The effect of minimizing amino acid excesses in broiler diets

Effects of Dietary Protein Levels, Net Energy Levels, and Essential Amino Acid-to-True Protein Ratios on Broiler Performance

Supplementing essential amino acids (EAAs) without considering non-EAA (NEAA) and energy contents in reduced-crude protein (CP) diets may alter EAA-to-true protein (E:T) and energy-to-protein ratios, potentially compromising growth. This study aimed to evaluate the effects of CP, E:T, and net energy (NE) on broiler performance. The treatments were as follows: T1-reduced CP (16%, RP), low NE (9.9 MJ/kg, LNE), low E:T (0.56, LE:T); T2-RP, LNE, high E:T (0.60, HE:T), with imbalanced EAA (excess Met and deficient Thr); T3-RP, high NE (10.4 MJ/kg, HNE), LE:T; T4-RP, HNE, HE:T; T5-normal CP (18%, NP), LNE, LE:T; T6-NP, LNE, HE:T; T7-NP, HNE, LE:T; and T8-NP, HNE, HE:T. The study employed as-hatched Cobb 500 broilers in two experiments. Exp.1 studied the broiler performance from d19 to 35, with eight replicates per treatment and 16 birds per replicate (n = 1024). Birds were randomly assigned to different treatments, and at the end of their lives, all were dissected to determine their sex and account for any gender-related effects. Exp.2 measured NE values in respiration chambers from d25 to 28, with six replicates per treatment, and two birds (a male and a female) per replicate (n = 96). The bird gender was determined through high-resolution melting curve analysis of feather DNA. The measured NE values were used to calculate NE intake (NEi) in Exp.1. The results showed that T4 improved (p < 0.001) weight gain (WG), feed conversion ratio (FCR), and NEi relative to T1, T2, and T3, and protein efficiency (WG/CP intake) relative to all treatments. The live performance (feed intake, WG, FCR) and NEi of birds fed T4 reached a level equal to those of birds fed NP diets (T5 to T8). These results suggest that a dietary E:T ratio of 0.60 is necessary to maximize nutrient utilization and to restore growth rate in broilers fed RP diets.

Growth performance and nitrogen excretion of broiler chickens fed low protein diets supplemented with crystalline amino acids

This study was conducted to determine the effects of amino acid (AA) supplementation in low-protein (LP) diets on growth performance and nitrogen (N) excretion. A total of 175 7-day-old Ross 308 male broilers, with a mean body weight (BW) of 165 g (standard deviation = 11.2 g), were grouped into five blocks by BW and allocated to seven treatments according to a randomized complete block design with five replicate cages at five birds per cage. Dietary treatments comprised a control diet containing 20.0% crude protein (CP) and six LP diets containing either 18.5% or 17.0% CP. These LP diets were supplemented with either no AA supplementation, indispensable AA, or both indispensable and dispensable AA (glutamic acid and glycine). Birds were fed experimental grower diets from day 7 to 21 and then commercial finisher diets until day 28. During the grower period (day 7 to 21), birds fed LP diets supplemented with indispensable AA exhibited greater (p < 0.05) BW, body weight gain (BWG), feed intake (FI), and gain-to-feed ratio (G:F) than birds fed LP diets without crystalline AA and were comparable to birds fed the control diet. During the finisher period (day 21 to 28), birds fed LP diets supplemented with indispensable AA showed greater (p < 0.05) BW than birds fed LP diets without crystalline AA, and their growth performance was comparable to birds fed the control diet. Throughout the overall period, supplementing indispensable AA in LP diets resulted in elevated (p < 0.05) BWG, FI, and G:F more than those of LP diets without crystalline AA and were comparable to those of the control diet. Supplementing indispensable AA in LP diets decreased amount and coefficient of N excretion as much as the control diet. Dispensable AA supplementation in LP diets did not influence growth performance and N excretion. In conclusion, supplementing indispensable AA in LP diets maintains growth performance and N excretion until the dietary CP lowers from 20.0% to 17.0% during the grower period. As long as dietary CP is above 17.0%, dispensable AA may not be deficient in LP diets during the grower period.

