Effect of exogenous corticosterone in genetically fat and lean chickens

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.     

The influence of dietary protein content on the performance of genetically lean or fat growing chickens

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.     

Effects of dietary fiber and threonine on performance,intestinal morphology and immune responses in broiler chickens

The present experiment was conducted to investigate the effects of fiber and threonine (Thr) on growth performance, intestinal morphology and immune responses of broiler chickens. A total of 420 one-day-old mixed sex broiler chicks (Ross 308) were randomly divided into 6 experimental diets and 5 replicates of 14 chicks based on a factorial arrangement (2 × 3) from 1 to 42 d of age. Experimental factors included dietary supplemental fiber type (no supplemental fiber [NSF], 30 g/kg sugar beet pulp [SBP] or 30 g/kg rice hull [RH]) and Thr inclusion level (100% or 110% of Thr requirement recommended by breeder company [Ross 308]). Growth performance of broilers was assayed at different periods of the experiment. Intestinal morphometric features were measured at 21 d of age. Antibody titer against sheep red blood cells (SRBC), Newcastle and influenza disease viruses were measured on d 30 of trial. Dietary inclusion of SBP and RH significantly decreased feed intake and weight gain during the entire rearing period (P < 0.05). Interaction of fiber and Thr had no beneficial effects on the performance of chickens across the entire rearing phase. Dietary supplementation of 110% Thr required level improved jejunal morphometric features (P < 0.05), whereas its inclusion with fibrous materials failed to show the same effects. Dietary supplemental Thr together with SBP significantly increased antibody production against SRBC (P < 0.05). In conclusion, although supplemental 30 g/kg fibrous materials impaired growth performance, inclusion of SBP along with 110% Thr level improved the humoral immunity in broiler chickens.     

Further investigations on protein requirement of genetically lean and fat 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.     

The effects of dietary protein independent of essential amino acids on growth and body composition in genetically lean and fat chickens

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.     

Behavioural and growth responses of broiler chickens to dietary water content and climatic variables

1. The behavioural responses and growth of broiler chickens were investigated over three seasons using two wet mashes with food:water ratios of 2:1 (HW) and 3:1 (MW).

2. Wet mashes fed in the hot dry season caused significantly lower rates of panting, a major thermoregulatory behaviour. This may be an indication of increased comfort in hot dry conditions for birds fed wet mashes.

3. Feeding activities of birds fed dry and wet rations respectively increased and decreased with decrease in seasonal temperature. The peaks of both feeding activity and consumption in the cool‐dry season were attained by birds fed dry diets and in the hot dry season by those fed wet mashes.

4. Diurnal distributions of food and water intakes were more even in the hot dry season for those fed wet mashes. This may again suggest a higher degree of comfort on the hot dry season when birds are fed wet mashes.

5. In the hot dry season, 60% of birds preferred wet mashes, whereas 80% of birds preferred dry meal in the cool dry season. This may be attributable to the lower temperature of wet mashes.

6. Similar patterns in feeding activity, food consumption and daily weight gain occurred in response to dietary presentation and season.

7. Feeding of dry meal under cool dry conditions and wet mashes in the hot season may be advantageous. Irrespective of season, water temperature may have to be raised to about 30°C before addition to meals for chicks under brooding. This may be necessary as preliminary investigations in this laboratory indicate that food temperatures below 22°C may at the brooding stage discourage food intake and activities.     

Corticosterone administration and dietary glucose supplementation enhance fat accumulation in broiler chickens

1. The effects of exogenous corticosterone administration and glucose supplementation on energy intake, lipid metabolism and fat deposition of broiler chickens were investigated. 2. A total of 144 three-d-old male chickens were randomly assigned to one of the following 4 treatments for 7 d: a low energy diet (10.9 MJ ME/kg, 200 g/kg CP) with or without corticosterone (30 mg/kg diet) and drinking water supplemented with glucose (80 g/l) or saccharine (2 g/l, control). 3. Body weight (BW) gain and breast and thigh muscle yields (% body mass) were all significantly decreased by corticosterone treatment. The relative cumulative feed intake (RCFI) and relative ME intake (RMEI), rather than the feed (FI) or ME intake (MEI) were increased by corticosterone administration. Both feed efficiency (FE) and caloric efficiency (CE) were decreased by corticosterone administration. Corticosterone administration had no obvious effect on water consumption. 4. Glucose supplementation had no influence on BW gain and breast and thigh muscle yield (as % of body mass). FI or RCFI was decreased while MEI or RMEI was increased by glucose supplementation. FE was improved by glucose treatment, whereas CE was reduced. 5. Liver weight and abdominal, cervical and thigh fat deposits were all significantly increased by either corticosterone or glucose treatment. 6. Plasma concentrations of glucose, urate, triglyceride, non-esterified fatty acids (NEFA), very low density lipoprotein and insulin were all significantly increased by corticosterone treatment. Glucose supplementation had no obvious influence on any of the measured plasma parameters except for NEFA, which were significantly increased. 7. Lipoprotein lipase activities in either cervical or abdominal adipose tissues, rather than in thigh fat tissue, were significantly elevated by either glucose or corticosterone treatment.     

