Further studies on the influence of genotype and dietary protein on the performance of broilers

The future of feed formulation for poultry: Toward more sustainable production of meat and eggs

Current methods for feed formulation are based on minimizing costs, not maximizing profits. Complex models of bird growth and reproduction as functions of genetic, feed and other environmental variables are being developed, but their adaptation has been slow. The development of profit maximizing models will evolve to center on the production functions of broilers and layers. The production functions are the relationship between the value of products (mainly meat and eggs) and the cost of feed. The production function is the tool used to maximize profits subject to all the various inputs, not just feed or nutrition. The production function is subject to the law of diminishing returns. The most profitable output levels are those where the marginal value (price) of the meat or eggs is just equal to the marginal cost of the inputs including feed, housing, processing and all other costs. Anything that affects the production function, bird genetics, feed quality, housing and environment, will be considered to maximize profits for the poultry firm. The profit maximizing models of poultry firms will improve as various technical improvements are made: metabolizable energy to describe ingredients will evolve to net energy systems that consider that the heat production (and therefore energetic efficiency) of broilers is different depending on the ingredients used to formulate the feed and the environmental temperatures under which they are reared. Amino acid needs will include a method to find the birds' needs for the non-essential amino acids. "Digestible" amino acid assays will differentiate between digestion and absorption to best balance various sources. The carbohydrate fractions of feed ingredients will be determined to optimize the use of exogenous enzymes. The value of meat and egg co-products will reduce overall costs (e.g., organic fertilizer for crop enhancement). Future profit maximizing production models will be ever evolving processes where field conditions and results are continually being utilized to re-calibrate the technical models so that the management team can use them with cost and return projections to decide on the best choices of inputs and outputs.

Assessment of the inclusion of a feed additive of sodium humate derived from freshwater sapropel in diets for broiler chickens

Background and Aim

Poultry production is the fastest growing livestock industry in the world, as the rapid growth of and efficient absorption of feed by poultry ensure the production of poultry meat with a relatively low carbon footprint. Seeking new ways to increase livestock productivity as well as poultry product quality, the number of research studies on the use of humic substances of various origins in livestock farming has increased significantly, emphasizing the role of feed additives derived from local resources. The unique capability of humic substances to improve metabolic processes allows the immune protection of the bird body to be strengthened and production efficiency to be increased. This study aimed to identify the effects of sodium humate (NaHum) on the growth performance of broiler chickens and selected blood and ileum microbiota parameters.

Materials and Methods

Dietary research was conducted 2 times under production conditions in a poultry facility of a commercial company, with 210 1-day-old, unsorted broiler chickens of both sexes (Ross 308). The broiler chickens were fed with standard commercial feed, the rearing period of 35 days, and slaughtered on day 36. Sodium humate additive was added to drinking water for the research groups of broilers in period from 8th to 35th day of life, 25 mL (Group 1, n = 2 × 35) and 50 mL (Group 2, n = 2 × 35) per liter of drinking water. Sodium humate contained an average of 4.48% dry matter, a kilogram of dry matter containing 104.3 g of crude protein, 3.6 g of crude fiber and 0.9 g of crude fat, 14.3 MJ of metabolic energy, and 5.8 MJ of energy for live weight gain, as well as a very high content of crude ash -759.8 g, including 4.2 g Ca, 4.2 g Na, and 4.81 g Fe, the dry matter digestibility of NaHum was 87.0%, and the absorption capacity of dry matter was 113.2%., the pH level was 13.0, i.e., alkaline. At the end of the dietary research, the productivity and economic efficiency of the research groups of broilers were calculated by live weight gain, carcass weight, feed conversation ratio, and blood and intestinal samples of broilers were analyzed to identify the effects of NaHum on the growth performance and health status of broilers.

Results

Dietary research found that adding 25 mL/L and 50 mL/L of NaHum to drinking water for the broiler chickens increased their live weights at the selling age, average live weight gains by 3.06-3.93%, and carcass weights by 5.07-6.06%, while feed conversion increased in terms of both live weight (1.5 and 1.51) and carcass weight (1.84 and 1.86) compared with the control group. The best economic performance in terms of the economic efficiency index and the cost index (CI) was found in Group 1, which was fed with the NaHum additive at an intake rate of 25 mL/L. The NaHum additive modulated the ileal microbiota and metabolic processes in the broiler body. At the same time, a significant decrease in the levels of total protein, alkaline phosphatase and phosphorus (P) in blood was found in the research groups.

Conclusion

Considering the positive effects of NaHum derived from freshwater sapropel on the productivity and economic efficiency of broiler chickens, the NaHum feed additive should be further investigated on a larger scale to obtain results that could reasonably be used in practice. This study concluded that a decrease in P levels in the blood was observed when NaHum was added to the drinking water; therefore, it is important to continue the research to draw reasonable conclusions on the effects of NaHum in liquid form on the health performance of farm animals.

