Effects Of Dietary Protein Levels Research Articles

Effects of dietary protein level on protein deposition in broilers: 2. Body composition, plasma metabolic profile and litter composition.

The aim of study was to evaluate the effects of three dietary protein levels on body composition, plasma metabolic profile and litter composition of broilers at 42 days of age. One-day-old unsexed Cobb 500 broilers (n=600) were randomly assigned in 3 groups with 4 replications per treatment. Three diets were formulated for each growth phases, to contain 3 levels of protein: high protein (HP), medium protein (MP) and low protein (LP). The diets were isocaloric, with similar content of digestible sulphur amino acids, lysine, calcium and available phosphorus. The empty body weight (BW) of broilers was influenced by the dietary treatments (+ 8% in HP, respectively - 7.7% in LP vs. MP; P 0.05). In general, plasma biochemical parameters were not influenced by the dietary protein levels (P>0.05). In conclusion, low protein diets can support similar quality performance that high or medium diets when the quality ingredients are used. The lower dietary protein level resulted in reduced nitrogen excretion, which is an important advantage for environmental safety.

Effects of dietary protein level on protein deposition in broilers: 1. Productive performance and carcass characteristics

The aim of study was to evaluate the influence of different levels of dietary protein on broiler performance and carcass characteristics from 1-42 days. One-day-old unsexed Cobb 500 broilers (n=600) were randomly assigned in 3 groups with 4 replications per treatment. The diets were formulated to contain 3 levels of protein: high protein (HP), medium protein (MP) and low protein (LP). The diets were isocaloric, with similar content of digestible sulphur amino acids, lysine, calcium and available phosphorus. In overall periods weight gain (WG) in the HP diet was higher with 4.28% and in the LP diet were lower by 4.44% vs. MP (P<0.0001). Feed conversion ratio (FCR) in overall period in the HP diet was reduced with 3.96% and in the LP diet was increased with 4.95% vs. MP (P<0.002). The feed intake (FI) was not influenced by the dietary protein level during overall period. Carcass yield and the percentage of broilers liver were not affected by the dietary protein level. Breast and legs yield were influenced by the dietary protein level, in LP diet was observed a decrease with 4.10% (P<0.04), respectively 4.47% (P<0.0001) vs. MP diet. The HP diet produced carcasses that contained lower levels (2.49%; P<0.0001) of abdominal fat than the LP diet (2.78%; P<0.0001). We concluded that the dietary protein level influences significantly the performance (weight gain, feed conversion ratio) and carcass parameters (breast and legs yield, abdominal fat) of broilers.

The effect of dietary protein levels on the expression of genes coding for four selected protein translation initiation factors in muscle tissue of Wujin pig

The objective of this study was to investigate the regulatory mechanism underlying the increased muscle protein accumulation in pigs while were fed a high protein diet. The eukaryotic initiation factors (eIFs) have been reported to involve in muscle protein synthesis. We investigated the mRNA and protein expression levels of eIF2B1, 4A1, 4B and 4E in Wujin pigs fed either a high protein (HP: 18%) or a low protein (LP: 14%) diet at 30, 60 or 100 kg body weight, based on real-time PCR and western blotting analyses. Our results indicated that the expression levels of eIF2B1 mRNA and protein were increased by HP diet at all body weight. The HP diet showed higher mRNA and protein levels of eIF4B gene at 60 and 100 kg. The protein expression of eIF4E phosphorylation was increased by HP diet only at 30 kg. These data suggested that the HP diet promoted porcine muscle protein accumulation mainly by up-regulating eIF2B1, 4B and 4E rather than 4A1 expression along the growth stages.

Dietary Protein Level and Water Temperature Interactions for Greenlip AbaloneHaliotis laevigata