Different amino acid supplementation patterns in low-protein diets on growth performance and nitrogen metabolism of goslings from 1 to 28 days of age

The investigation aimed to explore the suitable amino acid (AA) supplementation pattern for goslings under low-protein diets. A total of 364 1-day-old male goslings were randomly divided into 4 experimental groups, with 7 pens containing 13 goslings each. The 4 groups were control (CP, 18.55%), LPM (CP, 15.55% + major AA), LPA (CP, 15.55% + all AA), and LPR (CP, 15.55% + AA content reduced proportionally to the control's CP). The corn-soybean meal diets are formulated according to the ideal AA model of goose and its nutritional requirements. The results indicated that the ADG and BW were the lowest, and the F: G was the highest in LPR (P < 0.05); the other three groups were not significantly different (P > 0.05). The ADFI and mortality were not different among all the groups (P > 0.05). Among the AA content in serum and breast muscle, lysine in serum significantly decreased compared with the control (P < 0.05). The UREA content was approximately 2-fold higher in the LPR group than in the LPM and LPA groups (P < 0.05). No difference in IgA, IgG, IgM, and IgE levels was observed among the groups (P > 0.05). The nitrogen excretion was decreased in LPM and LPA compared to the control and LPR (P < 0.05). Nitrogen deposition did not differ among groups (P > 0.05). Nitrogen utilization was highest in the LPA and LPM groups, followed by the control group and LPR (P < 0.05). In conclusion, the patterns of supplementation of major AA and all AA in low-protein diets (CP, 15.55%) had no adverse effect on the growth performance compared with the control (CP, 18.55%) of the goslings. Besides, the two patterns could decrease nitrogen excretion and increase nitrogen utilization. Furthermore, from the perspective of dietary cost and environmental protection, the pattern of supplementing major AA in a corn-soybean meal low-protein diet is suggested.

Amino Acids Supplementation Affects Sustainability of Productive and Meat Quality, Survivability and Nitrogen Pollution of Broiler Chickens during the Early Life

The response to amino acid (AAs) supplementation on broiler production, carcass and meat traits and nitrogen in the excreta during the early growth period was evaluated. Two experiments were performed during 1-28 d (245 birds, experiment 1) and 1-21 d of age (455 birds, experiment 2). In both experiments, the positive control (PC) diet had 22.5% crude protein (CP) and the negative control group (NC) diet had around 18% CP with the same methionine (Met) plus lysine (Lys) concentration as the PC diet. In experiment 1, the NC diet was fed to the other five groups supplemented with synthetic amino acids, such as L-arginine (Arg), L-threonine (Thr), L-valine (Val), L-isoleucine (Ile) or all these AAs, respectively. In experiment 2, the NC diet was formulated to contain 18% CP with either corn-soybean meal and animal protein or with only vegetable protein. Both NC diets were offered to the other ten groups with synthetic amino acids such as L-Arg, L-Thr, L-Val, L-tryptophan (Trp) or a combination of all these AAs plus L-isoleucine (Ile), respectively. In conclusion, broilers fed 18% CP supplemented with DL-Met plus L-Lys showed lower performance and a European production efficiency value (EPEV); Arg, Thr and Val addition improved growth, the feed conversion ratio and EPEV of the diets containing animal protein only, but broiler performance and EPEV was lower than with PC, indicating that DL-Met, L-Lys, L-Arg, L-Thr and L-Val supplementation may be limited in low-protein diets. Furthermore, a low-protein diet supplemented with amino acids did not affect the survivability of broilers up to 28 days of age.

Effects of different feeding regimens with protease supplementation on growth, amino acid digestibility, economic efficiency, blood biochemical parameters, and intestinal histology in broiler chickens

Background

This study was conducted to estimate the impacts of using varied feeding regimens with or without protease supplementation on the growth performance, apparent amino acid ileal digestibility (AID%), economic efficiency, intestinal histology, and blood biochemical parameters of broiler chickens. Three hundred one-day-old chicks (Ross 308 broiler) were randomly allotted to a 3 × 2 factorial design. The experimental design consisted of three feeding regimens; FR1: a recommended protein SBM diet, FR2: a low-protein SBM diet, and FR3: a low-protein diet with the inclusion of 5% DDGS and 5% SFM, with or without protease supplementation (250 mg/kg).

Results

Increased feed intake and feed conversion ratio were observed in the FR3 treatment during the starter stage and decreased body weight and body weight gain during the grower stage. However, there was no significant effect of the different feeding regimens, protease supplementation, or interaction on the overall performance. The economic value of diets also remained unaffected by the different feeding regimens, protease supplementation, or interaction. Protease supplementation resulted in lowering the AID% of tryptophan and leucine. Reduced AID% of methionine was evident in the FR2 + VE and FR3 − VE treatments. Histological findings substantiated the FR3 treatment mediated a decrease in the duodenal and jejunal villous height (VH), jejunal villous width (VW), and ileal VW, whereas, increase in the ileal crypt depth (CD). The FR2 + VE treatment reduced the VH:CD ratio in the duodenum. The duodenal CD and the jejunal goblet cell count were reduced as a consequence of protease supplementation. The FR3 + VE treatment documented a rise in duodenal CD, while an increase in the jejunal goblet cell count was observed in the FR3 − VE treatment. The FR3 treatment enhanced the IgM serum levels compared to the FR1 and FR2 treatments. IgM serum levels were also elevated following protease supplementation. FR3 + VE treatment increased IgM serum levels. The highest serum ALP was found in the FR3 treatment, whereas the lowest level was obtained in the FR2 treatment.

