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1. Protein utilisation and turnover were measured in male chickens sampled from a line selected for high breast yield and a randombred control line (lines QL and CL, experiment 1) and in male chickens sampled from lines selected for either high or low abdominal fatness (lines FL and LL, experiment 2). In each experiment, 18 birds per line were given iso-energetic (12.9 MJME/kg) diets containing either 120 or 220 g CP/kg from 21 to 29 d (experiment 1) and 33 to 43 d (experiment 2). 2. Measurements were made of growth rate, food intake, body composition, excreta production and Ntau-methylhistidine excretion as a measure of myofibrillar protein breakdown, and fractional rates (%/d) of protein deposition, breakdown and synthesis were calculated. 3. In experiment 1, there were no significant differences between the line means for the fractional measures of protein turnover, but there was marked differential response in the two lines in the fractional rates of protein deposition, breakdown and synthesis, to increase in protein intake. The positive slope of the regressions of fractional (%/d) protein deposition and synthesis rates on protein intake (g/d/kg BW) were approximately 1.4- and 2.0-fold higher respectively in the QL than the CL line birds, and the negative slope of the regression of fractional breakdown rate on protein intake was approximately threefold greater in the CL than the QL line birds. 4. In experiment 2, fractional deposition rate was 6.2% lower, but fractional breakdown rate 9.4% higher in the LL than the FL birds, whilst there was essentially no difference in response of the FL and LL birds in the components of protein turnover to increase in protein intake. Line differences in deposition and breakdown rates were thus a reflection of the considerably higher (20%) food and hence protein intake in the FL than the LL birds. 5. The differential line responses in protein turnover in the two experiments suggest that selection for increased breast muscle yield and for reduced body fatness manipulate different physiological pathways in relation to protein turnover, but neither selection strategy results in an improvement in net protein utilisation at typical levels of protein intake by birds on commercial broiler diets, through a reduction in protein breakdown rate.

1. Selected Fat or Lean chickens differ in their plasma glucose insulin relationship: in the fed or fasted state, Fat chickens have a lower glycaemia associated with normal or higher insulinaemia, depending upon the difference in glycaemia. 2. Conversely, chickens selected for low fasting glycaemia (LG) are fattier than their counterparts selected for high fasting glycaemia (HG), although the divergence in fat content is lower than in the Fat-Lean model. 3. The plasma glucose insulin relationship has been investigated in males of the HG and LG lines in the F4 and F5 generations. 4. A difference in glycaemia is suggested during embryonic development and was present at hatching and later on in the fasted or the fed state; insulinaemia did not differ. 5. During refeeding after an overnight fast, glycaemia differed between lines (except at intermediate times); cumulative food intake and insulinaemia were similar. 6. During a glucose tolerance test, glucose disposal rate and insulinaemia were rather similar. 7. Exogenous insulin exerted a very similar hypoglycaemic effect in both lines. 8. Other variables (body temperature, plasma concentrations of potassium and alpha NH2-non protein nitrogen) did not differ between HG and LG chickens. 9. In conclusion, HG and LG chickens do not exhibit any differences in glucose disposal rate, insulinaemia (in various nutritional conditions) or sensitivity to exogenous insulin, which contrasts with Fat or Lean chickens and may explain why HG and LG chickens have diverged to a lesser extent in fat content.

1. Growth performance between 28 and 49 d of age and carcase composition at 49 d in genetically lean (LL) and fat (FL) broilers fed on diets varying in non-essential amino acid (NEAA) concentrations were compared in 2 experiments. In experiment 1, 3 crude protein (CP) contents (133, 155, and 178 g/kg) were compared. In experiment 2, 4 CP levels (131, 150, 170 and 189 g/kg) were compared. All diets were supplemented with synthetic amino acids to cover the EAA requirement of the LL birds. 2. Weight gains of FL chickens were not affected by dietary treatments, while those of LL increased when CP level increased. 3. Reducing CP content always increased body lipids, abdominal fat and food conversion ratio in both lines in both experiments; however, the effect on abdominal fat was more pronounced in the FL birds. 4. Reducing CP concentration always decreased breast muscle proportion in both lines in both experiments, even when growth rate was not affected by CP. 5. It is concluded that LL chickens require diets more concentrated in NEAA than fat chickens and that there seems to be an effect of NEAA on breast muscle development.

Insulin signaling [tyrosine phosphorylation of insulin receptor (IR), insulin receptor substrate-1 (IRS-1), Src homology and collagen protein (Shc) and phosphatidyl inositol 3'-kinase activity (PI 3'-kinase)] was studied in the liver and thigh muscles of fat (FL) and lean (LL) chickens. These lines result from a divergent selection on abdominal fat pad size. The divergence is of metabolic origin. Extreme nutritional states were studied (fed, 48-h starved and 30-min refed). Such conditions significantly altered insulin signaling in chicken liver, but surprisingly not in the muscle (except the phosphorylation of Shc in the refed state). No major differences that could account for this divergence were found in muscle. Liver IR number and Shc protein did not differ between genotypes. Liver IRS-1 (protein and messenger) was lower in the fed state and higher in the starved state in FL compared to that in LL chickens. In the fed state, tyrosine phosphorylation of liver IR, IRS-1 and Shc action was higher in FL than in LL chickens that in the absence of insulin resistance rely on higher plasma insulin levels. In the starved state, phosphorylation of liver IR was lower, but the phosphorylation of IR and IRS-1 were higher in LL than in FL chickens, most likely in response to higher plasma glucose and insulin in the lean genotype. In the refed state, the phosphorylation of liver IR and IRS-1 did not differ between genotypes despite significantly lower plasma insulin in FL chickens. Finally, PI 3'-kinase was not affected by the genotype. A significant activation of early steps of insulin signaling in liver of fed FL chickens may at least partly account for their increased liver lipogenesis and ultimately their fattening.

