Thesis (M.Sc) (Agriculture) --University of Limpopo,2009. / The study was conducted to determine the effect of dietary energy level and tanniniferous Acacia karroo leaf meal level of supplementation at finisher stage on performance and carcass characteristics of male and female Ross 308 broiler chickens. Three hundred and sixty, 21-day old male and female broiler chickens were assigned to twelve treatments with three replications of ten birds in a 2 (sex) x 3 (dietary energy level) x 3 (tanniniferous Acacia karroo leaf meal level) factorial, complete randomized design. Supplementation with Acacia karroo leaf meal had no effect on diet intake, digestibility and live weight of broiler chickens. However, supplementation with 9 and 12 g of Acacia karroo leaf meal per kg DM feed reduced fat pad weights in male broiler chickens by 26 and 29 percentage points, respectively. Similarly, supplementation with 9 and 12 g of Acacia karroo leaf meal per kg DM feed reduced fat pad weights in female chickens by 26 percentage points. These reductions were achieved without any significant reduction in feed intake and digestibility. However, the physiological explanation for this effect is not clear and it, thus, merits further investigation. / National Research Foundation.

Optimal nutritional management of growing pigs is constrained by lack of quantitative information on the response of animals between 30 and 110 kg live weight to dietary energy content. Under 'ideal' conditions modern genotypes appear to adjust feed intake to maintain a constant DE intake over a much wider range of dietary energy concentrations than previously thought (Mullan et al, 1998). However, under commercial pen conditions, voluntary feed intake is lower, pigs respond in terms of both growth rate and feed conversion to dietary DE density considerably above the levels currently thought to maximise biological and economic responses. The present study was designed to provide information on the response of growing pigs to dietary energy content under ideal and commercial housing conditions for two growth periods 30-60kg liveweight and 60-100kg liveweight. The results of the pigs kept under individual (ideal) housed conditions were consistent with the literature in that they adjusted their voluntary feed intake with digestible energy density to maintain a constant energy intake. The results of the pigs kept in groups (commercial) housing conditions tended to increase their daily energy intake as the energy density of the feed increased. This increase in energy intake improved the growth rate of the pigs and increased the fat deposition of those pigs. Economic analysis of the experiments involving pigs in groups indicates that formulating diets to a least cost per megajoule of digestible energy is not the most profitable point to set the digestible energy density. Modelling programs need to be used to determine where the least cost per unit of growth of the pig occurs. This is the most economical digestible energy density to formulate too. This will have major impact on the cost of production of piggery operations as the cost of energy is the single most important parameter in the cost of producing a pig.

Optimal nutritional management of growing pigs is constrained by lack of quantitative information on the response of animals between 30 and 110 kg live weight to dietary energy content. Under 'ideal' conditions modern genotypes appear to adjust feed intake to maintain a constant DE intake over a much wider range of dietary energy concentrations than previously thought (Mullan et al, 1998). However, under commercial pen conditions, voluntary feed intake is lower, pigs respond in terms of both growth rate and feed conversion to dietary DE density considerably above the levels currently thought to maximise biological and economic responses. The present study was designed to provide information on the response of growing pigs to dietary energy content under ideal and commercial housing conditions for two growth periods 30-60kg liveweight and 60-100kg liveweight. The results of the pigs kept under individual (ideal) housed conditions were consistent with the literature in that they adjusted their voluntary feed intake with digestible energy density to maintain a constant energy intake. The results of the pigs kept in groups (commercial) housing conditions tended to increase their daily energy intake as the energy density of the feed increased. This increase in energy intake improved the growth rate of the pigs and increased the fat deposition of those pigs. Economic analysis of the experiments involving pigs in groups indicates that formulating diets to a least cost per megajoule of digestible energy is not the most profitable point to set the digestible energy density. Modelling programs need to be used to determine where the least cost per unit of growth of the pig occurs. This is the most economical digestible energy density to formulate too. This will have major impact on the cost of production of piggery operations as the cost of energy is the single most important parameter in the cost of producing a pig.