Conclusion

Low-protein SBM-based diets could be used without affecting the birds’ growth. Altered morphometric measures of the intestine and increased IgM and ALP levels indicated the low-protein SBM/DDGS-SFM diet-induced damage of the intestinal histoarchitecture and immune system of birds. These different diets and protease supplementation failed to affect economic efficiency positively.

Effects of lysine biomass supplementation on growth performance and clinical indicators in broiler chickens

Production of crystalline amino acids (AA) through microbial fermentation concomitantly provides an AA-enriched biomass that may serve as a cost-effective supplement for broiler chickens. We investigated the effects of feeding a fermentation biomass product containing approximately 62% Lys on growth performance, organ growth, and clinical outcomes of broilers. Beginning at 2 d post-hatch, a total of 360 Ross 308 chicks were randomly assigned to 1 of 5 treatments provided to 12 replicate cages of 6 birds. Practical corn-soybean meal-based dietary treatments included: negative control (NC; no supplementation of L-Lys, 1.01 and 0.86% standardized ileal digestible Lys in starter and grower phases, respectively), NC + 0.23% L-Lys HCl (positive control; PC), and NC supplemented with 0.30, 0.90, or 1.50% Lys biomass (LB) in both phases. Feed and water were provided ad libitum throughout the study. Individual bird and feeder weights were recorded on study day 0, 10, 21, and 35. At study conclusion, birds from each treatment were randomly selected to collect blood and tissue samples. The PC and 0.30% LB diets elicited similar overall (day 0–35) body weight gain and birds were heavier (P < 0.001) than the NC and other LB treatments. The PC, 0.30% LB, and 0.90% LB groups had better (P < 0.001) overall feed conversion ratio than NC. Some LB-supplemented treatments elicited increased (P < 0.001) relative spleen and ileum weight compared with NC and PC. Heterophils were increased (P < 0.001) in LB treatments compared with PC and NC. Lymphocytes were decreased (P < 0.001) in LB treatments compared with NC, and 1.50% LB was similar to PC. This resulted in an increased (P < 0.001) heterophil-to-lymphocyte ratio in some LB treatments, which may have resulted from general AA supplementation or the LB product. Collectively, these results suggest that addition of up to 0.30% LB restored growth performance when added to a Lys-deficient practical diet and elicited results identical to the Lys-adequate PC diet with no negative clinical effects.

Effect of reduced dietary protein and supplementation with a docosahexaenoic acid product on broiler performance and meat quality

1. Chicken breast meat is a lean meat due to its low content of intramuscular fat (IMF) resulting in an overall lower acceptability by consumers due to a decrease in juiciness, flavour and increased chewiness. Recently, studies performed in pigs suggested the possibility of increasing IMF by decreasing dietary crude protein (CP) content, an effect possibly mediated through an increased lipogenesis. 2. Dietary supplementation with lipids rich in omega 3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) may modulate an increase in the content of these fatty acids in meat from monogastric animals and, thus, promote the daily intake of n-3 LC-PUFA by humans. 3. LC-PUFA are very susceptible to oxidation, resulting in off-flavours that affect meat quality and consumers' acceptability. 4. This trial was conducted to assess the effect of reducing dietary CP, from 21% to 17%, on chicken's meat IMF content and, simultaneously, to evaluate if a complementary supplementation with a proprietary n-3 LC-PUFA source (DHA Gold™) could improve meat quality. These effects were assessed by measuring productive performance and meat quality, oxidative stability, sensory traits and fatty acid profile. 5. A reduction in CP content of broiler diets, from 21% to 17%, balanced for lysine, improved performance while it was not sufficient to increase IMF content in chicken meat. In contrast, DHA Gold™ supplementation had a positive impact both in broiler productive parameters and in meat fatty acid profile. 6. In addition, incorporation of 7.4% of DHA Gold™ in the diet promoted carcass yield but negatively affected chicken meat acceptability by consumers, due to a decrease of meat oxidative stability. 7. Overall the data suggest that neither a dietary supplementation with DHA Gold™ nor a reduction in CP have a direct positive effect in the levels of IMF present in broiler meat.

