Protein-sparing Action Research Articles

Momordica charantia saponins administration in low-protein-high-carbohydrate diet improves growth, blood biochemical, intestinal health and microflora composition of juvenile common carp (Cyprinus carpio).

An 8-week feeding trial was conducted to explore the feasibility of Momordica charantia saponins (MCS) administration to facilitate the protein-sparing action of high carbohydrate in diets for juvenile common carp (Cyprinus carpio) with initial mass of 5.41±0.02g. Based on our previous study, four diets with different the ratio of protein and carbohydrate (P/C ratio) were designed: 32%P/40%C, 30%P/43%C, 28%P/46%C, 28%P/46%C supplemented with 0.16% MCS (28%P/46%C+MCS). Each diet treatment was divided into 3 replicates. Results revealed that 30%P/43%C group increased growth performance and intestinal digestion, decreased intestinal inflammation, and optimized the intestinal microbiota compared to 32%P/40%C group, which presented the stronger protein-sparing action of high carbohydrate. But if the P/C ratio reduced to 28%P/46%C or less, the saving action would be restrained. However, compared to the 30%P/43%C and 28%P/46%C groups, 28%P/46%C+MCS group significantly elevated growth performance and activities of digestive enzymes and antioxidative enzymes, whilst the opposite trend occurred in the contents of glucose, triglyceride, total cholesterol, low density lipoprotein cholesterol, blood urea nitrogen, glutamic oxalacetic transaminase, glutamic-pyruvic transaminase and malondialdehyde. In addition, 28%P/46%C+MCS group markedly upregulated the expressions of GH/IGF axis genes, genes involved in protein synthesis, antioxidant genes and anti-inflammatory cytokine, whilst the opposite trend occurred in the expressions of pro-inflammatory cytokines. Moreover, 28%P/46%C+MCS group obtained the remarkably higher Enterococcus proportion and lower Lactococcus proportion compared to the 30%P/43%C and 28%P/46%C groups, whereas the opposite occurred in 30%P/43%C group, which indicated that there existed differences in the improvement mechanism on intestinal microflora composition between MCS and appropriate P/C ratio. Combined with the above mentioned changes in our research, we concluded that 0.16% MCS administration in a 28%P/46%C diet could facilitate the protein-sparing action of high carbohydrate in diets for common carp, which could decrease the 5% dosage of soybean meal and synchronously reduce the 4% crude protein of diets without affecting the growth and immune ability for common carp.

Improvement in the growth status and carbohydrate utilization of Labeo rohita (Hamilton, 1822) fingerlings with dietary supplementation of chromium picolinate.

A 60-day feeding experiment was conducted to evaluate the effects of dietary chromium (Cr) on carbohydrate utilization and growth performance of Labeo rohita fingerlings. Fishes were fed with four high carbohydrate (53%), isonitrogenous (crude protein 35%), and isocaloric (415 Kcal, 100 gm-1) experimental diets containing different levels of dietary chromium picolinate (Cr-Pic) viz.0, 400, 800, and 1200 μg kg-1 diet. Weight gain (WG%), specific growth rate (SGR), feed efficiency ratio (FER), and protein efficiency ratio (PER) were significantly increased at 800 μg kg-1 diet chromium supplementation (P < 0.05). Cr-Pic supplementation (800 μg kg-1) also significantly (P < 0.05) enhanced the protein: DNA ratio in muscle, while DNA: RNA and DNA: tissue ratios were significantly (P < 0.05) decreased indicating higher growth. Significantly higher amylase, protease, and lipase activities were recorded in 800 μg Cr-Pic kg-1 diet fed fishes (P < 0.05), while any of the experimental groups showing no significant (P > 0.05) change in hexokinase activity, indicating normal glycolysis in all. Furthermore, significant (P < 0.05) decrease of glucose-6-phospatase activity in 800 μg Cr-Pic kg-1 diet fed group, showcasing an evidence for protein-sparing action with Cr-Pic supplementation. Significantly (P < 0.05) higher serum insulin and liver glycogen in 800 μg Cr-Pic kg-1 diet fed fishes denote an improvement in carbohydrate metabolism. However, significantly (P < 0.05) higher ATPase and SOD activities were also observed when chromium supplementation was more than 800 μg kg-1 diet, indicating stress at higher level. The present study indicates that growth and carbohydrate utilization can significantly (P < 0.05) be improved by feeding the L. rohita fingerlings with Cr-Pic (800 μg kg-1 diet) supplemented diet in laboratory condition.