Characterization of growth patterns and carcass characteristics of male and female broilers from four commercial strains fed high or low density diets

Over the last few decades, the poultry industry has seen the emergence of various market segments that are beneficial for rearing various flock sizes. Two concurrent experiments consisting of 1,200 broilers each were conducted to evaluate the effects of broiler size and diet on the performance of four commercially available broiler strains, including 2 standard yielding (SY) and 2 high yielding (HY) strains. Within each experiment (Experiment 1: males, Experiment 2: females), a small bird (38 and 40 d processing) and big bird (47 and 54 d processing) debone market were targeted to give variable carcass size. Two polyphasic diets were fed based on varying of amino acid densities. The low-density diet (L) consisted of 1.20, 1.10, 1.00, and 0.96% digestible Lys and the high-density diet (H) consisted of 1.32, 1.21, 1.10, and 1.06% across the 4-phases, respectively, with similar essential amino acid to digestible Lys ratios between the L and H diets in each phase. Weekly BW, BW gain, feed intake, and feed conversion ratio were assessed, as well as processing yields during both experiments. Broilers fed the H diets responded better than those fed the L diets, regardless of sex, with increased BW and decreased FCR (P < 0.05). Male HY strains provided the highest carcass yields (P < 0.05) compared to SY strains, with no differences observed in females (P > 0.05). High density diets (Diet H) also produced increases in carcass, breast, and tender yield (P < 0.05) for males, but that trend was not present in carcass yield for females (P < 0.05). Overall, strain impacted performance traits and carcass yields. Therefore, the use of specific strains and amino acid density for various market segments is beneficial for integrators to maximize return.

Multiple Amino Acid Supplementations to Low-Protein Diets: Effect on Performance, Carcass Yield, Meat Quality and Nitrogen Excretion of Finishing Broilers under Hot Climate Conditions

The objective of this study was to evaluate the effect of low-protein diets with amino acid supplementation on growth performance, carcass yield, meat quality and nitrogen excretion of broilers raised under hot climate conditions during the finisher period. In trial 1, broilers from 28 to 49 days of age were fed 18% crude protein (CP) as a positive control or 15% CP supplemented with (1) DL-methionine (Met) + L-lysine (Lys), (2) Met + Lys + L-Arginine (Arg), or (3) Met + Lys + L-Valine (Val). In trial 2, broilers from 30 to 45 days of age, were fed an 18% CP diet as a positive control or 15% CP supplemented with Met, Lys, Arg, Val, L-Isoleucine (Ile) or combination with glycine (Gly) and/or urea as nitrogen sources: (1) Met + Lys, (2) Met + Lys + Arg, (3) Met + Lys + Val, (4) Met + Lys + Ile, (5) Met + Lys + Arg +Val + Ile + Gly, and (6) Met+ Lys + Arg + Val + Ile + Gly + urea. Protein use was improved by feeding low-protein amino acid-supplemented diets as compared to the high-protein diet. Feeding 15% crude protein diet supplemented with only methionine and lysine had no negative effects on carcass yield, CP, total lipids and moisture% of breast meat while decreasing nitrogen excretion by 21%.

Response of two broiler strains to four feeding regimens under hot climate

In total, 392 male broilers were randomly distributed in a factorial arrangement of 2 × 4, with two commercial broiler strains (Arbor Acres (AA) and Hubbard (Hub)) and four (NRC, Degussa, CVB, and strain guides) different feeding regimens (FR), totaling eight treatments and seven replicates, with seven broilers in each one. The following parameters were evaluated: bodyweight gain (BWG), feed intake (FI), feed conversion ratio (FCR), carcass yield, meat quality, nutrient intake, and its correlation with BWG. Interaction strain type × FR was significant for BWG, FI, and FCR, with the AA broilers showing higher BWG and FI and lower FCR than the Hub broilers. There was no difference in BWG, FI, and FCR of the AA broilers regardless of FR they were on, but the Hub broilers had lower BWG when they were fed according to the Degussa and CVB regimens; BWG and FCR were negatively affected. During the starter phase, BWG of the AA broilers was significantly correlated with feed, metabolisable energy (ME), lysine, and sulfur amino acids (SAA) intake. However, BWG was correlated with feed and ME intake and feed intake from 1 to 31 and from 1 to 42 days of age, respectively. In the Hub chicks, ME and crude protein intake and lysine and SAA intake were inversely correlated with BWG from 1 to 31 days and from 1 to 42 days of age, respectively. There was no significant effect of FR on dressed carcass weight or relative gizzard, pancreas, and liver weights and on intestinal weight; however, abdominal fat and spleen differed significantly with FR. Strain type significantly affected the relative weight of the intestines. There was no significant effect of FR and/or strain type on meat moisture, crude protein, lipid and ash content, or pH, colour, meat juiciness and tenderness (meat softness). In conclusion, AA strain of broiler performed better than the Hub strain under the different FR in all the evaluated production phases, but neither FR nor strain type affected carcass characteristics.