Land-based grow-out of greenlip abalone (Haliotis laevigata) in Australia is predominantly practiced using a single-diet feeding strategy, despite geographical and seasonal differences in water temperature that influence feed intake and growth. This 12-wk study investigated the interactions between 2 abalone year classes (1 y old, 1.8 g; 2 y old, 22.9 g), 3 water temperatures (14°C, 18°C, and 22°C), and 4 dietary protein levels (1 y old: 27%, 30%, 33%, and 36% crude protein; 2 y old: 24%, 27%, 30%, and 33% crude protein) to evaluate the potential to use diets to suit specific water temperatures and aged animals. Diets were formulated to be isoenergetic (∼12.5 MJ/kg digestible energy), and contain fat levels of ∼3.6% and digestible protein levels ranging from 17.99%–28.57%. Feed was fed to excess daily and uneaten food was collected. Temperature significantly affected the specific growth rate of both year classes of abalone. There was no significant effect of dietary protein level on specific growth rate; however, abalone compensated for a reduction of dietary protein by consuming more feed. This observation was evident with significant increases in feed conversion ratios as dietary protein levels decreased for both year classes. With the exception of abalone grown at 14°C, when protein deposition decreased with increasing dietary protein level, protein deposition increased with an increase in dietary protein for both year classes. For 1-y-old abalone, as temperature increased from 14-22°C, the optimum crude dietary protein levels increased from -29%-∼35%. For 2-y-old abalone, the optimum crude protein level appeared to be less, and increased from 24% at 14°C to 34% at 22°C. There is scope to use multidiet feeding strategies in the production of greenlip abalone.

Comparative Histological Changes in the Greenlip AbaloneHaliotis laevigataGastrointestinal Tract in Response to Water Temperature, Different Dietary Protein Levels, and Animal Age

The land-based culture of greenlip abalone Haliotis laevigata in southeastern Australia is carried out using seawater that is prone to seasonal temperature fluctuations and is done almost exclusively using artificial feeds. Although some nutrition research has been done to identify the optimum dietary protein level, typically farms use only 1 diet for grow-out after the juveniles are weaned. Little consideration has been given to the effects of fluctuating water temperatures and dietary protein levels on the morphology of the gastrointestinal tract (GIT) of abalone. Because these factors are known to impact growth in other aquatic species, it is important that they are investigated further to improve growth in abalone species. In this study, the histological changes of the GIT of greenlip abalone in response to 2 water temperatures and 4 dietary levels of crude protein (juvenile, 27% and 36%; subadult, 24% and 33%) for juveniles (1.75 g) and subadults (22.93 g) were investigated. The epithelial thickness of the stomach and crop; intestinal villus height, width, and area; lamina propria height; and stomach, crop, and intestinal neutral and acidic goblet cell numbers were measured. The stomach epithelium was significantly thicker at 14°C than 22°C in both juveniles and subadults, whereas the crop epithelium was significantly thicker at 22°C than 14°C in juveniles. The crop epithelial thickness of subadults was reduced by increasing dietary protein; however, juveniles did not show the same response. Juvenile abalone were more sensitive to temperature fluctuations than subadults, whereas significant effects of dietary protein levels were only observed in subadults. The alterations in the morphology of the GIT did not appear to be detrimental to the health and growth of the abalone. Further research is required to investigate the interactive effects of water temperature and dietary ingredients, particularly in regard to antinutritional factors, on the morphology and function of the GIT to improve our understanding of abalone physiology.

Effects of dietary protein level on growth and body composition of mudfish, Heterobranchus longifilis fingerlings

Heterobranchus longifilis fingerlings of mean weight 1.648 g were stocked in plastic aquaria of 0.049 m3 at a rate of 10 fish per aquarium. Fish were fed with diets containing 30, 35 and 40% protein in triplicate for 10 weeks using fish meal as the main protein source. Growth of H. longifilis was significantly different (P < 0.05) among treatments with increasing dietary protein levels. Mean weight gain, length increase, relative growth, specific growth rates, survival and feed conversion ratio for fish fed 40% protein diet were 6.99 ± 1.70 g, 43.58 ± 7.64 mm, 469.26 ± 114.28%, 4.05 ± 0.19% day -1 , 100% and 1.12 ± 0.06, respectively. Protein efficiency ratio was also significantly higher (P < 0.05) for fish fed diet containing 40% protein compared to fish fed 30 and 35% protein. Percent protein in carcass of fish (22.92%) was significantly higher (P < 0.05) and the fat level was fairly similar with all diets fed. Results of this study indicate that H. longifilis fingerlings had the best growth when fed with a 40% dietary protein. Keywords : Heterobranchus longifilis , fingerlings, dietary protein, growth, body composition African Journal of Biotechnology Vol. 12(9), pp. 971-975

Effects of Dietary Protein Level on Growth Performance, Carcass Composition and Survival Rate of Fry Monosex Nile Tilapia, Oreochromis niloticus Reared under Re-circulating System