The body’s protein-sparing action of fat mass during short term fasting acts via proteolysis regulation

The body’s protein-sparing action of fat mass during short term fasting acts via proteolysis regulation

Growth performance and metabolic response of juvenile grouper Epinephelus moara (Temminck &amp; Schlegel, 1842) fed low dietary protein and high lipid levels

Nine test diets were formulated at three low levels of crude protein (P; 35%, 40% or 45%) and three high levels of crude lipid (L; 9%, 12% or 15%) to investigate whether Epinephelus moara differs in the nutrient requirements from any of the other closely-related grouper species, and if there are any indications that a further decrease in protein with increasing dietary lipid would induce a higher protein-sparing effect. Fish (20.34 ± 0.82 g/ind) were distributed among 27 experimental cages (100 cm diameter, 80 cm depth), with 20 fish per cage and three replicates for each test diet. The experiment was conducted over an 8-week period at a temperature of 23.9–25.7°C. Weight gain and specific growth rate (SGR) tended to increase either with an increase in dietary protein level (at the same lipid level) or with the increase in dietary lipid level (at the same protein level, except at the 45% protein level). The highest weight gain and SGR occurred in fish fed the diet P45/L12. The serum cholesterol, high-density lipoprotein-cholesterol (HDL-C) and low-density lipoprotein-cholesterol (LDL-C) contents in fish were significantly increased as the dietary lipid increased. The increase of dietary protein significantly decreased the activities of serum and hepatic alanine aminotransferase (ALT) as well as aspartate aminotransferase (AST). Hepatic fatty acid synthase (FAS) activity significantly increased with the decrease of dietary protein and lipid levels (p < .05). However, lipoprotein lipase (LPL) activity showed an inverse trend compared to FAS. Hepatic glutamate dehydrogenase (GDH) activity significantly increased with the increase in the dietary protein level. In conclusion, the results reveal that growth performance and metabolic responses of E. moara are dependent on dietary protein and lipid levels, and that protein-sparing action can be induced by increasing the dietary lipid. To support the feeding and growth of juvenile E. moara under the present conditions, 45% protein and 12% lipid are adequate.

Growth, feed utilization and body composition of juvenile golden pompanoTrachinotus ovatusfed at different dietary protein and lipid levels

A feeding trial was conducted to determine the suitable dietary protein and lipid levels for juvenile golden pompano Trachinotus ovatus reared in net pens. Ten test diets were formulated at five levels of crude protein (330, 370, 410, 450 or 490 g kg−1) and two levels of crude lipid (65 or 125 g kg−1). Golden pompano fingerlings (initial body weight 4.7 g ind−1) were fed the test diets for 8 weeks. Weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), nitrogen retention efficiency (NRE), energy retention efficiency (ERE), condition factor (CF), hepatosomatic index (HSI), body protein content and total nitrogen waste (TNW) were dependent on both dietary protein and lipid levels. Feed intake (FI) and viscersomatic index (VSI) were dependent on dietary protein level, while body lipid content was dependent on dietary lipid level. Weight gain increased with increasing the dietary protein level (at the same lipid level) but was lower at the dietary lipid level of 65 g kg−1 than at 125 g kg−1 (at the same protein level). Fish fed at the dietary protein levels of 460–490 g kg−1 had higher WG and lower FCR than at 330–410 g kg−1. Energy retention efficiency tended to increase with increasing the dietary protein level from 330 to 410 g kg−1, while no significant difference was found in nitrogen retention efficiency between the dietary protein levels (at the same lipid level). Results of this study suggest increasing the dietary lipid level from 65 to 125 g kg−1 could not induce protein-sparing action in golden pompano, and the suitable dietary protein and lipid levels for juvenile golden pompano reared in net pens should be 450–490 and 65 g kg−1.