Free availability of high-energy foods led to energy over-ingestion and protein under-ingestion in choice-fed broilers

The objective of this study was to compare energy and protein content of the diet selected by choice-fed broilers with that of broilers fed a balanced diet. One hundred and eighty 1-day-old male broilers were randomly assigned in groups of 10 to one of three experimental treatments (n = 6). Control broilers were fed a standard balanced diet, whereas choice-fed broilers were fed three foods which were more concentrated (Choice C+ treatment) or less concentrated (Choice C- treatment) in protein, carbohydrate or fat. We evaluated food intake behavior, nutrient intake, and performance parameters of broilers from 2 to 7 weeks of age. Choice C+ broilers showed enhanced preference for the high-fat food, which led to higher energy intake and lower protein intake than those of control broilers at 2 to 4 weeks of age. Body weight, weight gain and feed conversion efficiency were negatively affected by diet selection of Choice C+ broilers. Choice C- broilers selected a balanced diet, and showed performance parameters similar to those of control broilers. Our results supported the hypothesis that free availability of high-energy foods bias ingestive behavior of choice-fed broilers toward selecting a diet with higher energy and lower protein than needed for normal growth.

Effect of dietary fish oil on n-3 fatty acid content of meat from broiler chickens fed low protein diets

An experiment was carried out to evaluate the effects of dietary fish oil and crude protein (CP) levels on fatty acid composition of the thigh and breast tissues of broiler chickens. Four hundred and fifty, 1-day-old mixed-sex broiler chicks were used in a completely randomised design with factorial arrangement consisting of two dietary CP levels (21 v. 18.0% and 19 v. 17.1% for grower and finisher diets, respectively), and three levels of fish oil inclusion (0, 2 or 4%). Specific increases in eicosapentaenoic acid (EPA, 20 : 5) and docosahexaenoic acid (DHA, 22 : 6) were observed in breast and thigh tissues as a response to increased fish oil supplementation. The n-6 : n-3 fatty acid ratio in breast and thigh meat samples decreased (P < 0.05) in birds fed low protein diets, but dietary protein level led to no alteration in the total n-3 fatty acids of the tissues (P > 0.05). Thigh tissue of chickens fed low protein diets had a higher concentration of DHA (P < 0.05), while the DHA and EPA concentrations in breast tissue were not affected by dietary protein level (P > 0.05). Results of the present study showed that fish oil can be used to fortify EPA and DHA levels in chicken meat and there is an interaction between dietary fatty acids and protein level on meat oxidative stability, and a reduction in dietary protein level may lead to a better oxidative stability of chicken meat.

Effect of cellulase supplementation in low-crude protein diets on performance, nitrogen excretion, fat deposition, hepatic lipogenic and lipolytic enzyme activity in broilers

1. Two experiments were conducted to investigate the effect of dietary enzyme supplementation of a low-protein diet on performance, nitrogen excretion, fat deposition, hepatic lipogenic and lipolytic enzyme activity in 7-21- (Experiment 1) and 21-42-d-old (Experiment 2) male broiler chicks. 2. Chicks were given diets containing 210 g (Experiment 1) or 170 g (Experiment 2) crude protein (CP)/kg (Control), amino acid-fortified diets 190 g (Experiment 1) and 150 g (Experiment 2) CP/kg (Low-protein), and a low-protein diet supplemented with 1000 U/kg of cellulase. 3. In Experiment 1, growth performance and abdominal fat deposition were not affected by dietary treatments, and birds given low-protein diets excreted less nitrogen. The activities of hepatic lipogenic and lipolytic enzymes were not different among the three dietary groups. 4. In Experiment 2, the dietary treatment did not affect growth performance or abdominal fat weight. Nitrogen excretion was significantly lower in chicks given the 150 g/kg CP diet than those on the 170 g/kg CP diet; however, nitrogen retention was no different among the treatments. Dietary CP and enzyme supplementation did not significantly affect hepatic enzyme activities. 5. These results suggest that CP content in the broiler diet can be reduced by 20 g/kg without lowering performance by the supplementation of crystalline amino acids, and can reduce nitrogen excretion by about 25%. Cellulase supplementation of a low-CP diet slightly lowered abdominal fat deposition; however, it did not significantly affect hepatic lipogenic and lipolytic enzyme activity.

