Postprandially, amino acids and di/tripeptides are thought to be primarily absorbed in the proximal small intestine. However, there have been no in vivo demonstrations of regional differences in amino acid transport dynamics between the proximal and distal small intestines. We monitored plasma amino acid responses in the jejunal and ileal mesenteric veins of rats after oral administration of a diet or an amino acid mixture (Expt 1) and in the portal vein after direct administration of the amino acid mixture into the lumen of the jejunum or ileum (Expt 2). In Expt 1, the total and some amino acid concentrations in the jejunal mesenteric vein were slightly higher than those in the ileal mesenteric vein after oral administration of the amino acid mixture, suggesting that the ileum actively transports luminal amino acids to the basolateral side, comparable to the jejunum. In Expt 2, portal amino acid concentrations were elevated to a greater extent after direct administration of the amino acid mixture into the ileal lumen than into the jejunal lumen. These results demonstrate regional differences in amino acid transport dynamics in vivo and suggest that the ileum has a higher capacity for transporting amino acids than the jejunum. Our findings highlight the importance of the ileum in postprandial amino acid absorption and metabolism.

Camelina cake (CAM) is a co-product proposed as an alternative protein source; however, piglet data are still limited. This study aimed to evaluate the effect of different doses of CAM in substitution of soyabean meal on the growth, health and gut health of weaned pigs. At 14 d post-weaning (d0), sixty-four piglets were assigned either to a standard diet or to a diet with 4 %, 8 % or 12 % of CAM. Piglets were weighed weekly. At d7 and d28, faeces were collected for microbiota and polyamine and blood for reactive oxygen metabolites (ROM) and thyroxine analysis. At d28, pigs were slaughtered, organs were weighed, pH was recorded on gut, colon was analysed for volatile fatty acids (VFA) and jejunum was used for morphological and gene expression analysis. Data analysis was carried out using a mixed model including diet, pen and litter as factors; linear and quadratic contrasts were tested. CAM linearly reduced the average daily gain from d0–d7, d0–d14, d0–d21 and d0–d28 (P ≤ 0·01). From d0–d7 increasing CAM linearly decreased feed intake (P = 0·04) and increased linearly the feed to gain (P = 0·004). CAM increased linearly the liver weight (P < 0·0001) and affected the cadaverine (P < 0·001). The diet did not affect the ROM, thyroxine, intestinal pH, VFA and morphology. All doses of CAM increased the α diversity indices at d28 (P < 0·05). CAM at 4 % promoted the abundance of Butyricicoccaceae_UCG-008. Feeding with CAM enhanced resilience in the gut microbiome and can be evaluated as a potential alternative protein source with dose-dependent limitations on piglet growth performance.

Mobilisation of seed storage reserves is important for seedling establishment in Arabidopsis. In this process, sucrose is synthesised from triacylglycerol via core metabolic processes. Mutants with defects in triacylglycerol-to-sucrose conversion display short etiolated seedlings. We found that whereas sucrose content in the indole-3-butyric acid response 10 (ibr10) mutant was significantly reduced, hypocotyl elongation in the dark was unaffected, questioning the role of IBR10 in this process. To dissect the metabolic complexity behind cell elongation, a quantitative-based phenotypic analysis combined with a multi-platform metabolomics approach was applied. We revealed that triacylglycerol and diacylglycerol breakdown were disrupted in ibr10, resulting in low sugar content and poor photosynthetic ability. Importantly, batch-learning self-organised map clustering revealed that threonine level was correlated with hypocotyl length. Consistently, exogenous threonine supply stimulated hypocotyl elongation, indicating that sucrose levels are not always correlated with etiolated seedling length, suggesting the contribution of amino acids in this process.