Genetically lean (LL) or fat (FL) male broiler chicken's were fed on 5 diets containing either 3.80, 4.27, 4.75, 5.22 or 5.70 g true digestible threonine per kg. Threonine deficiency induced a more pronounced reduction in growth in the LL than in the FL but did not influence abdominal fat and breast muscle proportions in either line. Plotting weight gain or protein gain against threonine intake suggests that the requirement of both lines is very similar in terms of mg per g of gain. Thus food intake or appetite should account for differences between genotypes. Requirement for true digestible threonine was estimated as 10.70 mg per g of weight gain or 63.8 mg per g of protein gain, using a linear regression approach. The quadratic polynomial equations suggest that the requirements are 13.9 and 12.4 mg digestible threonine per g of gain for LL and FL respectively.

1. The aim of the study was to determine the ideal ratio of the essential amino acids lysine (Lys), methionine (Met), threonine (Thr), tryptophan (Trp), arginine (Arg), valine (Val) and isoleucine (Ile) and to assess the required dietary lysine concentration for optimum performance in broiler chickens of 2 commercial strains from 20 to 40 d of age. 2. An identical basal diet was used throughout all experiments. It consisted mainly of maize and soyabean meal and contained 172 g crude protein and 13.2 MJ AME(N) per kg. For each experiment, the basal diet was adequately supplemented with all essential amino acids except the one to be tested, which was supplemented in 6 graded concentrations in exchange for maize starch. One (Met, Trp, Arg, Val, Ile) or 2 (Lys, Thr) growth trials were conducted per amino acid tested and the response in weight gain, food: gain ratio, breast meat yield and abdominal fat were examined. 3. The ideal amino acid ratio relative to Lys (expressed as a percentage) was calculated to be 75% Met+Cys, 63% Thr, 19% Trp, 112% Arg, 71% Ile and 81% Val on a true faecal digestible basis when the data were subjected to broken-line regression analysis. From both lysine studies the concentration for optimum food: gain ratio was calculated, by exponential regression analysis, to be 11.5 g true faecal digestible lys per kg diet.

1. Male broilers (n = 1521) from 247 families were reared from 4 to 6 weeks of age at 22 degrees or 32 degrees C. 2. Genetic correlations between measurements recorded at 22 degrees C and 32 degrees C were 0.73 +/- 0.12 for weight gain between 4 and 6 weeks and 0.74 +/- 0.08 for food conversion ratio (FCR). Genes controlling weight gain at both temperatures differed to some extent. 3. Heritability of weight gain from 4 to 6 weeks was much lower at 32 degrees C than at 22 degrees C (0.13 +/- 0.03 vs 0.24 +/- 0.04): selection for increased body weight will thus be much less efficient at 32 degrees C than at 22 degrees C. 4. Conversely, heritabilities of the FCR were very similar at the 2 temperatures (0.28 +/- 0.04 at 22 degrees C and 0.27 +/- 0.04 at 32 degrees C). Selecting for FCR would thus be efficient at 32 degrees C too. 5. These results justify, at least under our experimental conditions, selecting broiler lines for improved growth performance at 22 degrees C. However, it could be more efficient if broilers are to be reared in hot climates to select for improved FCR rather than for increased body weight.

Lysine exerts specific effects on body composition at dietary levels higher than that required for maximum growth rate, which also results in an improved feed conversion ratio (FCR). As a consequence of these differences, it becomes apparent that there is a hierarchy of requirements. The requirement for maximum gain is lower than that for breast meat (BM) yield, which is lower than the requirement for FCR; and lastly, the requirement for minimum abdominal fat (AF) percentage is the highest of all. Threonine, on the other hand, does not appear to exhibit so pronounced an effect on body composition, whereas, in the case of valine, these effects seem to be absent. These different effects of lysine, threonine, and valine can induce different amino acid requirement profiles according to the criteria used for determining the requirement. Moreover the particular mathematical model being used to calculate amino acid requirements can also influence amino acid requirement profiles.

1. Male broilers were reared in individual cages from 23 to 44 d of age. The effect of 2 temperatures (22 degrees and 32 degrees C) and 2 crude protein (CP) levels (160 and 200 g/kg) were studied. The low protein diet was supplemented with lysine, methionine, arginine, threonine and valine in order to meet requirements. 2. At 22 degrees C, a reduced CP content did not affect growth rate and breast muscle but slightly increased adiposity and food to gain ratio (FCR). Water consumption was reduced. 3. High temperature reduced growth rate and absolute and proportional breast muscle weight, and increased adiposity and FCR. These effects were more pronounced with the low CP diet. Water consumption was also reduced. 4. It was concluded that reducing CP content did not seem a good way to help broilers to withstand hot conditions. This experiment suggests that amino acids other than lysine, methionine and cystine are probably involved in the detrimental effect of high temperature.

Full-sibling normal (na/na) and naked neck (Na/na) chickens were fed from 28 to 42 d of age on one of five diets with different SAA contents (from 5.4 to 7.0 g/kg). The experimental diets were made by adding DL-methionine to a well-balanced corn, soybean, and cornstarch diet containing 5.4 g SAA/kg and 161 g crude protein/kg. Dietary SAA influenced the growth rate of both genotypes similarly. There were no significant differences (P > 0.125) in body weight gain due to genetics or a diet by genetics interaction. Body weight gains were maximized at 6.24 +/- 0.45 (R2 = 0.171) and 5.96 +/- 0.52 g/kg SAA (R2 = 0.107) for the na/na and Na/na stocks, respectively. There was a significant SAA by genotype interaction for feed efficiency: the na/na birds were more efficient at low SAA levels, but the Na/na birds were more efficient at high SAA levels. Feather weight gain increased in a linear manner with increasing dietary SAA and was greater in na/na than Na/na birds with high dietary SAA concentrations. Abdominal fat decreased with increasing dietary SAA; and although the Na/na birds had significantly more abdominal fat than their na/na siblings (P = 0.049), on average the difference was small and complicated by differences in body weight. Analysis of covariance showed (a significant interaction) that the relationship between abdominal fat and body weight was different for the na/na and Na/na chickens. Although the shape of the response curves of na/na and Na/na chickens to dietary SAA are different, the quantitative requirements are very similar during the growing period.

