth performance of the pigs at any age but from 30 to 51 days of age, post weaning diarrhoea (PWD) was higher (P<0.001) and the TTAD and AID of all nutrients were lower for pigs fed the R-SBM diet than for pigs fed the HP-SBM or the SPC diets. However, no differences between the HP-SBM and the SPC containing diets were detected for any trait. The TTAD of organic matter (P=0.07) and gross energy (GE) (P=0.05) tended to be higher for the micronized HP-SBM than for the ground HP-SBM and that of GE was higher (P<0.05) for US meal than for the ARG meal. Pigs fed R-SBM had lower villus height (P<0.01) than pigs fed HP-SBM or SPC but no differences in ileal mucosal morphology were detected between SPC and HP-SBM containing diets. It is concluded that feeding the HP-SBM or SPC-reduced PWD and improved nutrient digestibility and ileal morphology as compared with feeding the R-SBM, but had no effect on pig performance. The inclusion in the diet of added value soya products (micronized SBM or SPC) in substitution of the R-SBM increased the TTAD of all nutrients and reduced PWD but had no advantage in terms of growth performance over the use of ground HP-SBM.

The use of carbohydrases and proteases in poultry production occasionally results in inconsistent physiological responses that are difficult to explain. However, it has previously been demonstrated that a substantial portion of the variation in enzyme efficacy is associated with the inherent ileal digestibility of starch, protein and lipid, and so an appreciation for the concentration of the undigested fractions of these nutrients in a diet may help to determine the magnitude and consistency of feed enzyme responses. Considering that the expense of in vivo physiological assays for the assessment of enzyme functional pattern is high, it is crucial to develop suitable in vitro methods to predict the magnitude of enzyme response. The purpose of the current paper is to describe inherent characteristics of poultry diets and feed ingredients in response to carbohydrases and proteases in order to aid the development of in vitro assays to predict feed enzyme functional patterns.

Measures of amino acid (AA) digestibility are used widely to estimate bioavailability of AA in feed and food ingredients for monogastric animals. In principle, the digestibility assay is simpler than in vivo assessments of AA bioavailability and allows for simultaneous estimation of the bioavailability of all AA in an experimental diet. It is generally assumed that absorption of intact AA in the hindgut of monogastrics is minimal, even though colonocytes do contain AA transporters and have been shown to absorb AA. This assumption is supported by the observation that infusion of AA into the hindgut does not improve nitrogen balance in monogastrics. In addition, growth performance of monogastrics is more highly correlated with ileal than faecal AA digestibility. Therefore, ileal digestibility coefficients provide better estimates of AA bioavailability than faecal digestibility coefficients. Measures of apparent ileal digestibility (AID) of AA are confounded with endogenous gut AA losses (EAAL). The curvilinear increase in AID of AA with increasing dietary AA level has been attributed to the relatively large contribution of EAAL to total ileal AA flows at low dietary AA levels. Subtracting basal EAAL from total ileal AA flows yields standardized ileal digestibility (SID) coefficients that appear to be more additive than AID coefficients in mixtures of feed ingredients. An implicit assumption when using SID AA coefficients in diet formulation is that the post-absorptive utilization of AA is not influenced by the dietary protein source. This assumption appears inappropriate when using feed or food ingredients that have been over-heated, induce large amounts of EAAL, or contain substantial amounts of fermentable fibre. Improved understanding of processes that contribute to the discrepancy between bioavailability and ileal digestibility will allow a more effective use of AA digestibility coefficients in diet formulation.

