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The objective of this study was to investigate the effects of diet composition on performance, slaughter yield and plasma metabolites, as different modern broiler strains show different responses to feed intake. Broilers of two commercial strains and of both sexes received one of three diets being different in energy and/or protein level [control diet, low energy/low protein diet (LM/LP) and low protein diet (LP)]. Low energy/low protein diet chickens were characterized by significantly lower body weights and feed intake compared with their LP and control counterparts. Broilers of the Cobb strain or broilers that were fed the control diet were most efficient in converting energy to body weight. No significant differences in plasma metabolites were detected due to diet composition or genotype. The diet with the lower energy and crude protein levels reached the lowest slaughter yield but the highest drumstick and wing percentages. The lowest mortality percentages were observed for broilers fed the LM/LP diet, and Cobb birds appeared to be more sensitive for metabolic disorders resulting in death. It is obvious from this study that different genotypes respond differently to changes in diet composition and therefore have adjusted nutritional requirements. [ABSTRACT FROM AUTHOR]

Abstract: To explore the mechanisms leading to excessive adiposity in chicken, we investigated the regulation of fatty acid oxidation depending on genotype-related body fatness and diet composition. mRNA expression and/or activity of proteins involved in mitochondrial energy metabolism were measured in liver and gastrocnemius muscle of genetically lean or fat chickens reared on a low-fat/high-protein diet or an isoenergetic high-fat/low-protein diet (HF/LP). Muscle expressions of the muscle isoform of carnitine-palmitoyltransferase 1 (M-CPT1) and PPARβ/δ were higher in fat than in lean chickens. This was also observed in liver, although only with the HF/LP diet for M-CPT1. This could stimulate mitochondrial fatty acid oxidation in fat chickens. Up-regulations of liver and muscle CPT-1 hepatic isoform, and muscle cytochrome-c-oxidase mRNA expressions, and of β-hydroxyacyl-CoA-dehydrogenase activities suggest higher fatty acid utilization with the HF/LP diet. PPARβ/δ and PGC-1α could control fatty acid oxidation in muscle and liver, respectively. Regulation of avian uncoupling protein (avUCP) mRNA was tissue-dependent. Predominantly expressed in muscle, it was stimulated in fat and in HF/LP-fed chickens, where it could be associated to the special need in muscle anti-oxidant pathways of fatter animals. In liver it was lower in fat than in lean chickens, and its potential function remains to be clarified. [Copyright &y& Elsevier]

Research has shown that broiler chickens reared on a low-protein diet have a more efficient protein digestion. However, information on the fate of absorbed amino acids in relation to the dietary crude protein level in poultry is sparse. Therefore, this study aimed at developing a methodology for a 1-13C1-leucine breath test combined with indirect calorimetry, and to apply this technique using broiler diets known to induce differences in protein retention. From 14 days of age onwards, broiler chickens were reared on one of two isocaloric diets with substitutions between fat and protein [low-protein (LP) vs. high-protein (HP) diet: 130.4 vs. 269 g protein/kg; and 101.8 vs. 27.9 g fat/kg]. Every 4 or 5 days, three chickens per diet were placed in the respiratory cells for 48 h. The broilers were intubated with 40 mg 1-13C1-leucine/kg body weight, followed by breath sampling for 4 h at 15-min intervals and mass spectrometric analysis of the 13C:12C ratio in the samples. The CO2 level in the respiratory cell air was monitored and excreta samples were collected. The methodology to studyl[1-13C1]leucine decarboxyation in chickens using a breath test combined with indirect calorimetry was accomplished. Results of the nitrogen balance test indicated that the LP broilers had an improved dietary protein retention compared with the HP animals. Moreover, LP chickens decarboxylated a significantly lower percentage ofl[1-13C1]leucine, demonstrating several ‘protein- or amino acid-sparing’ mechanisms in animals reared on a diet with lower protein level, both at the digestive and at the postabsorptive level. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the role of diet-induced thermogenesis (DIT) in the regulation of feed intake in age-matched broiler and layer cockerels. In addition, the effect of genotype on endocrine functioning and key metabolites of the intermediary metabolism as well as on the expression of muscular uncoupling protein (avUCP) was explored. One-day-old male broiler (Ross) and layer (ISA Brown) chicks were reared under standard conditions on commercial broiler starter and finisher diets. From 22 d of age, twice per week, 3 broiler and 6 layer cockerels were placed in open circuit respiratory chambers. After adaptation, the animals were feed-deprived for 24 h, and heat production was measured by indirect calorimetry. During the subsequent 7-h refeeding period, feed intake and DIT were measured. Blood samples were taken after feed deprivation and refeeding. Muscle samples were taken after refeeding for determination of avUCP expression. A significantly higher heat production per metabolic BW (MBW) in the layer compared with the broiler cockerels, independent of nutritional state, suggests that the broilers used a greater proportion of the metabolizable energy intake for growth. The DIT per MBW and per gram of feed intake was higher for the layer than for the broiler cockerels. However, feed intake per MBW was also significantly higher in the layer cockerels. Thus, no feedback effect of DIT on feed intake per MBW was observed, and the model formulated for adult mammals relating feed intake to DIT could not be corroborated. The muscular expression of avUCP was not different between genotypes, which does not support the hypothesis of an involvement of avUCP in the higher DIT measured in layer cockerels. Circulating uric acid, glucose, triglyceride, and free fatty acid levels were significantly elevated in the layer compared with the broiler cockerels. As the diet was formulated according to broiler requirements, the higher metabolite levels of the layer cockerels might reflect a relative oversupply of dietary nutrients. [ABSTRACT FROM AUTHOR]

