Carcass Protein Content Research Articles

Extent to Which Crude Protein May Be Reduced in Corn-soybean Meal Broiler Diets Through Amino Acid Supplementation

This study was conducted to explore the extent to which CP can be reduced in corn-soybean meal broiler starter diets by amino acid supplementation while maintaining adequate performance. Using corn and soybean meal of known composition, diets were formulated by linear programming using a minimum of 107.5% of NRC (1994) amino acid recommendations. No minimum CP was required; as each amino acid became limiting crystalline sources were provided to meet the minimum specification. In sequence these were Met, Thr, Lys, Val, Ile, Arg, Phe, and Trp, resulting in eight treatments ranging from 16.61 to 22.48% CP. All diets contained 0.3% sodium bicarbonate and 0.2% aluminum hydroxide as a buffer and antacid. Three additional treatments utilized potassium sulfate to maintain a minimum dietary electrolyte balance (Na + K - Cl) of 250 meq/kg. Each treatment was fed to twelve replicate groups of six male broiler chicks from 1 to 21 d. Reducing CP below 20% while providing indispensable amino acids resulted in a significant reduction in body weight (BW) and feed conversion ratio (FCR). Crude protein content of freeze-dried carcasses declined and fat content increased as diet CP decreased. Feather content (actual weight or % of BW) was not affected until the CP was reduced to less than 18%. Maintaining dietary electrolyte balance at 250 meq/kg in reduced CP diets had no significant effect on any parameter.

Effects of dietary protein level on growth performance, carcass composition and ammonia excretion in juvenile silver perch ( Bidyanus bidyanus)

Juvenile silver perch were fed various dietary protein levels to investigate their growth performance, carcass proximate composition and 24 h postprandial accumulated ammonia excretion. White fish meal was the primary protein source in the study. Eight experimental diets containing 13–55% protein with 15.06 MJ/kg diet were fed to three-replicate eight groups of eight fish (mean weight: 2.72 g) for 8 weeks. Both percent weight gain and feed efficiency significantly increased with increasing dietary protein levels up to 37%, while there were no significant differences for protein levels from 37 to 55%. Application of broken line regression analysis to percent weight gain provided an estimate of 42.15±1.87% dietary protein for maximum growth. The protein efficiency ratio and productive protein value were inversely correlated with dietary protein level. The hepatosomatic index and intraperitoneal fat ratios were also inversely related to dietary protein level. Fish fed diets containing 43% dietary protein had significantly higher condition factor than fish fed lower dietary protein levels, but fish fed only 13% dietary protein had the longest relative gut length. The protein content of the fish carcasses increased with dietary protein levels up to 31%, but no significant difference was found with protein levels higher than 37%. Lipid content decreased with increasing dietary protein levels and dry matter content also slightly decreased. The amount of postprandial ammonia excreted by silver perch within 24 h was linearly related to dietary protein level.

Larger diet-induced thermogenesis and less body fat accumulation in rats fed medium-chain triacylglycerols than in those fed long-chain triacylglycerols.

It has been previously shown that a diet containing medium-chain triacylglycerols (MCT) leads to less body fat accumulation as compared to a diet containing long-chain triacylglycerols (LCT). We investigated the involvement of diet-induced thermogenesis in the accumulation of body fat in rats fed a diet containing MCT. Twelve male Wistar rats were administered 1 g of MCT or LCT by gavage, and their oxygen consumption was measured for 6 h (experiment 1). Forty male Wistar rats were fed a diet containing 10% MCT or LCT for 6 wk, and their body composition was determined (experiment 2). In experiment 1, oxygen consumption increased to a greater extent after MCT administration than after LCT administration. Diet-induced thermogenesis was significantly (0.67 +/- 0.14 kcal) larger after the administration of 1 g of MCT. In experiment 2, there were no differences in food intake or carcass protein content between the LCT group and MCT group. However, carcass fat and intra-abdominal fat content were significantly lower in rats fed MCT than in those fed LCT. We calculated that ingestion of 1 g of MCT decreased body fat by 0.94 +/- 0.27 kcal relative to the ingestion of LCT. These results suggest that the larger diet-induced thermogenesis observed in rats fed MCT, compared to that of those fed LCT, is one of the main factors involved in the suppression of body fat accumulation in rats fed MCT.