Growth, feed utilization and body composition of Asian catfish (Pangasius hypophthalmus) fed at different dietary protein and lipid levels

This study examined the effect of dietary protein and lipid levels on growth, feed utilization and body composition of Asian catfish Pangasius hypophthalmus reared in cages. Eight test diets were formulated at four protein (340, 380, 420 and 460 g kg−1 crude protein) and two lipid (50 and 90 g kg−1 crude lipid) levels. Fish (initial weight 4.7 g fish−1) were fed the test diets for 8 weeks. Final body weight, weight gain (WG), feed intake (FI), feed conversion ratio (FCR), contents of crude protein, lipid and energy in whole body were dependent on both dietary protein and lipid levels, while specific growth rate (SGR), hepatosomatic index and body moisture content were dependent on dietary lipid level. The WG and SGR increased with the increase in either dietary protein level (at the same lipid level) or lipid level (at the same protein level). The FI and FCR decreased with the increase in dietary protein level (at the same lipid level) or lipid level (at the same protein level). Protein sparing action occurred in case dietary lipid level increased. Fish fed the diet containing 453 g kg−1 crude protein and 86 g kg−1 lipid had the highest WG and SGR, but the lowest FI and FCR, among the diet treatments. There were no significant differences in the protein retention efficiency (PRE) and energy retention efficiency (ERE) among the diet treatments, although PRE and ERE were relatively high in fish fed the diet containing 453 g kg−1 crude protein and 86 g kg−1 lipid. At the end of the feeding trial, body protein content increased, while body lipid content decreased, with the increase in dietary protein content at the same lipid level. Our results suggest that dietary levels of 450 g kg−1 crude protein and 90 g kg−1 lipid are adequate to support fast growth of P. hypophthalmus reared in cages.

Effects of supplemental dietary l-carnitine and ractopamine on the performance of juvenile rainbow trout, Oncorhynchus mykiss

This study was carried out to investigate a possible protein-sparing action of l-carnitine and ractopamine in rainbow trout, Oncorhynchus mykiss. An 8-week feeding trial was carried out to evaluate the effects of supplementation of three levels of l-carnitine (0, 1 and 2 g kg−1) and two levels of ractopamine (0 and 10 mg kg−1) on growth performance, fillet fatty acid compositions and blood biochemical parameters in a 3 × 2 factorial experimental design. Ractopamine and 1 g kg−1 carnitine improved the specific growth rate (1.03% and 1.05% day−1), feed conversion ratio (FCR, 1.3 and 1.29), protein efficiency ratio (PER, 1.88 and 1.85) of fish and crude protein (73.5 and 73.8) content of fish fillet. l-carnitine and ractopamine increased the levels of albumin, total protein and globulin in the serum of fish. Apart from eicosapentaenoic acid and docosahexaenoic acid, other fatty acids of fish fillet were increased by ractopamine, while total saturated fatty acids were almost intact. However, the total n-3 poly unsaturated fatty acids were reduced by l-carnitine supplementation (P<0.05). The present study showed that 1 g kg−1l-carnitine and 10 mg kg−1 ractopamine each can improve the performance of rainbow trout and their combination in diet could enhance the protein level and change the fatty acids profile in fillet muscle.

The dietary protein requirement of the Malaysian mahseer, Tor tambroides (Bleeker), and the lack of protein-sparing action by dietary lipid

Two sequential feeding trials were conducted, firstly, to determine the optimal protein requirement for Tor tambroides (Bleeker) fingerlings, and secondly, to investigate the potential protein-sparing effect of dietary lipid when dietary protein is below the requirement. In Experiment 1, triplicate groups of hatchery-raised F 1 generation of T. tambroides were fed semi-purified diets containing one of five dietary protein levels (30 to 50%) for 8 weeks. Fish of initial weight 20.9 ± 0.1 g were fed close to apparent satiation in two equal feedings per day. Growth performance and feed conversion ratio generally improved with increasing dietary protein ( P < 0.05) and polynomial regression analysis revealed a maximum specific growth rate at 48% dietary protein. This corresponded to a protein to energy ratio of 26 mg protein per kJ gross energy. In Experiment 2, a 3 × 2 factorial design was employed in which six diets with 30, 35 or 40% protein and 10 or 15% lipid, respectively, were fed to triplicate groups of T. tambroides (initial weight 0.67 ± 0.15 g) at close to apparent satiation for 12 weeks. No interaction ( P > 0.05) between dietary protein and lipid levels was observed for all growth parameters determined indicating a lack of protein-sparing action by dietary lipid. Daily feed intake was slightly lower in fish fed higher protein diets but dietary lipid level had no apparent effect. Hematocrit and body-organ indices were not significantly affected by diet. Whole-body proximate composition and tissue lipid and protein content were generally not affected by diet even though high fat deposition was observed in the visceral cavity and liver of fish possibly indicating the excess energy content present in all the experimental diets. This study provided the first reported data on the nutrient requirement and body composition of T. tambroides, a mahseer species with aquaculture potential.