Fry monosex Nile tilapia ( Oreochromis niloticus ) were fed in five dietary protein levels (21%, 25%, 32% 37% and 45%) to investigate casual effects on growth performance, carcass composition and survival rate. Tests were carried out in 10 glass tank (50 x 25 x 40 cm) containers (50 L) of reticulating system maintained at 30 ± 1°C. At the beginning of tests, one hundred tilapia fry were randomly divided into five different groups with two replicates. Diets were fed to duplicate groups of ten fry with an initial weight of 1.25 ± 0.25 g/fish during 42 days. The results showed significant effects of dietary protein on growth performance of reared fish. Weight gain (WG) and Specific Growth Rate (SGR) increased significantly with increasing dietary protein levels between 32.38% and 37.63%. However, 45.5% of crude protein showed less important increase in growth parameters. The best Feed Conversion Rate FCR (1.26) was noticed in diet containing 37.63% of crude protein. Accordingly, higher survival rate (%) was recorded in fish fed on diets containing 32.38 and 37.63%. There was no significant difference in protein body content of tilapia fed on five diets as compared to the initial fish. Lipid body content increased significantly with high dietary protein levels from 21.88% to 45.50%. The carcass crude lipid was recorded as higher (9.4%) in the fry fed on diet containing 45.50% protein, followed by fish fed on diet having protein 21.88%. From results, diet containing 37.63% crude protein appears to be more suitable for monosex Nile tilapia growth, in related experience conditions. In this line, it is recommended to feed monosex tilapia fry.

Protein requirement for Trichogaster lalius, blue variety

The objective of the present study was to evaluate the protein requirement of juvenile Trichogaster lalius, blue variety. The experimental design was of randomised blocks (B1 = initial weight of 1.04±0.05 g and B2 = 1.36±0.02 g), with two replicates within each block and five treatments (230, 270, 310, 350 and 390 g CP/kg diet). The fish were fed to satiation, three times a day for 90 days. The study evaluated: survival rate, weight gain, final length, feed intake, feed conversion ratio, protein efficiency ratio, specific growth rate and condition factor. There was a linear effect of dietary protein levels for protein efficiency ratio, specific growth rate (positive linear effect) and feed conversion ratio (negative linear effect). For weight gain, final length, feed intake and condition factor a quadratic effect of dietary protein levels was observed, with estimated values of 409.8, 366.2, 317.4 and 365.0 g CP/kg diet, to improve their performance parameters. Analysis of growth based on the length of the fish shows that 366.2 g of CP/kg diet meets the protein requirement of juvenile Trichogaster lalius, blue variety.

Effect of dietary protein level on retention of nutrients, growth performance, litter composition and NH3 emission using a multi-phase feeding programme in broilers

Three experiments were conducted to study the effect of dietary protein level on the retention of nutrients, growth performance, litter composition and NH3 emission in broiler chickens kept under laboratory conditions (housed in cages, Exp.1) or in commercial conditions (in pens, Exp.2; or whole houses of a farm, Exp.3). All the trials were performed according to a factorial experimental design, involving a 4-stage feeding programme and two levels of dietary crude protein (CP) for each period: control vs. low crude protein (CP reduced by 1.5%). In Exp.1, the coefficients of total tract apparent retention of dry matter and CP were higher in the birds fed the low CP diet (p&lt;0.05). On average, reducing the CP of the diet led to a 4.8% reduction in the nitrogen excreted per CP intake. In Exp.2, the feed conversion ratio was higher in birds fed the low CP diet from 22 to 35d (p&lt;0.05), from 35 to 42d (p&lt;0.01), and over the whole experimental period (p&lt;0.01). In Exp.3, low CP diets decreased the nitrogen content of the litter in the finisher period (p&lt;0.05). The average NH3 concentration and emission from 33 to 42d were lower in the low CP house (p&lt;0.01), with a 16% decrease in the cumulative NH3 emission. Therefore, the reduction in dietary CP content by 1.5% reduced the potential environmental impact, although it had a negative effect on the feed efficiency of broilers.