Low birth weight (LBW) neonates show impaired growth compared with normal birth weight (NBW) neonates. Glutamine (Gln) supplementation benefits growth of weaning piglets, while the effect on neonates is not sufficiently clear. We examined the effect of neonatal Gln supplementation on piglet growth, milk intake and metabolic parameters. Sow-reared pairs of newborn LBW (0·8–1·2 kg) and NBW (1·4–1·8 kg) male piglets received Gln (1 g/kg body mass (BM)/d; Gln-LBW, Gln-NBW; n 24/group) or isonitrogenous alanine (1·22 g/kg BM/d; Ala-LBW; Ala-NBW; n 24/group) supplementation at 1–5 or 1–12 d of age (daily in three equal portions at 07:00, 12:00 and 17:00 by syringe feeding). We measured piglet BM, milk intake (1, 11–12 d), plasma metabolite, insulin, amino acid (AA) and liver TAG concentrations (5, 12 d). The Gln-LBW group had higher BM (+7·5%, 10 d, P = 0·066; 11–12 d, P < 0·05) and milk intake (+14·7%, P = 0·015) than Ala-LBW. At 5 d, Ala-LBW group had higher plasma TAG (+34·7%, P < 0·1) and lower carnosine (–22·5%, P < 0·05) than Ala-NBW and Gln-LBW, and higher liver TAG (+66·9%, P = 0·029) than Ala-NBW. At 12 d, plasma urea was higher (+37·5%, P < 0·05) with Gln than Ala supplementation. Several proteinogenic AA in plasma were lower (P < 0·05) in Ala-NBW v. Gln-NBW. Plasma arginine was higher (P < 0·05) in Gln-NBW v Ala-NBW piglets (5, 12 d). Supplemental Gln moderately improved growth and milk intake and affected lipid metabolism in LBW piglets and AA metabolism in NBW piglets, suggesting effects on intestinal and liver function.

The experiment was conducted to investigate the effects of dietary threonine (Thr) on growth performance and muscle growth, protein synthesis and antioxidant-related signalling pathways of hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂. A total of 1200 fish (14·19 (se 0·13) g) were randomly distributed into six groups with four replicates each, fed six diets with graded level of Thr (9·5, 11·5, 13·5, 15·4, 17·4 and 19·3 g/kg diets) for 56 d. Results showed (P < 0·05) that dietary Thr (1) increased percentage weight gain, specific growth rate, feed efficiency and protein efficiency ratio; (2) up-regulated growth hormone (GH), insulin-like growth factor 1 (IGF-1), proliferating cell nuclear antigen, myogenic regulation factors (MyoD, Myf5, MyoG and Mrf4) and myosin heavy chain (MyHC) mRNA levels; (3) increased muscle protein content via regulating the protein kinase B/target of rapamycin signalling pathway and (4) decreased malondialdehyde and protein carbonyl contents, increased catalase, glutathione-S-transferase, glutathione reductase and GSH activities, up-regulated mRNA levels of antioxidant enzymes related to NFE2-related factor 2 and γ-glutamylcysteine ligase catalytic subunit. These results suggest that Thr has a potential role to improve muscle growth and protein synthesis, which might be due to the regulation of GH-IGF system, muscle growth-related gene, antioxidative capacity and protein synthesis-related signalling pathways. Based on the quadratic regression analysis of specific growth rate, the Thr requirement of hybrid catfish (14·19–25·77 g) was estimated to be 13·77 g/kg of the diet (33·40 g/kg of dietary protein).

Some amino acids (AA) act through several signalling pathways and mechanisms to mediate the control of gene expression at the translation level, and the regulation occurs, specifically, on the initiation and the signalling pathways for translation. The translation of mRNA to protein synthesis proceeds through the steps of initiation and elongation, and AA act as important feed-forward activators that are involved in many pathways, such as the sensing and the transportation of AA by cells, in these steps in many tissues of mammals. For the translation, phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) is a critical molecule that controls the translation initiation and its functions can be regulated by some AA. Another control point in the mRNA binding step in the translation initiation is at the regulation by mammalian target of rapamycin, which requires a change of phosphorylation status of ribosomal protein S6. In fact, the change of phosphorylation status of ribosomal protein S6 might be involved in global protein synthesis. The present review summarises recent work on the molecular mechanisms of the regulation of protein synthesis by AA and highlights new findings.

