The IMTA-cultivated Chlorophyta Ulva spp. as a sustainable ingredient in Nile tilapia (Oreochromis niloticus) diets

Increasing levels of a mixture of Ulva spp. produced in an integrated multi-trophic aquaculture (IMTA) system were evaluated in Nile tilapia juveniles for partial replacement of dietary fish meal. A control diet (CTRL) was compared with three experimental diets containing 10 % (U10), 15 % (U15), and 20 % (U20) of Ulva spp. meal. Triplicate groups of fish (13 g initial body weight) were fed each diet for 63 days at 26 °C. Nutrient apparent digestibility coefficients and nitrogen retention efficiency did not vary significantly among diets. By the end of the trial, all groups of fish more than tripled their initial body weight. Specific growth rate and final body weight of U10 diet were similar to CTRL and significantly higher than U15 and U20 diets. Increasing Ulva dietary incorporation levels significantly increased feed conversion ratio (FCR), from 1.0 (CTRL) to 1.4 (U20). Fish fed with U10 diet had the highest protein efficiency ratio and nitrogen retention efficiency allowing this fish to growth and reach a final body weight similar to the CTRL group. Protein content was highest in fish fed with the CTRL diet, whereas the highest lipid content was observed in fish fed with U20 diet. The results show that the incorporation of IMTA-produced Ulva meal in Nile tilapia diets is possible up to 10 % without compromising growth performance, protein utilization, and protein retention of juveniles. The high capacity of Nile tilapia to digest all experimental diets suggests that Ulva meal is a practical partial replacement for fish meal in Nile tilapia diets.     

Inclusion of alternative marine by-products in aquafeeds with different levels of plant-based sources for on-growing gilthead sea bream (Sparus aurata,L.): effects on digestibility,amino acid retention,ammonia excretion and enzyme activity

The search for new sustainable aquafeeds for the species with greater economic importance, such as the gilthead sea bream in Europe, is one of the main challenges in the aquaculture sector. The present work tested fishmeal replacement by a mixture of plant meals at different levels, as well as the use of marine by-products with attractant properties and high-quality protein in high plant protein diets. In order to do that, effects on growth and biometric parameters, digestibility, amino acid retention, excreted ammonia and proteases and amylase activity were assessed, using six different diets: FM100 (100% of protein provided by fishmeal), FM50 (50% of replacement), FM25 (75% of replacement) and FM0 (100% of replacement), but also FM25+ (75% of replacement and 15% of squid and krill meal inclusion), and FM0+ (100% of replacement and 15% of squid and krill meal inclusion). In group FM0, a clear impact of dietary changes was observed on growth, survival and ammonia excretion. Amino acid retention in group FM0+ was also significantly affected, which can be explained by the limited content of certain amino acids in this diet. On the other hand, no significant differences were observed in most biometric parameters or in enzyme activity. In conclusion, complete fishmeal replacement can be achieved by using a mixture of plant-based sources, but supplementation with complementary marine ingredients can prevent detrimental effects on growth, survival, nutritional parameters and protein metabolism.     

Effect of partial substitution of dietary protein by a single gluconeogenic dispensable amino acid on hepatic glucose metabolism in rainbow trout (Oncorhynchus mykiss)

Our objective was to understand the influence of dietary gluconeogenic amino acids on hepatic glucose metabolism in rainbow trout (Oncorhynchus mykiss). We analyzed the effects of partial substitution of dietary protein by a single gluconeogenic dispensable amino acid (DAA: alanine, aspartic acid or glutamic acid), on the regulation of hepatic glycolytic and gluconeogenic enzymes. We fed juvenile rainbow trout with isonitrogenous and isoenergetic diets in which part of nitrogen from fishmeal was replaced by nitrogen from one of the three DAA. Fish were fed over 9 weeks and samples withdrawn 6 h after feeding or 5 days after food deprivation. Our data did not show a clear effect of an excess of DAA on activities of glycolytic enzymes (glucokinase and pyruvate kinase) compared to the control diet. In contrast, feeding caused a significant repression of gluconeogenic enzyme activities (glucose-6-phosphatase, fructose-1,6-bisphosphatase and mitochondrial phosphoenolpyruvate carboxykinase) only in fish fed the three DAA substituted diets. However, these differences were insufficient to affect postprandial glycemia significantly. In conclusion, an excess of dietary DAA tested does not seem to modify glycemia or to have a negative impact on dietary carbohydrate utilization in rainbow trout.     