Partition of metabolizable energy, and prediction of growth performance and lipid deposition in broiler chickens

The study presented here consisted of the calculation of cross relationships between growth performance parameters, body growth composition, and feed characteristics, using data from an experiment reported in 2 previous publications. In the previous experiment, 30 pelleted diets were given to broiler chickens (8/diet) (21 to 35 d) for in vivo measurement and prediction of AMEn and net energy (NE) values of diets, using 3 trials with 10 diets/trial. In the course of NE determination, individual values for growth, feed intake, and deposition of lipid and protein were measured. Average energy deposited as lipid and protein represented 25.4 and 19.1% AME intake, respectively. Using a multiple regression predicting AME intake, the partial efficiencies of AME for energy deposition as lipid and protein were calculated to be 91.6 and 67.3%, respectively, and the daily amount of AME required for maintenance was evaluated at 0.683 MJ/kg BW0.7. The mean diet NE/AMEn ratios were predicted by an equation combining the lipid content of body growth (positive coefficient) and the apparent digestible protein (ADP) to AMEn ratio (ADP/AMEn), with a quadratic expression for the latter variable. This quadratic response expressed a positive asymptotic relationship, with a plateau for ADP/AMEn values above 1.45 [%/(MJ/kg)]. The equations predicting growth always included either the dietary percentage of water-insoluble cell wall or the AMEn value. The other major parameters predicting growth were either the lipid content of body growth or the CP/AMEn ratio. In many cases, quadratic responses were observed in growth prediction equations. Regressions predicting feed efficiency showed only linear responses. Feed efficiency was predicted precisely by multiple linear regressions based only on AMEn and a dietary protein parameter. According to these regressions, 1% CP was equivalent to 0.247 MJ/kg AMEn in terms of feed efficiency. The most efficient regression predicting the individual lipid content of body growth combined the protein efficiency value (negative coefficient), the CP/AMEn ratio (negative coefficient), AMEn (positive coefficient), and the feather content of body growth (positive coefficient).

Does the Naked Neck Meat Type Chicken Yield Lower Methionine Requirement Data?

Simple Summary

It was hypothesized that naked neck chickens could have a lower methionine requirement according to their reduced feather coverage. The hypothesis was examined by nitrogen balance studies and non-linear model application for estimating methionine requirement data of naked neck chickens. It was concluded that naked neck birds do not require less methionine than normally-feathered birds.

Abstract

Methionine (Met) requirement studies with homozygous (Na/Na) and heterozygous (Na/na) naked neck meat type chicken utilized 144 birds of average weight (50% each genotype and sex) within two N balance experiments involving both the starter (d10–20) and grower period (d25–35). The birds were randomly allotted to five experimental diets with graded protein supply and Met as the limiting amino acid. The proportion of native feed protein sources (soy protein concentrate, maize, wheat, fishmeal and wheat gluten) was kept constant to ensure a uniform protein quality in all diets. The Met requirement depending on genotype, sex, age period and growth performance (protein deposition) was estimated using a non-linear modeling procedure of N utilization in monogastric animals. On average, 0.47% (Na/Na) and 0.45% (Na/na) dietary Met was established as adequate in the starter diet, as well as 0.37% (Na/Na) and 0.36% (Na/na) Met in the grower diet for both of the sexes. In conclusion, the Met requirement of the naked neck chicken is not significantly different from its normally-feathered counterparts. In addition, the low feather production was not reflected by reduced requirement for Met in naked neck birds. However, these conclusions are valid only at the given Met:Cys ratio (1:1) in the experimental diets.

Nutrient density and slaughter age have differential effects on carcase performance, muscle and meat quality in fast and slow growing broiler genotypes

1. A 2 × 2 factorial design was used to investigate the differences in carcase, muscle and meat characteristics between fast and slow growing genotypes fed on low nutrient (LND) or high nutrient diets (HND) at their respective slaughter ages. 2. The birds were randomly assigned to treatments with 5 replicates of 145 birds for Wens Yellow-Feathered Chicken (WYFC, 5·75 birds/m(2)) or 115 birds for White Recessive Rock Chicken (WRRC, 7·25 birds/m(2)), according to the commercial recommendations for the two breeds and were fed on HND or LND. Birds were slaughtered at 63 d and 105 d of age. 3. The results showed WRRC had higher carcase yield and meat yield than that of WYFC, lower fat content, higher moisture content and lower cooking loss. The meat from WRRC was less tender and contained lower levels of polyunsaturated fatty acids (PUFA). 4. Birds fed on HND had higher breast meat yield, myofiber area and protein content in the breast muscle and lower fat content than birds fed on LND. The thigh muscle of birds fed on HND had higher levels of PUFA. Age had a positive effect on carcase parameters, but a negative effect on pH, meat tenderness and cooking loss, and the two genotypes exhibited different responses to the influence of nutrient density and age. 5. Genotype and age had the largest effect on carcase performance and meat quality. LND benefited meat quality and WRRC had larger responses in meat yield and shear force when fed on HND.