For this study, threonine (Thr) deficiency was hypothesised to exacerbate the intestinal damage induced by feed withdrawal with coccidial infection because of its high obligatory requirement by the gut; two dietary Thr treatments (0·49 and 0·90 %) were applied to chicks from 0 to 21 d of age. At 13 d of age, feed was withdrawn for 24 h from one-half of birds of each dietary treatment with subsequent gavage of a 25× dose of coccidial vaccine. Overall, there were four treatments with eight replicate cages per treatment. Under combined challenge, birds fed the Thr-deficient diet had 38 % lower 13–21-d body weight gain (P≤0·05) compared with birds fed the Thr-control diet. At 21 d, the challenged group fed low Thr had higher number of oocysts (+40 %, P=0·03) and lower crypt depth (−31 %, P<0·01). In addition, birds fed the low-Thr diet had higher gut permeability as measured after 2 h of administration of fluorescein isothiocyanate-dextran (3–5 kDa, P<0·01), which may be attributed to decreased IgA production (P=0·03) in the ileum. In caecal tonsils, the challenged group fed low Thr had lower CD3:Bu-1 ratio (P≤0·05), along with a tendency for lower CCR9 mRNA expression in birds fed the low-Thr diet (P=0·10). In addition, Thr deficiency tended to increase IL-10 mRNA expression regardless of infection (P=0·06), but did not change interferon-γ mRNA expression upon coccidial infection (P>0·05). Overall, Thr deficiency worsened the detrimental effects of combined feed withdrawal and coccidial infection on growth performance and oocyst shedding by impairing intestinal morphology, barrier function, lymphocyte profiles and their cytokine expressions.

The present study conducted a 9-week feeding trial to investigate the effects of threonine (Thr) on the digestion capacity and hepatopancreas gene expression of juvenile blunt snout bream (Megalobrama amblycephala). For this purpose, three tanks (300 litres/tank) were randomly arranged and assigned to each experimental diet. Juvenile fish were fed with diets containing graded Thr levels (0·58, 1·08, 1·58, 2·08 or 2·58 % of the diet) to apparent satiation four times daily. At the end of the feeding trial, the results indicated that hepatopancreas weight, hepatosomatic index, hepatopancreatic protein content, intestinal weight, intestosomatic index and intestinal protein content increased with increasing dietary Thr levels up to 1·58 % and thereafter decreased (P< 0·05). The activities of chymotrypsin, trypsin, amylase and lipase elevated as dietary Thr levels increased up to 1·58 % (P< 0·05), while these activities decreased in most cases after 1·58 % dietary Thr except for chymotrypsin and trypsin in the hepatopancreas (plateau 1·58–2·08 % Thr). The relative gene expression levels of chymotrypsin, trypsin, amylase, lipase, target of rapamycin and insulin-like growth factor-I were up-regulated, and the highest values were observed with 1·58 % dietary Thr or 1·58 and 2·08 % dietary Thr, whereas the relative gene expression levels of eukaryotic translation initiation factor 4E-binding protein 2 gradually decreased (P< 0·10) as dietary Thr levels increased up to 1·58 % and thereafter significantly increased (P< 0·05), which could explain that about 1·58 % dietary Thr could improve the growth and development of digestive organs and activities of digestive enzymes of juvenile blunt snout bream.

The experiment was conducted to evaluate the effects of dietary threonine (Thr) supplement on reproductive performance and immune function of the male mice challenged with pseudorabies virus (PRV). Kun-Ming male mice were assigned randomly to four groups with different Thr levels (0.70%, 0.88%, 1.10% and 1.30%). Half of the mice in each group were injected with PRV or phosphate-buffered saline (PBS) after 5 weeks’ adaptation to diets. The second experiment examined the effects of dietary Thr level on copulation rate, pregnancy rate and average number per litter of PRV- or PBS-challenged male mice that copulated with adult female mice on the 9th day post PRV challenge. Sperm quality and testosterone of mice were decreased after PRV infection, but this effect was attenuated by increasing Thr levels. Copulation and conception rates were increased with increasing Thr levels (P = 0.14), but litter size was not affected (P > 0.05). In the PBS and PRV groups, mice fed higher levels of Thr had increased immunoglobulin (Ig)G, IgA and IgM concentrations. The PRV-specific antibody level, interleukin (IL)-1β and tumor necrosis factor (TNF)-α concentration in PRV groups enhanced with increasing Thr levels; however, there was no difference in PBS groups. Furthermore, higher toll-like receptor (TLR)2 and TLR9 expressions in testis were observed by PRV challenge compared with PBS groups, and higher Thr supplement attenuated PRV-challenged induced the upregulation effect of TLR2 and TLR9 mRNA expression in testis (P < 0.05). These data suggest that higher Thr consumption was recommended in order to counteract the deleterious effects of virus invasion, possibly through the downregulated expression of TLRs, and thus to improve immunity and reproduction performance of male mice challenged with PRV.