Ocular responses to ammonia in broiler chickens

In two trials, 60 male commercial broilers were placed in each of eight environmentally controlled chambers receiving 0, 25, 50, or 75 ppm aerial ammonia from 1 to 28 days. Birds exposed to 25 ppm (lower concentration) ammonia gas developed ocular abnormalities but at a slower rate when compared with birds exposed to 50 and 75 ppm (higher concentrations). Birds exposed to higher concentrations also developed more severe lesions. With little atmospheric ammonia present after 28 days of the grow-out stage, the corneas indicated signs of healing. Lymphocytes and heterophils were seen in the iris at 49 days in ammonia-exposed birds even when ammonia exposure was terminated at 28 days. The lower ammonia concentrations resulted in abnormalities that were slight when compared with those seen at the higher ammonia concentrations. As measured by the incidence of inflammatory infiltrates in the trachea, lung, and air sacs, respiratory tract tissues did not appear to be affected by any tested level of aerial ammonia. The findings in this investigation represent the first report indicating that ammonia-induced uveitis in chickens clears rapidly after exposure to ammonia ceases.     

Effects of dietary threonine and crude protein on growth performance, carcase and meat composition of broiler chickens

1. The aim of the study was to investigate the effects of dietary threonine (Thr) and crude protein (CP) in maize-soybean meal based diets on the growth performance, carcase traits and meat composition of broiler chickens and to determine the dietary Thr requirement for optimum performance (weight gain and feed conversion efficiency (FCE)) at 0 to 3 weeks and 3 to 6 weeks of age. 2. Two basal diets that differed in CP (191.3 or 179.7 and 176.7 or 165.4 g/kg at 0 to 3 and 3 to 6 weeks, respectively) were formulated to have identical contents of Thr (6.0 and 5.4 g/kg), energy (12.97 and 13.39 MJ ME/kg) and other essential amino acids except for Gly + Ser. Basal diets were supplemented with L-Thr from 0.6 to 1.8 g/kg in 0.6 g/kg increments. Broiler chicks (540) were randomly allocated to 9 dietary treatments with 6 replicates of 10 (5 female, 5 male) chicks. 3. A significant interaction between dietary CP and Thr was found for feed intake, body weight (BW) gain and FCE. Increasing Thr supplementation improved feed intake, BW gain and FCE, especially in high CP diets in both feeding periods. 4. Incremental increases in dietary Thr increased breast yield at both CP levels and drumstick yield only on high CP diets. The proportion of thigh decreased with Thr concentration. Liver weight was significantly reduced by Thr supplementation; abdominal fat was not affected. 5. Estimated Thr requirements for FCE increased as dietary CP increased according to an exponential model. This model indicated higher Thr requirements than those of broken-line models for growth performance.     

Effects of dietary chitosan on fat deposition and lipase activity in digesta in broiler chickens

1. The effect of dietary chitosan on fat deposition and lipase activity in the small intestinal contents was investigated in broiler chickens fed an adequate or high metabolisable energy (ME) diet. 2. Male broiler chickens at 14 d old were fed on the adequate or high ME diet supplemented with 0 or 50 g/kg chitosan, which has a low viscosity, for 3 weeks. 3. Dietary chitosan did not affect food intake, body weight gain or food efficiency in either dietary ME groups. 4. Dietary chitosan reduced the excessive abdominal fat deposition induced by the high ME diet. 5. Dietary chitosan increased the weight of intestinal contents irrespective of dietary ME concentration. 6. Dietary chitosan decreased the lipase activity per g of small intestinal contents. 7. These results suggest that dietary chitosan with low viscosity decreases lipase activity and fat absorption in the small intestine, consequently resulting in a reduction of fat deposition in broiler chickens. 8. It was concluded that dietary chitosan with low viscosity can decrease body fat deposition without reducing food intake and body weight gain in broiler chickens.     

