Heat-exposed chickens exhibit a lower growth rate and a depressed protein retention which may result from an alteration in protein metabolism. A high-protein diet seems to be beneficial under hot conditions because it tends to improve growth. Effects of high ambient temperature (32 vs. 22°C) and dietary crude protein (25 vs. 20%) on muscle protein turnover were investigated in finishing broiler chickens. At 5-6 wk of age, protein synthesis was measured in vivo in the Pectoralis major, Sartorius and Gastrocnemius muscles (flooding dose of [ 3 H]-phenylalanine). Protein breakdown was determined in the same muscles as the difference between protein synthesis and deposition. Chronic heat stress markedly reduced protein synthesis, irrespective of muscle type (P Ͻ 0.05). This was mainly related to the lower capacity for protein synthesis (muscle RNA/Protein) (P Ͻ 0.01). Chronic heat exposure also decreased protein breakdown in the P. major and Sartorius; this effect was not observed in the Gastrocnemius. Protein synthesis was more affected than breakdown, leading to reduced protein deposition, at least in the P. major and Gastrocnemius muscles. Increasing dietary protein content had no significant impact on muscle protein turnover. Particularly at 32°C, the high-protein diet did not significantly modify either protein synthesis, ribosomal capacity or translational efficiency. However, it favored muscle protein deposition, which was probably related to reduced proteolysis. In conclusion, we showed that chronic heat exposure decreased muscle protein deposition, mainly by reducing protein synthesis. Under these conditions, the impaired protein synthesis was not restored by a 5% higher protein intake. J.

We analysed the respective influences of age and lysine deficiency on skeletal muscle and liver protein turnover. Growing male broilers were fed ad fibirum on isoenergetic diets containing 2OOg crude protein/kg which varied in their lysine content (77 or 101 g/kg). Fractional rates of protein synthesis (FSR) were measured in vivo in the liver and the pectoralis mapr muscle of 2, 3-and 4-week-old chickens (flooding dose of ~-[4-~H]phenylalanine). Fractional rates of proteolysis (FBR) were estimated for the same tissues as the difference between synthesis and growth. Over the %week period liver FSR and FBR were unchanged, whereas muscle FSR decreased with age. This developmental decline was related to the lower capacity for protein synthesis (Cs) without any modifications of the translational efficiency. Whatever the age, lysine de5ciency resulted in significant decreases in body weight, tissue protein content and tissue protein deposition, apparently because of reduced amounts of proteins synthesized. We recorded a difference in the response of the two tissues to lysine deficiency, the pectoralis major being more sensitive than the liver. When comparing birds of the same age, liver FSR and FBR were not modified by the diet, whereas muscle FSR, Cs and FBR were higher in chicks fed on a lysini?-deficient diet than in the controls. Conversely, when chicks of similar weights were compared, the main effect of the dietary deficiency was an increase in muscle FBR. The results suggest that lysine deficiency not only delayed chick development 90 that protein turnover was affected, but also induced greater changes in metabolism. Thus, the principal mechanism whereby muscle mass decreased appeared to be a change in FBR. Lysine: Protein turnover: ChickenThe poultry industry aims to increase the efficiency of the transformation from feed to animal proteins to provide consumers with a product containing more lean and less fat, and to reduce N excretion which is a source of pollution. At present, synthetic amino acids are added to low-protein diets to obtain a well-balanced feed. A deficiency in a single essential amino acid can indeed disrupt growth mechanisms: it decreases chick growth, feed intake and N balance (Akinwande & Bragg, 1985;Okumura et al. 1985; Kino & Okumura, 1986a, b). It caused a reduced protein deposition in the whole body and in the pectoralis major muscle of 3-week-old chickens mainly because lower amounts of protein were synthesized each day (Kino & Okumura, 1987; Tesseraud er al. 1992). To our knowledge, all of the studies concerning the effect of an amino acid deficiency have compared chicks at the same chronological age, when chicks fed on a control or an amino acid-deficient diet did not only have different body weights but had, also, different tissue protein masses and different rates of tissue development. To understand better the reduction of growth performance associated with the deficiency of a particular amino acid, we analysed the effect of dietary lysine on in vivo protein turnover using 2-, 3...

The effects of two environmental temperatures (22 and 32 C, constant) and five dietary protein contents (10 to 33% CP) were investigated in 4- to 6-wk-old broiler chickens. High ambient temperature reduced growth rate, feed efficiency, and breast muscle proportion and increased abdominal fat proportion. Irrespective of ambient temperature, increasing dietary protein content improved growth performance and carcass characteristics. At 32 C, there was a greater heterogeneity of the data, and bird responses were lower than at 22 C. We concluded that under conditions of chronic heat exposure, diets containing the highest protein levels, 28% and 33% compared with 20% CP, slightly improved chick performance. However, the effect was low and, in our experimental conditions, modifying dietary protein supply (variations in the total quantity of protein) is not sufficient to help broilers to withstand hot conditions.

This study was undertaken to determine if pea (Pisum sativum L.) protein structure could explain pea protein digestion. A nitrogen-free (NF) diet and two diets containing either whole ground peas or a globulin fraction purified from peas were fed to 3-week-old chickens. Sodium dodecyl sulfate polyacrylamide gel electrophoresis was used to estimate the relative rates of degradation of proteins subfractions in the gastrointestinal contents of chicks. Proteins were quantified by image analysis of Coomassie blue stained bands. Convicilin disappeared already in the gizzard. Legumin α and vicilin were still present in gizzard but disappeared in jejunum. The polypeptides shown to persist until the end of digestive tract were albumin PA2, lectin, and polypeptides of MW in the range 19500−25000 originating presumably from legumin. An endogenous protein of about 57 000 was observed until terminal ileum. Apparent ileal protein digestibility was high and slightly lower for pea diet (89.5%) than for globulin diet (93.3%). Results suggested that, although some pea proteins appeared less susceptible to hydrolysis, they represented only a small amount at the terminal ileum. Keywords: Pea proteins; globulin; chick; digestion; electrophoresis

It has been previously established that growth and carcass qualities of chicks are modified by genotype and dietary amino acid supply. In this study, we evaluated the effects of lysine deficiency and genetic selection on muscle protein metabolism. Chicks originating from an experimental line selected for breast development (QL) and its control line (CL) were provided ad libitum access to isoenergetic diets containing 20% crude protein but differing in their lysine content (0.75 or 1.01%). Protein fractional synthesis rates (FSR) were measured in vivo in the pectoralis major and sartorius muscles of 3-wk-old chickens (flooding dose of [3H]phenylalanine). Fractional breakdown rates (FBR) were estimated as the difference between synthesis and deposition. Lysine deficiency reduced (P < 0.001) growth performance and muscle weights and increased (P < 0.05) muscle FSR, capacity for protein synthesis (muscle RNA:Protein, Cs) and FBR. Although QL birds grew faster and had heavier pectoralis major muscles than CL birds (P < 0.05), there was no line difference in sartorius weight (P = 0.15). No difference between the lines was observed in sartorius protein metabolism (P > 0.14). In the pectoralis major muscle, chicks of both lines receiving an adequate lysine intake also exhibited similar protein turnover rates. However, in chicks fed the lysine-deficient (0.75% lysine) diet, FSR and Cs were higher in QL than in CL chicks (P < 0.05), and FBR tended (P = 0.07) to be higher in QL chicks. This increased protein turnover in the QL birds on the lysine-deficient diet suggests that the responsiveness of muscle protein metabolism to amino acid supply is modified by genetic selection for breast development.