The true ileal digestibility assay provides the most informative measure of digestibility to assess bioavailability of amino acids in foods for humans. To determine ‘true’ estimates of ileal amino acid digestibility, requires that endogenous amino acids present in digesta at the terminal ileum be quantified. The amounts of endogenous amino acids in ileal digesta can be determined after feeding an animal or human a protein-free diet (traditional approach) or by various methods after giving a protein-containing diet. When the protein-free method has been applied with adult human subjects an overall mean value (three separate studies) for endogenous ileal nitrogen flow of 800 mg N/d has been reported. This value is considerably lower than a comparable value obtained after feeding protein of 1852 mg N/d (mean of four separate studies), and thus endogenous ileal N and amino acids should be measured under conditions of protein alimentation. There is some confusion concerning the terminology used to define digestibility, with the term “true” digestibility having different adopted meanings. Here, true amino acid digestibility is defined as apparent amino acid digestibility corrected for the basal amino acid losses determined after giving either a protein-free or a protein-containing diet. Basal losses should be determined at a defined dry-matter and protein intake. The protein-free diet approach to determining endogenous amino acids is considered unphysiological and basal losses refer to ileal endogenous amino acid flows associated with digesta dry-matter flow, and not including “specific” effects of dietary factors such as non starch polysaccharides and anti nutritional factors. Arguments are advanced that the enzyme hydrolysed protein/ultra filtration method may be suitable for routine application with a cannulated pig model, to obtain physiologically-valid basal estimates of ileal endogenous amino acids to allow calculation of true ileal amino acid digestibility in the pig, and then prediction (via statistical relationships) of true coefficients of amino acid digestibility in humans.

Ileal digestibility in growing pigs fed starch-based diets with inclusion of four tropical leaves in a meal form was studied in a 5 × 5 Latin square design. Five diets were formulated with only casein as protein source in the basal diet (CAS), and casein plus dry cassava (CA) leaves, casein plus dry sweet potato (SP) leaves, casein plus dry cocoyam (CO) leaves and casein plus erythrina (ER) leaves in the other four diets. All diets contained the same amount of CP (14%), either provided by only CAS or a combination of casein and 250 g of leaf meal per kg of diet in the other diets. Leaves were separated manually from stems, and only the leaf part was used. A protein-free diet was fed during a sixth period in order to estimate the endogenous protein losses and calculate the CP- and amino-acid (AA)-standardized ileal digestibility (SID) values. The values for the foliages were calculated according to the difference method, assuming no interaction between the foliage and the casein. The ileal tract apparent digestibility of CP, organic matter and energy was higher in diet CAS than in the other diets (P < 0.05). The SID of CP and AA was close to 0.950 for casein, whereas the SID of AA was markedly lower in the foliages; the SID of indispensable and dispensable AA was highest in CO (0.500 and 0.352) and lowest in ER (0.170 and 0.195); intermediate values were obtained for SPs (0.367 and 0.349) and CA (0.232 and 0.242) leaves. Accordingly, the SID of lysine was highest (0.538) for CO leaves and lowest (0.126) in ER leaves; intermediate values were measured for CA and SP leaves. These low SID values in foliage meals must be related to the high levels of dietary fibre and the presence of secondary metabolites (tannins). These results suggest that it is only possible to replace a fraction of the conventional protein sources such as soyabean meal by tropical foliages in growing pig diets with a preference for CO leaves.

Two experiments were conducted to evaluate the nutritional value of three cultivars (Promore, Kiev mutant and Ultra) of white lupins (Lupinus albus L.) for broilers. In experiment 1, the apparent metabolisable energy (AME) and ileal amino acid digestibility coefficients of the three cultivars were determined. The cultivar effects were significant (P < 0.05) for AME, but the ileal amino acid digestibility coefficients were similar (P > 0.05) between cultivars. The AME value of Ultra cultivar was lower (P < 0.05) than those of Promore and Kiev mutant cultivars. In Experiment 2, using the AME and ileal digestible amino acid values determined in Experiment 1, diets containing 200 g/kg of lupin were formulated and the effects of feeding these diets on performance, digestive tract development and excreta quality of broiler starters were investigated. Weight gain, feed intake and feed per gain of broilers fed diets containing white lupins were similar (P > 0.05) to those fed the maize–soybean meal diet. The performance of birds fed diets containing different cultivars of white lupins was similar (P > 0.05). Several digestive tract parameters were influenced by the dietary inclusion of white lupins. In particular, the relative liver weight and the relative empty weights of small intestine and caeca in birds fed diets containing white lupins were higher (P < 0.05) than those fed the maize–soybean meal diet. No differences (P > 0.05) were observed in the excreta quality scores between the birds fed the maize–soybean meal diet and those fed diets containing white lupins.