Modulation of blackspot seabream (Pagellus bogaraveo) intermediary metabolic pathways by dispensable amino acids

The objective of the present work is to investigate the main metabolic pathways by which dispensable amino acids (DAA) are diverted towards lipid formation in blackspot seabream. For that purpose, a control diet was formulated to contain 45% of crude protein (7.2 g N/100 g dry matter) mainly supplied by fish meal (45P). In two other diets, 22.2% of the dietary nitrogen (1.6 g N/100 g dry matter) was replaced by an equivalent amount of nitrogen provided by two different mixtures of DAA: alanine and serine (diet AS) or aspartic and glutamic acid (diet AG). A fourth diet (diet 35P) only containing 35% of crude protein (5.6 g N/100 g dry matter) was included in order to analyze the possible additive effects of DAA. Compared to fish fed diet 35P, blackspot seabream appear to make a more efficient use of the nitrogen provided by alanine and serine than that provided by aspartic and glutamic acids in terms of growth. Contrary to fish fed AG, fish fed AS attained similar specific FAS activities as 45P fed fish, suggesting a further role of alanine and serine on this lipogenic pathway. Dietary nitrogen reduction (45P vs. 35P) or its replacement by a mixture of aspartic and glutamic acids (diet AG) were shown to up-regulate phosphoenolpyruvate carboxykinase (PEPCK) but without, however, any effect on plasma glucose levels. Dietary nitrogen level and nature seems to exert a complex regulation on energetic pathways through the gluconeogenesis/tricarboxylic acids cycle interaction.     

Effect of Dietary Addition of Amino Acids and Proteins on the Activities of Some Urea Cycle Enzymes in Rat Liver

The activities of ornithine transcarbamylase, arginine synthetase and arginase in the liver of rats receiving basal diets containing 25% casein supplemented respectively with arginine, aspartic acid, glutamic acid, glycine, a mixture of arginine, aspartic acid and glutamic acid, egg albumin, casein, wheat gluten and gelatin have been determined.

These urea cycle enzymes in rats receiving diets supplemented with the various nitrogen sources were generally increased, but the increments were due to the increase of the ingested amount of nitrogen, and not the specific effect of the individual amino acids or proteins. The excretion of urinary urea in general was increased proportionally with the elevations of these enzyme activities, independent of the nature of the dietary nitrogen.     

The role of energy,serine, glycine,and 1-carbon units in the cost of nitrogen excretion in mammals and birds

The efficiency with which dietary protein is used affects the nitrogen excretion by the animal and the environmental impact of animal production. Urea and uric acid are the main nitrogen excretion products resulting from amino acid catabolism in mammals and birds, respectively. Nitrogen excretion can be reduced by using low-protein diets supplemented with free amino acids to ensure that essential amino acids are not limiting performance. However, there are questions whether the capacity to synthesize certain nonessential amino acids is sufficient when low-protein diets are used. This includes glycine, which is used for uric acid synthesis. Nitrogen excretion not only implies a nitrogen and energy loss in the urine, but energy is also required to synthesize the excretion products. The objective of this study was to quantify the energy and metabolic requirements for nitrogen excretion products in the urine. The stoichiometry of reactions to synthesize urea, uric acid, allantoin, and creatinine was established using information from a publicly available database. The energy cost was at least 40.3, 60.7, 64.7, and 65.4 kJ/g excreted N for urea, uric acid, allantoin, and creatinine, respectively, of which 56, 56, 47, and 85% were retained in the excretion product. Data from a broiler study were used to carry out a flux balance analysis for nitrogen, serine, glycine, and so-called 1-carbon units. The flux balance indicated that the glycine intake was insufficient to cover the requirements for growth and uric acid excretion. The serine intake was also insufficient to cover the glycine deficiency, underlining the importance of the de novo synthesis of serine and glycine. One-carbon units are also a component of uric acid and can be synthesized from serine and glycine. There are indications that the de novo synthesis of 1-carbon units may be a “weak link” in metabolism, because of the stoichiometric dependency between the synthesized 1-carbon units and glycine. The capacity to catabolize excess 1-carbon units may be limited, especially in birds fed low-protein diets. Therefore, there may be an upper limit to the 1-carbon-to-glycine requirement ratio in relation to nutrients that supply 1-carbon units and glycine. The ratio can be reduced by increasing uric acid excretion (i.e., reducing protein deposition) or by dietary supplementation with glycine. The hypothesis that the 1-carbon-to-glycine requirement ratio should be lower than the supply ratio provides a plausible explanation for the growth reduction in low-protein diets and the positive response to the dietary glycine supply.     