Glycine supplementation to low protein, amino acid-supplemented diets supports optimal performance of broiler chicks

Six experiments were conducted to determine the effects of low CP in diets for broilers and to evaluate limiting essential and nonessential amino acids (AA) in these diets. All experiments were conducted with Ross x Ross broilers in brooder batteries from 0 to 17 or 18 d posthatch. Treatments were replicated with 6 pens of either 5 or 6 broilers each. In Experiment (Exp.) 1, corn-soybean meal diets were formulated to 16.18, 17.68, 19.18, 20.68, or 22.18% CP. The 22.18% CP diet provided 1.23% Lys and 0.89% TSAA, met or exceeded all nutrient requirements of young broilers, and served as the positive control (PC) diet in all experiments. Increasing dietary CP linearly increased final BW, daily gain (ADG), and gain:feed (G:F) (P < 0.005). In Exp. 2, additions of crystalline essential (EAA) or nonessential AA (NEAA) were added to the low CP diet to simulate the AA profile of the PC. Daily gain, final BW, and G:F were decreased (P < 0.01) when CP was reduced, but the addition of the NEAA increased final BW, ADG, and G:F (P < 0.07) to the level of broilers fed the PC. Addition of EAA alone was without effect. In Exp. 3, chicks fed diets with supplemental Glu, Ala, Asp, or Pro had reduced daily feed intake (ADFI), ADG, and final BW (P < 0.05) compared with the PC diet. Addition of Gly or the combination of Gly, Glu, Asp, Ala, and Pro to the low CP diet increased G:F (P < 0.01) compared with chicks fed PC, and ADG was not different from that of broilers fed the PC diet. In Exp. 4, chicks were fed either the PC diet, the low CP diet with Gly + Ser concentrations of 1.23, 1.35, 1.47, 1.59, 1.71, 1.83, 1.95, or 2.07%, or a 10th diet that contained 1.23% Gly + Ser and with Glu to equal the N concentration of the 2.07% Gly + Ser diet. Final BW, ADG, and G:F were increased linearly (P < 0.001) as the concentration of dietary Gly + Ser was increased. Chicks fed the low CP diet with 2.07% Gly + Ser had growth performance that was not different from that of chicks fed the PC. The addition of Glu to the low CP diet was without effect. In Exp. 5, chicks were fed the PC with additions of 0, 0.15, or 0.30% Gly or the low CP diet containing 1.60, 1.72, 1.84, 1.96, 2.08, 2.20, or 2.32% Gly + Ser. Glycine addition to the PC had no effect, but Gly addition to the low CP diet increased G:F linearly (P < 0.001). Growth performance of chicks fed the low CP diet with 2.32% Gly + Ser was equal to that of chicks fed the PC diet. In Exp. 6, chicks were fed the PC or the low CP diet containing 1.80, 1.95, 2.10, 2.25, 2.40, 2.55, 2.70, 2.85, or 3.00% Gly + Ser. Glycine addition to the low CP diet increased G:F linearly (P < 0.001). In summary, low CP diets result in optimal growth of broilers with Gly + Ser levels of 2.44%.

Dietary glycine needs of broiler chicks

Dietary Gly might become a limiting factor in all-vegetable diets fed to broiler chicks when low CP is formulated in combination with marginal levels of dietary Thr and Ser. A study was conducted to evaluate dietary Gly needs of broiler chicks. Day-old Ross 508 male chicks were placed in 32 floor pens (15 chicks/pen). Chicks were fed a common prestarter diet from 0 to 7 d of age and then fed a diet that contained progressive amounts of dietary Gly ranging from 0.62 to 1.22% from 7 to 20 d of age. Treatment effects were observed for weight gain and feed conversion. Chicks responded in a quadratic manner to supplementation with dietary Gly. The dietary Gly level necessary to support maximum growth and feed conversion for the chick from 7 to 20 d of age was estimated to be at 0.98 (1.76% Gly + Ser) and 1.02% (1.80% Gly + Ser), respectively. Plasma Thr and Ser were unaffected by Gly supplementation, but plasma free Gly increased linearly. Dietary Gly may need to be considered as a limiting nutrient in early nutrition, especially if CP is low, and only vegetable ingredients are being used.

Efeito da Suplementação de Metionina Sobre o Desempenho e a Avaliação de Carcaças de Frangos de Corte

Um experimento foi conduzido para avaliar os efeitos da suplementação de metionina em dietas de crescimento (22 a 42 dias de idade) sobre o desempenho, rendimento e composição química da carcaça de frangos de corte. Foram utilizados 2000 frangos de corte da linhagem comercial Ross, sexados, distribuídos em um delineamento ao acaso, em esquema fatorial 2 x 5 (sexo e níveis de metionina) com quatro repetições de 50 aves cada. As dietas foram formuladas para conter 100% ,110%, 120%, 130% e 140% dos níveis de metionina recomendados pelo NRC (1994). Aos 42 dias de idade, as aves foram abatidas para avaliar a quantidade de gordura abdominal, bem como o rendimento e a composição química da carcaça. Ao aumentar o nível de metionina da dieta, não houve efeito (p> 0,05) sobre o ganho de peso, consumo de ração, conversão alimentar, mortalidade, gordura abdominal, e rendimento de carcaça, bem como, umidade, proteína, gordura e cinzas do peito e pernas. Não foi verificado efeito (p>0,05) de interação entre nível de metionina e sexo, mas as fêmeas apresentaram maior percentual de gordura abdominal (p<0,05) que os machos. Como o nível de metionina não afetou o desempenho, rendimento e composição química da carcaça, concluiu-se que a recomendação sugerida pelo NRC (1994) de 0,38% para frangos de corte no período de 22 a 42 dias de idade está adequada.