Stress and Nutritional Quality of Broilers

Broiler chicks were reared in environmental chambers. All birds were started under ideal conditions, i.e., 30.6 C with 35% RH. Beginning at Day 36, half of the chicks were maintained at 24 C and 35% RH. The other half were subjected to a cyclic temperature-RH regime that approximated a typical August day in central Mississippi (heat treatment). Half of each of the described groups received implants of osmotic pumps that released adrenocorticotropin (ACTH) at 8 IU/kg BW/d for 7 d. The remaining birds received placebo pumps. The main effects of ACTH and heat treatments were similar. Both treatments caused reductions in BW, carcass weight (CW), carcass protein (CP), and muscle calorie (C) content. ACTH, but not heat, reduced carcass moisture (M). Carcass fat and ash, however, were not affected. Most changes were not reversed after 1 wk of recovery. Although visible signs of pale, soft, exudative muscle (PSE) were present, “white” areas of muscle were absent. The decreased meat yield and detrimental changes in meat quality suggest that stress, whether induced hormonally or by exposure to over-heating, caused losses that were as severe as those associated with PSE under field conditions.

Dietary biotin requirement determined for Indian catfish, Heteropneustes fossilis (Bloch), fingerlings

Triplicate groups of Indian catfish, Heteropneustes fossilis (Bloch), fingerlings (average wet weight 3.55 ± 0.03 g) were fed semi-purified diets containing six levels of biotin (0, 0.086, 0.26, 0.86, 2.5 and 4.3 mg kg−1 diet) for 15 weeks. After 42 days of feeding, fish fed the control (no biotin) diet had developed severe deficiency signs characterized by convulsions, heavy mortality, listlessness, poor feed conversion and feed intake, dark skin colour, tetanus and weight loss. None of these signs was seen in fish fed biotin-supplemented diets. Among all the biotin-supplemented diets, percentage weight gain was significantly highest for fish fed the diet supplemented with 0.26 mg of biotin kg−1 and significantly lowest for fish fed the diet supplemented with 0.086 mg of biotin kg−1. Feed conversion ratio (FCR) and protein efficiency ratio (PER) patterns were similar to that of percentage weight gain. The carcass protein and lipid contents were influenced by the dietary biotin up to fish fed 0.26 mg of biotin kg−1. Significantly higher body biotin content, liver pyruvate carboxylase and acetyl CoA carboxylase activities were observed in fish fed biotin-supplemented diets than in fish fed the control diet. Broken-line analyses showed that the optimum dietary requirement for biotin for maximal weight gain, body biotin content, liver pyruvate carboxylase and acetyl CoA carboxylase activities was about 0.25 mg kg−1. Associated liver pyruvate carboxylase and acetyl CoA carboxylase activities for normal growth ranged from 105 to 120 units mg−1 protein and from 9 to 11 units mg−1 protein respectively.

The dietary protein requirement of a bagrid catfish, Mystus nemurus (Cuvier & Valenciennes), determined using semipurified diets of varying protein level