Within the South African feedlot industry, there are currently several different roughage sources available for use in feedlot finishing diets. To evaluate the influence of dietary energy and fibre source on rumen function in feedlot animals, four roughage sources (wheat straw, Eragrostis curvula hay, cottonseed hulls and maize silage) were used in combination with hominy chop or dry rolled maize in two experiments. Four Beefmaster steers (270kg ±15kg) fitted with ruminal cannulae were used in two separate experiments in a 4 x 4 Latin square design. Experiment 1 was conducted to evaluate each roughage source in combination with hominy chop namely: wheat straw, hominy chop (WSHC); Eragrostis hay, hominy chop (EHHC); cottonseed hulls, hominy chop (CHHC); and maize silage, hominy chop (MSHC). Experiment 2 was conducted to evaluate each roughage source in combination with dry rolled maize (DRM) namely: wheat straw, dry rolled maize (WSDRM); Eragrostis curvula hay, dry rolled maize (EHDRM); cottonseed hulls, dry rolled maize (CHDRM); and maize silage, dry rolled maize (MSDRM). Diets were designed to contain equal amounts of energy, starch, crude protein, neutral detergent fibre (NDF) and 7.5% roughage source in both experiments. All diets were evaluated for particle size distribution through the Penn State Forage Particle Separator (PSPS) and ruminal fermentation parameters (volatile fatty acid composition, VFA; rumen ammonia nitrogen, NH3-N; lactate and ruminal pH) were compared for each experiment. Results from experiment 1 showed that animals fed the MSHC had the lowest (P<0.05) concentration of VFA while animals fed the CHHC diet produced the highest (P<0.05) ruminal propionate concentration, lowest (P<0.05) acetate: propionate ratio and had the lowest (P<0.05) ruminal pH during the 24h observation period. Time intervals below pH 5.6 and pH5.2 for CHHC was 940 minutes (P<0.05) and 388.75 minutes respectively. Measurements for rumen NH3-N concentrations and lactate did not differ between treatments. Results from experiment 2 revealed that animals fed WSDRM had numerically the lowest concentration of VFA and differed (P<0.05) from CHDRM and MSDRM diets. Propionate and acetate as well as A:P ratios for CHDRM were numerically higher than other treatments but differed (P<0.05) from the WSDRM diet. Rumen NH3-N concentrations did not differ but lactate concentrations were higher for EHDRM when compared to the MSDRM and WSDRM diets (P>0.05). Ruminal pH observations showed steers consuming the MSDRM diet to have the lowest mean ruminal pH of 5.53 which differed (P<0.05) from the WSDRM diet with a mean ruminal pH of 6.1. Time periods spent below pH 5.6 and 5.2 for steers consuming the MSDRM diet was highest at 703.75 and 306 minutes respectively and differed from steers consuming the WSDRM diet. Results from these experiments indicated that different roughage sources in combination with specific energy sources resulted in different rumen fermentation characteristics. Evaluation of particle size distribution from the roughage source, particularly the large pool (upper and middle sieve sizes on PSPS) further revealed that particle size alone does not explain all variation in fermentation patterns alone but the digestible NDF as percentage of total NDF for these fractions could be a valuable predictor for chewing and rumination activity to ultimately establish a more optimal ruminal pH. / Dissertation (MSc(Agric))--University of Pretoria, 2011. / Animal and Wildlife Sciences / unrestricted

Thesis (M.Sc. (Agriculture)) --University of Limpopo, 2010 / Ten experiments were conducted to determine the effect of dietary energy to protein ratio level on growth and productivity of indigenous Venda chickens raised in closed confinement from day-old up to thirteen weeks of age. The ten experiments were based on five different energy levels of 12.2, 13, 13.2, 13.4 and 14 MJ ME/kg DM. Each dietary energy level had five different levels of protein concentrations of 220, 190, 180, 170 and 160 g/kg DM, thus ending up with twenty five different dietary energy to protein ratio levels. Experiments 1 to 5 examined the effect of dietary energy to protein ratio on productivity of unsexed Venda chickens aged one to six weeks. Experiments 1 to 5 each commenced with 160 unsexed day-old indigenous Venda chicks with an initial weight of 25 ± 2 g per bird and each lasted for a period of six weeks. In each experiment, the chicks were randomly assigned to five