L-carnitine improves egg production in black neck ostriches

The important functions of L-carnitine are fostering the oxidation of long-chain fatty acids by mitochondria and stimulating protein-sparing action by increasing energy derived from lipids. The present study was conducted to investigate dietary effects of L-carnitine on egg production of breeder ostriches. Ninety black neck ostrich breeder birds (60 females and 30 males) were examined randomly (completely randomised design) within three treatments and five replicates for 7 months in breeding season. A basal diet was formulated and used for the control group (L1), while two levels of L-carnitine, 250 mg/kg and 500 mg/kg, were included in the basal diet for treatments L2 and L3, respectively. The egg production percentage, egg weight and defective eggshell percentage were measured. The supplementary diet with 500 mg/kg L-carnitine increased (P &lt; 0.01) the egg production percentage. Means (±s.e.) of egg production percentage for L1, L2 and L3 were 9.68, 12.95 and 17.13% (±1.08), respectively. L-carnitine had no effect on the egg weight and the defective eggshell percentage. The results suggest that basal diet supplemented with 500 mg/kg L-carnitine can increase the egg production percentage of ostriches.

Effects of feed composition on life history developments in feed intake, metabolism, growth and body composition of European eel, Anguilla anguilla

To examine the effect of feed composition on changes in feed intake and subsequent feed utilization with age, five populations of European eel, with an average initial body weight of 5 g each fed a different diet, were monitored for 302 d. The five feeds differed in their content of crude protein (33–63% DM), crude fat (6–28% DM) and calculated carbohydrates (NFE; 15–42% DM) such that five levels of digestible protein/digestible energy (DP/DE) were realised: 13, 16, 21, 28 and 29 g MJ − 1 . At three points in time, with three size groups, nitrogen and energy balance studies were conducted in which next to feed intake and growth also digestibilities of dry matter, protein, fat, NFE and energy as well as O 2 consumption and NH 4–N excretion were measured. Due to the distinct life history of the semelparous, in the present study predominantly male eel, a well-defined goal in terms of mature size and composition could be inferred, presumably to maximize their lifetime reproductive output. In order to reach this goal the animal needs to survive and to grow and voluntary feed intake of the eels could be adequately described with the feed intake model ‘eating to requirements subject to constraints’, where voluntary feed intake is considered to originate from a requirement for maintenance (survival) and a requirement for growth. Live weight gain is almost completely based on protein deposition (PD) and eels, like other animals, strive to reach a genetically determined growth potential (PDmax) thought to be driven by the difference from the mature protein mass (Ptmax). Body lipid content increases with size and varied with diet from a minimum of 25% at high DP/DE ratios to a maximum of 33% at low DP/DE ratios, at body weights of 130–140 g. Preferable allocation of dietary protein to PD (protein sparing action of non-protein energy) was confirmed as marginal efficiency of protein utilization increased with decreasing DP/DE ratio from 0.29 to 0.54. Marginal energetic efficiency of PD, k p was 0.54 and marginal energetic efficiency of LD, k f varied from 0.67, indicating de novo lipid synthesis (from dietary protein) at high DP/DE ratios, to 0.93, indicating direct lipid synthesis (from dietary lipid) at low DP/DE ratios. Marginal efficiencies did not differ from those of other fish or other farm animals. Differences between fish species in feed intake and utilization of feeds differing in macronutrient composition, as well as life history developments in feed intake and feed utilization are therefore based on differences in growth rate, in turn with mature weight (Ptmax), and body composition (LD/PD ratio).

Growth performance and body composition of white seabream (Diplodus sargus) juveniles fed diets with different protein and lipid levels

An 83-day feeding trial was carried out to determine the effect of different dietary protein and lipid levels on the growth performances and carcass composition of white seabream. Juveniles (10.7±0.2 g) were fed to satiation on four diets, varying in protein (15% and 28%) and lipid (12% and 16%) levels. The best growth performance was observed in fish fed on diets with higher protein level. Dietary lipids did not affect growth performance. Voluntary feed intake decreased with a increasing dietary protein level at both dietary lipid levels. Feed conversion ratio improved with the increase in dietary protein and lipid levels. Carcass composition remained unaltered by dietary protein levels (P>0.05). Carcass protein content tended to decrease, while lipid content tended to increase in groups fed on 16% lipid, compared with the 12% lipid groups. Additionally, protein retention was higher in fish fed on low-protein and low-lipid levels, compared with the high-protein and high-lipid group (29% vs. 19%). Lipid retention increased significantly with dietary protein level (P<0.001). Energy retention improved with dietary protein, but was not affected by dietary lipid levels. On the basis of our results, feeding white seabream on 15% dietary protein had a negative effect on growth and feed utilization. Dietary lipid did not induce a protein-sparing action in Diplodus sargus juveniles.