Genetic variability of metabolic characteristics in chickens selected for their ability to digest wheat

Improving feed efficiency remains crucial for poultry production. Birds have previously been selected on their ability to digest their diet, as assessed by AMEn (Apparent ME corrected for 0 nitrogen). Such selection, for either a high (D+) or a low AMEn (D-), affects energy, nitrogen, lipid, and starch digestibility. The aim of this study was to establish whether selection on the digestive ability of birds modified metabolic traits. A total of 630 broiler chickens of the eighth generation of a divergent selection experiment on AMEn were used for this purpose. A balance trial was performed to determine energy, nitrogen, and phosphorus retention. Growth performance was recorded and body protein and lipid deposition assessed by breast and abdominal fat yields. Tibia development and mineralization were also studied and heat production was indirectly assessed through the measurement of body temperature during fasting and feeding. Phenotypic correlations estimated within line showed that an increased efficiency was associated to fatter birds and more solid bones in D- but not in D+ line, whereas increased consumption was associated with more solid bones in D+ but not in D- line. The heritability estimates for metabolic traits were relatively high, except for temperature traits (from 0.08 to 0.12), ranging from 0.28 to 0.56 for body composition, and from 0.38 to 0.77 for bone characteristics. Breast meat yield did not differ between the 2 lines whereas a slight increase in abdominal fat yield was observed in the high-digestion line (D+). The relative dry tibia weights and ash weights were greater in D+ birds (+6.56 and +8.06%, respectively) but the lengths and the diameters of the tibia were lower (-7.89 and -3.77%, respectively). Finally, AMEn was poorly correlated with almost all metabolic traits (ranging from -0.10 to 0.20), indicating that the ability of the animal to digest its diet is genetically independent of post-digestion metabolic traits.

Effect of different levels of amino acids on carcass composition and yield in broilers

An experiment was conducted to evaluate the carcass yield and composition of 200 Arian male broilers fed diets (starter and grower) with different levels of amino acids requirements (high, medium, standard and low amino acids) in a completely randomised experimental design. All diets were isocaloric and isonitrogenous. Increased proportion of breast and thigh to bodyweight ratio were also obtained by increasing the level of amino acids from standard to high amino acids at 42 days of age (P < 0.05). In broilers receiving 120% of National Research Council amino acids, bodyweight at 42 days of age increased significantly by 202 g compared with standard amino acids diet. Feeding broilers with a high amino acid diet significantly (P < 0.05) increased carcass, breast, thigh and abdominal fat weights compared with standard group. Treatment with high amino acids had significantly higher levels of crude protein, lysine, and methionine percentage of breast and thigh meat in Arian broilers. The results of this study suggest that additional amino acids in starter and grower diets optimised bodyweight gain in Arian broiler, whereas reductions in amino acid levels reduced growth and liveweight.

Dietary balanced protein in broiler chickens. 1. A flexible and practical tool to predict dose–response curves

An empirical model of exponential form was developed, different versions of which can be used to predict growth rate, feed conversion and carcase and breast meat yield of broiler chickens as a function of dietary balanced protein (DBP) content. The model was developed to support decision-making by nutritionists. The model helps in determining DBP contents that maximise profit. The model avoids the practical disadvantages of existing methods. In contrast with mechanistic models, only data that are generally known by broiler nutritionists are required as input. Compared with predictions derived from one or a few feeding trials, the model predictions are more accurate (because the model was derived from many data-sets) and more flexible (because a description of the type of broiler was included as input for the model). Broiler response studies from the literature and the Nutreco Poultry and Rabbit Research Centre (27 data-sets in total) were used in the model development to select significant variables, to quantify the parameters and to evaluate the accuracy of the predictions. Input variables were DBP content, maximum performance level, age, year (indicating genetic potential) and sex. The model, including the assumption that the shape of the dose-response curves to DBP content is independent of broiler and feed characteristics, gave an accurate simulation of growth rate, feed conversion and breast meat for nearly all data-sets. Effects of DBP content on carcase yield were relatively small, except for carcases without skin and skin fat.

Dietary Nitrogen Intake Regulates Hepatic Malic Enzyme Messenger Ribonucleic Acid Expression

Increased dietary protein intake rapidly (3 h) decreases malic enzyme and increases hepatic histidase mRNA expression. Experiments were conducted to determine the role that individual dispensable amino acids and nonprotein N sources might have in regulating the activity of these enzymes and to determine if the addition of a N supplement to a practical broiler diet during the entire rearing period would reduce abdominal fat accumulation in broilers. Broiler chicks were fed a basal diet containing 22% protein or this diet supplemented with 9.5% l-Glu, 5% Gly, 6% l-Ala, 5.08% ammonium bicarbonate, or 4.25% dibasic ammonium phosphate for 24 h. Each of the dietary supplements added 0.90% total N to the diet. Hepatic malic enzyme mRNA expression was significantly (P < 0.05) depressed in chicks fed any of the supplemented diets compared with chicks fed the basal diet. Histidase mRNA expression, however, was only significantly increased in the chicks fed the basal diet supplemented with Gly. Broilers fed practical corn-soybean meal starter and developer diets supplemented with 2.3, 4.7, or 9.5% Glu from 0 to 40 d of age had significantly smaller abdominal fat pads relative to BW than broilers fed the unsupplemented corn-soybean meal diets. Feeding the Glu supplements, however, reduced the overall BW gain of broilers by 100 to 150 g compared with broilers fed the unsupplemented diets. The results suggest that hepatic mRNA expression of malic enzyme may be regulated by total dietary N intake, whereas hepatic mRNA expression of histidase may be regulated by specific amino acids.