Effects of Dietary Protein Level on Growth Performance, Muscle Composition, Blood Composition, and Digestive Enzyme Activity of Wuchang Bream (Megalobrama amblycephala) Fry

The purpose of this study was to determine the dietary protein requirement and effects of dietary protein level on growth performance, muscle composition, blood composition, and digestive enzyme activity in Wuchang bream fry. Five isoenergetic and isolipidic semi-purified diets were formulated to contain 28%, 30%, 32%, 34%, or 36% (dry matter) dietary protein. Diets were fed to triplicate groups of 25 fishes (16.08±0.03 g) to near satiation three times a day in a closed recirculation system for 10 weeks. Weight gain, specific growth rate, and feed conversion ratio significantly improved as the dietary protein content increased up to 34%. The protein efficiency ratio, hepatosomatic index, and viscerosomatic index significantly dropped as the dietary protein rose while the Fulton condition factor was positively correlated to the dietary protein level. Increased dietary protein resulted in increased muscle protein content and decreased lipid content. Red blood cell, hemoglobin, and hematocrit counts increased significantly with the increase in dietary protein. Serum triiodothyronine and thyroxine significantly rose as the dietary protein rose but serum aspartate aminotransferase significantly dropped. Intestinal protease and amylase activity rose significantly with the increase in dietary protein while lipase tended to drop. On the basis of broken-line regression analysis of weight gain and FCR, the dietary protein requirement of Wuchang bream fry is 32-33%.

Effect of dietary protein level and quebracho tannin on consumption of pine needles (Pinus ponderosa) by beef cows

<h2>ABSTRACT</h2> Ponderosa pine trees occupy over 15 million hectares of rangeland in western North America. Pregnant cows often consume pine needles (PN), and subsequently abort. The protein-to-energy ratio may be important in the ability of cattle to tolerate dietary terpenes. Tannins often co-occur with terpenes and may also influence diet selection. The objective of this experiment was to determine if the protein-to-energy ratio or the addition of quebracho tannin to cattle diets would influence PN consumption. In trial 1, 15 cows in moderate body condition were assigned to high (15.4% CP), medium (10.2% CP), or low (4.9% CP) dietary protein treatments for 12 d. In trial 2, 15 cows were assigned to high (5%), medium (2.5%), or no (0%) quebracho tannin diets for 8 d. In both trials, green PN were offered at 0930 h for 90 min. There was a treatment effect (P = 0.05) and a treatment × day interaction (P = 0.01) for PN consumption, as cattle on the high CP treatment consumed more PN than cattle on the medium and low CP diets for 4 and 6 d, respectively. Initially, treatments did not differ (P > 0.09), but from d 3 to 9 cattle on the high CP treatment ate more PN than the other treatments. There was a day × treatment interaction (P = 0.002) for PN consumption; cattle on the 2.5% tannin treatment consumed less PN than did animals on the other treatments. Cattle are apparently unable to tolerate high quantities of PN terpenes on a low-protein diet. Tannins may influence PN consumption, but the mechanism is unknown.

Effect of Dietary Protein Level and Strain on Growth Performance of Heat Stressed Broiler Chicks

An experiment was carried out to study the effect of heat stress on growth performance of three broiler strains fed two different level of dietary protein. Three hundred and sixty, one day old unsexed broiler chicks (120 for each strain, Ross, Cobb and Hubbard strain), were randomly assigned in factoria l arrangement. The total number of chicks for each strain was divided into two groups (A and B), with six replicates (10 chicks per each). Group (A) for each strain was fed on diet contained (23%) Crude Protein (CP) as starter diet for the first four weeks of age and then replaced by a diet contained (21%) CP as finisher diet. Group (B) for each strain was fed a diet contained (21%) CP as starter diet for the first four weeks and then shifted to a diet contained (19%) CP as finisher diet. The minimum and maximum range of ambien t temperature during the experimental period was 34-93°C. Feed intake, body weight gain and feed conversion ratio were recorded on weekly basis throughout the entire duration of experiment, however feed intake per bird for Ross, Cobb and Hubbard strains were 3127.54, 3074.69 and 2850.17g respectively. The results revealed that birds in group (A) for each strain were significantly higher (p<0.05) in live body weight and growth performance than those in group (B) moreover Ross strain got the highest significant (p<0.05) live body weight gain in comparison with Cobb and Hubbard strains. The interaction between strain and diet was significantly (p<0.05) increased for live body weight.