Growth and nitrogen metabolism of sea bass fed graded levels of nucleic acid nitrogen from yeast or RNA extract as partial substitute for protein nitrogen from fish meal

RiassuntoPrestazioni zootecniche e metabolismo azotato della spigola in risposta alla parziale sostituzione nella dieta di azoto proteico da farina di pesce con acidi nucleici da lievito o da RNA estratto da lievito Lo studio ha valutato la risposta zootecnica e metabolica di spigole alimentate per 84 giorni con diete isoprotei che dove quote progressive di azoto (N) proteico da farina di pesce erano parzialmente sostituite da N da acid nucleici (NAN) sotto forma di lievito di birra o di RNA (NAN 1,0-4,2% N totale). Le prestazioni zootecniche non sono state modificate dalla fonte o dal livello di NAN nella dieta, ma la ritenzione azotata è peggiorata (P<0,05) nei pesci alimentati con i livelli più elevati di NAN. Le concentrazioni plasmatiche di purine e loro cataboliti come pure l'escrezione di urea e l'attività epatica dell'enzima uricasi, sono aumenti parallelamente al livello di ingestione di NAN. I risultati ottenuti indicano che la sostituzione ancorché parziale di N-proteico con NAN nella dieta non da luogo a risparmio proteico nella spigola dove il catabolismo degli acidi nucleici della dieta è attivo e modulabile da fattori alimentari.

Comparison of starch utilization in fingerlings of two Asian catfishes from the Mekong River (Pangasius bocourti Sauvage, 1880, Pangasius hypophthalmus Sauvage, 1878)

Five diets were formulated to provide an isoproteic daily dietary intake of 15 g kg-1 day-1, while maintaining daily starch intake ranging from 0 to 40 g kg-1 day-1. The 4-week experiments started with initial mean weights of 4.7 and 4.4 g for Pangasius bocourti and P. hypophthalmus, respectively. The results clearly show the protein sparing action of starch in both species. Best protein retention was obtained with starch intake of 20 and 10 g kg day-1 for P. bocourti and P. hypophthalmus, respectively, which was equivalent to 40 and 20% starch in the feed. Pangasius bocourti and P. hypophthalmus fingerlings attained maximal growth with starch intake of 30 and 10 g kg-1 day-1, equivalent to 60 and 20% starch in the feed. It was noted that body lipid accumulation was much higher in P. bocourti than in P. hypophthalmus, and that excess dietary starch intake depressed diet digestibility and growth. (Resume d'auteur)

Effects of dietary carnitine and protein energy:nonprotein energy ratios on growth, ammonia excretion and respiratory quotient in African catfish,Clarias gariepinus(Burchell) juveniles

Two separate feeding experiments were carried out to determine the effects of dietary carnitine supplements on growth rates, total ammonia nitrogen (TAN) excretion and respiratory quotient rates (RQ) in the African catfish, Clarias gariepinus (Burchell), juveniles fed various diets differing in protein energy:nonprotein energy ratio (PE:NPE). In Experiment 1, 540 fish (20.9 ± 1.0 g) were evenly distributed into six dietary groups and fed in duplicate aquaria (N = 12 aquaria) to apparent satiation over a 41-day period, until all fish attained an individual final weight of 156.9 ± 10.8 g. Diets were formulated to contain two levels of carnitine (80 and 660 mg kg−1) and three levels of PE:NPE (0.7, 0.9 and 1.4). Sampling was divided into two size ranges, according to the predicted individual end-weight of 60 g (days 0–16) and 160 g (days 16–41). In Experiment 2, 240 fish (16.5 ± 0.2 g) were distributed in four 140-L aquaria connected to a respirometer and preconditionally fed twice a day at a restricted feeding level of 24 g kg−0.8 day−1 for a 25-day period (final weight of 77.5 ± 1.5 g). Four isonitrogenous diets (368 g kg−1 crude protein) were formulated to contain two levels of fat (85 and 175 g kg%−1) and two levels of carnitine (40 and 600 mg kg−1), in a 2 × 2 factorial design. From days 20–25, three respirometric trials were carried out, during which total ammonia nitrogen (TAN) and RQ were determined over 24 h. In both experiments, carnitine supplemented fish accumulated 2.5−4 times more carnitine in their tissues than fish fed a basal level (P < 0.05). In Experiment 1, the smallest fish (<60 g) fed 660 mg carnitine showed significantly higher growth rates and lower feed conversion rates than 80 mg carnitine supplemented fish only when the dietary PE:NPE ratio was low (0.7). Additionally, dietary carnitine significantly increased protein:fat ratios in the whole body, suggesting a protein-sparing action. In Experiment 2, high carnitine supplements decreased both TAN excretion and RQ rates in fish <80 g.