Effect of dietary phosphorus concentration and electrolyte balance on the growth performance of broiler chickens

The performance of 1680 male and female broiler chickens given diets with either a low (4.7-4.3 g/kg) or high (8.9-8.2 g/kg) content of inorganic phosphorus and four (150, 200, 250 and 300 mEq/kg) electrolyte balances (Na+K-Cl) was measured from 1-d-old to 49 d of age. Diets with the higher concentration of inorganic phosphorus reduced body weight gains in the starter (P less than 0.01) and finisher (P less than 0.05) phases but the efficiency of food utilisation was reduced only in the starter phase (P less than 0.05). The reduction in body weight gain was greater in males than in females. The growth depression caused by the higher concentration of inorganic phosphorus in the finisher diets was partially alleviated by increasing the electrolyte balance to either 250 or 300 mEq/kg diet. The higher concentration of inorganic phosphorus significantly reduced the dressing percentage and increased the abdominal fat pad weight and litter moisture content. Electrolyte balance had no significant effects on efficiency of food utilisation, abdominal fat pad weights or litter moisture content. Neither the dietary concentration of phosphorus nor the electrolyte balance had a significant effect on mortality or ash content of the tibia.     

Effect of dietary energy restriction on retention of protein,fat and energy in broiler chickens

1. Broiler chickens were fed 60–100% of recommended energy intakes to study the effects of energy restriction on protein and fat retention.

2. At an energy retention of 179 kJ/kg W ^0·75 d, only protein was retained. At higher energy intakes, each increment in retention had a rather constant composition: about 85% energy in fat and 15% in protein. At lower energy intakes body fat was mobilised whereas protein was deposited.

3. The efficiencies of energy retention in protein and fat were estimated to be 0·66 and 0·86 respectively.

4. The rather constant composition of additional retained energy after additional energy supply provides an explanation for a linear relationship between energy intake and energy retention.     

A deficient or an excess of dietary threonine level affects intestinal mucosal integrity and barrier function in broiler chickens

The aim of this study was to investigate the effects of deficient or excess of dietary threonine (Thr) levels on intestinal integrity and barrier function of broilers. A total of 432 1‐day‐old commercial broilers (Arbor Acre) were assigned to four experiment groups consisting of six replicates of 18 birds. The treatments were designed as follows: 85%, 100%, 125% and 150% of NRC (Nutrient requirements of poultry (9th edn). Washington, DC: The National Academies Press, 1994) recommendations. The results indicated that expressions of jejunal and ileal secretory immunoglobulin A (sIgA) mRNA were increased linearly or quadratically by increasing Thr (p < .05), and the highest sIgA mRNA abundance was obtained in 125% Thr level. Likewise, the intestinal sIgA content showed similar increasing trend with the intestinal sIgA gene expression in this instance. The high level of Thr inclusion upregulated mucin 2 (MUC2) mRNA expression in the jejunum and ileum (p < .05). In addition, on day 21, the expression levels of jejunal zonula occludens‐2 (ZO‐2) and ileal zonula occludens‐1 (ZO‐1) decreased then increased with increasing Thr level (p < .05), whereas, the mRNA expressions of occludin in the jejunum and ileum had no significant difference amongst groups (p >.05). On day 42, Thr treatments did not affect the mRNA abundance of measured genes in the jejunum and ileum (p > .05). These findings suggested that Thr might be a nutrient immunomodulator that affects intestinal barrier function, moreover, 125% of the NRC (1994) recommendations Thr level was optimum.     

Responses of broiler chickens to dietary protein: effects of early life protein nutrition on later responses

1. A study was conducted with modern broiler chicks to test the effects of early life protein nutrition and sex on responses in growth and body composition to dietary protein at a later age. Effects on the incidence of metabolic disorders were also evaluated. 2. From 11 to 26 d of age (EXP1), birds were given 8 diets varying in balanced protein to energy ratio (BPE ratio) between 0.575 and 1.100 g digestible lysine per MJ AMEn. Birds from two treatment groups in EXP1 (BPE ratio of 0.725 and 1.025 g/MJ, respectively) were subsequently used in a test from 26 to 41 d of age (EXP2). In EXP2, 8 diets were used, varying in BPE ratio between 0.500 and 1.025 g/MJ. 3. Responses in weight gain and feed conversion to BPE ratio in EXP2 changed considerably when BPE ratio in EXP1 was modified, irrespective of sex. Up to 10% improvement in both weight gain and feed conversion in EXP2 was observed if BPE ratio in EXP1 was 0.725 compared with 1.025 g/MJ. With males, however, the effect of treatment in EXP1 on weight gain in EXP2 was present only at high BPE ratios. 4. For the relative gain of breast meat and abdominal fat, but not for carcase, the responses of male broilers to BPE ratio in EXP2 were altered by the BPE ratio in EXP1. With females, responses in composition of the gain to diet in EXP2 were independent of BPE ratio in EXP1. 5. The incidence of metabolic disorders was low, irrespective of treatment in EXP1. The lower BPE ratio in EXP1 increased mortality in EXP2 from 0.8 to 3.6%. 6. Our findings show that broiler responses to dietary protein depend on previous protein nutrition and sex. Effects of early life protein nutrition on incidence of metabolic disorders were not observed. The results strongly suggest that protein levels in grower and finisher diets should not be optimised independently, but simultaneously.     