Effects of dietary protein levels and environmental zinc exposure on the growth, feed utilization, and biochemical variables of Nile tilapia, Oreochromis niloticus (L.)

This study was based on a 3 × 2 factorial design with two levels of dietary protein (25% or 45%) and three zinc (Zn) concentrations (0.0, 3.5, and 7.0 mg L−1). This study was conducted to evaluate if dietary protein levels could influence effects of water-borne Zn on Nile tilapia, Oreochromis niloticus (L.). Fish (7.2–7.8 g) were fed on 25% or 45%-crude protein (CP) diets and under each dietary protein level, fish were exposed to 0.0 (control), 3.5, or 7.0 mg L−1 Zn over 6 weeks. The results showed that the unionized ammonia in water increased significantly with the increase of dietary protein levels and/or Zn concentrations. The growth, survival, and feed utilization of the fish significantly increased when dietary protein level was high and Zn concentration was low. CP and total lipids contents in whole-fish body were significantly affected by protein levels and Zn concentrations; but there was no interaction between the two factors. Ash content and Zn residuals in whole-fish body increased significantly with increasing Zn concentrations only. Glucose, aspartate aminotransferase, alanine aminotransferase, and creatinine increased significantly, while protein and lipids in serum decreased significantly with increasing protein levels and/or Zn concentrations. The cortisol value in fish serum increased significantly with the increase of Zn concentrations; while it was not affected by dietary protein levels. This study concluded that the increase in dietary protein levels could minimize the deleterious effects of Zn on Nile tilapia performance.

A high protein diet upregulates whole‐body protein turnover during energy deficit

The effects of dietary protein level on whole‐body protein turnover (WBPTO) during energy deficit (ED) are not well described. Using a randomized‐block design, 24 males and five females (21 ± 3 yr) participated in a controlled trial. Volunteers consumed either standard (SP; 0.8 g·kg−1·d−1), moderate (MP; 1.6 g·kg−1·d−1), or high (HP; 2.4 g·kg−1·d−1) protein diets for 31 days. A weight maintenance (WM, days 1–10) period was followed by 21 days of ED (days 11–31), during which energy intake was restricted to 60% of total daily energy expenditure. Whole‐body protein breakdown, synthesis, and oxidation were determined at rest during WM (day 10) and ED (day 31) using primed, continuous [13C]‐leucine infusions. Volunteers lost (P &lt; 0.05) 3.3 ± 0.9 kg body mass in response to ED regardless of dietary protein level. Protein breakdown decreased (P &lt; 0.05) in response to ED for SP and MP diets, but did not change for HP. Synthesis decreased (P &lt; 0.05) following ED regardless of dietary protein level. Protein oxidation (μmol·kg−1·h−1) increased linearly between SP (9.7 ± 0.5), MP (11.8 ± 0.5), and HP (13.9 ± 0.5) diets during WM, with increased oxidation observed only for HP (16 ± 0.7) during ED (diet‐by‐energy interaction, P &lt; 0.05). These data demonstrate that the level of dietary protein intake modulates WBPTO during sustained ED, as consumption of a high protein diet upregulates WBPTO during ED.

Effect of dietary protein level and source on digestive proteolytic enzyme activity in juvenile Senegalese sole, Solea senegalensis Kaup 1850

The effect of dietary protein level and protein source on growth and proteolytic activity of juvenile Solea senegalensis was studied. In Experiment 1, fish were fed on four experimental diets containing increased protein levels (36, 46, 56 and 67%). In Experiment 2, Senegalese soles were fed on five diets with partial substitution of fish meal by soybean meal, soybean protein concentrate, soybean protein isolate, wheat gluten meal or pea protein concentrate. Results prove that growth and proteolytic activity in the distal intestine of fish were affected by the quantitative increase in dietary protein. The origin of protein source used in the elaboration of experimental diets affected both the amount and composition of the alkaline proteases secreted into the intestinal lumen; however, it did not decrease animal growth. Juvenile Senegalese sole showed capability to modulate digestive protease secretion when the concentration and/or source of dietary protein were modified. Quantity and quality of dietary protein affected protein hydrolysis in Senegalese sole intestine. This study establishes that 30% fish meal protein can be replaced by soybean derivatives without affecting intestinal proteases. Replacement with wheat gluten meal or pea protein concentrate should be taken cautiously, but further research is needed to establish whether growth performance and digestive enzyme physiology of Senegalese sole are affected by plant protein-supplemented diets in a long-term trial.

