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.

Susceptibility to liver steatosis was studied in Landes and Poland geese, which are hyper- and hyporesponsive, respectively, to overfeeding. Plasma lipoproteins were characterized at different stages of the overfeeding process, whereas fatty liver composition was determined after completion of overfeeding and slaughtering. Before overfeeding, plasma lipoprotein profile was typical of birds in both breeds, except that very low density lipoproteins (VLDL) were low in triglyceride (approximately 30%). Moreover, high-density lipoprotein (HDL) concentration was higher in the Poland geese (6.44 vs 4.97 g/L). During overfeeding, hepatic lipogenesis was increased, and fatty liver resulted from accumulation of primarily triglyceride (approximately 95% of lipid content), but also of all other lipids. This accumulation was significantly greater in the Landes geese for all lipids but phospholipid. Thus, the liver weight was 100% higher in this breed (1,005 g vs 485 g), whereas lipid release during sterilization was twofold higher (26.3 vs 7.5%). Parallel, plasma concentration and triglyceride content of hepatic lipoproteins, VLDL and HDL, increased about one- to twofold, this effect being greater in the Poland geese. Therefore, channeling of triglyceride towards secretion rather than in situ storage may be responsible for the hyporesponsiveness of this breed to overfeeding. In both breeds, and especially in the Landes geese, a relative deficiency in phospholipid synthesis together with an enhanced secretion may be limiting factors of hepatocyte hypertrophia and, therefore, of steatosis.

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...

In response to overfeeding for the production of "foie gras," the Poland goose differs from the Landes goose by a lesser susceptibility to hepatic steatosis, resulting in a lower accumulation of hepatic triacylglycerol (TG), together with a greater exportation of hepatic phospholipid (PL) in very low density lipoproteins (VLDL) and high density lipoproteins (HDL) (Fournier et al., 1997). A study was designed 1) to compare the liver composition in overfed and nonoverfed geese of the two breeds of geese and 2) to determine whether the differential channelling of lipids in response to overfeeding is reflected in the PL and fatty acid profiles of the different hepatic lipids, whether stored or secreted. In nonoverfed geese, there were no breed-related differences in liver weight (approximately 90 to 100 g), hepatic lipid content (3 to 4%), and lipid and PL composition. However, plasma VLDL and HDL of the Landes breed contained a higher phosphatidylcholine (PC) to phosphatidylethanolamine (PE) ratio than those of the Poland breed (20.7 and 33.8 vs 12.6 and 25.6 in VLDL and HDL, respectively). After 14 d of overfeeding, hepatic PL profiles were identical in the two breeds and similar to that in control livers; choline-containing PL accounted for 95% of total PL. In contrast, plasma HDL concentrations of the Landes geese were lower than those of the Poland geese (9.4 vs 12.9 g/L) and their PC:PE (13.6%) and PL-polyunsaturated fatty acids (PUFA) content (25%) were decreased compared with the Poland geese (21.2 and 30%). It is likely that the higher susceptibility to fatty liver of the Landes breed involves a differential channelling of PL, resulting in a greater hepatic retention of PC and PUFA that are necessary for plasma membrane growth and cell hypertrophy.

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