1. Three experiments performed to study the effects of amino acid imbalances on the growth of genetically lean (LL) and fat (FL) male chickens from 28 to 42 d of age were described by Leclercq et al. (1994). The plasma amino acid concentrations of birds on selected treatments from that paper are reported here. In experiment 1, three dietary concentrations of digestible lysine were compared (4.75, 6.75 and 7.75 g/kg). In experiment 2, two dietary concentrations of digestible arginine were compared (6.53 and 10.00 g/kg). In experiment 3, three diets were compared: a high-protein diet (189 g CP/kg), a low-protein diet containing added essential amino acids (144 g CP/kg), and this low-protein diet supplemented with 40 g/kg of non-essential amino acids (NEAA; glutamic and aspartic acids). 2. The present results are compared with two earlier reports on the same genotypes. The LL consistently had lower plasma concentrations of methionine, cystine, phenylalanine, isoleucine and valine, and higher concentrations of histidine, than the FL chickens. In 4 of 5 experiments, LL leucine concentrations were lower, and glutamic acid, tyrosine, glutamine and alanine were higher, than in the FL. The other amino acids measured; arginine, lysine, aspartic acid, glycine and serine, exhibited variable responses among the experiments. 3. When the limiting essential amino acids, lysine and arginine, were added to a deficient diet, the plasma concentration of the supplemented amino acid increased while the others remained constant or decreased. 4. When glutamic and aspartic acids were added to the low protein diet, plasma amino acid responses were similar to those of adding a limiting amino acid to a deficient diet, except that alanine exhibited a dramatic increase. 5. Although there were genotype by diet interactions for several amino acids, the interactions were caused by differences in the degree of the responses, not in their direction. 6. These results suggest that the FL and LL genotypes do not utilise various amino acids with the same efficiency and, as a consequence, the ideal profile of dietary amino acids should not be the same for both lines. The results support the hypothesis that selection for fatness and leanness changed the amino acid requirements independently of the effects of food intake.

1. Three experiments were performed to study the effects of amino acid imbalance on the growth of genetically lean (LL) or fat (FL) male chickens from 28 to 42 d of age. In experiment 1, five concentrations of digestible lysine were compared (4.75, 6.75, 7.75, 8.75 and 9.75 g/kg). In experiment 2, four concentrations of digestible arginine were compared (6.53, 7.69, 8.84 and 10.0 g/kg). In experiment 3, three diets were compared: a high-protein diet (189 g CP/kg), a low-protein diet containing added essential amino acids (EAA) (144 g CP/kg) and this low-protein diet supplemented with 40 g/kg of non-essential amino acids (NEAA) (glutamic acid+aspartic acid). 2. LL birds exhibited a lower growth rate than the FL when the diet was deficient in either lysine or arginine. Plotting weight gain against lysine or arginine intake suggested that most of this effect was caused by variations in food intake. 3. When protein gains (body or total proteins) were plotted against lysine or arginine intake, LL chickens appeared more efficient than FL chickens. 4. Similar growth rates, although slightly lower in FL, were obtained with low- and high-protein diets. However, NEAA supplementation of the low-protein diet reduced adiposity of LL and did not modify that of FL. Increasing crude protein content (all amino acids) was more effective than NEAA supplementation in decreasing the adiposity of both lines.

1. Plasma growth hormone (GH) pulsatility and hepatic GH receptor characteristics were compared in experimental lines of meat-type chickens selected for high (HF) or low (LF) abdominal fat content. 2. Mean GH concentration, baseline and amplitude of pulses were slightly, but not significantly, greater in LF chickens. Length and frequency of pulses were similar. 3. LF chickens exhibited higher plasma triiodothyronine (T3) concentrations. This difference between genotypes disappeared when the diet was supplemented with 1 mg/kg T3. 4. Specific binding of GH to liver membranes was higher for the fat line but was depressed by T3 supplementation to the same level in both lines. No difference was observed between lines for affinity constants. 5. It is concluded that direct selection for leanness has a less pronounced, if any, effect on GH pulsatility as compared with selection for food conversion efficiency; therefore, different physiological mechanisms are triggered to achieve leanness.

1. Genetically lean (LL) or fat (FL) male chickens were exposed to either high (32 degrees C) or control (22 degrees C) ambient temperature up to 9 weeks of age. They were fed on one of two isoenergetic diets differing in protein content: 190 or 230 g/kg. 2. At 22 degrees C, weight gain of LL broilers was the same as in FL chickens, but at the high temperature LL birds grew to a greater weight than FL ones. 3. Food conversion efficiency was not affected by ambient temperature in LL chickens but was depressed in FL ones at 32 degrees C. 4. Increasing dietary protein content did not alleviate heat-induced growth depression irrespective of the genotype. 5. Gross protein efficiency was higher in LL chickens and was less depressed at 32 degrees C than in FL birds. 6. Fat deposition decreased with increasing protein concentration at normal temperature in both genotypes; at high temperature, high protein content enhanced fatness, particularly in LL chickens. 7. Thus, genetically lean broilers demonstrated a greater resistance to hot conditions: this was indicated by enhanced weight gain and improved food and protein conversion efficiencies.

1. Genetically lean (LL) or fat (FL) male chickens were fed from 28 to 47 days of age on 5 experimental diets differing by their methionine+cystine content (5.4, 5.8, 6.2, 6.6 and 7.0 g/kg, respectively). 2. Growth rate of LL chickens was reduced by the lower sulphur-containing amino acid (SAA) concentrations whereas that of FL was not modified. 3. LL chickens exhibited a larger feather protein gain than FL, which was stimulated by SAA intake. 4. SAA retention, when plotted against SAA consumption, was always greater in LL than in FL. 5. Large differences were observed between genotypes for plasma-free amino acids. Lysine, glutamic acid, histidine and serine were found at significantly higher concentrations in LL birds. Branched amino acids, aromatic amino acids, SAA and arginine were found at higher concentrations in FL. No differences were observed for aspartic acid, glycine, alanine and total amino acids. Methionine supplementation decreased free amino acid concentrations, with the exceptions of arginine and leucine. 6. It is concluded that lean chickens require a higher dietary concentration of SAA than FL. This is mainly caused by their lower food consumption and their greater feather synthesis. However, LL use SAA more efficiently than FL.