The objective of the study was to determine the coefficients of ileal apparent digestibility (CIAD) of sorghum protein and amino acids (AA) in weaned piglets and growing pigs. Digestibility coefficients were estimated using the regression and difference methods for the weaned piglets; and the direct and difference methods for the growing pigs. To test the hypothesis that CP and AA digestibility of sorghum is lower in weaned piglets than in growing pigs, two experiments were conducted. In experiment one, 20 weaned piglets were fitted with a ‘T’ cannula at 21 days of age and were fed for 2 weeks one of five dietary treatments: a reference or control diet providing 200 g of CP/kg from casein (C) as the sole protein source, and four casein–sorghum (C–S) diets kept isoproteic to C by the appropriate adjustment of C and maize starch proportions; the amount of sorghum (S) in these diets was 135, 307, 460 and 614 g/kg. In experiment 2, fifteen castrated pigs weighing 57.8 ± 2.8 kg were used and randomly allotted to one of three dietary treatments: a reference casein–maize starch diet containing C as the sole protein source, a C–S diet, both diets containing 160 g of CP/kg, and a fortified S diet containing 68 g of CP/kg. In piglets the CIAD for CP and AA decreased linearly (P < 0.05) as the amount of S in the diet increased. The average ileal digestibility of AA from C was 0.858 ± 0.111, and decreased to 0.663 ± 0.191 at the higher S level. The CIAD estimated using the regression or difference methods were similar for leucine, cysteine, glutamic acid, serine, alanine and tyrosine, and different for the other AA. In growing pigs the CIAD of protein and AA (except alanine and cysteine) were similar (P > 0.05) for the C and the C–S diets, but higher (P < 0.05) than those for the S diet. The CIAD for S obtained by the difference method were higher (P < 0.05) than those obtained using the direct method, except for lysine, isoleucine, valine, methionine, threonine and cysteine. The results indicate that except for lysine and cysteine, growing pigs’ ability to digest AA and protein is superior than weaned piglets.

Piglets, separated from their dam at 12 days of age and fed a milk substitute hourly, were used as a model for suckling. Animals were fitted with a terminal ileal T-cannula and a jugular vein catheter. At 28 days of age, half of the pigs had a dietary change to a cereal-based weaner diet fed as slurry, and the others remained on milk substitute. Animals were labelled by oral administration of 15N-labelled yeast for 10 days (days 15 to 25). Blood samples were taken twice a day to monitor 15N enrichment of the blood plasma. Diets included polyethylenglycol (PEG 4000) to allow calculation of apparent ileal digestibility of nitrogen and individual amino acids. Ileal bacterial nitrogen was calculated from D-alanine content of the digesta. Furthermore, small intestinal (SI) villus height and crypt depth were measured. Feed intake was increased by the dietary change. The total nitrogen flow was 3.2 ± 0.4 g/day and 5.9 ± 0.4 for the milk and weaner diet, respectively. Endogenous nitrogen flow at the terminal ileum was similar for both groups (milk diet 2.4 ± 0.4 v. weaner diet 2.2 ± 0.3 g/day), whereas the bacterial nitrogen content (0.08 ± 0.01 g/day milk diet v. 0.15 ± 0.01 g/day weaner diet, P < 0.01) and exogenous nitrogen flow (0.94 ± 0.16 g/day milk diet v. 3.29 ± 0.12 g/day weaner diet, P < 0.001) increased significantly in the weaner-diet group. The ileal apparent digestibility coefficient of protein was 0.81 ± 0.06 and 0.68 ± 0.01 for the milk replacer and the weaner diet, respectively. Morphology measurements made along the SI at 25%, 50% and 75% were similar between piglets fed milk replacer and those fed a cereal-based weaner diet. The only statistical effect (P < 0.01) of dietary change was an increase in crypt depth in the weaner-diet group. In conclusion, pigs, following a dietary change analogous to weaning, lack the capacity to fully digest a standard weaner diet. This may result in an increased nutrient content entering the large intestine and an altered microbiota. In the absence of a period of anorexia, often associated with traditional weaning, we saw no evidence of villous atrophy, but report here a significant crypt hyperplasia, especially at the 75% level, as a result of dietary change.