Efeito da Energia, Relação Energia: Proteína e Fase de Crescimento Sobre o Desempenho e Composição de Carcaça de Frangos de Corte

Dois experimentos (EXP) avaliaram os efeitos da redução de proteína bruta (PB) em dietas com alta (A) (3.200kcal EM/kg) e baixa (B) (2.900kcal EM/kg) energia, sobre o desempenho e composição de carcaças de frangos de corte machos. Os níveis de PB foram reduzidos para obter as relações energia: proteína (E:PB) 139, 146, 153 e 160 (kcal/%) para as dietas iniciais (EXP 1), e 160, 167, 174 e 181(kcal/%) para as dietas de crescimento (EXP 2), em ambos os níveis de energia, mantendo constantes os níveis de MET+CIS e LIS. Todas as aves receberam uma mesma dieta antes (EXP 2) ou após (EXP 1) o fornecimento das dietas experimentais. O fornecimento das dietas A proporcionou melhor desempenho, no entanto resultou em maior deposição de gordura nas carcaças. No EXP 1, as aves alimentadas com as dietas B apresentaram ganho de peso (GP) similar àquelas alimentadas com as dietas A no período total (1 a 42 dias), porém melhor conversão calórica (CC) (kcal/kg) (p<0,01). Foi observada também melhor CC, com relação E:PB 139. Menores níveis de PB dietética resultaram, algumas vezes, em um menor GP, porém sempre foi verificada uma pior CC nas relações mais amplas E:PB. Em ambos os Experimentos (EXP), o maior nível de energia e a redução da PB dietética melhoraram a utilização da PB consumida.

Protein and body weight accretion of chicks on diets with widely varying contents of soyabean meal supplemented or unsupplemented with its limiting amino acids

1. Two studies were conducted to evaluate the effects of relative deficiencies of methionine and threonine on the growth performance of 8- to 21-d-old chicks fed on isoenergetic diets containing a wide range of crude protein (CP) concentrations from dehulled soyabean meal (SBM). 2. Chicks fed on graded levels of SBM containing supplemental methionine and threonine (BAL) accreted whole-body protein more efficiently (P < 0.05) than those receiving graded levels of unsupplemented SBM (DEF), and superior (P < 0.05) growth performance was also obtained at lower CP levels when chicks were fed on the BAL diets. 3. Voluntary food intake increased between 30 and 220 g CP/kg in chicks fed on DEF diets, whereas food intake of chicks fed on BAL diets increased only between 30 and 100 g CP/kg, after which it decreased between 100 and 220 g CP/kg. 4. Protein efficiency ratio (g gain per g protein intake) decreased with each incremental increase in CP between 30 and 260 g CP/kg, regardless of whether diets were BAL or DEE 5. These data indicate that maintaining a balanced ratio of amino acids is a preferable approach when poultry producers are interested in employing low CP diets for economic, physiological or environmental reasons.

The effect of dietary crude protein on growth, ammonia concentration, and litter composition in broilers

An experiment was conducted to determine the effect of diets with reduced CP and supplemental amino acids on broiler performance, N excretion, litter characteristics, and equilibrium NH3 gas concentration. Results suggest that reducing CP (and lysine) below 241 g/kg (13.7 g/kg lysine) in the diets fed during the first 3 wk may slightly increase feed:gain and therefore may not be advisable. During the period 22 to 43 d of age there were no significant differences in weight gain and BW at 6 wk of age when reducing CP from 215 g/kg (11.5 g/kg lysine) to 196 g/kg (11.3 g/kg lysine), but feed intake and feed:gain ratio increased. However, reducing CP did cause equilibrium NH3 gas concentration and litter N to decline by 31 and 16.5%, respectively. Both of these advantages will improve air quality within the housing facility and possibly reduce heating costs during winter associated with higher ventilation rates required to reduce elevated NH3 gas concentrations.