1. Carcase composition, fat deposition and the activities of three liver lipogenic enzymes were compared in turkeys and chickens fed ad libitum on two different isocaloric diets, respectively adapted to chickens (C) and to turkeys (T). Diets differed in their protein content, being higher by 60 g/kg in diet T. 2. Chickens were much fatter than turkeys and exhibited higher activities of acetyl-coenzyme A carboxylase (EC 6.4.1.2) and malic enzyme (EC 1.1.1.40). 3. The carcase composition of turkeys was not influenced by the type of diet administered, while chickens fed on diet C were fatter than chickens fed on diet T. Compared to diet T, diet C enhanced malic enzyme activity, whatever the species and age. 4. A good correlation between abdominal fat and total fatness was observed in both species but especially in turkeys. 5. In conclusion, hepatic lipogenesis is much lower in turkeys than in chickens.

1. Genetically lean (LL) or fat (FL) chickens were fed from 28 to 42 d of age on one of 6 diets with different protein contents (from 73 to 208 g/kg). In order to keep a constant amino acid balance the experimental diets were made by diluting a well-balanced protein-rich diet with a protein-free diet. 2. Dietary protein influenced the growth rate of both genotypes similarly. However, maximum weight gain was reached in LL at a lower protein intake than in FL. 3. Regression between total protein gain (body protein + feather protein) or body protein gain and protein intake exhibited significantly different slopes, that of LL being superior to that of FL. 4. At a given protein intake, feather protein gain was also superior in LL to FL. Moreover feather protein, as a percentage of total protein gain, was superior in LL to FL. When the dietary protein fell below 126 g/kg, feather protein represented a higher proportion of total protein gain. 5. Multiple linear regressions of protein intake (as the dependent variable), and body weight and protein gain or weight gain (as the independent variables) suggest that the maintenance requirement for protein is similar in both lines but that the protein efficiency for growth is significantly superior in LL. 6. In a second experiment both genotypes were offered either a single high protein diet (232 g/kg) or a single medium protein diet (186 g/kg) or had free-choice between a high (269 g/kg) and a low protein (145 g/kg) diet. In free-choice feeding, FL chickens selected an overall dietary protein content which was significantly lower (179 v. 200 g/kg) to that of LL. In both genotypes, free-choice feeding led to fatter and less efficient chickens than predicted by the linear regression between adiposity or food conversion and protein content.

Two experiments were conducted to investigate the effect of dietary protein content (170 to 230 g/kg in Experiment 1 and 131 to 251 g/kg in Experiment 2) and initial growth rate, estimated from live body weight at 4 wk of age, on growth rate from 4 to 7 wk of age, nitrogen retention, energy metabolism, and amino acid catabolism in genetically fat (FL) and lean (LL) lines of chickens. There was no difference between lines in energy utilization either in metabolizability or in expenditure (basal metabolic rate, maintenance, or diet-induced thermogenesis). The only divergence between lines was in the partition of a similar amount of retained energy between lipid and protein deposition. In both experiments, LL chickens showed greater protein retention efficiency than FL birds; moreover, the LL line did not appear more sensitive to low dietary protein contents than the FL line. Selecting birds on their growth rate or live body weight at 4 wk of age resulted in the selection of different rates of fattening. Indeed, the slow-growing FL and LL chickens differed less in their nitrogen metabolism than did fast-growing birds, which were also fatter. The lower protein retention efficiency observed in FL chickens was related to an increase of dietary amino acid degradation as revealed by a greater rate of uric acid excretion in the fed state.

1. Apparent metabolisable energy corrected to zero-nitrogen retention (AMEn) was measured using the European reference procedure in 9 European laboratories. Seven pelleted diets were evaluated. AMEn was measured with adult cockerels and young birds. 2. Between-laboratory standard deviations were for dry matter (DM) 12.5 g/kg, gross energy 0.085 MJ/kg DM, Kjeldahl nitrogen 0.768 g/kg DM, AMEn (adults) 0.256 MJ/kg DM, and AMEn (young) 0.337 MJ/kg DM. Corresponding coefficients of variation between laboratories were 1.42, 0.45, 2.15, 1.88 and 2.60% respectively. 3. AMEn values of experimental diets were always significantly lower when measured with young birds. This effect was more pronounced when diets contained added fat. 4. Tallow or soyabean oil were incorporated into two basal diets at 40 g/kg inclusion rate. No significant differences were observed between AMEn values of either diet with adults or young birds, suggesting that AMEn energy values of these fats are indistinguishable at this inclusion rate. 5. Similar AMEn values were obtained in young birds by estimating nitrogen accretion, either by the difference between intake and excreta nitrogen or by measuring body weight gain. Determined AMEn values were very similar to those predicted using three different regression equations.

1. A common reference procedure adopted by several European laboratories to determine apparent metabolisable energy corrected to zero-nitrogen balance (AMEn) is described. 2. Reproducibility has been estimated by comparing results from 4 diets measured in 7 laboratories. The standard deviations between laboratories of dry matter, gross energy, Kjeldahl nitrogen and AMEn were respectively, on average, 11.29 g/kg, 0.242 MJ/kg, 1.56 g/kg and 0.380 MJ/kg dry matter; the corresponding coefficients of variation between laboratories were 1.27, 1.29, 4.39 and 2.92%. 3. Effect of food intake was tested by comparing AMEn from birds fed either 0.90 or 0.45 of ad libitum: the amount of food intake had a negligible effect on AMEn values. Endogenous energy losses corrected (EELn) or not (EEL) to zero nitrogen balance were estimated either by regression between excreted energy and ingested energy or in fasted and glucose-fed cockerels. EELn estimated by regression was, on average, 8.7 kJ/bird/d.; it was independent of diet composition. EEL and EELn determined in fasted or glucose-fed birds were higher than those determined by regression. 4. AMEn values measured by individual laboratory procedures were very close to those obtained by the reference method, except from laboratories using a tube feeding procedure, where deviations were probably a consequence of overestimated EEL.

