-In a factorial experiment, two series of feeds containing excess dietary protein, differing in amino acid balance (i.e. balanced (BPS) and unbalanced (UPS) amino acid mixture), and with a range of protein contents (400, 300 and 200 g CP·kg -1 ) at the same energy content of 13 MJ AME·kg -1 were offered at two levels of feeding (ad libitum or 0.75 of ad libitum intake) to 4320 broiler chickens between 10 and 24 days of age. Growth rate was significantly lowered by feed restriction. There was also a significant (P < 0.001) effect of dietary protein on the combined weight of the proventriculus and gizzard but only for the birds on the restricted feeding regime. Relative pancreatic weight increased (P < 0.001) with an increase in dietary protein level for the birds fed restricted amounts of BPS. The crypt depth of chicks on the ad libitum feeding regime was higher (P < 0.01) for the chicks on the BPS than for those on the UPS diet. The protein content of the jejunal mucosa was higher (P < 0.001) for birds fed ad libitum on the UPS diet than on the BPS diet. Daily feed allocation had a significant (P < 0.01) effect on jejunal protein content in birds that received the BPS diet, this being reduced in birds on restricted feeding. Maltase (P < 0.001) and sucrase (P < 0.01) activities were significantly reduced in chicks offered ad libitum access to the UPS diet. At high dietary CP, the specific activity of alkaline phosphatase was lower (P < 0.001) in chicks on the UPS diet than in those fed the BPS diet. Anim. Res. 51 (2002) 501-515  INRA, EDP Sciences, 2002 DOI: 10.1051/animres:2002038Résumé -Effets de la concentration en protéines, de l'équilibre en acides aminés et du niveau d'ingestion de l'aliment sur la croissance, le développement du tube digestif et la structure de la muqueuse jéjunale chez le poulet de chair. Six aliments isoénergétiques (13 MJ EMa·kg -1 ) selon le plan factoriel : 3 concentrations en protéine brute (400, 300 et 200 PB g·kg -1 ) × 2 équilibres en acides aminés (BPS = équilibré, UPS = déséquilibré par rapport aux besoins), ont été offerts à deux niveaux d'ingestion (ad libitum ou 75 % de l'ad libitum) à 4320 poulets de chair entre 10 et 24 jours d'âge. La vitesse de croissance était significativement réduite par la restriction alimentaire. Un effet du taux protéique sur le poids combiné du proventricule et du gésier était significatif (P < 0,001) mais uniquement chez les poulets restreints. Le poids relatif du pancréas augmentait (P < 0,001) avec la concentration du régime protéines BPS chez les poulets restreints. La profondeur des cryptes des villi de l'intestin était plus profonde chez les poulets nourris ad libitum avec les régimes BPS par rapport aux régimes UPS (P < 0,01). La concentration en protéine de la muqueuse jéjunale était supérieure chez les poulets consommant ad libitum les régimes UPS par rapport à ceux ingérant les régimes BPS (P < 0,001). La restriction alimentaire réduisait également la teneur en protéine du jéjunum (P < 0,01) chez les poulets consommant les régim...

1. Various theories have been proposed to explain the reduced performance of broilers when given feeds excessively high in protein, but a satisfactory solution to this problem had, up to now, not been found. Three experiments were conducted to test the hypothesis that the efficiency of utilisation of protein (e) is a linear-plateau function of the ratio between the feed apparent metabolisable energy and digestible crude protein contents (AMEn:DCP) and that dietary protein quality, feed allocation and sex do not influence this relationship. 2. A 'linear-plateau' model successfully described the efficiency of protein utilisation (e) as a function of AMEn:DCP in all three experiments. In Experiment 1, with both sexes being both ad libitum and control fed, the breakpoint was at 58.6 MJ AMEn/kg DCP. In Experiment 2, both sexes were fed balanced and unbalanced protein series, and at different rates, the slopes of the ascending part of the linear-plateau relationships for the different treatments were the same for all treatments (0.0204), and the inflection point was at 71 MJ AMEn/kg DCP. Using similar treatments in Experiment 3, the breakpoint for the balanced protein was 72 MJ/kg and for the unbalanced, 64, with a combined slope of 68 MJ AMEn/kg DCP. 3. The three experiments provide adequate evidence that e is a linear-plateau function of the dietary AMEn:DCP ratio with a breakpoint of around 66.2 ± 1.98 MJ AMEn/kg DCP. Below this critical ratio, food intake declines as does protein and lipid retention. 4. That broilers, like pigs, exhibit an energy-dependent phase when high-protein feeds are offered is of practical importance when formulating pre-starter feeds for broilers and starter feeds for turkey poults as the e of such feeds may well fall below the maximum due to the lack of dietary energy required to process the high dietary protein contained in such feeds resulting in poorer performance than expected.

1. A mixture experiment was used to measure the biological performance (weight gain and food conversion efficiency) of broilers from 7 to 21 d of age when Fed 1 of 13 combinations of 3 protein sources. The objective was to determine the combination of ingredients that would maximise biological performance. 2. The experiment consisted of 2 diet series: in the 1st series, the 3 protein sources used were fishmeal, sunflower oilcake meal and soyabean oilcake meal, and in the 2nd, the soyabean oilcake meal was supplemented with DL-methionine. The combinations of 2 and 3-component mixtures that maximised performance in the 2 series were then compared with the selections made by chickens offered a choice of 2 or 3 components separately. 3. In all cases, the choices made by the broilers coincided with those mixtures that maximised performance. 4. It is clear from this experiment that broiler chickens will attempt to maximise performance by choosing the best possible combination of protein sources when given the opportunity to do so.

Dehydration can be extremely damaging to the performance and welfare of indigenous chickens. The effect of water restriction on haematological and biochemical parameters was compared in Naked Neck (NNK) and Ovambo (OVB) chickens. A total of 54 8-week-old pullets each of NNK and OVB chickens with an initial average weight of 641 6 10 g/bird were randomly assigned to three water intake treatments with three replications, each having six birds. The water restriction treatments were ad libitum, 70% and 40% of ad libitum intake. Nine experimental pens with a floor space of 3.3 m 2 per strain were used. Feed was provided ad libitum. Packed cell volume (PCV), erythrocyte count (RBC), mean corpuscular volume (MCV) and total leucocyte count (WBC), and biochemical parameters (uric acid (UA)), creatinine (CREAT), total protein (TP), albumin (ALB), globulin (GLOB), triglyceride (TGA), total cholesterol (TC), high-(HDLC) and low-(LDLC) density lipoprotein cholesterol and activity of alanine transaminase (ALT), alkaline phosphatase (ALP) and aspartate transaminase (AST) were determined from blood collected after 60 days of water restriction. PCV was higher (P , 0.05) in NNK than OVB chickens offered water ad libitum, but similar in birds offered 70% and 40% of ad libitum. There were no differences in RBC and MCV values between strains, but MCV was higher in birds on 40% than 70% of ad libitum water intake, irrespective of strain. Naked neck chickens had higher (P , 0.05) WBC values than OVB at 40% restriction level, but lower WBC than OVB at 70% water restriction level. UA, CREAT, TGA, TC, LDLC, TP and GLOB increased (P , 0.05) with each increment in water restriction, but the increase in CREAT and TC was more pronounced in OVB than NNK chickens. The opposite was observed for UA. ALT activity indicated that liver function was not affected by water restriction. It was concluded that the two strains can withstand up to 40% of ad libitum water restriction, but NNK tolerated water stress better than OVB chickens.

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