Effects of dietary protein content, addition of nonessential amino acids and dietary methionine to cysteine balance on responses to dietary sulphur-containing amino acids in broilers

1. Two experiments were conducted with male broiler chicks from 2 to 5 weeks of age to determine the effect of dietary protein content and amino acid balance on the response to dietary sulphur-containing amino acids (SAA) in terms of performance and carcase quality. 2. In experiment 1, 5 graded amounts of a DL-methionine and L-cysteine (1:1 by weight) mixture were added to basal diets containing 197 or 233 g crude protein/kg. The diets containing 197 g protein/kg were fed with or without the further addition of 36 g crude protein/kg from nonessential amino acids. The amino acid balance of all diets was kept constant for all essential amino acids except the SAA. In experiment 2, 5 graded amounts of SAA from either a crystalline source (DL-methionine or a mixture of DL-methionine and L-cysteine) or from intact proteins were added to a diet containing 208 g protein/kg. 3. At each protein concentration there were significant responses to the SAA addition in weight gain, food conversion efficiency, and carcase quality. Non-linear exponential regression analyses were used to describe bird responses to SAA concentration. The broiler chick's requirement for SAA increased with increasing dietary protein concentrations ranging from 197 to 259 g protein/kg. 4. The utilisation of SAA differed also with differences in origin (crystalline or peptide-bound), and methionine:cysteine balances. Compared to DL-methionine, a 1:1 mixture of DL-methionine and L-cysteine was only 81% or 86% as effective in supporting growth or food conversion, respectively. SAA from added protein was even less effectively utilised. 5. The addition of nonessential amino acids tended to decrease food intake without affecting SAA utilisation. 6. Slaughter yield and breast meat yield were clearly increased while fat deposition was clearly decreased, by SAA addition. The response in breast meat yield suggested an important economic benefit for further meat processing. Nitrogen retention was significantly enhanced by SAA supplementation from crystalline sources, and this led to reductions of up to 30% in the amount of nitrogen excreted per kg weight gain.

Maximum nutritional response to poor-quality protein and amino acid utilisation

1. Although the theory of responses to amino acids suggests that, providing sufficient of the limiting amino acid is fed, it should be possible to elicit maximum growth response, maximum response is not usually elicited by poor quality proteins. 2. It has been suggested that this failure to elicit maximum response is a reflection of poorer limiting amino acid utilisation from poor-quality proteins. This interpretation conflicts with the theory of general amino acid imbalance which proposes that amino acid excesses do not impair the utilisation of the limiting amino acid. 3. Three protein mixtures of different quality were made by mixing maize gluten meal and soyabean protein concentrate in constant proportions, supplementing with tryptophan, threonine and arginine to adequacy and varying amino acid score (0.62, 0.71 or approximately 10) by varying additions of free lysine. The 3 mixtures were diluted with protein-free ingredients to produce 3 diet series, each providing 3.7, 6.5, 9.2, l2.0, 14.8 and 17.5 g lysine per kg. Each diet was fed to 4 cages of 2 chickens each from 4 to 14 d of age in a randomised block experiment. Food intake, body-weight and body-nitrogen gain were measured. 4. Differences in protein quality were confirmed by regression analyses of bodyweight response to protein intake (Net Protein Ratio) and body-nitrogen response to nitrogen intake (Net Protein Utilisation) in the linear range. Regression analyses in the linear range of body-weight or body-nitrogen response to lysine intake showed no adverse effect of protein quality on lysine utilisation. Curvilinear analysis (Reading flock response model) confirmed this finding. 5. Maximum response could not be obtained with the poorest protein quality. It is illogical to invoke impaired utilisation of the limiting amino acid to explain this. A small decrease in net energy yield of the diet may be sufficient to explain the effect, but it is more likely that the depletion of the limiting amino acid from tissue (muscle) protein which results from feeding poor-quality protein explains the effect.

Effect of dietary protein, essential and non-essential amino acids on the performance and carcase composition of male broiler chickens