The digestibility of nonstarch polysaccharides (NSP) were measured in cockerels. Muscovy ducks, and rats by using four diets where the only sources of NSP were wheat bran (Diet B), whole wheat grain (Diet W), soybean meal (Diet S), or white lupin meal (Diet L). The four diets contained similar amounts of crude protein (24.4%), lipids (5.2%), and NSP (6.9%). The proportions of water-soluble NSP in total NSP were 11.1% (Diet B), 19.7% (Diet W), 8% (Diet S), and 11.5% (Diet L). The NSP contents of feed and excreta were determined by measuring their individual sugars, using gas-liquid chromatography of alditol acetate derivatives. The digestibility values of NSP ranged from 21.9% (Diet W) to 13% (Diet L) for cockerels, from 18.7% (Diet W) to 7.9% (Diet L) for ducks, and from 85.7% (Diet L) to 44.1% (Diet B) for rats. These results suggest that cockerels and ducks were only able to digest the water-soluble fraction of the nonstarch polysaccharides. The pectic polymers, which were major components in water-insoluble NSP of Diets S and L, were digested to a high extent by the rats. The digestible-energy (DE) values, calculated for the birds from the apparent metabolizable-energy values corrected for nitrogen retention (AMEn), were very similar when cockerels and ducks were compared; the differences between bird species did not exceed .23 MJ per kg of dry matter. In all cases, the DE values were higher for rats than for birds. These results suggested that the main factor responsible for the differences in DE values between rats and birds was the ability to digest NSP, which was higher for the rats than for the birds.

Metabolism of very low density lipoproteins (VLDL) has been compared in fat (FL) and lean (LL) lines of chicken. When refed after fasting, plasma triglyceride concentration reached a significantly higher plateau in FL, although their feed consumption was lower than in LL. Newly synthesized VLDL were studied using anti-lipoprotein lipase antibodies. VLDL triglyceride (TG) concentrations were increased by antibody injection and reached a higher concentration in FL plasma than in LL. Newly synthesized VLDL exhibited a similar lipid composition. Fatty acid profiles were also similar when birds ingested a very low fat diet. Comparison of in vitro affinity of lipoprotein lipase and VLDL from both genotypes did not reveal any difference in Km and Vmax. [14C]labelled VLDL from fat or lean donors were prepared and were injected into chickens from both genotypes. Fractional rate constants did not differ between lines. However, as plasma VLDL-TG pools were very different, plasma turnover was higher in FL than in LL. About 3-fold more VLDL-TG were incorporated in abdominal fat of FL than in LL. Difference in fattening between both genotypes seem to be due to both increased VLDL secretion and VLDL removal from plasma without difference in VLDL characteristics.

1. Apparent (AME) and true (TME) metabolisable energy values of four diets, containing 50 or 150 g animal fat or maize oil/kg, were estimated in young and adult chickens. The diets were given with and without a supplement of 5 g bile salts/kg. Three feeding rates, ad libitum, and 1/6th or 1/3rd of ad libitum were compared. 2. In younger birds, endogenous energy losses were higher when measured in starved birds than when estimated by regression analysis. 3. In young birds, feeding rate had no effect on AME of diets containing 50 g lipids/kg but it significantly affected TME. These results were reversed in adults. AME and TME values of diets containing 150 g lipids/kg were affected by the feeding rate in both young and adult birds. 4. Bile salts increased metabolisable energy values of diets containing high concentrations of saturated fatty acids and their effect was more pronounced in young birds.

A radioimmunoassay (RIA) of chicken growth hormone (c-GH) has been developed using growth hormone produced by recombinant DNA technology. The best rabbit antiserum was used at 1/300,000 final dilution. Hormone labelling by iodine-125, achieved by chloramine T, allowed a specific activity of 3.7 MBq/micrograms. The equilibrium curves show that optimal conditions of incubation were reached at room temperature for 24 h. This RIA used a second sheep antibody which precipitated the whole c-GH bound to the first antibody in the presence of polyethylene glycol solution (6%) at room temperature for 30 min. In our conditions, sensitivity was about 30 pg of c-GH per tube. Coefficient of variation was around 10%. No cross reaction was found with avian LH and prolactin. Thyrotrophin-releasing hormone (TRH) injection to young chickens induced 20-fold higher plasma c-GH concentrations. Simultaneous injection of somatostatin and TRH slightly reduced these concentrations. Hypoglycemia induced by insulin led to a drop of the plasma c-GH concentration. Conversely, refeeding or glucose load induced slight increases of the c-GH level. Genetically fat chickens tended to exhibit higher plasma c-GH concentrations than lean chickens.

In two experiments, sister pairs of chicks, one dwarf (dw) and one nondwarf (Dw+), were reared in individual cages to 5 weeks of age. Chicks carrying the sex-linked recessive dw gene were identified at hatching by the closely linked fast feathering gene (k). The dwarf chicks showed a 27% reduction in weight gain, a reduced body temperature, increased carcass content of lipid, and increased lipid 14C activity from injected 14C-labeled acetate. The augmented accumulation of carcass lipid in the dwarf chicks was shown to be a result of increased lipogenesis and decreased energy expenditure. An autosomal dominant gene for naked-neck (Na), present in half of the pairs of chicks, also caused increased lipogenesis. Naked-neck birds showed increased energy expenditure in a cool environment and perhaps a greater flexibility of body temperature regulation. An interaction between the dw and Na genes was apparent under cool environmental conditions and may have been due to a suppression by the dw gene of the Na gene's effect on thermoregulation, possibly by slowing down lipid degradation.

Two experiments were conducted to investigate the effects of pair-feeding, nutritional status (fasting vs feeding ad libitum) and supplementing diets with alanine (2 g/kg), threonine (2 g/kg), glutamic acid (5 g/kg) and arginine (5 g/kg) on growth performance, body composition and free plasma amino acid levels in genetically lean (LL) or fat (FL) chickens of 4 to 7 weeks of age. When fed ad libitum, FL chickens ate more than LL birds and showed higher lipid and protein gains. However, when pair-fed, FL birds exhibited increased lipid retention but lower protein gain. Growth performance and body composition were not significantly affected by the addition of glucogenic amino acids to the diets. However, amino acid supplementation slightly improved food to gain ratios but depressed gross energy and protein efficiencies in both lines. FL chickens had lower plasma levels of most glucogenic amino acids and higher levels of branched-chain and sulphur amino acids than LL birds, irrespective of diet and nutritional status. These results are discussed in relation to hormonal characteristics of FL and LL birds.