Effects of dietary protein levels on digestibility of nutrients and growth rate in young female mink (Mustela vison)

This study investigated digestibilities of nutrients and feed efficiency in female mink at the different dietary protein levels during the mink growth period. Effects of dietary protein on growth performance of minks were also measured. Sixty 45-day-old healthy female minks were randomly assigned to 6 treatment groups with 10 animals in each group. Animals were fed diets varying in protein levels: 28% (Group I), 30% (Group II), 32% (Group III), 34% (Group IV), 36% (Group V) and 38% (Group VI), respectively. The digestibilities of key nutrients were determined on Day 14 after initiating the experiment and the last 3 days. From the beginning of the study, body weight and feed intake were weighed and recorded every other week in order to calculate the average daily bodyweight gain and the feed efficiency. The trial had demonstrated that nitrogen intake was greatly significantly different, which was affected by dietary protein levels (p < 0.001). Growth performance of minks was impaired when dietary protein level was at 28%. When dietary protein level was at 34%, minks had the best daily gains, feed efficiency, and digestibilities of some key nutrients.

Effects of dietary protein level and source on the growth and survival of two genetic lines of specific-pathogen-free Pacific white shrimp, Penaeus vannamei

An eight-week trial compared the performances of two genetic lines of Penaeus vannamei, T-line and G-line, fed with different levels and sources of dietary protein. Both lines were originated from the same founder populations but had gone through genetic selection targeting different breeding goals for more than four generations. T-line was bred for fast growth and Taura syndrome viral disease resistance, and G-line was bred for fast growth and production yield under super-high density. Five dietary treatments were employed: two commercial diets and three semipurified diets (A, B, and C). The semipurified diets were formulated at similar levels of digestible energy. Diet A contained 35% crude protein (CP), from marine meals (fish, 15%, and squid, 15%). Diet C contained 35% CP from a reduced marine protein level from fish (11.5%) and squid meals (11.5%). Diet B contained only 20% CP but had the same level of marine protein as diet C. The two commercial shrimp feeds, containing 35% and 40% protein, served as reference diets. Three replicate tanks per dietary treatment were used. Each tank was stocked with 50 tagged shrimp (25 each of T-line and G-line) and 100 untagged shrimp, with average initial weight (IWT) of 10.4g, at a density of 107/m2.Diet significantly affected shrimp growth (p<0.0001) but did not interact with shrimp line. Shrimp fed either diet A or diet C grew over 25% faster than those fed diet B or either of the two commercial diets.Diets A and C yielded similar growth (0.30 to 0.33g/day) and survival rates (83 to 93%) to a harvest size of over 29g per shrimp, suggesting that the soy protein isolate that replaced part of the marine protein in diet C can serve as a good alternative protein source. Growth rates of the two shrimp lines were similar regardless of dietary protein levels or sources, but dietary plant protein level did interact with shrimp line when the measure was survival: T-line survived better than G-line on average when fed diet B, a nutritionally inferior diet containing 20% protein and no plant protein, but not when fed diet C, containing 35% protein, 15% of which was of plant origin (soybean). Microsatellite marker analyses quantified the genetic relationship of the two lines and confirmed that they were the most closely related of the lines derived from the same founding stock. This preliminary study provided information that will be useful for further studies of the relationship between dietary nutrition and genetics and for exploration of the potential of genetic selection for improving the efficiency of plant protein use in shrimp.

Effects of dietary protein level on growth performance, nitrogen and energy budget of juvenile hybrid sturgeon, Acipenser baerii ♀ × A. gueldenstaedtii ♂