1. The present study was conducted to determine the possibility of using low-protein broiler diets supplemented with synthetic amino acids. The effects on performance, carcase composition and nitrogen retention were evaluated. 2. A starter diet was given, ad libitum, from 7 to 21 and a finisher diet from 21 to 42 d of age. Body weight, weight gain, food intake and food conversion (FC) were determined at 3 and 6 weeks of age. Abdominal fat deposition (AFD), carcase yield, carcase fat and protein and nitrogen retention were determined at 6 weeks of age. During the starter period chicks were given a 231 g/kg crude protein (CP) diet and a low protein diet supplemented with synthetic amino acid, a: to National Research Council recommendations, b: to the concentration of the control diet, and c: in agreement with the pattern of body composition. Glutamic acid and glycine were added to some diets as sources of non-essential amino acids (NEAA). All diets contained 12.62 MJ metabolisable energy (AMEn)/kg. The diets administered between 3 and 6 weeks were comparable to the starter diets, except that they contained more AMEn (12.85 MJ/kg) and less protein. 3. Performance equal to that of high protein controls was obtained with birds fed a low protein diet supplemented with synthetic essential and NEAA to the amounts in the control diet or based on the amino acid profile of body protein. This was not achieved with low protein diets supplemented with synthetic amino acids to the amounts recommended by NRC. 4. Without altering performances, the efficiency of protein utilisation of birds fed on low protein diets was superior to that of birds fed on the commercial control diet and their nitrogen excretion was reduced by 26%. The percentage carcase yield and protein was unaffected by the dietary regimen but carcase fat content and AFD increased as the protein content of the diet decreased. 5. These results show that it is possible to obtain the same performances with low protein diets supplemented with synthetic amino acids, using an ideal amino acid balance. However, low protein diets result in a higher carcase fat content.

Effects of dietary sulfur amino acids and crude protein on the performance of finishing broilers

The effects of different combinations of dietary methionine + cystine (Met + Cys) and dietary crude protein (CP) in finishing broilers were investigated in two growth studies. In Exp. 1, male broilers 29 to 42 days of age were fed 18 diets containing 16.9%, 18.7%, or 20.4% CP with six levels of Met + Cys within each protein level. Similarly, in Exp. 2 another 12 diets containing either 18.0 or 21.5% CP were fed to male broilers 29 to 48 days of age. In general, the Met + Cys requirement for optimum feed conversion was higher than for maximum growth. In both experiments, between 0.80% and 0.85% methionine + cystine optimized feed conversion. These dietary levels were valid for a 13.05 MJ ME/kg diet fed to broilers growing from 1.2 kg to 2.2 kg (Exp. 1), or for a 13.60 MJ ME/kg diet fed to broilers growing from 1.3 kg to 3.0 kg (Exp. 2). The Met + Cys requirement was not consistently affected by the dietary CP content in Exp. 1. In Exp. 2, increasing dietary CP from 18.0% to 21.5% tended to increase the Met + Cys requirement for optimum feed conversion. A dietary CP level of 18.0% to 18.7% supported performance and carcass fat deposition equal to diets containing 20.4% or 21.5% CP, respectively, when the sulfur amino acid content was adequate.

Amino acid fortification of a low-protein corn and soybean meal diet for chicks

Seven experiments were conducted to investigate whether a 19% CP corn and soybean meal (CS) diet could be fortified properly with amino acids (AA) to produce performance in 1- to 3-wk-old chicks equal to that obtained with a 23% CP, CS diet supplemented with Met. In one experiment, the assay was carried out to 6 wk of age. During 4- to 6-wk posthatching, the positive control was a 20% CP, CS diet with added Met and the low-protein diet was a 16% CP, CS diet fortified with limiting AA. The two most limiting AA in the low-protein diet (19% CP) were found to be Met and Lys. Arginine, Val, and Thr were observed to be limiting as well. Weight gain and feed efficiency were substantially increased and body fat content decreased when the low-protein diet was supplemented with the five limiting AA and amino nitrogen in the form of Glu. Addition of potassium had no effect on performance of chicks fed the AA-fortified, low-protein diet. With all trials considered together, chicks fed the low-protein diet fortified with the five limiting AA and Glu gained at the same rate with similar feed efficiency and had estimated body fat levels comparable to birds fed the 23% CP, positive control diet. From 3 to 6 wk of age, chicks fed the AA-fortified, 16% CP diet had growth performance similar to chicks fed the 20% CP, positive control diet.

Broiler weight gain and carcass composition when fed diets varying in amino acid balance, dietary energy, and protein level

Three experiments were conducted with broiler chicks where diet composition varied with respect to dietary protein, energy, and essential amino acid (EAA) balance. Birds fed diets varying widely in EAA balance and protein and energy levels performed differently with respect to percentage carcass fat and protein. The absolute carcass protein deposition remained relatively constant between treatments, but body fat content varied depending on level of energy intake. Although abdominal fat content varied with level of dietary protein and energy, these values did not correlate well with total carcass fat deposition. Carcass fat deposition correlated well with dietary energy intake, which in turn appeared to be influenced by birds eating to satisfy their EAA requirement. With diets of similar EAA balance, birds appeared to have similar EAA intakes rather than similar energy intakes. Birds fed diets with similar EAA levels, but varying widely in level of nonessential amino acids, energy, or both consumed similar amounts of feed and deposited similar amounts of carcass protein. The present data suggest that level and balance of EAA can have a significant effect on feed intake, thereby influencing weight gain and carcass composition.