1. The effects of daily injections of corticosterone (1 or 5 mg/bird) on growth, fat deposition, liver lipid and plasma concentrations of uric acid, glucose, insulin and growth hormone were studied using genetically selected lines of fat (FL) and lean (LL) chickens. 2. Both doses of corticosterone depressed body weight gain and increased the liver lipid and the abdominal fat to the same extent in both lines. 3. In both lines, corticosterone caused a dose-dependent increase in the plasma concentrations of uric acid, glucose and insulin in the fasted and refed states. 4. In untreated birds, plasma concentrations of growth hormone (GH) were slightly higher in FL than in LL chickens and slightly decreased during refeeding. The response was not modified by injection of 1 mg corticosterone. Injections of 5 mg decreased plasma GH in both lines in the fasting state and in LL chickens during refeeding. In contrast, the same dose increased GH in FL chickens during refeeding. This contradiction remains unexplained. 5. The results suggest that corticosterone sensitivity is not involved in difference of fattening between FL and LL chickens.

Lipogenesis was studied in vivo in genetically fat and lean male chickens at 2, 5 and 15 weeks of age using tritiated water. At 2 and 5 weeks of age, the liver was the major site of de novo fatty acid synthesis rather than the carcass. Per 100 g of tissue lipogenesis was greater in the carcass at 15 weeks of age than at 2 or 5 weeks. Lipogenesis in the liver did not vary according to age. At 15 weeks of age there was no observable exaggeration in the degree of fattening (as in genetically obese rodents) of fat line chickens. The regulation of fattening in fat line chickens, at least at the onset of sexual maturity, appears to be different to that in genetically obese rodents.

Genetically lean or fat male chickens were fed from 3 to 8 weeks of age on four diets of different protein content: 152, 172, 191 or 211 g/kg. The two lower protein contents depressed growth of lean chickens but had no adverse effects on fat chickens. In both lines increasing dietary protein decreased food: gain ratio and abdominal fat desposition relative to live body weight. Protein deposited and the efficiency of utilisation of dietary protein were higher in all instances in lean birds.

1. Two lines of broilers exhibiting low (LG) or high (HG) plasma glucose concentrations were selected from a pure line of White Rock chickens. 2. Realised heritabilities were close to 0.25 in both lines. 3. The LG line was significantly fatter than the HG line; this difference was more pronounced in females than in males. 4. Food was utilised less efficiently by the LG line than by the HG one.

Four types of diet were tested: 960 g maize/kg (M), 960 g wheat/kg (W), 463 g maize added to 497 g of smooth peas/kg (PM) and 463 g wheat added to 497 g smooth peas/kg (PW). Three treatments were applied to each of these 4 diets: grinding (OP), one steam pelleting (1 P) and two successive steam pelleting (2 P). The pelleted diets were ground before feeding. Adult cockerels received all the diets whereas rats received only W and PW diets. Apparent metabolisable energy values corrected for N-equilibrium (AMEn), protein and starch digestibilities were measured in adult cockerels. Digestible energy (DE) values were measured in rats. The AMEn values of cereals remained practically unchanged by pelleting, whereas that of smooth peas was increased by between 1.8-4.6% after pelleting. Pelleting also induced 3.5 and 5.4% increases respectively in the digestibilities of pea protein and starch. Pelleting did not change the DE values measured in rats. The AMEn values of smooth peas mixed with maize were 4.6% higher than those of smooth peas mixed with wheat. The true digestibility of pea protein was 8.4% higher in the former mixture, whereas the pea starch digestibility remained unchanged. Calculation showed that most of the pea AMEn variations could be explained in terms of variations in protein and starch digestibilities.

An experiment was conducted to investigate possible differences in plasma hormone levels between females of two lines of chickens selected for high (FL) or low (LL) abdominal fat content. Blood was taken at weekly intervals from 6 weeks of age to sexual maturity, and assays were performed for luteinizing hormone (LH), growth hormone (GH), and estradiol (E2). Age-related increases in the plasma titers of LH and estradiol were found while GH remained low apart from initial and final fluctuations. There was no difference between the strains in plasma E2, only minor differences in plasma GH, but a clear-cut difference was observed in plasma LH during the prepubertal period. Plasma LH tended to be higher in the LL, but the reason for this remains unclear.

In vivo lipogenesis was estimated in liver and carcass of male chickens selected for leanness (LL) or fatness (FL) by use of tritiated water. Effects of nutritional state and of a high fat diet (90 g/kg) were examined. Different classes of liver lipids were also measured. Fed birds exhibited enhanced hepatic lipogenesis, which was more pronounced in FL than in LL birds (+73%, mean of three experiments). Extrahepatic lipogenesis was poorly influenced by nutritional state in LL birds and not modified in FL ones. The high fat diet induced a fall in liver triacylglycerol and reduced de novo lipogenesis more drastically in liver than in carcass of both lines. Reduction of carcass lipogenesis was less pronounced in FL than in LL. Starvation led to a fall in liver triacylglycerols, nonesterified fatty acids and free cholesterol. The fat diet had similar but less pronounced effects. In most circumstances FL chickens exhibited a higher liver triacylglycerol content than LL ones. Comparison of fed and refed birds 100 min after the beginning of refeeding showed that de novo lipogenesis did not reach a plateau and differences between lines were still not significant.

The plasma lipoprotein profile has been determined in fasted and refed 5-week-old male broilers selected for low or high adiposity. Lipoprotein classes were subfractionated by density gradient ultracentrifugation, appearing as distinct bands with the following densities: very low density lipoprotein (VLDL), d less than 1.013 g/ml; low density lipoprotein (LDL), d 1.023-1.046 g/ml and high density lipoprotein (HDL), d 1.052-1.130 g/ml; the physiochemical characteristics (chemical composition, electrophoretic mobility and particle size) of these particles were then assessed. HDL, seen as a single band, represented 80% of total lipoproteins, with VLDL and LDL accounting for 1% and 16%, respectively, in fasted birds. Lipoprotein profiles were similar in fasted and refed animals of both lines, with the exception that VLDL levels were some 14-fold and 7-fold higher in the lean and fat lines, respectively, in the refed state. The VLDL of fasted birds of both lines were enriched in protein and relatively homogeneous in size; by contrast, VLDL in the refed state contained more triglyceride and less cholesteryl ester and protein and were larger and more heterogeneous, possibly representing a mixture of portomicrons and VLDL of hepatic origin. Birds of the fat line in both nutritional states differed from lean birds in exhibiting elevated plasma lipid and lipoprotein [VLDL, intermediate density lipoprotein (IDL) and HDL] levels, evidence that liver activity is directed toward increased lipoprotein production and secretion in that line.