Clinical Uses of Insulin-like Growth Factor I

Insulin-like growth factor I (IGF-I) has acute insulin-like metabolic effects and long-term anabolic actions. The therapeutic potential of recombinant human IGF-I treatment is being investigated in various growth hormone-resistant and insulin-resistant disorders. Recent studies have shown that IGF-I may substitute for growth hormone in promoting linear growth in children with growth hormone insensitivity. The anabolic, protein-sparing action of IGF-I is being evaluated as a potential therapy for adults with catabolic diseases. Patients with insulin-dependent diabetes mellitus have reduced endogenous IGF-I production, and studies are in progress to determine whether treatment with IGF-I in addition to insulin may improve their metabolic/anabolic status. Insulin-like growth factor I treatment may reduce glucose and triglyceride levels in adults with non-insulin-dependent diabetes mellitus and in some patients with extreme insulin resistance. Further studies are needed to evaluate the efficacy and safety of IGF-I treatment in these and other conditions and to provide a better understanding of this hormone's normal physiologic role(s) and complex relations with growth hormone and insulin.

The effect of dietary L-carnitine on the growth performance in fingerlings of the African catfish (Clarias gariepinus) in relation to dietary lipid.

The effect of dietary L-carnitine on the growth and growth efficiency of African catfish (Clarias gariepinus, Burchell 1822) fingerlings was investigated. Six dietary levels of L-carnitine, varying from the control level (about 125 mg/kg) to 3920 mg/kg, were each tested at two dietary lipid levels (96 and 155 g/kg). The diets were isonitrogenous and were fed to thirty-six experimental groups of 100 fish weighing 5 g at a feeding level of 25.2 g/kg live weight (w)0.8 per d, during 18 d. The average final weight varied from 19.1 to 28.0 g. At a dietary lipid level of 96 g/kg the metabolic growth increased from 30.8 to 36.5 g/kg w0.8 per d. At the higher dietary lipid level the metabolic growth increased from 30.9 to 35.4 g/kg w0.8 per d. To assess the dose-response relationship between dietary L-carnitine and growth performance in the African catfish a linear-plateau model was fitted to the experimental data. According to this model, metabolic growth was at a maximum at L-carnitine levels of 500 mg/kg and above at a lipid level of 96 g/kg and at L-carnitine levels of 684 mg/kg and above at a lipid level of 155 g/kg. The fitted maximum metabolic growth was higher at a dietary lipid level of 96 g/kg (35.9 g/kg w0.8 per d) than at 155 g/kg (34.7 g/kg w0.8 per d). Feed conversion improved significantly with increasing dietary levels of L-carnitine, reaching a fitted plateau at L-carnitine levels of 448.8 and 236.7 mg/kg respectively for the high and low dietary fat levels. Other growth efficiency variables, e.g. protein efficiency ratio, protein retention and energy retention improved accordingly. Taking into consideration that all fish received the same amount of feed, the results of the present study demonstrate that the positive effect of increased levels of dietary L-carnitine is the result of an improved feed utilization, probably because of a stimulated protein-sparing action.