Lack of effect of dietary energy-to-protein ratio and energy concentration on the response of broiler chickens to virginiamycin.

1. Two factorial experiments were carried out with male broiler chicks from 6 to 28 (experiment 1) and from 7 to 49 (experiment 2) d of age to evaluate the combined effect of virginiamycin (VIR), dietary energy concentration, and energy-to-protein (E:P) ratio on performance and the utilisation of dietary nutrients. 2. VIR had no significant effect in either experiment on food intake or weight gain, but significantly improved food efficiency up to 28 d of age (P less than 0.001 and P less than 0.05 in experiments 1 and 2, respectively). 3. VIR consistently and significantly (P less than 0.01) decreased fat excretion, improved fat relative retention and increased dietary AMEn. VIR also significantly (P less than 0.01) increased relative retention of dry matter, while it did not affect nitrogen balance. 4. Neither of the variables of performance and utilisation of dietary nutrients was affected by the interactions between VIR and either dietary E:P ratio or energy concentration. It is concluded, therefore, that the effect of VIR in increasing the utilisation of dietary energy does not depend on the above factors.     

The effects of dietary energy concentration on growth rate and conversion of energy to weight gain in broiler chickens

Eight diets, their metabolisable energy (ME) concentrations ranging from 2.3 Mcal/kg to 3.6 Mcal/kg (9.6 to 14.1 MJ/kg) were fed to each of four pens of broilers in two trials. Food intake was inversely related to energy concentration but the ME required by each sex to reach a given live‐weight was quite similar. Birds on the diets with a medium energy concentration (about 3.1 Mcal/kg (13.0MJ/ kg)) required slightly less ME than those on other diets and generally reached the required live‐weight earlier than those on other diets. Birds in the first trial required less of any particular diet than their counterparts in the second trial, reflecting the lower ambient temperatures recorded during the latter trial. Mortality recorded from 14 d of each trial was generally lower for birds on the medium energy concentration diets and dressed carcass percentage higher than those on other diets.

The results of the present study are in agreement with the recent recommendation (National Research Council, 1971) of 3.2 Mcal ME/kg (13.4 MJ/kg) for broiler diets. However, it is suggested that minimum and maximum values be given in such recommendations; this would allow greater flexibility and a wider range of ingredients in diet formulation.     

Effect of in ovo threonine supplementation on early growth,immunological responses and digestive enzyme activities in broiler chickens

1.?The effects of injecting threonine in ovo on early growth, some immunological responses and the activity of digestive enzymes of broiler chicks were investigated. Fertile eggs were distributed into 6 groups, each of 60. These were: untreated control, sham control, 10, 20, 30 or 40 mg threonine. Threonine was dissolved in 0·5 ml sterile saline and inoculated into the yolk sac of the 14-d-old embryo through the narrow end of the egg.

2.?The ratio of chick to egg weight was 1·6% higher in the group given 30 mg threonine and at 28 d of age chicks receiving threonine were 29 to 79 g heavier than untreated controls.

3.?Food conversion ratio until 7 d after hatching was improved in those chicks receiving 10, 20 or 40 mg threonine but there was no significant effect on the activities of amylase, pepsin or trypsin.

4.?The humoral response to sheep red blood cells was significantly greater in those groups receiving 10, 20 or 30 mg threonine supplementation than in untreated controls.

5.?The response to phytohaemagglutinin-P, a measure of the cell-mediated immune response, was not affected, however.

6.?It is concluded that injections of 20 to 30 mg threonine into yolk sac can improve post-hatching growth and humoral responses of broiler chicks.     