treatments with four replications, each having eight birds. Thus, 20 floor pens (1.5 m2 /pen) were used in total for each experiment. All the five experiments were carried out around the same time. A complete randomized design was used for each experiment. A quadratic regression model was used to determine the ratios for optimum feed intake, growth rate, feed conversion ratio, live weight, metabolisable energy and nitrogen retention in each experiment while a linear model was used to determine the relationship between optimal responses in the above variables and dietary energy to protein ratio levels. Dietary energy to protein ratio level for optimal response for any variable was relative and depended on the energy to protein ratio values of the diet. Energy to protein ratios of 63, 67, 70, 74 and 78 MJ ME/kg protein promoted optimal live weights of 415, 408, 370, 365 and 344 g at six weeks of age for diet energy levels of 12.2, 13, 13.2, 13.4 and 14 MJ ME/kg DM, respectively. However, optimal response trends for different variables were also influenced by the dietary energy to crude protein ratio. Optimal feed intake increased linearly with increasing dietary energy to protein ratio levels. Similarly, optimal metabolisable energy level increased linearly with increasing dietary energy to protein ratio levels without any increase in live weight. On the other hand, increasing dietary energy to protein ratio level decreased growth rate with a linear deteriorating feed conversion ratio,thus, negatively affecting live weight of the chickens at six weeks of age. However, increasing dietary energy to protein ratio levels improved efficiency of protein utilization with a linear deteriorating metabolisable energy utilization. In experiments 1 to 5, correlation analysis indicated that optimal feed intake, feed conversion ratio and metabolisable energy level were positively and strongly correlated with dietary energy to protein ratio levels while optimal live weight, growth rate and nitrogen retention were negatively and strongly correlated with dietary energy to protein ratio levels. The study indicated that a diet containing a crude protein content level of 178 g/kg DM and an energy level of 14 MJ ME/kg DM allowed for optimal utilization of absorbed protein and energy for growth in unsexed indigenous Venda chickens aged between one and six weeks. Experiments 6 to 10 examined the effect of dietary energy to protein ratio level on productivity of male Indigenous Venda chickens raised in closed confinement from seven up to 13 weeks of age. Each experiment commenced with 100 seven-week old male Venda chickens with an initial weight of 320 ± 2 g per bird. In each experiment, the chickens were randomly assigned to five treatments with four replications, each having five birds. Thus, 20 floor pens (1.5 m2/pen) were used in total for each experiment. All the five experiments were carried out around the same time and for a period of seven weeks. A complete randomized design wasused for each experiment. A quadratic regression model was used to determine energy to protein ratios for optimum feed intake, growth rate, feed conversion ratio,live weight, metabolisable energy, nitrogen retention, carcass yield, breast meatyield and fat pad deposition in each experiment while a linear model was used to determine the relationship between optimal responses of the above variables and dietary energy to protein ratio levels. Energy to protein ratios of 60, 71, 66, 72 and 71 MJ ME/kg protein promoted optimal live weights of 1167, 950, 983, 1235 and 1172 g at thirteen weeks of age for diet energy levels of 12.2, 13, 13.2, 13.4 and 14 MJ ME/kg DM, respectively. Optimal response trends in feed intake, growth rate, feed conversion ratio, nitrogen retention, and metabolisable energy intakes in male Venda chickens tended to increase with increase in dietary energy to protein ratio level. In contrast, optimal carcass and breast meat yield tended to decrease with increasing dietary energy to protein ratio level. However, optimal live weight and fat pad remained unchanged with increase in dietary energy to protein ratio value. Additionally, increasing dietary energy to protein ratio level improved efficiency of protein utilization with deteriorating metabolisable energy utilization.On the other hand, experiments 6 to 10 showed that optimal feed intake, growth rate, feed conversion ratio, live weight, metabolisable energy level, nitrogen retention and fat pad were