Triplicate groups of Mystus nemurus (Cuvier & Valenciennes) were fed isoenergetic semipurified diets containing seven dietary protein levels from 200 to 500 g kg–1 diet for 10 weeks. Dietary protein was supplied by graded amounts of a protein mixture (tuna muscle meal:casein:gelatine) at a fixed ratio of 50:37.5:12.5. Mystus nemurus fingerlings of initial weight 7.6 ± 0.2 g were fed close to apparent satiation at 2.5% of their body weight per day in two equal feedings. Growth performance and feed utilization efficiency increased linearly with dietary protein level from 202 to 410 g kg–1 diet and declined with protein levels of 471 g kg–1 diet or above. Protein efficiency ratio and apparent net protein utilization started to decline when the fish were fed with dietary protein levels exceeding 471 g kg–1 diet. Fish fed with lower protein diets (202–295 g kg–1 diet) had significantly (P < 0.05) higher carcass lipid content compared with fish fed with higher protein diets. Carcass lipid contents were inversely related to moisture content. Dietary protein did not significantly affect fish carcass protein and ash content. Using two-slope broken-line analysis, the dietary protein requirement for M. nemurus based on percentage weight gain was estimated to be 440 g kg–1 diet with a protein to energy ratio of 20 mg protein kJ–1 gross energy. This level of protein in the diet is recommended for maximum growth of M. nemurus fingerlings weighing between 7 and 18 g under the experimental conditions used in this study.

Increased body fat in streptozotocin diabetic rats treated with intensive subcutaneous insulin therapy vs. islet transplantation

The continued development of novel insulin treatment is predicated on the hypothesis that strict glycemic control is necessary to prevent the secondary complications of diabetes. Although dramatically successful in reducing selected secondary complications, intensive insulin therapy has consequences. These include hypoglycemia, weight gain, and body fat accumulation. In the present studies we compared a model of intensive insulin therapy in diabetic rats and contrasted weight gain and body fat accumulation with pancreatic islet transplantation. Female Wistar Furth rats (173 g) administered streptozotocin (55 mg x kg(-1), iv) remained diabetic (DB) for four or nine weeks. At week three, a third group was transplanted (TRAN) with islets of Langerhans (3519 +/- 838 150 microm islets); one week later group four began intensive subcutaneous insulin therapy (ISIT; 4 x 0.5-1.0 U regular insulin x day(-1)). Within one week ISIT rats had normalized plasma glucose; levels were not different from age matched controls (CN) or TRAN animals (ISIT 10.6 +/- 1.7, CN 7.2 +/- 0.4, TRAN 7.7 +/- 0.8 mmol x L(-1), P > 0.05). The cumulative occurrence of one episode of hypoglycemia (< 2.8 mmol x L(-1)) occurred in 50% of ISIT rats. At study termination, body weight of ISIT and CN rats did not differ (199 +/- 4 vs. 207 +/- 3, P > 0.05). While carcass protein content was similar for TRAN, ISIT, and CN animals, the body fat of ISIT animals was 24% greater than in CN rats and 21% greater than in TRAN rats (P < 0.05). Correlation of body fat vs. plasma glucose illustrated hypoglycemia contributed to the body fat gain of ISIT rats (n = 8, r = -0.70, P = 0.0535). These studies illustrate a disproportionate gain of body fat from ISIT, an effect not observed with islet transplantation. Thus, the metabolic benefit ascribed to islet transplantation appears related to the absence of hypoglycemia.

Efeito da temperatura ambiente e da restrição alimentar sobre o desempenho e a composição da carcaça de frangos de corte

O objetivo deste experimento foi estudar os efeitos da temperatura ambiente e da restrição alimentar sobre o desempenho produtivo, o rendimento das carcaças e dos cortes nobres e os teores de gordura, água e proteína das carcaças e os teores de glicogênio do fígado de frangos de corte em diferentes condições ambientais. O delineamento experimental usado foi em blocos casualizados, em esquema fatorial 5 x 2 (programa alimentar e sexo) com duas repetições dentro de cada ambiente e 14 aves por unidade experimental. Aos 42 dias de idade, o consumo de ração e o ganho de peso foram influenciados negativamente pela temperatura e pelo sexo, porém não foram afetados pelo programa de restrição alimentar. Os rendimentos de carcaça e de cortes nobres não foram influenciados pela temperatura, pelos programas de restrição alimentar e pelo sexo. Os programas de restrição alimentar e a temperatura não influenciaram os teores de gordura, água e proteína da carcaça. As fêmeas apresentaram maior teor de gordura nas carcaças. Já os teores de glicogênio do fígado foram negativamente influenciados pelos programas de restrição alimentares e pelo sexo, porém não foram afetados pela temperatura.