The objective of the two studies was to determine the bioavailability of threonine (thr) and tryptophan (trp) in peanut meal, relative to l-thr and l-trp, for starter pigs using the slope-ratio bioassay. Basal diets (BDs) contained surfeit amounts of all amino acids for 10 to 20 kg pigs, except for thr (Experiment 1) or trp (Experiment 2). In the first study, four reference diets were formulated by supplementing the BD with 0, 0.4, 0.8 or 1.2 g of l-thr/kg at the expense of cornstarch; two test diets were formulated by replacing cornstarch in the BD with peanut meal at 32 or 64 g/kg of diet to supply 0.4 or 0.8 g thr/kg, respectively. Four reference diets consisting of the BD supplemented with 0, 0.15, 0.3 or 0.45 g of l-trp/kg at the expense of cornstarch and two test diets in which cornstarch in the BD was replaced with peanut meal at 30 or 60 g/kg of diet to supply 0.14 or 0.28 g trp/kg, respectively were used in the second study. Body weight gain responded in a linear way to supplemental l-thr or thr from peanut meal (P < 0.001). There was a linear response (P < 0.001) to thr supplementation from l-thr or peanut meal in gain-to-feed ratio. The addition of trp to the BD linearly increased (P < 0.05) body weight gain, feed intake and gain-to-feed ratio regardless of the trp source. Common-intercept, multiple linear regression in slope-ratio methodology using weight gain or gain-to-feed ratio as dependent variables and supplemental thr intake as independent variable gave relative bioavailability estimates of 71.9% or 75.7%, respectively. Corresponding values for trp were 92% and 75.7%. The fiducial limits for none of the relative bioavailability estimates included 100%. The data from these studies suggest that the bioavailabilities of thr and trp in peanut meal are less than those of l-thr and l-trp, and that the bioavailabilities of thr and trp in peanut meal are 72% to 76% and 76% to 92%, respectively.

High dietary threonine extraction by the digestive tract suggests that threonine contributes to maintain gut integrity. The aims of this study were to investigate the intestine development and the growth performance of early-weaned piglets pair-fed either a control well-balanced (C: 9.3 g threonine/kg diet) or a low-threonine diet (LT: 6.5 g threonine/kg diet) for 2 weeks. As expected, LT piglets presented lower plasma free threonine compared with C piglets (118 v. 356 ± 12 μmol/l, P < 0.001). Dietary threonine supply altered neither growth performance nor growth of the intestine and of the other portal-drained viscera (stomach, spleen and pancreas). Nevertheless, villus height was reduced in the ileum of the LT piglets compared with C piglets (446 v. 714 ± 74 μm, P < 0.05). This was also associated with a decrease in crypt width (P < 0.05) and villus height-to-crypt depth ratio (P < 0.05). Whereas maltase and lactase activities did not change between the two groups, aminopeptidase nitrogen activity was decreased in the ileum of LT piglets (269 v. 374 ± 27 IU/mg protein, P < 0.05). The number of mucin-containing goblet cells was not modified in the ileum and in the proximal part of the large intestine of the LT piglets compared with the C piglets. In conclusion, despite no alteration of intestinal growth, villus hypotrophy associated with a reduction of aminopeptidase nitrogen activity suggest an alteration of the structure of the ileum in early-weaned piglets fed a diet supplying inadequate dietary threonine.