positively and poorly correlated with dietary energy to protein ratio levels while optimal carcass weight and breast meat yield were negatively and poorly correlated with dietary energy to protein ratio levels This study indicated that a diet containing 193 g CP/kg DM and an energy level of 14 MJ ME/kg DM allowed for optimal utilization of absorbed protein and energy for growth in male indigenous Venda chickens aged between seven and thirteen weeks.It is, therefore, concluded that optimal response trends for different variables in growing unsexed Venda chickens offered diets differing in optimal dietary energy to protein ratio levels are influenced by the diet crude protein content rather than the feed energy level per se. Diets containing decreased dietary energy to protein ratio levels may promote improved growth rate and efficient feed conversion ratio while naturally restricting feed intake. Diets containing increased dietary energy to protein ratio levels favoured efficient utilization of consumed dietary protein. However, with such diets, protein became limiting and birds increased their feed intake attempting thereby to obtain more of the limiting protein in order to meet their protein requirement regardless of the energy value of the diet.It is, also, concluded that growing male Venda chickens increased their feed intake with increase in dietary energy to protein ratio. This is contrary to what has been observed in broiler chickens which decrease their intake with increase in diet energy value. It is suggested that this might reflect the differences between indigenous and broiler chickens in terms of their genetic and physiological abilities to regulate their feed intakes according to dietary energy levels. / National Research Foundation (NRF)

Marketplace volatility in the pork industry demands that producers re-evaluate production practices in order to remain profitable. Stocking density and dietary energy concentration independently affect performance and economic returns of growing finishing pigs. However, there is limited information on whether the interaction between these two factors is important for optimizing productivity and maximizing economic returns. The objective of this study was to determine if the dietary energy concentration that maximizes performance and economic returns varies with stocking density. Treatments were arranged as a 2 × 3 × 3 factorial included; sex (barrows and gilts), dietary energy (2.15, 2.30 and 2.45 Mcal NE/kg) and stocking density (14, 17 or 20 pigs per pen providing 0.92, 0.76 and 0.65 m2 per pig, respectively). A total of 932 pigs were used with three replications of 18 treatments. Pigs were randomly assigned to pens within sex to achieve an average initial BW of 75 kg. Wheat and barley based diets were formulated to meet or exceed the pigs’ nutrient requirements (National Research Council, 2012) and were fed in three phases within sex at each energy concentration. Overall (75 to 118 kg BW), as dietary energy increased from 2.15 to 2.45 Mcal NE/kg, ADG increased from 1.17 to 1.23 kg/d, ADFI decreased from 4.09 to 3.77 kg/d, G:F improved from 0.29 to 0.33 and caloric intake increased from 8.81 to 9.29 Mcal NE/d (P < 0.05). When stocking density was increased from 14 to 20 pigs per pen, ADG (1.21 to 1.17 kg/d), ADFI (4.00 to 3.82 kg/d) and caloric intake (9.19 to 8.12 Mcal NE/d) decreased (P < 0.05). Neither dietary energy concentration nor stocking density had a significant effect on the utilization of calories for growth (Gain:Mcal). Feeder visits per pig and time at the feeder per pig were decreased when stocking density increased from 14 to 20 pigs per pen (P < 0.01). Total time at the feeder and time at the feeder per pig were increased when dietary energy decreased from 2.45 to 2.15 Mcal of NE/kg. Per pen, aggressive incidents at the feeder increased (P < 0.05) and there was a tendency for increased aggressive incidents per pig (P = 0.09) when stocking density was increased. There was a linear increase (P < 0.01) in income over feed cost (IOFC) with increased stocking density, and there was a tendency (P = 0.08) for a linear increase in IOFC when dietary energy was increased. The dietary energy which maximized the IOFC did not vary with stocking density. Dietary energy and stocking density independently affect pig performance, behavior, and economic returns and the optimal dietary energy does not depend on stocking density (dietary energy by stocking density interaction).