Diurnal ammonia and urea excretion rates in European sea bass, Dicentrarchus labrax fed diets containing mixtures of canola and cotton seed oil at two different ambient temperature

The knowledge about the combined effects of higher temperature and dietary nutrient quality on the diurnal nitrogenous excretion rates is very limited in farmed fish species including European sea bass. Therefore this study investigated the combined effects of increasing levels (30 vs. 60 %) of dietary fish oil replacement by equal mixture of cotton seed oil (CSO) and canola oils (CO) and two different ambient temperature (24 vs. 30 °C) on diurnal total ammonia and Urea–N excretion rates in European sea bass (Dicentrarchus labrax). Experimental diets were fed to fish three times (08:30–13:30–18:30 h) at a fixed rate of 3 % BW.d⁻¹. The daily consumed nitrogen and energy intake of fish were similar during the investigation in different dietary treatments. However, the daily excretion rates of TAN, total nitrogen (TAN+Urea–N) and total nitrogen expressed as a proportion of consumed nitrogen by the European sea bass maintained at 30 °C were found to be significantly (P<0.001) higher (40 to 50%) than fish maintained at 24 °C in all the dietary treatments suggesting higher rates of deamination of ingested amino acids with increased temperature. Daily urea–nitrogen excretion of fish accounted for between 20–30 % of total ammonia–nitrogen excretion rates for each dietary treatment at 24 and 30 °C and appeared to be slightly increased by the temperature but neither the temperature nor the amount of plant oil mixture inclusion in diets or the interaction of these two factors had a significant effect on the urea nitrogen excretion rates of fish in different dietary treatments. However, Urea–N excretion rates in fish fed fish oil only (FO) diet were significantly higher (P<0.05) compared to that of fish fed diets containing increasing amount of plant oil mixture (VOM30 and VOM 60) during the light-on phase of the sampling period at 24 °C indicating periodic enhancement of permeability for urea at excretion sites. Further research is needed in order to elucidate the mechanism of nitrogenous excretion in European sea bass fed plant oil containing diets under extreme summer time temperatures employing total dietary fish oil replacement to reveal the possible effects of alteration in cell membrane phospholipid composition on enzymes responsible for nitrogenous excretion and/or detoxification.     

The utilization of nitrogen for growth in mice fed blends of purified proteins

Reasons for differences in growth of weanling mice fed different blends of purified proteins in diets apparently adequate in indispensable amino acids were investigated. Dietary nitrogen provided at increasing levels from a mixture of casein, gelatin, and zein, or from these plus gliadin and lactalbumin resulted in similar weight gains and efficiency of feed utilization in weanling mice. These responses were always lower (P less than 0.05) than for mice fed the control diet. When diets were based on true digestible nitrogen and amino acids, weight gains and feed efficiency decreased (P less than 0.05) as the dietary nitrogen level increased. High plasma glycine concentrations and high phenylalanine to tyrosine ratios were associated with high dietary glycine levels provided by gelatin. When a mixture of constant proportions of protein sources, predominantly casein, supplied most of the dietary nitrogen, small increases in weight gains and feed efficiency were observed as the nitrogen level in the diet increased. Varying the proportions of sources, which increased the percentage of gelatin, resulted in decreased gains in response to more dietary nitrogen. Replacing the amino acids found in gelatin by crystalline L-amino acids and replacing glycine by glutamic acid improved gains and feed efficiency (P less than 0.05) compared with gelatin-containing diets. These studies demonstrated that glycine at dietary concentrations of approximately 1-2%, either from gelatin or as the free amino acid, inhibited growth and feed utilization of growing mice.     