The suitability of the pig as an animal model for predicting protein digestibility in man was evaluated. Healthy adult human subjects (mean body weight 67 kg; n 11) and growing pigs (mean body weight 40 kg; n 15) were fed semi-synthetic mixed meals containing, as a sole source of N, casein (C), hydrolysed casein (HC) or rapeseed isolate (R). There was no prior adaptation to the test meal. Ileal digesta were sampled through a naso-ileal tube (human subjects) or a post-valve T-caecum cannula (pigs) after ingestion of a bolus meal. The protein sources were 15N-labelled. Amino acid (AA) digestibilities were not determined for R. Ileal apparent N digestibility was markedly lower (14–16 %; P < 0·001) in human subjects than in pigs (C, HC, R). Similarly, most apparent ileal AA digestibilities were lower (8 % on average; P < 0·05) in human subjects (C, HC). Ileal true N digestibility was slightly lower (3–5 %; P < 0·001) in human subjects than in pigs (C, HC, R) and most true ileal AA digestibilities were similar (P>0·05) between the species (C, HC). Exceptions were for phenylalanine, tyrosine, lysine, histidine and aspartic acid for which digestibilities were lower (3 % on average; P < 0·001) in human subjects. A similar ranking of the diets was observed for true ileal N digestibility between species. The inter-species correlation for true ileal digestibility was high for N (r 0·98 over 3 × 2 data; P = 0·11) and AA (r 0·87 over 26 × 2 data; P < 0·0001). Overall, this supports the use of the pig as a model for predicting differences among dietary protein digestibility, especially regarding true ileal N digestibility, in man.

Two experiments were conducted to examine the effects of lupin particle size on amino acid (AA) and energy digestibility and fermentation characteristics in pigs. Expt 1 examined the effects of lupin variety (cv. Tanjil and Mandelup) and lupin particle size (746, 888, 1099 and 1136 μm) on the total-tract apparent digestibility of dietary components in 63·5 (sd 7·28) kg pigs. While variety had no effect on total-tract apparent digestibility, decreasing particle size of lupins linearly increased total-tract apparent digestibility of crude protein of diets containing 350 g lupins per kg (P < 0·01). Expt 2 examined the effect of lupin particle size (567, 995, 1198, 1250 and 1304 μm) on digestion and fermentation characteristics in 29·8 (sd 2·9) kg pigs. Pigs were fed the respective diets ad libitum for the first 2 weeks and fed at three times maintenance energy level in the third week. Pigs were euthanised under sedation at 46·7 (sd 4·21) kg to collect digesta samples along the intestinal tract. Decreasing particle size increased apparent ileal and total-tract digestible N (P < 0·01) and the apparent and standardised ileal digestible AA content (P < 0·05– < 0·001) of lupins. Decreasing particle size of lupins linearly decreased the molar proportion of straight-chain volatile fatty acids (sum of acetic, propionic and butyric acids; VFAAPB), while branched-chain fatty acids (sum of valeric, caproic, isobutyric and isovaleric acids) were linearly increased (P < 0·001). The results demonstrated that particle size of lupins is a critical factor influencing nutrient, especially AA, utilisation efficiency and fermentation characteristics in the gastrointestinal tract of pigs.