This study investigated the effect of nutritional energy levels on meat quality characteristics, through effects on the fatty acid profiles of the subcutaneous fat in sheep. Two rations containing 11. 76MJ ME/kg DM and 10 .18MJ ME/kg DM were fed to Dorper and SA Mutton Merino wethers from respectively 20.51 ± 2.51kg and 22.30 ± 3.99kg to 25, 31, 37 and 43kg live mass. M.longissimus lumborum samples were removed and a trained taste panel evaluated sensory parameters on a lOcm unstructured scale. Subcutaneous fat samples and plasma samples were collected, and various carcass measurements were taken. It was found that high energy nutrition significantly increased the concentration of unsaturated fatty acids in the subcutaneous adipose tissue, with subsequent effects on the fat quality and sensory properties of lamb. Both the aroma and incipient juiciness of taste samples from wethers on the high energy treatment were noticeably improved, while the increased amount of fat, coupled with its poor consistency significantly impaired the overall acceptability of taste samples. / Dissertation (MSc Agric)--University of Pretoria, 1992. / gm2014 / Animal and Wildlife Sciences / Unrestricted

Energy balance refers to the relationship between energy intake and energy expenditure. Epidemiological studies have established a clear association between energy balance and cancer, however the underlying mechanisms are unclear. The objective of the current study was to evaluate the impact of caloric consumption on epithelial carcinogenesis and identify potential mechanisms of inhibition or enhancement. Using ICR female mice, we demonstrated that positive energy balance enhanced, while negative energy balance inhibited susceptibility to multistage carcinogenesis in mouse skin. We next evaluated diet-induced changes in the epidermal proliferative response. Calorie restriction (CR) significantly reduced epidermal hyperproliferation, in the presence and absence of tumor promotion, as compared to diet-induced obesity (DIO). Additional studies were conducted to determine the impact of dietary manipulation on TPA-induced growth factor signaling. CR reduced, while DIO increased insulin like growth factor-1 receptor (IGF-1R) and epidermal growth factor receptor (EGFR) activation, which subsequently modulated signaling downstream to Akt and mTOR. These diet-induced changes in growth factor signaling were confirmed under steady-state conditions in multiple epithelial tissues (i.e., skin, liver and dorsolateral prostate) in multiple mouse strains (FVB/N, C57BL/6 and ICR). Further analyses demonstrated that caloric consumption directly correlated with levels of cell cycle progression related proteins and inversely correlated with levels of cell cycle inhibitory proteins. Genetic reduction of circulating IGF-1, liver IGF-1 deficient (LID) mouse model, inhibited two-stage skin carcinogenesis, reduced epidermal hyperproliferation and attenuated IGF-1R and EGFR growth factor signaling during tumor promotion, similar to CR, suggesting a potential for IGF-1R and EGFR crosstalk. Further studies, demonstrated that IGF-1 induced EGFR activation in cultured mouse keratinocytes, possibly due to IGF-1R and EGFR heterodimerization or IGF-1 induced changes in EGFR mRNA expression. In vivo, CR reduced, while DIO increased IGF-1R and EGFR association during tumor promotion. Furthermore, CR attenuated EGFR ligand mRNA expression both in the presence and absence of TPA treatment. Collectively, these findings suggest that dietary energy balance modulates epithelial carcinogenesis, at least in part due to diet-induced changes in levels of circulating IGF-1, which then modulate IGF-1R and EGFR crosstalk and downstream signaling to cell cycle related proteins, subsequently altering epidermal hyperproliferation. / text