Threonine Requirement of Slow-Growing Male Chickens Depends on Age and Dietary Efficiency of Threonine Utilization

Nitrogen-balance experiments were conducted with a total of 288 male chickens to assess Thr requirement data on 2 commercial slow-growing genotypes (I 657 and Red JA from Hubbard ISA) by use of a modeling procedure described previously. Six graded levels of dietary protein supply from high-protein soybeanmeal were used within 4 age periods (period I: 10 to 25 d; period II: 30 to 45 d; period III: 5 to 65 d; and period IV: 70 to 85 d). The provided dietary amino acid ratio (Lys:Met+Cys:Thr=1:0.85:0.54), with 3.87% Thr in the feed protein, identified Thr as the first limiting dietary amino acid. The nitrogen maintenance requirement (NMR) was established by exponential approximation of N excretion depending on N intake (on average, NMR=173 mg of N/BWkg0.67 per d). The theoretical maximum for daily N deposition was estimated by the Levenberg-Marquardt algorithm (SPSS program, version 11.5) and by exponential fitting of N balance data depending on N intake. The observed dietary Thr efficiency was used to model Thr requirements for a given protein deposition depending on age. The optimal dietary Thr concentration (percentage of feed) was established by different predictions for daily feed intake. Daily CP deposition of approximately 60% of the potential required 0.83 and 0.87% (10 to 25 d), 0.73 and 0.75% (30 to 45 d), 0.66 and 0.69% (50 to 65 d), and 0.51 and 0.53% (70 to 85 d) of Thr in feed for genotype I 657 and genotype Red JA, respectively (average daily feed intakes of 30, 75, 100, and 100 g in age periods I to IV). Results of model calculations need verification in comparative growth studies with assessment of nutrient deposition and varying dietary Thr efficiencies.

Modeling of Threonine Requirement in Fast-Growing Chickens, Depending on Age, Sex, Protein Deposition, and Dietary Threonine Efficiency

In addition to dose-response studies, modeling of N utilization, depending on intake of the first limiting amino acid in the diet, is one of the tools for assessing amino acid requirements in growing animals. Based on a verified nonlinear N-utilization model and following the principles of the diet dilution technique, N-balance experiments were conducted to estimate the Thr requirement of fast-growing chickens (genotype Cobb), depending on age, sex, CP deposition. and efficiency of dietary Thr utilization. Different predictions were made for the feed intake to conclude the optimal Thr concentration in the feed. The results are based on N-balance experiments with a total of 144 male and 144 female growing chickens within 4 age periods (I: 10 to 25 d; II: 30 to 45 d; III: 50 to 65 d; IV: 70 to 85 d), using diets with graded protein supply (6.6, 13, 19.6, 25.1, 31.8, and 37.6% CP in DM) from high-protein soybean meal with a constant amino acid ratio and Thr as the first limiting amino acid (3.87 g of Thr/100 g of CP; dietary Lys:Thr = 1:0.54). The observed optimal Thr concentration (% of feed) was influenced by age, sex, level of CP deposition, dietary efficiency of Thr utilization, and predicted feed intake. For male chickens, assuming an average CP deposition (60% of the potential) and average efficiency of Thr utilization, 0.78% (10 to 25 d), 0.73% (30 to 45 d), 0.65% (50 to 65 d), and 0.55% (70 to 85 d) total dietary Thr were observed as optimal total Thr concentration in the diet (corresponding to 60, 135, 160, and 180 g of daily feed intake, respectively). Data are discussed in context with the main factors of influence like age, sex, level of daily CP deposition, efficiency of dietary Thr utilization, and predicted feed intake.