Three experiments were carried out to compare plasma lipid and glucose concentrations in genetically lean (LL) and fat (FL) male chickens. The fat birds always displayed lower glycemia than the lean ones, irrespective of the diet (low-fat or fatty) and nutritional state (fed or fasted). Conversely, triglyceridemia was higher in the fat than in the lean line, particularly in the fed condition. This difference was more pronounced in the birds fed on a low-fat diet and became still more marked as they aged. No consistent differences were found between the two lines as to cholesterolemia and non-esterified fatty acid concentrations. Injections of Triton WR 1339 increased triglyceridemia; this effect tended to be more pronounced in the fat birds. The rate of increase of triglyceridemia did not plateau as the dose of Triton increased. The injection of Triton frequently led to convulsions and death. It is concluded that this model of genetic fatness is different from the monogenic models of mammalian obesity since hypertriglyceridemia was not systematic and was not associated with hyperglycemia or hyperinsulinemia.

1. Ten-week old broiler females were force-fed (FF) for 3 days or 3 weeks. 2. Control livers were lighter in weight and contained less total lipid, neutral lipid and phospholipid than either FF group, which did not differ. 3. Radioactivity incorporated into liver neutral lipid fractions from 1-[14C]acetate injection was greater in birds FF 3 weeks than controls. Those FF 3 days were intermediate. In all groups, the triglyceride fraction contained 90-94% of isolated radioactivity, the cholesterol fraction 4-8% and the cholesterol ester fraction 1-2%. 4. Plasma lipids were elevated in the birds FF for 3 weeks, but not in those FF 3 days. After injection of 1-[14C]acetate, plasma lipid specific radioactivities were not different between the 3 groups at 20 and 60 min post injection, but were greater in the controls at 120 min.

Genetically fat and lean breeders were compared for laying performance and glucose tolerance. Laying females were fed ad libitum or restricted (85% ad libitum). Ad libitum-fed fat breeder hens (FL) were lighter and produced lighter eggs than lean hens (LL). However, the yolk percentage of the egg and yolk output were higher in FL. Differences in the glucose-insulin balance were consistently observed between lines in females at 203 and 326 days and in males at 203 days of age. The FL birds displayed lower plasma glucose and higher plasma insulin concentrations for a given plasma glucose level. Feed restriction reduced egg output, yolk output, yolk lipids, and plasma insulin levels during glucose tolerance in females at 326 days of age. Therefore, the glucose-insulin imbalance previously described in young FL birds persists in adults. The enhanced propensity of the FL to synthesize and deposit lipids also affects vitellogenesis. Insulin is also implicated in vitellogenesis.

The storage capacity for plasma triglyceride in abdominal adipose tissue has been investigated in two lines of chickens selected for either high or low adiposity (fat line and lean line, respectively). Adipose tissue cellularity and lipoprotein lipase (LPL) activity were estimated in 2- and 5-wk-old birds. In 2-wk-old birds, cellularity and LPL and glycerophosphate dehydrogenase (GPDH) activity were evaluated in the stromavascular fraction. At both ages studied, the fat line exhibited a twofold increase in mature fat cell number and a marked hypertrophy. LPL activity per cell did not differ with genotype, regardless of the nutritional state; however, LPL activity per whole fat pad was higher in fat birds. In 2-wk-old fat chickens, the stromavascular fraction was characterized by an increase in cell number and a decrease in LPL activity, while GPDH was unchanged. Finally, adipocyte hyperplasia in the fat line appeared to reflect an excessive proliferation of precursor cells. The higher LPL activity in fat birds resulted mainly from cell hyperplasia, rather than from a greater intrinsic activity of adipocytes. Consequently, enhanced fatty acid uptake by adipose tissue represents a major factor in determination of adiposity in the chicken.

A trial was carried out using 3-week-old chickens of a commercial breed to study the effects of either a fat-free diet or a diet containing 150 g/kg of animal fat on the endogenous energy losses measured with starved birds. The effects of the addition of different levels of bile salts to such diets and the accuracy of true metabolizable energy (TME) with respect to the other modes of expression of metabolizable energy were also examined. The excreted endogenous energy values were shown to vary not only according to the type of diet (P less than .01) but also in relation to the dietary intake level (P less than .01). Because it is directly related to endogenous energy, TME proved to be an inaccurate parameter in young chicks unless values were corrected for N-balance. If the values of both apparent metabolizable energy (AME) and TME are corrected for N-balance, they are normally comparable and independent of the dietary intake level if the diet contains virtually no added fat. These findings indicate that most of the endogenous excreta are composed of nitrogenous metabolites. However, neither AME nor TME values of fat-rich diets are independent of dietary intake. The addition of bile salts had no effect on the metabolizable energy values of the fat-free diet. However, in the case of the diet rich in saturated fats, they compensated either for insufficient bile secretion or for endogenous bile salts degraded by the intestinal microflora. Thus, the digestive utilization of dietary fat, especially that of the saturated fatty acids, palmitic and stearic acids, was increased. In addition, metabolizable energy was significantly improved (P less than .01) by the addition of bile salts when the dietary intake level increased to the ad libitum level.

In vivo lipogenesis was studied in genetically lean or fat male chickens using tritiated water. Fatty acid synthesis was more pronounced in liver than in other tissues in both lines. Liver synthesis was 26% higher in fat birds than in lean. The liver of fat chickens were heavier than those of lean chickens. This difference was partly due to the triglyceride content of the fat line liver.

Thyroid hormones were measured in plasma of genetically lean (LL) or fat (FL) chickens at different ages. No differences were observed at hatching or at adult age. More triiodothyronine (T3) and less thyroxine (T4) were found in the plasma of LL than in FL at the fed state during the growth period. This difference disappeared as the birds approached sexual maturity. Dietary supplementation by T3 increased the plasma concentration of T3 at the fed state. It did not influence growth rate, feed efficiency and body temperature. T3 supplementation tended to decrease abdominal fat proportion. It is suggested that the difference in plasma T3 would account for only a small proportion of the between-genotype differences in fattening.