Ce travail de thèse a eu pour objectif d’identifier les mécanismes majeurs intervenant dans la régulation de l’adiposité musculaire chez la truite arc-en-ciel. Pour cela, nous avons analysé les effets combinés de la sélection génétique et de l’alimentation, facteurs prépondérants de variation de l'adiposité. Deux lignées de truites arc-en-ciel sélectionnées sur la teneur en lipides du muscle dorsal ("muscle gras" et "muscle maigre"), ont été nourries pendant 6 mois avec un régime contenant 10 ou 23% de lipides (% de la matière sèche). Nous avons mesuré l'activité et/ou l'expression d’enzymes clé des principales voies métaboliques intervenant dans l'utilisation de l'énergie, puis développé une analyse différentielle globale à l’échelle du transcriptome (microarray nylon) et du protéome (électrophorèse bidimensionnelle). Ces analyses portent sur le muscle blanc, tissu cible de la sélection, et le foie, carrefour métabolique et site majeur de la lipogenèse chez les poissons. Les résultats obtenus confirment l’effet inhibiteur d’un apport alimentaire riche en lipides sur la lipogénèse et la désaturation des acides gras dans le foie, déjà observé chez des individus de plus grande taille, et fournissent de nouvelles connaissances sur l’effet exercé sur les autres voies, en particulier la protéolyse. Ces analyses ont également permis de mettre en évidence des différences métaboliques existant entre lignées, qui concernent non seulement le métabolisme des lipides mais aussi celui des autres substrats énergétiques. Il apparaît que les deux moyens utilisé pour augmenter la teneur en lipides du muscle mettent en jeu des mécanismes moléculaires différents. Nos travaux ont permis d’identifier deux gènes dont l’expression est augmentée dans le muscle en réponse à un apport alimentaire riche en lipides et par la sélection génétique en faveur d’un indice d’adiposité musculaire élevé, et qui pourraient être des marqueurs moléculaires de l’adiposité musculaire. / The objective of the study was to identify genes and proteins that are involved in the control of muscle fat deposition in rainbow trout. We analyzed the combined effects exerted by genetic selection and dietary treatment, which are the two main factors that can be used to manage body fat content. Two lines of rainbow trout, obtained after 3 generations of divergent selection for high or low muscle fat content, were fed diets containing either 10% or 23% lipids (% dry matter), for six months. We analyzed the activity and gene expression of key enzymes involved in energy utilization, and performed a more global approach through transcriptome (nylon microarray) and proteome (two- dimensional electrophoresis) analysis. We analyzed the liver, which is the centre of intermediary metabolism and the main site of lipogenesis in fish, and the muscle, the target tissue of the selection provedure. The results confirmed the depressing effect exerted by a lipid rich diet on lipogenesis and fatty acid desaturation, already described in larger size fish, and provided new insight about the effect exerted on the other metabolic pathways, in particular the proteolysis. These analyses pointed out metabolic differences existing between lines. They involved not only lipid metabolism, but also the other pathways of nutrient utilization. With regard to their muscle-fattening effect, the dietary treatment and the genetic selection appear to act through different molecular mechanisms. These analyses allowed the identification of two genes that are over-expressed in muscle upon both high dietary lipid supply and upward selection for muscle fat content, suggesting that these two genes could be relevant molecular markers of muscle fattening.

O cachara, Pseudoplatystoma fasciatum, é um siluriforme carnívoro da América do Sul. Apesar da importância da espécie para pesca e piscicultura, não há uma dieta específica e nem as exigências nutricionais determinadas. O objetivo deste projeto foi determinar a digestibilidade aparente da energia e proteína de diferentes alimentos de origem animal e vegetal e, com os valores da digestibilidade dos ingredientes, elaborar rações para determinar as exigências em proteína, energia e relação energia:proteína para o cachara. Para o ensaio de digestibilidade, 105 juvenis de cachara (82,35 ± 17,7 g; 23,04 ± 1,6 cm) foram distribuídos em 21 gaiolas cilíndricas plásticas de 80 L e alimentados até a saciedade aparente em duas refeições diárias (20h00min e 22h00min) com dietas teste obtidas a partir da adição de 0,1% de óxido crômico III e substituição de 30% de uma ração referência (RR; 46% proteína bruta; 4600 kcal energia bruta) pelos seguintes ingredientes: farinha de peixe, farinha de carne e ossos, farinha de vísceras, farinha de penas, farinha de sangue, farelo de soja, farelo de trigo, milho moído e glutenose de milho. Após a última refeição, os peixes