Effect of fermentation on the nutritive value of sesame seed meal in the diets for rohu, Labeo rohita (Hamilton), fingerlings

Six isonitrogenous (350 g kg−1 crude protein) and isoenergetic (17573 kJ kg−1) experimental diets incorporating raw and fermented sesame (Seasamum indicum) seed meal at 200, 300, and 400 g kg−1 into a fishmeal based diet were fed to rohu Labeo rohita fingerlings for 60 days and the growth performance and feed utilization efficiency of the fish was studied. The antinutritional factor phytic acid, from raw sesame seed meal, could be reduced below detection limit by fermentation with lactic acid bacteria (Lactobacillus acidophilus). Fermentation of the oilseed meal resulted in reduction of the tannin content from 20 to 10 g kg−1. In terms of growth response, feed conversion ratio and protein efficiency ratio, a diet containing 400 g kg−1 fermented sesame seed meal resulted in a significantly (P < 0.01) best fish performance. In general, growth and feed utilization efficiencies of fish fed fermented sesame seed meal diets were superior to those fed raw oilseed meal diets. Apparent protein digestibility (APD) values decreased with increasing levels of raw oilseed meal. APD was, however, significantly (P < 0.01) higher at all levels of incorporation of fermented sesame seed meal, while diets containing raw oilseed meal resulted in poor protein and lipid digestibility. Carcass protein and lipid contents of fish fed fermented sesame seed meal diets increased with increasing level of incorporation, being highest with 400 g kg−1 fermented oilseed meal-containing diet. The results showed that sesame seed meal may be incorporated in carp diets up to 200 g kg−1 and 400 g kg−1 in raw and treated (fermented) forms respectively.

Fat storage capacity in growth-selected and control mouse lines is associated with line-specific gene expression and plasma hormone levels.

For a detailed understanding of the complex traits growth and fat storage, a dissection into single genetic entities is mandatory. Therefore, blood plasma concentrations of hormones and the expression of selected genes were measured in extremely differentiated mouse lines. Genes were selected as candidates which might influence the complex traits body weight and fat accumulation, and which are located in chromosomal regions recently identified to affect trait differences between the lines. The mouse lines were selected for high body weight (DU6), high carcass protein content (DU6P) and unselected controls (DUKs). In the selected lines DU6 and DU6P, mean body weights at the age of six weeks were about twice as high as the DUKs, whereas total fat weight was increased 2.2-fold in DU6 mice compared to DU6P and 3.2-fold in comparison to DUKs. Blood plasma concentrations of insulin-like growth factor 1 (IGF-1), growth hormone (GH), insulin and leptin, were measured in all lines at three weeks and at six weeks of age. Expression patterns of the genes encoding growth hormone (Gh), insulin-like growth factor 1 (Igf1), lipoprotein lipase (Lpl), glycerolphosphate dehydrogenase 1 (GDC-1), and adipocyte protein 2 (Ap2) were analyzed by Northern blot hybridization. In line DU6, highly significant increased concentrations of insulin and leptin were observed at six weeks of age; at this stage, IGF-1 concentrations were elevated in the two selected lines compared to controls with maximal concentrations of IGF-1 and GH in DU6P. The amount of mRNA for GH in the pituitary gland, for Igf1 in the liver and for LPL in epididymal fat tissue was significantly elevated in the two selected lines compared to controls at the age of three weeks, but not at six weeks. IGF-1 and GDC-1 mRNA concentrations were significantly higher in the DU6 mice than in the DU6P (P < 0.01) and the DUKs (P < 0.001) mice examined at both ages. The results prove line-specific concentrations of the analyzed hormones and the transcription amounts of Gh, Igf1, GDC-1 and Lpl. The measured differences are either direct genetic effects or secondary changes, resulting from different food consumption.