To more precisely formulate feed and predict animal performance, it is important to base both the recommendations and feed formulations on digestible rather than total amino acid contents. Most published data on the digestibility of amino acids in feed ingredients for poultry are based on excreta digestibility. Ileal digestibility is an alternative and preferred approach to estimate amino acid availability in feed ingredients. Both methodologies are described and assessed. In addition, the differences between apparent and standardised (in which corrections are made for basal endogenous losses) digestible amino acid systems are discussed. The concept of a standardised digestibility system as a mean of overcoming the limitations of apparent digestibility estimates is proposed. In this context, different methodologies for the determination of basal endogenous amino acid losses are discussed. Although each methodology suffers from some limitations and published data on endogenous losses at the ileal level in growing poultry are limited, averaged data from repeated experiments using the ‘enzymatically hydrolysed casein’ method are considered as the best measure of basal losses. Standardised ileal amino acid digestibility values of 17 feed ingredients commonly used in broiler nutrition are presented including grains (barley, corn, sorghum, triticale, wheat), grain by-products (wheat middlings, rice pollard), plant protein sources (soybean meal, canola meal, corn gluten meal, cottonseed meal, lupins, peas/beans, sunflower meal), and animal by-products (feather meal, fish meal, meat and bone meal). This comprehensive set of the ileal amino acid digestibility of feed ingredients in broiler nutrition may serve as a basis for the establishment of the system in broiler feeding and for further research.

Sweet lupin (Lupinus albus), a protein-rich legume devoid of anti-nutritional factors, is considered to have a high potential for protein nutrition in man. Results concerning the nutritional value of lupin protein are, however, conflicting in animals and very scarce in human subjects. Furthermore, where fibre-rich protein sources are concerned, the long-term nutritional results are often obscured, particularly since fibre-promoted colonic fermentation may bias the energy supply and redistribute N flux. We therefore studied, during the postprandial phase, the bioavailability and utilisation of lupin-flour protein in nine healthy men who had ingested a mixed meal containing intrinsically 15N-labelled lupin flour as the protein source (Expt 1). The real ileal digestibility (RID) and ileal endogenous N losses (IENL) were assessed using a perfusion technique at the terminal ileum, and the N content and 15N enrichment of ileal samples. Lupin flour exhibited a high RID of 91 (SD 3) % AND LOW IENL (5·4 (sd 1·3) mmol N/h). Postprandial dietary deamination was also assessed from body dietary urea and urinary dietary N excretion, and compared with results in nine healthy men following an isoenergetic meal containing a 15N-soyabean-protein isolate with a similar RID, as a control (Expt 2). Postprandial dietary deamination was similar after lupin and soyabean meals (17 (sd 2) and 18 (sd 4) % ingested N respectively). We therefore conclude that lupin protein is highly bioavailable, even if included in fibre-rich flour, and that it can be used with the same efficiency as soyabean protein to achieve postprandial protein gain in healthy human subjects.

Two experiments were conducted to determine apparent ileal digestibility of amino acids (AIDAA) and nitrogen (AIDN) in cottonseed meal (CSM) and soyabean meal (SBM) fed to growing pigs. In the first experiment, twenty-four male pigs (37·3 (SE 2·7) kg) were individually penned and randomized to either CSM or SBM diets. The diets contained 40% of the protein meal (either CSM or SBM) in a wheat starch-sucrose (1:1, w/w) base containing vitamins and minerals, and Cr2O3 as an indigestible marker. Pigs were acclimated to the experimental diets over a 3d period and on day 4 through to day 14 were offered 1800g/d of the diet. Diets were offered in three meals/d from day 4 to day 11 and in eight meals/d from day 12 to day 13. After the eighth hourly-meal on day 14, twelve pigs were anaesthetized with halothane while the remaining twelve pigs were CO2-stunned and processed using commercial slaughter procedures. Ileal digesta were collected from a 1500 mm portion of the terminal ileum of each pig and subsequently analysed for amino acids, N, organic matter and Cr. Results indicated that AIDAA of CSM and SBM were lower when digesta were collected following CO2-stunning than when digesta were obtained under halothane anaesthesia. Consistently, AIDN in CSM (0·51 v. 0·56) and SBM (0·55 v. 0-71) were lower (P <0·05) in CO2-stunned pigs than in halothane-anaesthetized pigs. Furthermore, when digesta collection was conducted under halothane anaesthesia, AIDN of CSM was lower (P < 0·001) than that of SBM. In the second experiment, six male pigs (45 (SE 2·6) kg) were fitted with T-piece cannulas implanted in the terminal ileum, housed individually in metabolism cages, and randomly allocated to either CSM or SBM diets in a single reversal arrangement. Ileal digesta were collected for AIDAA and AIDN determination. Although statistical comparisons could not be made between the two experiments, the AIDAA and AIDN data obtained via cannulated pigs were similar to those values obtained using the halothane-anaesthesia method. Overall, the CO2-stunning method is not recommended for studies of amino acid or nitrogen ileal digestibilities, but may be useful for the study of other dietary constituents.