Effects of a dietary organic acid mixture and of dietary fibre levels on ileal and faecal nutrient apparent digestibility, bacterial nitrogen flow, microbial metabolite concentrations and rate of passage in the digestive tract of pigs

Six 34-kg barrows were fitted with a post-valve T-caecum cannula and assigned to six dietary treatments according to a 6 × 5 change-over design to study how a mixture of formic acid, sorbate, and benzoate (0 or 8.4 g/kg feed) influences apparent ileal and faecal digestibility coefficients, bacterial nitrogen (N) flow, microbial metabolite concentrations, and passage rate in pigs fed isoenergetic diets with medium, high, or very high fibre content (neutral-detergent fibre (NDF): 199, 224, and 248 g/kg dry matter, respectively). These barley and soya-bean meal based diets contained 0, 75, and 150 g/kg barley fibre (NDF: 577 g/kg) and 0, 8, and 16 g/kg rapeseed oil, respectively. The dietary organic acid mixture improved the apparent ileal digestibility of 14 of the 17 amino acids analysed (P < 0.05). Increasing levels of dietary fibre linearly decreased the apparent ileal digestibility of six of the 17 amino acids analysed (P < 0.05). Ileal flows of bacterial N and amino acids as assessed on the basis of purine flow were decreased by the dietary organic acid mixture (P < 0.05) but were not affected by dietary fibre level (P>0.05). As assessed on the basis of diaminopimelic acid flow, bacterial N flow was increased by both the dietary organic acid mixture and increased dietary fibre levels (P < 0.05). The dietary organic acid mixture reduced the concentration of lactic acid and increased that of acetic acid in ileal digesta (P < 0.05), while dietary fibre levels had a quadratic effect on concentrations of acetic, propionic, and butyric acid (P < 0.05). The mean retention time of Co (solute marker) and Yb (particle marker) in the large intestine decreased in a linear manner by increasing dietary fibre levels (P < 0.05) but was not affected by the dietary organic acid mixture (P>0.05). The results show that a dietary organic acid mixture has a positive effect on the apparent ileal digestibility of most amino acids irrespective of dietary fibre levels. This could be at least partly related to changes in bacterial N flow in the ileum. However, different bacterial markers showed opposite effects on bacterial N flow, which makes it questionable to use a constant bacterial marker / bacterial N ratio to estimate bacterial N flow. Increasing levels of dietary fibre had negative effects on the apparent ileal amino acid digestibilities and shortened the mean retention time of digesta in the large intestine.     

Effect of various kinds of dietary protein and supplementation with limiting amino acids on growth,haemolymph components and uric acid excretion in the silkworm, Bombyx mori

Effects of various kinds of dietary protein on growth of the silkworm, Bombyx mori, were determined using semi-synthetic diets. Also, the ingestion, digestion and utilization of dry matter and of nitrogen were measured. Nutritive effects of dietary proteins and supplementation of limiting amino acids on haemolymph protein and amino acids pattern were also investigated. Larval growth was largely dependent on the dietary proteins. When the larvae were reared on a diet containing weakly nutritive proteins such as gluten and zein, haemolymph protein was decreased and uric acid excretion was markedly accelerated. The free amino acid composition of the haemolymph manifested characteristic patterns according to the kinds of dietary protein.The supplementation of gluten and zein with their limiting amino acids resulted in a rise of haemolymph protein and a drop in uric acid excretion. The amino acid patterns in the haemolymph were greatly changed according to supplementation.     