Estimation of Nitrogen Maintenance Requirements and Potential for Nitrogen Deposition in Fast-Growing Chickens Depending on Age and Sex

Experiments were conducted to estimate daily N maintenance requirements (NMR) and the genetic potential for daily N deposition (ND(max)T) in fast-growing chickens depending on age and sex. In N-balance studies, 144 male and 144 female chickens (Cobb 500) were utilized in 4 consecutive age periods (I: 10 to 25 d; II: 30 to 45 d; III: 50 to 65 d; and IV: 70 to 85 d). The experimental diets contained high-protein soybean meal and crystalline amino acids as protein sources and 6 graded levels of protein supply (N1 = 6.6%; N2 = 13.0%; N3 = 19.6%; N4 = 25.1%; N5 = 31.8%; and N6 = 37.6% CP in DM). The connection between N intake and total N excretion was fitted for NMR determination by an exponential function. The average NMR value (252 mg of N/BW(kg)0.67 per d) was applied for further calculation of ND(max)T as the threshold value of the function between N intake and daily N balance. For estimating the threshold value, the principle of the Levenberg-Marquardt algorithm within the SPSS program (Version 11.5) was applied. As a theoretical maximum for ND(max)T, 3,592, 2,723, 1,702, and 1,386 mg of N/BW(kg)0.67 per d for male and 3,452, 2,604, 1,501, and 1,286 mg of N/BW(kg)0.67 per d for female fast-growing chickens (corresponding to age periods I to IV) were obtained. The determined model parameters were the precondition for modeling of the amino acid requirement based on an exponential N-utilization model and depended on performance and dietary amino acid efficiency. This procedure will be further developed and applied in the subsequent paper.

Performance of Different Broiler Genotypes Fed Diets with Varying Levels of Dietary Crude Protein and Lysine

Two experiments were conducted to determine if a 3-way interaction among genotype, dietary lysine, and CP is an important influence on dietary responses. The genotypes were Ross 308 and Cobb in experiment 1 and Ross 508 and Arbor Acres Classic in experiment 2. The experimental designs were completely randomized with an incomplete 2 x 2 x 3 factorial arrangement of treatments. On d 7 of experiment 1, 4 replicate pens of 6 chicks each were fed 1 combination of dietary lysine and CP (17% CP with 0.6, 0.7, and 0.8% lysine and 23% CP with 0.7, 0.8, and 0.9% lysine) until d 21. On d 17 of experiment 2, 4 replicate pens of 35 chicks each were fed 1 combination of dietary lysine and CP (17% CP with 0.7, 0.8, and 0.9% lysine and 23% CP with 0.8, 0.9, and 1.0% lysine) until d 42. On d 43 of experiment 2, 3 birds per pen were processed. Regression analysis showed differences (P < 0.05) due to genotype for body weight gain (BWG), feed intake, and feed conversion ratio (FCR) in experiment 1, and BWG, carcass yield, breast fillet and tender yields, and abdominal fat pad percentage in experiment 2. Increasing dietary CP decreased abdominal fat pad percentage in both experiments; however, increasing dietary lysine only decreased this parameter in the starter-phase chicks. In both experiments, Ross broilers had a greater response to supplemental lysine when 17% CP was fed, but less response to supplemental lysine when 23% CP was fed for both BWG and FCR (3-way interaction). Three-way interactions between dietary CP and lysine levels and genotype were observed for BWG (P < 0.01), feed intake (P < 0.01), and FCR (P < 0.02) in experiment 1 and for feed intake (P < 0.06) and FCR (P < 0.03) in experiment 2. The 3-way interactions demonstrate that quantitative differences exist between genotypes in response to increasing dietary levels of CP and lysine.

Broiler responsiveness (Ross x 708) to diets varying in amino acid density

Sex-separate male and female broilers (2,592 broilers; Ross x 708) were placed in 144 floor pens (12 replications per treatment) and fed diets containing high (H) and moderate (M) amino acid density from 1 to 55 d of age. Diets were formulated using ileal digestible amino acid ratios to Lys. Six dietary treatment combinations (MMMMM, HMMMM, HHMMM, HHHMM, HHHHM, and HHHHH) were implemented in 5 diet phases (1 to 5, 6 to 14, 15 to 35, 36 to 45, and 46 to 55 d of age). Male birds were heavier (P < or = 0.05) and had lower (P < or = 0.05) feed conversion, abdominal fat, and breast yield than female birds. Birds fed H diets in the first 3 phases had optimal (P < or = 0.05) BW and feed conversion (d 35, and 45), but optimal (P < or = 0.05) feed conversion at d 55 warranted H diets in all phases. Breast meat (d 35) and carcass (d 55) relative to BW were highest (P < or = 0.05) in birds fed H diets in the first 3 phases; however, differences in 55 d breast meat yield did not occur. Results indicate that amino acid needs of Ross x 708 broilers are most critical from 1 to 35 d of age. Predicted economic margins were advantageous in birds fed H diets resulting in dollar 0.12 and dollar 0.05/bird more income over feed costs at 35 and 55 d, respectively, in comparison with birds fed M diets.