Two experiments were conducted to investigate whether the utilization of lysine in growing pigs is affected by the level of excess protein in the diet. Nine lysine-deficient diets containing 100,200 or 300g crude protein/kg and between 1·2 and 6·8 g ileal digestible lysine/kg were prepared. In the first experiment the apparent ileal digestibility of lysine in three of the nine diets was determined using pigs with simple T-cannulasand Cr2O3, as an indigestible marker. Ileal digestibility of lysine in the other diets was calculated by interpolation. In the second experiment N retention, as a measure of lysine utilization, was determined in all nine diets using growing pigs over the weight range 30–50 kg. The effect of excess protein on lysine utilization was assessed by comparing the regression of N retention v. lysine (ileal digestible) intake at the three levels of protein. Increasing ileal digestible lysine in the diets resulted in a linear increase in N retention with all three protein levels and there was no significant difference amongst the three regressions, indicating that lysine utilization was not affected by the level of protein.Therefore, all data were pooled together to calculate a single regression for all treatments.An increase of 1·0 g ileal digestible lysine led to an increase of 1·43 g N or 8·96 g protein (N x 6·25) retained. Assuming a lysine concentration in the retained body protein of 65–72 mg/g, lysine was utilized with an efficiency of 0·58–0·65

Two experiments were conducted to determine apparent ileal DM and crude-protein (CP) digesibilities in rations fed to pigs. An evaluation was made of Cr2O3 and HCl-insoluble ash as digestive markers. In addition, the effects of body weight (BW) on apparent ileal DM and CP (N x 6.25) digestibilities were studied. In Expt 1, thirteen barrows averaging 35 kg BW were fitted with post-valve T-caecum (PVTC) cannulas to determine the apparent ileal DM and CP digestibilities of a wheat gluten-bran ration (B2) and a soyabean-meal ration (E1). Immediately after morning feeding ileal digesta samples were collected on an hourly basis for a total of 12 h. Subsequently, N and marker contents were determined in the samples. The postprandial patterns of N and Cr passage were more similar than those of N and HCl-insoluble ash. Therefore Cr2O3 is more suitable as a marker than HCl-insolube ash. The apparent ileal CP digestibility coefficient of ration B2 derived using Cr2O3 as a marker was significantly (P > 0.05) higher by 0.018 compared with the value obtained using HCl-insoluble ash. The corresponding values for ration E2 obtained using Cr2O3 and HCl-insoluble ash were both 0.825. In Expt 2, apparent ileal DM and CP digestibilities were determined in eighteen rations using twelve barrows also fitted with PVTC cannulas (BW from 40 to 100 kg). The protein sources for these rations were from different groups of feedstuffs. In four and three of the rations apparent ileal DM and CP digestibilities respectively were significantly different (P < 0.05) when assessed using the two markers. The digestibility coefficients were not systematically higher or lower for either marker. Absolute differences were < 0.049 on average. Significant effects of live weight on apparent ileal CP digestibilities were found.