The nature of the ingested protein has no effect on lean body mass during energy restriction in overweight rats

Severe energy restriction in obesity not only leads to fat mass loss but also to lean mass loss. The aim of this study was to compare the capacity of casein, a slowly digested protein, and milk soluble proteins (MSP; rapidly digested) to limit the loss of lean mass induced by energy restriction. Obesity was first induced in male Wistar rats by a 5-week feeding with a high-fat high-sucrose diet. The impact of energy restriction was then studied with high-protein (32%) diets containing either casein, MSP, or a 50/50 mixture of both proteins for 3 weeks (n = 10 per group). Food intake, body weight, nitrogen balance, creatinine, and 3-methyl-histidine excretion were measured during energy restriction. Then, tissue weights, plasma metabolic parameters (amino acids, glucose, insulin, cholesterol, triglycerides), and in vivo liver and extensor digitorum longus (EDL) muscle protein synthesis rates were measured in postabsorptive state at the end of the experimental period. Although significant differences relevant to protein metabolism were observed between groups (protein intake, plasma amino acid concentrations, fecal nitrogen excretion, muscle protein synthesis rates), week per week, there were no significant differences in nitrogen balance whatever the protein used. In conclusion, our results show that in young overweight energy restricted rats, using a high-protein diet, the nature of protein intake has no influence on body protein retention.     

Increasing dispensable amino acids in diets of kittens fed essential amino acids at or below their requirement increases the requirement for arginine

Summary Kittens fed diets containing 0.75 × the NRC (1986) essential amino acid requirement (EAArq) and 210 to 560g crude protein(CP)/kg diet exhibited, with increasing CP: 1) decreasing weight gain, 2) decreasing plasma arginine concentrations, 3) increasing urinary orotic acid excretion, 4) increasing plasma glutamic acid concentrations, and 5) plasma isoleucine concentrations at levels that suggest a marginal isoleucine deficiency. Kittens fed a control diet (CD) containing 1.5 × EAArq and 350 g CP/kg diet had maximal weight gains and no orotic aciduria. It was concluded that the decreased weight gain and adverse metabolic effects were caused by arginine deficiency and possibly glutamic acid toxicity induced by high dietary dispensable amino acids. Kittens fed the diets containing 1.0 × EAArq and 350 and 560 g CP/kg diet had depressed plasma arginine and elevated glutamic acid concentrations and orotic aciduria. These results indicate that 10 g arg/kg diet is not adequate at CP concentrations above 280 g/kg and the calculated requirement of arginine is (0.02 g arginine/g CP) × (Y g CP/kg diet) + (4.0 g arginine/kg diet) where Y is the dietary CP level.Abbreviations CD control diet - CP crude protein (g CP/kg diet = g nitrogen/kg diet × 6.25) - DAA dispensable amino acids - EAA essential amino acids - EAArq essential amino acid requirement     

The Role of Dispensable Amino Acids for the Maximum Growth of Chick

Chicks were fed on the purified diets of which amino acid pattern was modeled after whole egg protein and crude protein content was 21.1%, changing the dietary ratio of indispensable amino acid nitrogen to dispensable amino acid nitrogen (I/D ratio) from 1/1.5 to 3/1 at regular intervals. The balances among amino acids in each indispensable and dispensable group of test diets were kept the same pattern as that of the whole egg, respectively. Optimum I/D ratio for normal chick growth was estimated to be in the range of between 1/1 and 1.5/1, because feed efficiency was the highest at the I/D ratio 1/1 and growth rate was the highest at the I/D ratio 1.5/1.

Chicks were killed and the serum was collected at the end of the experiment. It was shown that the I/D ratios of free amino acid in the serum of chicks were strongly influenced by that of diet.

White Leghorn chicks fed on the Scott’s reference amino acid diet grew as well as those fed on a conventional chick starter. Nitrogen retention of the former was a little less than that of the latter, but the amount of carcass fat of the former was almost twice as much as the latter.

Growth rate of chick was considerably reduced, when glutamic acid which is the only dispensable amino acid in the Scott’s diet was replaced by a mixture of glutamic acid, aspartic acid, alanine and serine, nitrogen content being kept at constant. Sufficient amount of glutamic acid in the Scott’s diet seems to be essential for the maximum growth of chick.     