The methionine cycle and methyl group metabolism are implicated in the long-term programming of metabolism. Diets deficient in folic acid, methionine and choline have been fed to pregnant rats to examine the effects on amino acid metabolism, choline reserves and DNA methylation in dam and fetuses. Animals were fed folate-deficient, folate-deficient with low methionine, folate-deficient with low choline and folate-deficient, low-methionine, low-choline diets starting 2 weeks before mating. The dams and their fetuses were subsequently killed on day 21 of gestation for analysis. Diets low in methionine reduced fetal and maternal weight. Folate deficiency increased the concentrations of homocysteine, glycine, serine and threonine in the maternal plasma, and this was exacerbated by the low-methionine diets. The changes in the amino acid profile in the fetal serum were similar but less pronounced. This result suggests that fetal metabolism was less perturbed. Folate deficiency increased free choline in the maternal liver at the expense of phosphocholine stores. It has been suggested that a deficiency in methyl donors in the diet during pregnancy may impact on key methylation reactions, including the methylation of DNA. Despite widespread changes in the metabolism of choline and amino acids, there was no change in the global methylation of cytosine in DNA from either maternal or fetal livers. This suggests a more indirect mechanism in which gene–nutrient interactions modify the process of differential methylation during development

Eighteen groups of seventy Atlantic salmon (Salmo salar L.) fry (initial mean body weight 0·8 (sd 0·01) g) were fed on semi-purified diets containing graded levels of l-threonine (Thr) in 15 litres aquaria at a temperature of 14·5±1°C. Doses of Thr represented 1, 31, 41, 51, 62, 72, 83 and 93% of its ideal level for optimumprotein deposition. Indispensable amino acids other than Thr were included in the same proportion (on a g/16g N basis) as in the Atlantic salmon fry whole-body carcass. Following 36d of feeding and a 36h fast, fry were killed for whole-body protein and amino acid analysis. Weight gain (r2 0·98), protein accretion (r2 0·97), and Thr accretion (r2 0·97) were linear (P<0·01) functions of Thr intake. Slope of the Thr accretion regression line showed that the efficiency of Thr utilisation above maintenance was 76%. At zero Thr intake, fry lost 5·4mg Thr/kg body weight0·75 per d. The Thr maintenance requirement was 7·2mg/kg body weight0·75 per d and the Thr requirement for growth was 66mg for 1g protein deposition. Increasing doses of Thr resulted in increased (P<0·05) concentrations of histidine and lysine, and decreased concentrations of isoleucine in whole-body protein. The maintenance need for Thr represented 13·4% of the total need for Thr. The data suggest that efficiency of Thr utilisation above maintenance is constant at all levels of Thr intake between 1 and 93% of the level required for optimum protein deposition.

In pigs the extensive threonine utilization by the splanchnic tissues explains the relative inefficiency of dietary threonine conversion for body protein accretion. Two experiments were conducted to estimate the contribution of the portal drained viscera (PDV) and the liver to threonine metabolism and especially catabolism in growing pigs. In the first experiment, four pigs were surgically prepared for chronic catheter insertion in the portal, hepatic and jugular veins and in the carotid artery. They were continuously infused with l-[1-13C]threonine through the jugular catheter. The PDV and total splanchnic viscera (PDV and the liver) extracted 14·3 and 18·8 % of arterial threonine input, respectively. In a second experiment, we studied the metabolism of dietary threonine in the PDV and the liver in six female growing pigs. Animals were surgically prepared as in the first experiment except that l-[1-13C]threonine and [15N]glycine were continuously infused in the duodenum for 10 h. Unlabelled and labelled threonine and glycine PDV, liver and splanchnic tissues balance were calculated from plasma samples taken during the last 2 h of this infusion. Splanchnic tissues extracted 60 % of infused labelled threonine, 88 % of which was extracted by PDV so that threonine extraction by the liver was low. Both the liver and the pancreas can degrade threonine through the l-threonine 3-dehydrogenase pathway but not the intestine. Our data suggest that threonine catabolism through the l-threonine 3-dehydrogenase pathway was only a minor component of total threonine utilization in the splanchnic tissues.