The effect of adding cottonseed hulls to casein- and cottonseed-kernel-based diets on the apparent and true ileal digestibility of N and amino acids, and the proportion of this effect accounted for by condensed tannin (CT), were determined using the growing rat. Sixtyrats were allocated randomly to ten semi- purified diets, containing either casein (four diets) or purified unheated solvent-extracted cottonseed kernel (six diets) as the sole protein source, with Cr2O3 added as an indigestible marker. Two of the casein diets contained no hulls whilst the remaining two diets contained 70 g cottonseed hulls/kg. Two of the cottonseed-kernel-based diets contained no hulls, with two containing 23 g hulls/kg and the remaining two containing 46 g hulls/kg. For each pair of diets, PEG was either included or excluded. The effect of CT was quantified by comparing control rats (-PEG; CTacting) with PEG-supplemented rats (+PEG; CT inactivated) at each level of dietary hulls. The rats were given their respective experimental diets for 14 d. Each rat was given the food ad libitumfor 10 min hourly from 08·00 to 18·00 hours. On day 14, samples of digesta were collected at death from the terminal 150 mm of ileum at 7 h from the first meal. Apparent and true ileal digestibilities were calculated for DM, N and the individual amino acids. The principal finding was that the inclusion of hulls depressed the apparent and true ileal digestibilities of N and amino acids, but with the response differing between diets. With the casein-based diet the mean apparent and true ileal amino acid digestibilities were significantly depressed from 0·89 and 0·96 to 0·85 and 0·92 respectively, by the inclusion of 70 g hulls/kg in the diet, and addition of PEG then restored these to 0·89 and 0·95. All of the depression could be explained by the CT content of the hulls. However, with the cottonseed-kernel-based diet the responses fell into three categories. The apparent and true ileal digestibilities of the essential amino acids cystine and methionine were not affected by hull addition, ileal digestibilities of leucine, isoleucine, lysine, threonine and valine were markedly depressed by hull addition with approximately 50% of the depression being explained by CT, whilst the ileal digestibilities of histidine, arginine and phenylalanine were depressed by hull addition but little or none of this effect could be explained by CT. Thus the effect of hulls on protein digestion clearly differed with source of protein. With the cottonseed-kernel-based diet it seems that components of the hulls other than CT also depressed the apparent and true ileal digestibilities of N and amino acids. The identity of these components is unknown.

Two growth experiments were conducted to determine the effect of heat on the utilization of ileal-digestible lysine from field peas (Pisum sativum cultivar Dundale) fed to growing pigs. Five lysine-deficient diets (0.36 g ileal-digestible lysine/MJ digestible energy (DE)) were formulated using raw field peas, and field peas heated to either 110°, 135°, 150°, or 165° for 15 min respectively in a forced-air dehydrator. Additional diets were formulated with supplements of free lysine to verify that lysine was limiting in the diets containing the raw peas, and peas heated to 150° or 165°. The growth performance and retention of ileal-digestible lysine by pigs given the diets was determined over the 20–45 kg growth phase. Heat had a significant quadratic effect (P < 0.01) on growth rate, with responses declining from 543 g/d with pigs given the raw peas, to 407 g/d for those given the peas heated to 165°. Similarly, crude protein deposition declined in a quadratic manner (P < 0.001) from 76 to 36 g/d for pigs fed on raw peas and peas heated to 165° respectively. Retention of ileal-digestible lysine was 0.85 in the pigs given the raw field peas and declined in a quadratic manner (P < 0.001) with the application of heat to 0.48 in those pigs given the peas heated to 165°. Pigs fed on field peas heated to 165° had increased (P < 0.05) liver weights. The results indicate that heat applied to protein concentrates, even at mild temperatures, renders lysine in a form that is apparently absorbed but inefficiently utilized by the growing pig. Consequently, ileal digestibility values for lysine in heat-processed meals are unsuitable for diet formulations.