Mathematical characterization of broiler carcass yield dynamics

Modeling of broiler chicken supply-chain economics depends on robust biological models of growth and yield of broiler chickens. In this paper, 8 dynamic nonlinear broiler carcass and carcass part yield models were evaluated statistically for their suitability for predicting weights of carcass parts. The analysis employed 4 sigmoidal (S) models (Gompertz, modified Gompertz, Richards, and Lopez) describing carcass part weight as a function of age, as well as 3 diminishing returns (DR) models (Lopez, Mitscherlich, and log linear), and a log-linear proportional yield (PY) model, which describe carcass part yield and weight, respectively, as a proportion of feather- and fat-free empty body mass (FFEBM). Three S models with a flexible point of inflection were better able to predict carcass part weights than a fixed point of inflection Gompertz model and, in general, the DR models. The log-linear models were the only models that converged in 100% of the evaluations. The allometric PY model predicted weights for most carcass parts with the smallest degree of error and with substantially less bias than the DR log-linear model. Estimates of the coefficients for the log-linear PY model are included for 12 key carcass parts. Estimates of carcass chemical composition are presented for the log-linear PY model.

Effect of different dietary ideal protein concentrations on broiler performance

1. The aim of the study was to examine the response of male broilers of different age categories to different dietary ideal protein (IP) concentrations and to compare the effects to IP recommendations based on single lysine (Lys) requirement studies from the literature. 2. Two experiments were carried out, in which diets containing different IP concentrations (9.0 to 14.4g apparent faecal digestible (AFD) Lys/kg) were fed to male broilers from 14 to 34 (Exp. 1) and 28 to 41 d of age (Exp. 2). The diets (12.88MJ AMEN/kg) were prepared by the dilution technique. The effect of dietary IP concentrations on weight gain, feed intake, feed conversion efficiency (FCE) and slaughter characteristics were studied in both experiments. 3. In Exp. 1, weight gain and FCE increased linearly and fat concentration in the carcase decreased with increasing IP concentration. In Exp. 2, weight gain and FCE improved exponentially, whereas breast meat yield improved linearly with increasing dietary IP concentration. On the basis of these results, it was concluded that the weight gain and FCE of male broilers respond to higher dietary IP levels than would be expected from single lysine requirement studies in the literature.

Effects of nutrient density on growth and carcass traits in fast- and slow-feathering female turkeys

Chickens have been sexed based on feather development at hatching for many years, but the slow-feathering gene has only recently been incorporated into a commercial line of turkeys. Female turkeys of a fast- and a slow-feathering strain were compared with regard to BW, gain, and carcass composition to 29 wk of age. A total of 432 fast-feathering (FF) and 432 slow-feathering (SF) poults were reared to 198 d on a control (CON) or a high-energy, high-protein (HIGH) diet. Data concerning BW and carcass characteristics (thoracic circumference and width, shank, keel, breast muscle, fat pad, and liver), feather scores, and breast muscle morphology were assessed over the course of the trial. Strain did not affect BW of the CON-fed birds until after 112 d, when FF birds were 3.1% heavier than SF birds. From 11 to 112 d, feeding the HIGH diet increased BW of SF birds significantly compared with birds fed the CON diet. From 170 to 198 d, FF birds were approximately 0.8 kg heavier than SF birds. At 42 and 84 d in FF birds, and at 84 d in SF birds, increased diet density increased measures of frame size and decreased liver weight. Breast muscle weight, area, and thickness were greater in SF than in FF birds at 42 and 84 d. Increased nutrient density increased feather score in SF birds at 32 (9.8%) and 56 d (7.1%).

Comparison of broiler performance when fed diets containing roundup ready (event RT73), nontransgenic control, or commercial canola meal

A 42-d experiment compared the nutritional value of genetically modified glyphosate-tolerant (Roundup Ready event RT73) canola meal to that of conventional canola meal when fed to rapidly growing Ross x Ross 508 broilers using a randomized complete block design. Five pens of males and 5 pens of females were used in each of 8 canola meal treatments (glyphosate-tolerant, nontransgenic control, and 6 commercial varieties). Broilers (10 birds/pen) were fed approximately 25% wt/wt canola meal during the first 20 d and 20% wt/wt canola meal thereafter. In general, performance response variables for glyphosate-tolerant canola meal were not different (P > 0.05) than those for the nontransgenic and commercial canola meals. Carcass fat pad, breast meat, thighs, legs, and wings (on a percentage basis) were similar across treatments (P > 0.05). Expressed as percentage of live weight, chill weight of the broilers fed diets containing glyphosate-tolerant canola meal was not different from those fed all other diets, but some differences were observed between the nontransgenic control and commercial diets. No major differences were observed in percentage of moisture, protein, and fat in breast or thigh meat (P > 0.05) across treatments. Comparisons of the glyphosate-tolerant canola diet to the population of all other diets (combining sexes) showed no major differences (P > 0.05) in performance, carcass yields, or moisture, protein, and fat in breast and thigh meat. Broilers fed diets containing glyphosate-tolerant canola meal had similar growth performance to birds fed nontransgenic control and commercial canola diets.