The main objectives of this study were to explore the role of diet-induced thermogenesis in the regulation of voluntary feed intake and to determine the glucose oxidation of broiler chicken strains, known to differ in glucose-insulin balance. From 2 to 7 wk of age, male broiler chickens of a fat and a lean line were reared on 1 of 2 isoenergetic diets with constant gross energy and carbohydrate levels but with substitutions between fat and protein. The low protein (LP/HF) diet contained 126 g of protein/kg and 106 g of fat/kg, whereas the low fat (LF/HP) diet contained 242 g of protein/kg and 43 g of fat/kg. There was no significant effect of the genetic background of the broilers on the glucose oxidation rate (as measured by stable isotope breath test) or protein oxidation (as measured by plasma uric acid levels). Considering the difference in carcass composition (fat content) of both lines, this leads to the hypothesis that the lines differ predominantly in fat metabolism. Although there was no line effect on plasma triglyceride and free fatty acid concentrations, it was hypothesized that there might be differences in fat oxidation or de novo lipogenesis, or both, between the genotypes. Diet-induced thermogenesis per metabolic body weight (kg of BW°75) per 24 h, expressed per gram of feed intake, was not significantly influenced by genetic background or by diet composition. Therefore, a model linking feed intake to diet-induced thermogenesis, as postulated for adult mammals, could not be corroborated for growing broiler chickens. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the influence of dietary macronutrient ratio on postprandial (5 or 48 h after refeeding) endocrine functioning and metabolites of the intermediary metabolism and to relate these parameters with dietary-induced alterations in energy, protein, and lipid metabolism. Male broilers were reared from 1 to 7 wk of age on isoenergetic diets with substitutions between fat and protein but similar carbohydrate contents [low protein (LP): 126 vs. 242 g protein/kg; low fat (LF): 43 vs. 106 g fat/kg]. The LP chickens had significantly increased postprandial plasma triglyceride levels. This was likely the result of stimulated hepatic lipogenesis, as corroborated by their significantly higher respiratory quotients. Plasma free fatty acid concentrations were higher in LP broilers, whereas glucose levels were unaffected by dietary composition, suggesting that source over free fatty acids. Plasma uric acid levels were lower in LP compared with LP chickens, indicating a more efficient protein retention in the former group. LP birds that were fasted and refed at 48 h had higher plasma 3,5,3'-triiodothyronine (T3) levels, corroborating their increased heat production. The postprandial T3 increase was more pronounced in the LF chickens, possibly induced by their higher protein consumption. In conclusion, diet-induced changes in heat production and energy partitioning are reflected in circulating levels of intermediary metabolites and hormones. Furthermore, nutritional studies should consider the ability of organisms to habituate to changed diet compositions and that alterations in feeding status follow higher-order responses. [ABSTRACT FROM AUTHOR]