Conjugated linoleic acid rapidly reduces body fat content in mice without affecting energy intake.

Recent reports have demonstrated that conjugated linoleic acid (CLA) has effects on body fat accumulation. In our previous work, CLA reduced body fat accumulation in mice fed either a high-fat or low-fat diet. Although CLA feeding reduced energy intake, the results suggested that some of the metabolic effects were not a consequence of the reduced food intake. We therefore undertook a study to determine a dose of CLA that would have effects on body composition without affecting energy intake. Five doses of CLA (0.0, 0.25, 0.50, 0.75, and 1.0% by weight) were studied in AKR/J male mice (n = 12/group; age, 39 days) maintained on a high-fat diet (%fat 45 kcal). Energy intake was not suppressed by any CLA dose. Body fat was significantly lower in the 0.50, 0.75, and 1.0% CLA groups compared with controls. The retroperitoneal depot was most sensitive to the effects of CLA, whereas the epididymal depot was relatively resistant. Higher doses of CLA also significantly increased carcass protein content. A time-course study of the effects of 1% CLA on body composition showed reductions in fat pad weights within 2 wk and continued throughout 12 wk of CLA feeding. In conclusion, CLA feeding produces a rapid, marked decrease in fat accumulation, and an increase in protein accumulation, at relatively low doses without any major effects on food intake.

Studies on energy metabolism in lines of mice selected for different growth parameters

Growth is a very complex physiological process and is controlled by many genes and therefore easy to manipulate by selective breeding. Such manipulation of growth was realized by long‐term selection of laboratory mice for different growth parameters (body weight, total protein amount in the carcass and an index combining body weight and endurance fitness) resulting in a high phenotypic and genetic differentiation compared to the nonselected control (Bünger et al. 1983, 1992, 1994; Renne et al. 1995). After 70 generations the 42‐day body weights increased from 28 g at the start of selection to 58.3 g, 51.9 g and 47.4 g in these lines, respectively (Bünger et al. 1994). At the same time the carcass protein content increased from 2.92 to 5.23 g in the line selected for protein mass without an increase of fat percentage up to the age of 42 days (Renne et al. 1995). In comparison with that, selection for body weight was accompanied by a marked increase of fat percentage up to this age as reported in literature for many long‐term selection experiments. Because of the different chemical composition of the body gain at relatively small differences in growth rate, these selected lines seemed to be suitable models for studying some aspects of energetic efficiency of growth. The results of a former experiment conducted in generations 32–42 suggested a higher efficiency of energy utilization in the line selected for body weight than in the other selected lines (Bünger et al. 1987). The objective of the present study was to characterize the energy metabolism of these different selected lines complementary to the studies on protein metabolism given by Schadereit et al. (1997, 1998).

Prediction of Carcass Fat, Protein, and Energy Content from Carcass Dry Matter and Specific Gravity of Broilers

Prediction of Carcass Fat, Protein, and Energy Content from Carcass Dry Matter and Specific Gravity of Broilers

Effect of dietary zinc supplementation and phytase pre-treatment of soybean meal or corn gluten meal on growth, zinc status and zinc-related metabolism in rainbow trout, Oncorhynchus mykiss

Rainbow trout, Oncorhynchus mykiss, were fed diets containing untreated or phytase-treated soybean meal and corn gluten meal with or without 50 mg supplemental zinc kg−1 to determine if dietary phytate caused a zinc (Zn) deficiency. Fish fed diets containing untreated soybean meal and corn gluten meal without supplemental Zn (basal diet) showed no signs of a Zn deficiency after 170 d of weight gain. Weight gain, carcass protein content, total bone Zn, and alkaline phosphatase and carboxypeptidase B activities were not significantly altered in fish fed the basal diet. Dietary phytate removal and supplemental dietary Zn were not required to prevent Zn deficiency in rainbow trout fed a plant-based diet. Although bone Zn concentrations were reduced in fish fed the basal diet, total bone Zn increased in all fish regardless of dietary treatment. Future assessments of Zn status of fish should be based on changes in Zn-dependent metabolism or total bone Zn rather than on bone Zn concentration.