Effects of amino acid supplementation on the nutritive quality of fermented linseed meal protein in the diets for rohu, Labeo rohita, fingerlings

A feeding trial was conducted for 8 weeks to examine the effects of partial substitution of fish meal (FM) protein (crude protein content: 58.5%) with linseed meal protein with and without supplemental amino acids in diets for rohu Labeo rohita (Hamilton), fingerlings (mean weight: 1.50 ± 0.3 g). Prior to incorporation into the diets, linseed meal was fermented with lactic acid bacteria ( Lactobacillus acidophilus ) to reduce/eliminate the antinutritional tannin and phytic acid factors. Twelve experimental diets (diets D1–D12) were formulated to replace the FM protein from a reference diet (RD) with linseed meal protein at different levels (four sets of diets, of which each set of three diets contained 25%, 50% and 75% replacement of FM protein by linseed meal protein, respectively). Diets D1–D3 were not supplemented with any amino acid. Lysine was supplemented in diets D4–D6. Diets D7–D9 were supplemented with methionine + cystine (together), and diets D10–D12 contained lysine and methionine + cystine (together). Lysine and methionine + cystine (together) were added to the diets at 5.7% and 3.1% of dietary protein, respectively. The groups of fish fed diets without amino acid supplementation had significantly lower percentages of weight gain, specific growth rate and high feed : gain ratio than the fish groups fed other experimental diets. The addition of lysine and methionine + cystine to the diet in which 50% of the FM protein was replaced by linseed meal protein (diet D11) significantly improved fish performance. The results of the present study suggest that rohu fingerlings can effectively utilize the supplemented amino acids and that linseed meal protein can replace up to 50% of the FM protein in rohu diets if the linseed meal is properly processed (fermented) and supplemented with the lacking amino acids.     

Carbohydrases and phytase with rice bran,effects on amino acid digestibility and energy use in broiler chickens

Protein sources from cereals are used in broiler diets, usually in order to reduce feeding costs. However, their efficient use in poultry diets is limited by the level of fiber whose compounds are resistant to digestion in the small intestine; due to this sugars are not digested by endogenous poultry enzymes. The aim of this study was to determine the effect of multi-carbohydrase (MC) and phytase (Phy) on the total retention of nutrients, retention of apparent metabolizable energy corrected for nitrogen (AME_N) (trial 1) and apparent and standardized ileal digestibility of amino acids (trial 2) of rice bran (RB). A total of 245-day-old male broilers (Cobb 500) was distributed at 21-day-old in a completely randomized design in a 2 × 2 + 1 (0 and 200 mg/kg MC; 0 and 50 mg/kg Phy, and basal diet – BD) factorial arrangement of treatments, to give seven replicates and seven birds per replicate. The BD based on corn (trial 1) and cornstarch and casein (trial 2) was used only to determine the coefficients of retention of nutrients and energy, and coefficients of digestibility of amino acids of the RB. The test diets were made by mixing BD and RB 7 : 3 wt/wt basis. There was interaction (P<0.05) between MC × Phy for DM, nitrogen and AMEN, retention and no interaction (P>0.05) for ash, calcium, phosphorous and NDF was observed. Enzymes interacted (P<0.05) on standardized ileal digestibility of arginine, histidine, leucine, methionine, phenylalanine, threonine, valine, aspartic acid, glutamic acid, proline and serine. Dietary combination of MC and Phy resulted in higher (P<0.05) standardized digestibility of arginine, histidine, methionine and threonine relative to single enzyme supplementation or control diet without enzymes. Enzyme isolated inclusions in the diets improved (P<0.05) standardized digestibility of methionine. The supplementation of carbohydrases and Phy in RB will improve the nitrogen, energy and amino acids utilization for broiler chickens.     

Effect of low-protein corn and soybean meal-based diets on nitrogen utilization,litter quality,and water consumption in broiler chicken production: insight from meta-analysis