An 8-week growth trial was conducted to estimate the optimal dietary protein level for juvenile hybrid sturgeon, Acipenser baerii ♀×A. gueldenstaedtii♂ (initial body weight, 25.1±0.12g). Effects of protein levels on nitrogen and energy budget of the fish were studied. Seven isoenergetic diets were formulated to contain seven levels of crude protein (250, 300, 350, 400, 450, 500 and 550gkg−1) and each diet was fed to triplicate groups of fifty fish at 21.4±0.6°C in twenty one 1m3 concrete tanks.The results showed that specific growth rate (SGR) increased when dietary protein levels increased from 250 to 400gkg−1 and then decreased significantly. Feed intake (FI) decreased steadily with increasing dietary protein levels. Fish fed 250gkg−1 protein diets showed the lowest feed efficiency (FE), and those fed 500 and 550gkg−1 protein diets showed significantly higher values than the other diets except 450gkg−1. Protein retention efficiency (PRE) was highest in 250–300gkg−1 groups, followed by 350–500gkg−1 groups and was significantly lower in 550gkg−1 group. Proportions of nitrogen intake (CN) allocated to excretory nitrogen (UN) were lowest in 250–300gkg−1 protein diets, followed by 350–500gkg−1 protein diets and highest in 550gkg−1 protein diet, whereas recovered (growth) nitrogen (RN) followed the inverse pattern with UN. Percentages of gross energy intake (IE) used for excretory energy (UE) increased steadily when dietary protein levels increased. Fish fed 400–550gkg−1 protein diets showed significantly higher proportion of metabolizable energy (ME) than those fed 250–350gkg−1 protein diets. The lowest and highest percentages of recovered (growth) (RE) were observed in 250 and 550gkg−1 groups. Nitrogen and energy budget equation of the fish fed 350gkg−1 protein diet was 100CN=11.72FN+58.78UN+29.50RN and 100IE=35.08FE+4.53UE+34.16ME+26.23RE.Five-parameter saturation kinetic model and second-order polynomial regression analysis indicated that the optimal dietary protein level for maximal growth of the fish was 340 and 370gkg−1. Diets with excessive protein contents not only resulted in inferior growth performance but also high proportions of protein and energy used for excretion.

Effect of Dietary Protein Levels on Sex Hormones in Growing Male Rats Kept under Constant Darkness

The purpose of this experiment was to clarify the effects of dietary protein levels on the gonadal development and sex hormones in male rats kept under constant darkness as a model of disturbed daily rhythm. Four-week-old male rats (Fischer 344 strain) were kept under constant darkness or normal lighting (12-h light/dark cycle). Two kinds of experimental diet were prepared, one with low dietary protein levels (9% casein) and one with normal levels (18% casein). Harper mineral mixture and Panvitan were used as mineral and vitamin sources, respectively. After 4 weeks, gonadal weight, serum testosterone, and other hormone contents were evaluated. The gonadal weight in the constant darkness groups (D-groups) was lower than that in the normal lighting groups (N-groups). Although the low-protein diet in the D-groups significantly reduced gonadal weight, the normal-protein diet mitigated the reduction of gonadal weight in rats kept under constant darkness. Serum testosterone and androstenedione concentrations were lower in D-group rats fed the low-protein diet. There were no effects of lighting condition or protein levels on serum luteinizing hormone (LH), follicle- stimulating hormone (FSH), or progesterone concentrations. These results indicate that the suppression of gonadal development in D-group rats fed the low-protein diet was caused by low testosterone, which we attribute to the inhibition of synthesized androstenedione, a precursor of testosterone. The present study showed that constant darkness and the low- protein diet inhibited the synthetic pathway from progesterone to androstenedione.

Effect of Dietary Protein Level on Growth Performance and Nitrogen Excretion of the Yellow Tail Cichlid, Pseudotropheus acei

A 12-week growth trial was conducted to determine the effects of dietary protein on the growth of the yellow tail cichlid, Pseudotropheus acei, and on water quality in closed recirculating systems. Six test diets were formulated to contain protein levels ranging 25-50% by substituting corn oil and a-starch for fishmeal. Diets were assigned to triplicate groups of 10 fish in a completely randomized design. The feed conversion ratios of fish fed the 35% and 50% crude protein diets were significantly (p&lt;0.05) lower than that of fish fed the 30% protein diet. The protein efficiency ratio declined as the dietary protein level increased. Dietary protein levels significantly influenced total ammonia-nitrogen excretion (TAN); fish fed 50% protein excreted higher concentrations of ammonia-nitrogen than fish fed 25-35% dietary protein (p&lt;0.05). Results suggest that inclusion of more than 35% protein in diets containing 10% crude lipid does not benefit juvenile yellow tail growth performance. Further, as TAN excretion and feed costs increased at protein levels beyond 35%, we recommend a diet containing 35% protein and 10% lipid for promoting good growth of juvenile yellow tail cichlids under the conditions used in the present trial.