Effect of food intake on protein quality measured in chicks by traditional or biochemical methods

Previous studies have shown that the activities of the hepatic enzymes xanthine dehydrogenase and nucleoside phosphorylase, as well as the uric acid excreted, can be used to determine the quality of the protein consumed in chickens, in a short time and using a small amount of the test protein. A common observation in protein quality evaluation is that the food intake of the control animals is considerably greater than that observed in those receiving proteins of low quality. Since this can affect the results, this study measured the quality of garbanzo bean and black bean proteins in chickens fed these beans ad libitum, feeding the bean diets at the level observed in the controls (soy protein+methionine) by enteral intubation or pair feeding the controls with the amount of food consumed by the chickens receiving the bean diets. In every case, protein quality was determined by protein efficiency ratio, net protein utilisation or the biochemical methods used in this study. The results showed that, when fed ad libitum, the animals assigned to the bean diets exhibited a lower food intake than the controls but, by tube feeding, food intake was made equal in both groups. Equal consumption, between these groups, was also obtained by reducing the amount of food offered to the controls to the levels measured in the groups assigned to the bean diets (pair feeding). These feeding strategies had a marked effect on growth, carcass protein content, protein catabolism and also in the results of protein quality. Thus, the control whose intake was reduced grew less, accumulated less protein in tissues and catabolised more of the protein consumed than the control fed ad libitum. In contrast, the chickens assigned to the bean diets, but whose food intake was increased by tube feeding, grew better, accumulated more protein in tissues and catabolised less protein. In general, the results of these experiments confirm the effectiveness of the biochemical methods for estimating protein quality and indicate that the protein quality of both garbanzo beans and black beans increased when it was measured at a food intake equivalent to that measured in the control animals. Since the overall purpose of this study was to evaluate techniques for protein quality determination meant to be applicable to humans nutrition rather than poultry nutrition, single proteins were used instead of combinations of proteins. © 1998 Society of Chemical Industry.

A deletion in the myostatin gene causes the compact (Cmpt) hypermuscular mutation in mice.

A deletion in the myostatin gene causes the compact (Cmpt) hypermuscular mutation in mice.

Dietary phosphorus requirement of juvenile tiger barb, Barbus tetrazona (Bleeker, 1855)

The effects of increasing dietary concentrations of phosphorus on growth, feeding efficiency and body composition were studied in the tiger barb (Barbus tetrazona) (Bleeker, 1855). Juvenile tiger barbs (initial weight 0.33 ± 0.02 g) were fed purified diets containing graded levels of KH2PO4 to provide 0.17--1.57% available dietary phosphorus for 8 weeks in freshwater glass aquaria. The weight gain, feeding efficiency and mineral composition of the whole body and bone were significantly (p < 0.05) affected by dietary phosphorus. Growth response data calculated by broken line analysis showed that the minimum dietary phosphorus level required for maximum growth was 0.52%. The carcass protein, fat and ash contents but not moisture were affected by various dietary phosphorus levels. Fish fed a low-phosphorus diet had high body crude fat

Composition analysis of pork carcasses by dual-energy x-ray absorptiometry.