Energy metabolism was investigated by using indirect calorimetry in growing chickens of similar body weight but genetically selected for high (fat line, FL) or low (lean line, LL) abdominal fat content. Twelve 5- and 7-wk-old male chickens of each line were exposed at two different ambient temperatures, 10 and 25 degrees C. Two birds from the same line were placed in each calorimeter chamber for a 6-d period (2 d fasting and 4 d feeding). Similar food intakes and metabolizabilities of diet corrected for nitrogen balance revealed that FL and LL chickens ingested the same amount of metabolizable energy (ME). Moreover diet-induced thermogenesis did not appear to be defective in FL birds, and the maintenance ME requirement was similar in both lines. However, the partition of retained energy between fat and protein did differ with increased protein deposition and conversely, decreased fat retention in LL chickens, irrespective of age or ambient temperature. FL birds catabolized a greater proportion of dietary amino acids as confirmed by the increase in uric acid excretion. Finally, energy expenditure was significantly and similarly enhanced in both genotypes by cold exposure.

1. The cell-wall material of white lupin (Lupinus albus L.) cotyledon is characterized by low contents of cellulose (47 g/kg) and lignin (17 g/kg) and a high content of pectic substances (710 g/kg). The digestion of lupin cell-wall material by adult cockerels was estimated using gas-liquid chromatographic analyses of alditol acetates derived from polysaccharide sugars. The analyses were performed in the destarched water-insoluble fractions of feed and excreta. Digestibility measurements were carried out using a 3 d balance period including a 2 d feeding period and a 24 h final starvation period. 2. In the first experiment, six animals were given a diet containing 510 g white lupin cotyledon flour/kg which was the only source of protein and cell walls in the diet. The apparent digestibility of cell-wall components was near zero. 3. In the second experiment, three diets were prepared by diluting a fibre-free basal diet (diet A) by a semi-purified cell-wall preparation introduced at two different levels: 100 g/kg (diet B) and 200 g/kg (diet C). The semi-purified cell walls were prepared from the white lupin cotyledon flour used in the first experiment. The true digestibilities of polysaccharides measured in birds given diets B and C were near zero. It is suggested that the measurement of the neutral-detergent fibre (NDF) content according to Van Soest & Wine (1967) is not a suitable procedure for estimating the undigestible fibre content in poultry nutrition as the cell-wall pectic substances are not included in the NDF measurement. 4. Addition of the semi-purified cell-wall preparation (Expt 2) resulted in a slight decrease in the apparent protein digestibility. This decrease might be explained by the addition of undigestible cell-wall protein. 5. Addition of the semi-purified cell-wall preparation (Expt 2) had no effect on the apparent lipid digestibility. 6. The metabolizable energy values of the basal diet fraction of diets B and C were calculated assuming that the added plant cell-wall fraction was of no energy value. These calculated values were similar to the measured metabolizable energy value of diet A (basal). Thus, the tested pectic plant cell walls seemed to act as a diluent. It is suggested that, on the point of the digestion yields, all types of plant cell walls would act as diluents, in poultry.

Insulin release from the perfused pancreas was studied in genetically selected fat and lean chickens. The previously described glucose insensitivity of the chicken pancreas cannot be overcome by 5 or 10 mM D-glyceraldehyde, suggesting that the resistance is not related to glucose metabolism before the triose phosphate step. At 42 mM, glucose induced a biphasic insulin release which was specific, since 42 mM mannitol did not elicit insulin release. Arginine (10 mM) or acetylcholine (0.1-1 microM), which in themselves do not cause insulin release, generated a biphasic insulin release in the presence of a low nonstimulating glucose concentration (14 mM); the effect was synergistic. In contrast to the glucose tolerance test observed in vivo, the pancreas from the fat line chicken in response to glucose or glucose plus arginine released significantly less insulin during the first phase. The significance of this defect awaits further elucidation. On the other hand, acetylcholine, a more potent secretagogue, did not reveal any significant difference between fat and lean chickens.

Fat (FL) or lean (LL) chickens have been obtained by divergent selection. In previous studies, FL chickens were consistently hypoglycemic (slightly) and had high plasma levels of insulin in response to glucose or refeeding from 5 to 8 wk of age. In these, at 12-13 days of age before any difference in fattening can be demonstrated, FL chickens exhibit a better glucose tolerance pattern and enhanced glucose-induced insulin levels but normal insulin levels during refeeding. Plasma levels of alpha-NH2 nonprotein nitrogen, uric acid, free fatty acids, and potassium were neither consistent nor significantly different between lines. Atropine, at high dose, blocked the absorption of glucose and at low dose had no major effect on glucose-induced insulin release in either line. At 8 wk, sensitivity to and disappearance of exogenous insulin were normal in FL birds. Propranolol slightly decreased plasma glucose and inhibited the hypokalemic effect of exogenous insulin to the same extent in both lines. Cerebrospinal fluid glucose level and liver glycogen content were similar in both lines in the fasting or the fed state, but liver glycogen was restored faster after refeeding in the FL, at least in older birds.

The late generations of fat (FL) and lean (LL) chickens were compared. In the fasted state, plasma glucose was lower in FL chickens, whereas insulin, T3, T4 and corticosterone were unchanged. In the fed state, plasma insulin and T4 were increased in FL chickens whereas glucose, T3 and corticosterone were unchanged. During ad libitum refeeding both plasma glucose and insulin, and to a lesser degree T3, were lower and T4 higher in FL chickens whereas corticosterone remained unchanged between lines. The low glucose and insulin levels observed in FL during refeeding, which were not observed in the F4 generation, were also found after force-feeding. In contrast, during oral glucose tolerance test, as in previous generations, a better glucose tolerance, higher plasma insulin and slightly higher free fatty acid levels were found in FL chickens. The hypoglycemic effect of exogenous insulin was very similar (and poor) in both lines in the fed state and was higher in FL than in LL chickens in the fasted state. From the present and previous studies, a change in the glucose-insulin balance and possibly, in T3, could account for the differences in fattening of both lines.