Effects of dietary lipid and carbohydrate levels on growth and body composition of juvenile red drum, Sciaenops ocellatus

Juvenile red drum (2.9 ± 0.3 g) were led one of six experimental diets (containing fish meal, crab meal, fish oil, wheat middlings, mineral and vitamin supplements, cellulose filler and binder) that provided 32% crude protein and 6 or 10% lipid, at three gross-energy (GE) levels ( 15.8 ± 0.3,17.1 ± 0.2 and 18.7± 0.3 kJ/g). Dietary carbohydrate (NFE) levels ranged from 24 to 39%. Significantly ( P < 0.05) higher weight gain (481%), feed efficiency (FE: 0.375), apparent net protein retention (ANPR: 19.77%) and apparent net energy retention (ANER: 10.81%) were associated with a diet containing 16.1 kJ GE/g, 10% lipid and 24% NFE. Survival (71–88%) did not differ significantly among dietary treatments. Weight gain, FE, ANPR and ANER of red drum was inversely related to dietary energy level and dietary carbohydrate content. Body lipid levels were significantly ( P < 0.05) higher in fish fed 10% lipid diets than in those fed 6% lipid. Dietary lipid exhibhted greater proteinsparing action than dietary carbohydrate, at all energy levels tested. The ability of juvenile red drum to utilize dietary carbohydrate as an energy source may be limited in comparison with warnwater omnivorous species like channel catfish and common carp.

Biochemical studies on the determination of optimum dietary protein to energy ratio for tiger prawn, Penaeus monodon (Fab.), juveniles

Six isonitrogenous pelletized diets with protein level of approx. 46% and energy level varying between 373.10 and 435.30 kcal/100 g were fed to groups of Penaeus monodon juveniles at 10% of total biomass in a 21-day study. At constant dietary protein level, weight gain, feed efficiency and protein utilization increased with increase in dietary energy level up to 412.60 kcal/100g. Further elevation in dietary energy content had no beneficial effect. Protein efficiency ratio (PER) remained negatively correlated to ratio up to the optimum dietary energy level (412.60 kcal/100 g). Digestible energy from dietary carbohydrate was seen to exert a transient protein-sparing action in these formulations.

Nitrogen conservation in starvation revisited: Protein sparing with intravenous fructose

The provision of small amounts of glucose during fasting is known to spare body protein and to attenuate markedly the metabolic response to starvation. These actions, which are not shared by fat, are generally thought to depend on the ability of exogenous glucose to stimulate insulin secretion. To determine whether fructose, a very weak insulin secretagogue, will also conserve nitrogen and alter the response to fasting, we infused small amounts of fructose, 100 g/d (375 kcal), into 7 obese subjects during a 10-day fast: 4 received fructose days 7 to 10, and 3 received fructose days 1 to 7. Fructose virtually abolished (all P < 0.05−0.01) the fasting induced: (a) fall in glucose and insulin and rise in glucagon, (b) fall in triiodothyronine, (c) ketosis and acidosis, (d) increased ammonia excretion, (e) hyperuricemia (and hypouricosuria), and (f) fall in plasma alanine and rise in branched chain amino acids. Fructuse also significantly reduced urinary sodium loss. Moreover, fructose exerted a prominent protein-sparing action, even though plasma insulin concentrations never exceeded postabsorptive levels. Excretion of total nitrogen was reduced by 40% to 50% during periods of fructose infusion, reflecting significant suppression of both urea and ammonia generation (all P < 0.05−0.01). Most plasma glucogenic amino acids rose significantly during fructose administration. We conclude that low-dose fructose infusion essentially abolishes the entire hormone-substrate response to fasting, and spares body protein without raising insulin above postabsorptive levels. Since fructose prevented (or reversed) the fasting-induced fall in plasma glucose, while simultaneously causing glucogenic amino acids to accumulate in plasma, our data suggest that fructose spares protein during fasting by replacing endogenous amino acids as gluconeogenic substrate. Suppression of acidosis may also conserve nitrogen by inhibiting renal ammoniagenesis. Liver and kidney, rather than skeletal muscle, may represent the primary sites where fructose exerts its protein-sparing action.

The protein-sparing action of protein feeding: absence of relationship to insulin secretion

The influence of a 2-day fast was compared with that of a modified fast (1.5 g beef protein hydrolysate per kg body wt) on nitrogen metabolism and insulin secretion in three normal young men. During the fast urinary urea excretion indicated a negative nitrogen balance of 10 to 12 g daily in each subjects. With protein feeding nitrogen equilibrium was approached in each instance. Insulin secretion as indicated by the urinary excretion of C-peptide dropped profoundly with fasting to levels which averaged just 13 to 22% of the control base-lines and remained at about these levels during the protein feeding. The fact that this sensitive indicator of insulin secretion disclosed no significant difference during fasting and protein feeding provides strong evidence that the protein-sparing influence of protein feeding cannot be ascribed to the decline in insulin secretion.