Dual-energy x-ray absorptiometry (DXA) was used as a noninvasive method to measure the composition of pig carcasses. A total of 181 half-carcasses (10 to 51 kg, from pigs slaughtered at approximately 30, 60, 90, and 120 kg) were scanned using a Lunar (Madison, WI) DPX-L densitometer. The DXA measurements of fat, lean, bone mineral, and total tissue mass were compared with chemical analysis for fat, water, protein, total ash, and scale weight. The mean value for total tissue mass by DXA was slightly less than the mean carcass weight (32.3 kg vs 33.6 kg, P > .05, R2 = .998). Although highly correlated (R2 = .81), the DXA measurement of the percentage of fat in the half-carcass was less (P < .001) than the chemical measurement (19.5 vs 24.9%). The DXA measurement of lean tissue mass (total mass less fat and bone mineral) was correlated with carcass protein (R2 = .97) and water (R2 = .99) content. The correlation (R2) between DXA bone mineral content and carcass ash content was only .68; however, DXA bone mineral content was more highly correlated with carcass weight (R2 = .93) than was carcass ash content (R2 = .70). When we used the DXA R value (ratio of the attenuation coefficients for fat and lean) to predict percentage of fat in the carcass, the mean value for predicted carcass fat was 25.9% (P > .05). Similarly, carcass protein and water content were predicted from DXA lean. Using DXA region of interest analysis, estimates of the fat content of the shoulder and ham regions were close to chemical values; however, DXA underestimated the fat content of the loin and side regions by 20 and 28%, respectively. When prediction equations were used to evaluate DXA measurements of the half-carcasses of 28 gilts and 37 boars slaughtered at approximately 120 kg, the half-carcasses of gilts contained more fat (33.9 vs 27.8%, P < .001), less protein (14.1 vs 16.1%, P < .001), and less water (45.9 vs 52.1%, P < .001) than those of boars. These results indicate that DXA could be a valuable research tool for measuring the composition of pig carcasses. On the basis of the results of this study, prediction equations were revised for the DXA estimation of fat, protein, and water content of the half-carcass: Fat (%) = 450 - (315 x DXA R value), Protein (g) = -145 + (.23 x DXA lean), and Water (g) = 150 + (.73 x DXA lean). Furthermore, it seems that separate prediction equations are needed for regional analysis.

Protein metabolism in mice selected for high carcass protein content or high body weight