Three experiments were conducted to examine the effect of heating field peas (Pisum sativum cultivar Dundale) on (1) proximate analysis and total amino acid composition, (2) ileal and faecal digestibilities of amino acids, and (3) digestible energy content. Alternative techniques for assessing ileal and faecal digestibilities and digestible energy respectively, were also investigated. Forced-air dehydrators were used to heat field peas at temperatures of 110°, 135°, 150° or 165°. In the first experiment the apparent ileal and faecal digestibilities of amino acids and the faecal digestibility of energy in the raw and heated field peas were determined using pigs fitted with ‘T’ -shaped cannulas. In the second, apparent ileal digestibility of amino acids and the faecal digestibility of energy were determined using the direct ileal and rectal sampling technique. This involved a single collection of digesta and faeces from the digestive tract of the pig while it was anaesthetized. The faecal digestibilities of amino acids and energy were determined using total faeces collection in the third experiment. In all experiments the respective field-pea treatments comprised 400 g/kg sugar-based diets and were the only source of amino acids. Heat significantly decreased the lysine (14.6–8.7 g/kg; P < 0.001), cystine (3.2–2.6 g/kg; P < 0.01) and arginine (16.7–14.5 g/kg; P < 0.05) contents of the heated peas. The ‘reactive’ lysine content of the field peas, as measured using the Silcock technique, was decreased by 0.11 and 0.30 with the application of heat at 150° and 165° respectively. Heat treatments did not alter the ileal digestibility of most amino acids. Only aspartic acid (0.72–0.58), glutamic acid (0.80–0.65) and the basic amino acids, lysine (0.79–0.56) and arginine (0.85–0.75), showed a significant linear decrease (P < 0.05) in ileal digestibility over the heat treatments, determined using the ileal cannulation procedure. Heating significantly (P < 0.05) decreased faecal digestibility for all amino acids. Faecal digestibility was consistently greater than ileal digestibility for the raw field peas; however, this difference decreased with heat application until faecal digestibility was equal or less than ileal digestibility at the 165° treatment. Heat linearly depressed digestible energy, diet dry-matter digestibility and diet energy digestibility. Losses in lysine, cystine and arginine are likely to be due to early and advanced Maillard reactions. Considerable binding of the remaining lysine also occurred as indicated by a decline in Silcock-reactive lysine. The results indicate that the direct ileal sampling technique is a viable alternative to the cannulation procedure for amino acids, but further method development is required to decrease the variability associated with measurements. The estimation of faecal digestibility using indigestible markers and the partial faeces collection technique was as efficient as total faeces collection. In general, ileal digestibility of amino acids showed little response to heating, however, any changes that were observed were greatest for lysine. In contrast, faecal digestibility of all amino acids was greatly reduced with increasing heat application. This response appeared to be largely due to the effect of heating on microbial degradation and synthesis of amino acids in the hind-gut, rather than a reflection of the changes within the protein induced by heating. This variable response makes faecal digestibility an unreliable estimator of amino acid ileal digestibility.

The effect of dietary protein content (25, 60, 95, 130, 165 and 200 g crude protein (N × 6.25)/kg diet) on the apparent and true ileal digestibilities of N and amino acids in meat-and-bone meal given to the growing rat was investigated. Semi-synthetic diets in which meat-and-bone meal was the sole protein source were given to 180 g body-weight rats for 14 d. On the fourteenth day the rats were fed and then killed 4 h after the start of feeding and digesta were sampled from the terminal 200 mm ileum. Endogenous amino acid excretion was determined for eighteen rats given an enzymically hydrolysed casein (EHC)-based diet and with subsequent treatment of the digesta using ultrafiltration. The EHC-fed rats were killed 3 h after the start of feeding and digesta were collected from the terminal 200 mm ileum. True ileal digestibility values determined with reference to Cr as a marker were higher than the corresponding apparent estimates. Apparent digestibility values of N and amino acids increased significantly (P < 0.001) with increasing dietary protein level; however, dietary protein content had no significant (P > 0.05) effect on the true ileal digestibilities of N and amino acids. The mean apparent ileal digestibility of N in meat-and-bone meal ranged from 65.6 to 75.3%. The corresponding range for the true ileal digestibility of N was 76.9 to 78.2%. True ileal digestibility, unlike apparent digestibility, appears to be independent of dietary protein level and may allow feed ingredients to be compared accurately even if they are ingested in different quantities.