eram transferidos para os aquários cônicos (200 L) acoplados a recipientes refrigerados para a coleta de fezes por sedimentação. Os melhores coeficientes de digestibilidade aparente da proteína (99,36%) e energia (86,25%) foram registrados para a farinha de vísceras de aves e farinha de carne e ossos, respectivamente, consideradas fontes alternativas adequadas para substituir com eficiência a farinha de peixe, ingrediente padrão para formulação de rações para o cachara. Em um segundo experimento foram determinados os melhores níveis de energia e proteína nas dietas para juvenis de cachara (53,6 ± 1,30 g e 20,1 ± 1,06 cm), distribuídos aleatoriamente em 75 gaiolas (210 L) alojadas em tanques de alvenaria (12 m3) com constante renovação de água e aeração e alimentados duas vezes ao dia (06h30m e 18h30m) por 60 dias com 25 dietas formuladas para conter cinco níveis de proteína digestível (32, 36, 40, 44 e 48%) e cinco níveis de energia digestível (3600, 3725, 3850, 3975 e 4100 kcal kg-1), em um delineamento inteiramente casualizado com um esquema fatorial 5 x 5 (n = 3). A energia e proteína dietética afetaram o ganho de peso, taxa de crescimento específico, consumo de ração, conversão alimentar, taxa de eficiência proteica, retenção de proteína, índice hepatossomático, índice lipossomático, índice viscerossomático, proteínas totais séricas e triglicerídeos no soro. A energia dietética afetou a retenção de energia pelo cachara, mas a retenção de fósforo e a composição do peixe inteiro não foram influenciadas pela dieta. Com os resultados é possível concluir que os níveis de 3600 kcal kg-1 de ED, 39% de PD e a relação ED:PD de 9,23 kcal g-1 garantem ótimo desempenho e retenção de nutrientes pelo cachara. / Striped surubim, Pseudoplatystoma fasciatum is a South American carnivore catfish of economic importance for fisheries and fish culture alike. However, in spite of its importance for the Brazilian aquaculture, there is no specific diet neither nutritional requirement determined for this specie. The aim of this study was thus determination of apparent digestibility coefficients of selected feedstuff and their use in diets for determination of protein, energy and energy:protein requirements of juvenile striped surubim. Juvenile striped surubim (82.35 ± 17.7 g and 23.04 ± 1.6 cm) were distributed in 21 cylindrical, plastic cages (80 L) and conditioned to a two daily meals (20h00m and 22h00m) feeding regimen on a practical, reference diet (RD) (460.0 g kg-1 crude protein (CP); 19.23 kJ g-1 gross energy (GE)). Test diets were obtained by adding 0.1% chromium III oxide and substituting 30% of one the following feedstuffs in RD: fish meal, meat and bone meal, poultry by-product meal, feather meal, blood meal, soybean meal, wheat bran, corn and corn gluten meal. After the last daily meal, fish were transferred to cylindrical-conical bottomed aquaria (200 L), coupled to refrigerated plastic bottles for feces collection by sedimentation. Best apparent digestibility coefficients of protein (99.36%) and energy (86.25%) were recorded for poultry by-product meal and meat and bone meal, respectively, so deemed ideal surrogate feedstuffs to fish meal, the standard protein source for the formulation and processing of diets for carnivore fish. For determination of best energy and protein level, juvenile striped surubim (53.6 ± 1.30 g and 20.1 ± 1.06 cm) were randomly distributed in 75 cages (210 L), housed in 12 m3 concrete tanks under constant water flow and aeration, and hand fed two daily meals (06h30m and 18h30m) for 60 days. Twenty-five diets were formulated to contain five levels of digestible protein (DP) (32, 36, 40, 44 and 48%) and five levels of digestible energy (DE) (3600, 3725, 3850, 3975 and 4100 kcal kg-1) in a randomized design, 5 x 5 factorial scheme (n = 3). The dietary energy and protein affected the weight gain, specific growth rate, feed intake, feed conversion rate, protein retention, hepatosomatic, liposomatic and viscerosomatic index, serum total protein and triglycerides, but energy retention was affected only by dietary energy. Phosphorus retention and whole body composition were not affected by diets. Estimated dietary requirement for the best performance and best nutrient retention of striped surubim were 3600 kcal kg-1 of DE, 39% of DP and a 9.23 kcal g-1 of DE:DP ratio.