The growing demand for high-value animal protein must be met using sustainable means that optimize the utilization of nutrients, especially nitrogen (N) so that excreta do not over-fertilize fields and end up causing soil acidification, waterway eutrophication and greenhouse gas emissions. Malodorous N compounds can cause respiratory diseases and poor growth in livestock. The increasing availability of feed-grade amino acids makes it possible to formulate low-protein diets for broilers and thereby reduce N excretion. However, published studies of the effects of such diets on broiler growth performance have been based on reducing CP contents gradually in a variety of ways that have given inconsistent results. Since the amount of published data is now large, a meta-analysis was performed in order to categorize diet formulation strategies and quantify their impact on N balance, water consumption, litter moisture, plasma uric acid. This showed that lowering the CP content of broiler diets generally means replacing some soybean meal with corn and hence increasing the starch content. However, since soybean meal is also a source of potassium, this reduces electrolyte balance. Lowering the CP content from 19% to 17% is associated with a 29% reduction of N excretion in broilers aged 0–21 d, and a 7% increase in N efficiency (N retention/N intake). Reducing the CP content from 19% to 17% decreases daily water consumption by 20.6 mL/bird, litter moisture by 2.2% and plasma uric acid by 0.56 mg/dL. This meta-analysis improves our understanding of the low-protein strategy and allows us to quantify its impact on N balance, litter quality and uric acid. It shows that managing N excretion is wholly beneficial and reduces litter wetness.     

Effect of dietary taurine supplementation on metabolome variation in plasma of Nile tilapia

Taurine has been considered as an essential nutrient for many aquaculture species. While dietary taurine supplementation is highly recommended, novelty studies on taurine metabolism in fish are needed. The present study aimed to provide insight into the molecular mechanisms involved in multiple metabolome changes in Nile tilapia (Oreochromis niloticus) by studying plasma metabolic profile changes in response to graded levels of dietary taurine supplementation. The analysis used proton nuclear magnetic resonance-based metabolomics. Four groups of tilapias were fed with four diets supplemented with 0.0, 0.4, 0.8 and 1.2% taurine for 84 days. Fish plasma was sampled at multiple time points to provide an accurate snapshot of specific metabolic profiles during growth. Under the effect of taurine supplementation, 21 and 12 metabolites in tilapia plasma shown significant changes in terms of time-dependence and diet-dependence, respectively. These metabolic changes in tilapia plasma were mainly associated with energy and amino acid metabolism, lipids, nucleotides and protein metabolism. The results indicate that 0.8% taurine supplementation could significantly improve the carbohydrate synthesis, protein digestion and absorption, and fat deposition of tilapia and thereby promoted growth and development of tilapia.     

Intake,digestibility and nitrogen utilization of Robinia pseudoacacia foliage fed to growing goat wethers

Black locust (BL; Robinia pseudoacacia L.), a native tree of southeastern USA known to contain substantial levels of condensed tannins (CT), was fed to 32, 4 month old (20.4 kg BW) Boer cross wether goats in two randomized complete block design trials. The objectives were to examine the effects of feeding hay diets containing several levels of fresh BL foliage on intake, digestibility, and N metabolism. First year (1999) diets were H_E (100% Eastern gamagrass [EGH; Tripsacum dactyloides L.] hay), H_EG (70% EGH and a 30% mixture of 59% ground corn [GC; Zea mays L.], 36% soybean meal [SBM; Glycine max L.], and 5% minerals), 25BL99 (75% EGH and 25% BL leaves), and 50BL99 (50% EGH and 50% BL leaves). Second year (2000) diets were H_O (100% orchardgrass [OGH; Dactylis glomerata L.] hay), H_OG (70% OGH and a 30% mixture of 63% GC, 37% SBM, and 5% minerals), 50BL00 (50% OGH and 50% BL leaves), and 75BL00 (25% OGH and 75% BL leaves). In 1999, apparent digestibilities of the diets in the order listed above were 62.4, 68.2, 58.0, and 60.6% (P = 0.001) for DM and 62.8, 72.5, 56.0, and 59.1% (P = 0.001) for crude protein (CP). Acid detergent lignin digestibilities were negative for diets 25BL99 (−56.7%) and 50BL99 (−49.3%), apparently due to the formation of insoluble tannin and lignin complexes during passage through the digestive tract. Intakes of DM were similar across diets. In 2000, apparent digestibilities of diet DM (64.4, 71.7, 64.8 and 65.4%) and CP (70.0, 76.0, 66.6, and 66.5%) did not differ. Lignin digestibilities were positive for diets 50BL00 (9.4%) and 75BL00 (29.6%) unlike those for year 1999. Overall, BL contained 10% CT and 18–34% hydrolyzable tannins. In 1999, N intake, urinary N (UN) excretion and N retained were higher for diet H_EG (P = 0.01) than diet H_E whereas fecal N excretion (FN) was similar for diets H_EG, 25BL99 and 50BL99. In 1999, FN excretion as a percentage of N intake was higher (P < 0.02) in the BL diets, although UN as a percentage of N intake did not differ among diets. In 2000, N intake and FN output were higher for BL diets compared to diets H_O (P = 0.01) and H_OG (P = 0.02). Fecal N as a percentage of N intake was lower (P = 0.01) for diet H_OG (24.0%) than for diets 50BL00 (33.4%) and 75BL00 (33.5%). Conversely, urinary N as a percentage of N intake was higher for diets H_O and H_OG compared to the BL diets (P = 0.02). Increased levels of dietary BL increased FN, suggesting that tannins formed insoluble protein complexes thus hindering digestibility.     