The aim was to determine whether dietary threonine levels affected hepatic insulin-like growth factor-1 (IGF-1) mRNA expression as well as plasma IGF-1 concentration and IGF binding protein (IGFBP) profile in growing pigs. Two male 6-week-old pigs from each of seven litters were used. Each littermate was assigned to one of two diets, control or low threonine (LT), providing per kg 14·3 MJ digestible energy in both diets, 170 g protein in the control diet and 167 g protein in the LT diet. The control diet contained all essential amino acids in the recommended amounts, including 8·2 g threonine per kg. The LT diet was similar but contained only 5·1 g threonine per kg. Pigs were pair-fed these diets for 3 weeks. Growth rate and food efficiency of pigs given the LT diet were significantly lower than those of pigs given the control diet (P 0·001). Plasma IGF-1 concentration of pigs given the LT diet was proportionately 0·44 lower than that of pigs given the control diet (P 0·01). Plasma free threonine concentration of pigs given the LT diet was lower than that of the pigs given the control diet (P 0·001). Plasma IGFBP2 level of pigs given the LT diet was significantly higher than that of pigs given the control diet (P 0·05). Pigs given the LT diet had a significantly lower plasma IGFBP3 level compared with their littermates given the control diet (P 0·05) suggesting that clearance rate of circulating IGF-1 was higher in the LT group. Dietary threonine level did not affect IGF-1 mRNA abundance in the liver. It is concluded that lower plasma IGF-1 level caused by reduced dietary threonine level may have been partly due to increased clearance rate of circulating IGF-1 but not due to IGF-1 gene expression in the liver.

An important objective of the least cost formulation of broiler diets is to provide sufficient amounts of the most limiting amino acids to support the needs of tissue maintenance and accretion while minimising any excesses. Threonine is the third most limiting amino acid in broiler diets behind the total sulphur-containing amino acids and lysine. Research into the threonine requirement of broilers is sparse compared with that of methionine and lysine. However, recent work on the threonine needs of growing and finishing broilers has been invaluable in helping commercial nutritionists determine the minimum amount of threonine required in least cost diet formulations. This review summarises this recent research. It also considers threonine needs for optimal immune system functions, feather growth, glycine requirements and gastrointestinal functions, as well as under conditions causing heat stress.

Two similar experiments (1 and 2) were conducted to measure the effects of a range of dietary threonine concentrations and environmental temperatures on the performance of pigs grown from 13 to 25 kg live weight. In both experiments 48 Large White x Landrace entire male pigs were assigned at 13 kg to one of six dietary threonine treatments (8·9 (T1), 7·6 (T2), 6·2 (T3), 4·9 (T4), 3·6 (T5) g/kg and T5 + supplemented threonine (T6)) and one of four temperature treatments (18, 22, 26 and 30°C). Animals were given ad libitum access to food until 25 kg live weight. There were significant interactions (P < 0·05) between temperature and threonine content on the rate of growth (ADG) with the highest gains on T1 and at 22°C. Similarly the response in food intake (FI) to dietary threonine was significantly (P < 0·01) modified by the ambient temperature. An increase in the supply of threonine in the diet resulted in significant increases (P < 0·001) in the gain per unit of food (FCE). A similar response to temperature occurred with the highest FCE recorded at 26°C and the lowest at 18°C. There was a 0·20 proportional reduction in body protein content at 25 kg live weight in pigs given T5 compared with those given T1 and similarly, excluding T6 because threonine may not have been the most limiting amino acid, the fat content was 1·37 higher for pigs on T5 versus T1, which had the lowest fat content. Similar trends occurred in protein and lipid growth rates with maximum protein deposition recorded on T1 (86 (s.e. 3·5) g/day) and maximum lipid deposition on T5 (108 (s.e. 5·8) g/day), over all temperatures. The response in total heat loss was similar to that observed in FI with the effect of decreasing threonine content being dependent on the environmental temperature. Linear regression of daily empty body threonine accretion on daily digestible threonine intake showed an average efficiency of threonine utilization for pigs between 12 kg and 25 kg live weight of 0·59 (s.e. 0·03). There were no differences in efficiency between temperatures. In conclusion, decreasing the threonine concentration below the requirement of the animal ‘resulted in a significant decrease in ADG, reduced FCE and fatter animals. Pigs given a diet deficient in threonine will attempt to maintain threonine intake as the concentration declines by increasing food intake but this compensation is dependent on the environmental temperature. Pigs are able to compensate better for a deficiency in threonine at 18°C and 22°C than at higher temperatures due to the animals being able to dissipate more heat at the lower temperatures.