SummaryProtein turnover, efficiency of growth and body composition were investigated in N balance experiments with growing male mice (26‐36 days of age) which were long‐time selected for high carcass protein amount (DU‐6P) or for high body weight (DU‐6) and in the unselected randomly bred control (DU‐Ks). In total 12 mice per line were housed singly in metabolic cages and had free access to a commercial stock diet (crude protein 267 g, gross energy 19 MJ/kg dry matter). N balance, whole body protein synthesis (PS, end‐product method, single dose of 15N‐labelled amino‐acid mixture), fractional myofibrillar muscle breakdown rate (FBR, 3‐methylhistidine method) and N distribution in the body were measured. Additionally, the maintenance nitrogen requirement (MNR) and the maximum possible rate of N accretion (MNA) of the different lines was estimated after feeding semi‐synthetic diets with increasing protein levels. Body weight of both selection lines was about twice that of the control mice at the same age. The DU‐6P mice synthesized and deposited more protein and less fat per unit metabolic BW, than the DU‐6 mice did. However, scaled to the corresponding body protein pools, the rates of protein synthesis were not significantly different between both selection lines in contrast to the deposition rate. Selection for high body weight resulted in higher body fat content, higher muscle FBR and a lower proportion of carcass N compared to DU‐6P mice. The protein synthesis (13‐14 g protein/kg BW0.75 per day) and MNR values (290‐305 mg N/kg BW0.75 per day) of the selected mice were higher than those of control mice (11 g protein and 265 mg N/kg BW0.75, respectively) and may be due to selection‐linked enlargments of visceral organs. The MNA of DU‐6P and DU‐6 mice amounted to 6 and 5 g protein/kg BW0.75, respectively, and the MNA of the controls was between these values. Compared to DU‐6, the higher protein accretion rate of DU‐6P mice seems to be due more to a lower muscle protein breakdown rate than an increased protein synthesis rate.ZusammenfassungProteinumsatz von Mäusen, die auf hohen Körperproteingehalt oder auf hohes Körpergewicht selektiert wurdenAn je 12 wachsenden männlichen Mäusen, die über 80 Generationen am 42. Lebenstag entweder auf hohen Proteingehalt im Schlachtkörper (DU‐6P) oder auf hohe Lebendmasse (DU‐6) selektiert worden waren, wurden Proteinstoffwechsel, Wachstumseffizienz und Körperzusammensetzung im Vergleich zur unselektierten Kontrollinie (DU‐Ks) untersucht. Die Tiere wurden einzeln in Stoffwechselkäfigen bei freiem Zugang zu Wasser und Altromin‐Zuchtfutter (Rohprotein 267 g/kg TS, Bruttoenergie 19 MJ/kg TS) gehalten. Neben der N‐Bilanz wurden Gesamtkörper‐Proteinsynthese (PS, Endproduktmethode, einmalige Gabe einer 15N‐Aminosäurenmischung, Auswertung mittels Kompart‐mentmodell), fraktionelle Muskelprotein‐Abbaurate (FBR, 3‐Methylhistidin‐Methode), Verteilung des Körperstickstoffs, N‐Erhaltungsbedarf (MNR, regressiv nach Fütterung semi‐synthetischer Rationen mit steigenden Proteinniveaus) sowie maximales N‐Ansatzvermögen (MNA) der Mauslinien gemessen. Die mittleren Lebendmassen (LM) der selektierten Tiere waren bei gleichem Alter etwa doppelt so hoch wie die der unselektierten Kontrolle. Pro kg metabolischer LM synthetisierten und deponierten DU‐6P‐Mäuse täglich mehr Protein als DU‐6‐Mäuse. Bei Bezug auf die entsprechenden Körperprotein‐gehalte waren die Unterschiede in den täglichen Proteinsyntheseraten beider Selektionslinien im Gegensatz zur Proteinansatzrate nicht mehr signifikant. Die Selektion auf hohe LM (DU‐6) führte zu höheren Körper‐Fettgehalten, zu höheren FBR und damit zu niedrigeren Körper‐N‐Gehalten im Vergleich zur Selektion auf hohen Proteingehalt (DU‐6P). Proteinsynthese (13–14 g Protein/kg LM0.75.d) und MNR (290–305 mg N/kg LM0.75.d) der selektierten Mäuse waren höher als die der Kontrolltiere (11 g Protein bzw. 265 mg N/kg LM0.75.d) und können mit den selektionsbedingten Vergrößerungen der relativen Organgewichte zusammenhängen. Die MNA‐Werte lagen zwischen 5 (DU‐6) und 6 g (DU‐6P) Protein/kg LM0.75.d. Der im Vergleich zur Linie DU‐6 höhere Proteinansatz der DU‐6P‐Tiere scheint mehr durch eine verminderte Muskelprotein‐Abbaurate als durch eine höhere Proteinsyntheserate bedingt zu sein.

Hormonal and metabolic adaptations to fasting in monosodium glutamate-obese rats.

The effect of fasting on hormonal and metabolic variables was evaluated in normal rats and in rats with obesity induced by neonatal treatment with monosodium glutamate (MSG). The hyperinsulinemia of the fed obese rats was reversed by fasting. Plasma corticosterone was also high in the fed obese and decreased to levels similar to fed controls, while it increased in the latter group during fasting. In contrast, thyroid hormone levels decreased in controls but increased in the obese rats in response to fasting. The fed obese group had lower carcass protein and higher carcass lipid contents than controls. In response to fasting, the decrements of the initial amount of both protein and fat were lower in MSG than in controls. Fasting induced a sustained increase in plasma free fatty acids only in the obese rats, although a single 100 mumol.l-1 dose of norepinephrine stimulated in vitro glycerol release more pronouncedly in epididymal adipocytes from control than obese rats. The results indicate that MSG-obese rats were able to mobilize fat stores during prolonged fasting. The high availability of lipid fuels and the sharp and sustained decrease in circulating corticosterone in the MSG group were probably important in diminishing body protein consumption during fasting.