Effect of ration level on nitrogen excretion, nitrogen retention and efficiency of nitrogen utilization for growth in largemouth bass (Micropterus salmoides)

Largemouth bass ( Micropterus salmoides ) with an average weight of 45.5 g were used to study ration level effects on nitrogen excretion, nitrogen retention, and gross efficiency of utilization of nitrogen for growth. Bass were starved 3 to 4 days and then each bass was placed into an aquarium containing a known volume of water. One day after the fishes were placed in aquaria, nitrogen excretion rates were determined; this rate is the maintenance nitrogen excretion. Each fish was then fed one or more shiners ( Notropis cornutus ); fish were fed only once. Nitrogen excretion measurements were made daily until the rates were similar to maintenance rates. The nitrogen excretion rates for each day after feeding which were above the maintenance nitrogen excretion were combined and reflect the total nitrogen excretion for a given ration level. All ration levels were converted to nitrogen consumption in mg and nitrogen absorption was calculated from subtracting the average faecal nitrogen from nitrogen consumption. From data on nitrogen consumption, nitrogen absorption, nitrogen excretion, and faecal nitrogen, calculations were made for nitrogen retention and gross efficiency of utilization of nitrogen for growth.
As ration level and nitrogen absorption increased, nitrogen excretion increased and is described by the equation, Y = 8.56+0.40 X , where Y is total nitrogen excretion and X is nitrogen absorption. Nitrogen retention also increased with nitrogen absorption and is described by the equation, Y =–8.57+0.60 X , where Y is nitrogen retention and X is nitrogen absorption. Efficiency increases rapidly above maintenance, but levels off at higher ration levels and approaches an asymptote of 60%.     

Effects of exogenous enzymes (phytase, non-starch polysaccharide enzyme) in diets on growth, feed utilization, nitrogen and phosphorus excretion of Japanese seabass, Lateolabrax japonicus

A feeding experiment was conducted to investigate the effects of exogenous enzymes (phytase, non-starch polysaccharide enzymes: WX and VP, supplied by DSM) on growth performance and excretion of Japanese seabass (Lateolabrax japonicus) (initial mass 6.26+/-0.10 g). A basal diet was used as a control that contained a mixed protein source, and lysine, methionine and valine were supplemented to simulate the essential amino acid pattern of fish meal. Four other diets were supplemented with 200 mg phytase (500 IU), 400 mg VP, 800 mg WX, or a combination of 800 mg WX and 400 mg VP per kg diet, respectively. Each diet was assigned to triplicate groups of fish in floating sea cages, and each cage was stocked with 60 fish. The results showed specific growth rate (SGR) and feed efficiency ratio (FER) were not significantly improved by the phytase supplementation. However, supplementations with WX and VP significantly enhanced the SGR and FER (P<0.05). Phosphorus retention was significantly increased by the supplementation with phytase, whereas nitrogen retention was also enhanced by supplementations of non-starch polysaccharide enzymes (P<0.05). The excretion experiment showed that the soluble phosphorus and ammonia nitrogen in starved fish were constant, irrespective of dietary treatments. The total phosphorus effluent in fish fed the diet with phytase supplementation was significantly lower compared with the control group after feeding to satiation (P<0.05), but soluble phosphorus excretion was still independent of dietary treatments. The ammonia excretion in satiated fish significantly decreased with supplementations of non-starch polysaccharide enzymes.