Broiler chicks were fed on chemically-defined crystalline amino acid diets containing graded levels of L-threonine (Thr) during the period 10–20 d post-hatching. Doses of Thr represented 5,10,15,40,55,70 and 95% of its ideal level for maximal weight gain and feed efficiency. Other amino acids were maintained at minimized excess levels that were 15% (of ideal) above the various doses of Thr. Following 10d of feeding and a 24h fast, chicks were killed for whole-body protein and amino acid analysis. Using pen accretion means, weight gain (r20·98), protein accretion (r2 0·99), and Thr accretion (r2 0·99) were linear (P<0·01) functions of Thr intake. Slope of the Thr accretion regression line indicated that 82% of the Thr intake was recovered in whole-body protein. At zero Thr intake, chicks lost 11·9 mg Thr/d. The Thr maintenance requirement was 45·7 mg/d per kg body weight 0·75. Increasing doses of Thr resulted in increased (P<0·05) concentrations of methionine, isoleucine, histidine and lysine in whole-body protein. Other indispensable amino acids, including Thr, also tended to increase. Whole-body glycine, proline, serine and cystine concentrations decreased (P<0·05) as Thr was increased in the diet. The maintenance need for Thr represented 5·5% of the total need for Thr. The data suggest that efficiency of Thr utilization is constant at all levels of Thr intake between 5 and 95% of the level required for maximal weight gain and feed efficiency.

Two experiments were designed to determine the tissue distribution of threonine oxidation through the threonine dehydrogenase (EC 1.1.1.103) pathway in pigs. The first experiment was conducted on eleven Piétrain x Large White piglets. The piglets were slaughtered at 5, 12 or 20 kg after 1 h of infusion with L-[U-14C]threonine (55 kBq/kg) mixed with unlabelled threonine (100 mg/kg). In the second experiment, four Piétrain x Large White and four Large White piglets (10 kg body weight) were infused with L-[1-13C]threonine (50 mg'kg) mixed with 50 mg'kg unlabelled threonine for 1 h, then killed for tissue sampling. In the two experiments, threonine dehydrogenase specific activity and threonine and glycine specific radioactivities and enrichments were measured in several tissues and in plasma. The higher level of labelling of threonine in the pancreas than in the liver suggested either a lower protein degradation rate or a faster rate of threonine transport in the liver than in the pancreas. Threonine dehydrogenase activity was found only in the liver and the pancreas. Whereas liver and pancreas threonine dehydrogenase specific activities were similar, glycine specific radioactivity and enrichment were 12- to 14-fold higher in the pancreas than in the liver. This is probably the consequence of a higher production rate of glycine from sources other than threonine (protein degradation, de novo synthesis from serine) in the liver than in the pancreas. Our results showed that Large White pigs could oxidize more threonine than Piétrain x Large White pigs. This could be related to the difference in growth performance and dietary N efficiency for protein deposition between these two genotypes.

A study was conducted to evaluate increasing dietary levels of threonine on performance and carcass quality of growing gilt pigs (live-weight period of 50 to 95 kg; no. = 384) by using two different types of basal diets. One basal diet (basal A) was composed of highly digestible food ingredients and the other diet (basal B) of less well digested food ingredients. Before starting the growth trial, Heal apparent digestibility ofamino acids of both basal diets was determined in an in vivo digestibility trial with pigs. Both basal diets were composed in such a way as to obtain equal contents for net energy and Heal digestible threonine, lysine, methionine + cystine and tryptophan. The content of Heal digestible threonine in both basal diets was approximately 3·3 g/kg, corresponding with a total threonine content of 4·8 g/kg in basal diet A and 5·4 g/kg in basal diet B. To both diets three graded dose levels (0·4, 0·8 and 1·2 g/kg) of L-threonine were added, providing at the highest supplemented level 4·5 g/kg Heal digestible threonine. The requirement for Heal digestible threonine was estimated to be 4·1 g/kg regardless of diet composition. This estimated requirement was mainly based on the results for food conversion efficiency. For obtaining maximum weight gain, the requirement for Heal digestible threonine was found to be somewhat higher than for maximum efficiency of food utilization. The estimated requirement figure of 4·1 g Heal digestible threonine corresponded with approximately 5·6 g total threonine per kg in basal diet A and 6·2 g/kg in basal diet B. Carcass quality was not affected by the content of threonine in the diets.