Effect of dietary lignocellulose on ileal and total tract digestibility of fat and fatty acids in broiler chickens

The study was conducted to determine the effect of a lignocellulose supplemented diet on apparent ileal and total tract digestibility of fat and fatty acids (FA) in broiler chickens. A total of 48 21‐day‐old male Ross 308 chickens were divided into four treatment groups (n = 12) with six replicates per treatment. From 21 to 42 days of age, the broilers were fed experimental diets varied in the amount of lignocellulose: 0%, 0.25%, 0.5% and 1%. Total excreta were gathered during the last 3 days of the feeding trial and digesta was collected from the ileum at 42 days of the bird age. Digestibility was determined by the indicator method. The ether extract content in diet/digesta/excreta was determined by the gravimetric method, and fatty acid methyl esters were analysed by gas chromatography–mass spectrometry. Fat digestibility measured to the end of the small intestine and in the whole gastrointestinal tract in birds was high and exceeded 90% and 87% respectively. Addition of lignocellulose (1%) increased (p < 0.05) ileal fat digestibility but had no significant effect on total tract fat digestion. Absorption of total fatty acids (TFA) as well as myristic (C14:0), palmitoleic (C16:1) and α‐linolenic (C18:3n?3) acids, estimated by both methods, was significantly higher in birds fed the diets supplemented with lignocellulose, especially at a dose of 1%. Total tract absorption of some dietary polyunsaturated fatty acids (PUFA) (C20:2, C20:4n?6) was significantly lower from diet supplemented with 0.5% and 0.25% lignocellulose. There was observed a decrease in apparent digestibility of fat and most examined fatty acids, when measured between terminal ileum and total gastrointestinal tract. The results suggest that lignocellulose can affect digestion and FA absorption in broilers but, as the effect of lignocellulose was not studied previously, further investigations are necessary to confirm the results of the present experiment.     

Influence of dietary conjugated linoleic acid isomers on early inflammatory responses in male broiler chickens

1. The influence of dietary conjugated linoleic acid isomer (CLA, 0 and 10 g/kg) on the metabolic and physiological responses to immune stimulation induced by a single injection of Salmonella enteritidis lipopolysaccharide (LPS) or repeated injections of LPS and Sephadex G-50 was determined in male broiler chicks. 2. In experiment 1, 10-d-old chicks were fed on experimental diets for 14 d and half of the birds fed on each diet were injected intraperitoneally with LPS (1.5 mg/kg body weight). In experiment 2,7-d-old chicks were fed on experimental diets for 18 d. Immune stimulation was started at 19 d old and continued for 5 d. Half of the birds fed on each diet were injected intraperitoneally with 0.25 mg/kg body weight of LPS at 19, 21 and 23 d of age, and with 250 mg/kg body weight of Sephadex at 20 and 22 d of age to stimulate the immune system. 3. In experiment 1, giving CLA prevented an increase in blood heterophil to lymphocyte ratio 7 h after a single injection of LPS, and increases in plasma ceruloplasmin and alpha 1 acid glycoprotein (AGP) 24 h after the injection, but not 7 h after the injection. CLA also prevented a decrease in food intake for 24 h after LPS injection. 4. In experiment 2, the CLA diet partially prevented reductions in body weight gain and weight gain to feed intake ratio caused by repeated injections of LPS and Sephadex. Feeding CLA prevented increases in plasma ceruloplasmin and AGP at 24 d of age caused by repeated injections of LPS and Sephadex, but not at 20 d of age. 5. These results suggest that feeding CLA alleviates some undesirable metabolic and physiological changes induced by immunological stimulation in male broiler chicks.     

Dietary isoleucine responses in male broiler chickens

1. Three experiments were conducted to measure growth and carcase responses of growing and finishing broilers fed on test diets formulated to be deficient in isoleucine (Ile). 2. Dose titration methodology was used to measure growth and carcase responses of growing and finishing broilers to graduations of Ile in three additional experiments. 3. The experiments were conducted from d 18 to 30, 30 to 42, and 42 to 56. 4. Broilers given Ile-deficient test diets had poorer weight gain, feed conversion and carcase responses than broilers fed on Ile test diets containing a surfeit of Ile. Adding supplemental Ile to the test diet resulted in equivalent growth and carcase responses to those of broilers fed on the control diet with equal Ile from intact protein sources. 5. Recommended total Ile needs varied between 6.7 and 7.1 g/kg from d 18 to 30, 6.4 to 6.6 g/kg from d 30 to 42, and 5.5 to 6.6 g/kg from d 42 to 56.