Impact of dietary amino acid concentration on growth, carcass yield, and uniformity of broilers

Two studies were conducted to measure the effects of dietary amino acid regimens (high, medium, low) and gender on Arbor Acres Plus broilers. Body weight, feed conversion, mortality, carcass yields, and uniformity served as criteria evaluated. Growth and feed conversion were improved in broilers fed diets with high amino acid concentration until 35 days of age. Yields of some carcass parts were improved up to 35 days of age as diet concentration was increased. Flock uniformity was decreased when dietary amino acid concentration was reduced. Male broilers exhibited faster growth rate, whereas females had improved feed conversion at 28 and 35 days of age, but no differences were observed at 14 and 49 days of age. Male broilers had lower breast meat yield and relative abdominal fat than females. Variability within females was lower than in males. Results indicate that when high dietary amino acid concentration was provided at an earlier age, reducing concentration at later feeding phases did not compromise growth or carcass yields. Furthermore, moderate to high dietary amino acid levels may help reduce variability within flocks.

Comparison of broiler performance when fed diets containing grain from YieldGard Rootworm (MON863), YieldGard Plus (MON810 × MON863), nontransgenic control, or commercial reference corn hybrids

Two 42-d experiments compared the nutritional value of YieldGard Rootworm corn (MON863; experiment 1) and YieldGard Plus corn (MON810 x MON863; experiment 2) to their respective nontransgenic controls and 6 commercial reference corn hybrids when fed to growing broilers. For each experiment, a randomized complete block design was used with 8 dietary treatments in each of 5 replicated blocks of pens. In experiment 1, no differences among diets were observed (P > 0.05) for final live weights and feed conversion. Broilers fed diets containing MON863 corn had adjusted feed conversion similar to the nontransgenic control and the population of control and commercial diets. On a weight basis, there were no differences among diets for chill, fat pad, and thigh, drum, and wing weights. Differences (P < 0.05) between MON863 and commercial corn diets were noted for breast meat, chill and thigh, drum, and wing weights on a percentage of weight basis. No differences were observed (P > 0.05) in the percentage of moisture, protein, and fat in breast meat or thigh meat across treatment diets. In experiment 2, there were no significant differences among diets for all broiler performance and carcass parameters evaluated. Broilers overall performed consistently and had similar carcass yields and meat compositions when fed diets containing MON863 corn or MON810 x MON863 corn as compared with their respective nontransgenic control and commercial diets, supporting a conclusion of similar feeding values among diets.

The influence of temperature on the threonine and tryptophan requirements of young broiler chicks

Two experiments were conducted to investigate the influence of a warm environment (35 degrees C) on the threonine and tryptophan requirements of young broiler chicks from 7 to 18 or 21 d of age. Seven hundred forty (experiment 1) and one thousand eight (experiment 2) 1-d-old Cobb x Cobb straight-run broiler chicks were raised in wire-floored battery brooders in moderate temperature rooms (33 to 34 degrees C). For the first 7 d, all chicks were fed a standard corn-soybean-meal-based crumbled starter diet. On d 7, six chicks each (experiment 1) and eight chicks each (experiment 2) were randomly assigned to individual pens. In experiment 1, chicks were fed a corn-peanut meal basal diet supplemented with six levels of threonine (0.630, 0.651, 0.673, 0.715, 0.758, or 0.800% of the diet). In experiment 2, chicks were fed a corn-corn gluten meal based basal diet supplemented with six levels of tryptophan (0.090, 0.115, 0.140, 0.165, 0.190, or 0.215% of the diet). Each dietary treatment was repeated with three pens in each room and three rooms at each temperature. Three rooms were set at a moderate temperature of 25 degrees C, and the other three rooms were set at a warmer temperature of 35 degrees C. Body weight gain, feed consumption, and feed conversion ratio were measured. The threonine requirements of young broiler chicks were 0.733 +/- 0.016% (R2 = 0.59) and 0.752 +/- 0.046% (R2 = 0.25) for body weight gain, and 0.744 +/- 0.016% (R2 = 0.67) and 0.722 +/- 0.016% (R2 = 0.47) for feed conversion ratio at 25 and 35 degrees C, respectively (broken-line linear model). The tryptophan requirements of young broiler chicks were 0.151 +/- 0.004% (R2 = 0.85) and 0.144 +/- 0.003% (R2 = 0.89) for body weight gain, 0.144 +/- 0.003% (R2 = 0.88) and 0.142 +/- 0.003% (R2 = 0.88) for feed consumption, and 0.146 +/- 0.005% (R2 = 0.76) and 0.127 +/- 0.002% (R2 = 0.94) for feed conversion ratio at 25 and 35 degrees C, respectively. On average, the threonine and tryptophan requirements of broiler chicks at 35 degrees C were very similar to those kept at 25 degrees C.

Comparison of broiler performance when fed diets containing grain from roundup ready (NK603), yieldgard x roundup ready (MON810 x NK603), non-transgenic control, or commercial corn

Two 42-d experiments compared the nutritional value of the glyphosate-tolerant corn event NK603 (Roundup Ready corn) (experiment 1) and the combined traits, insect-protected corn event MON 810 (YieldGard com) x glyphosate-tolerant corn event NK603 (experiment 2) to their respective non-transgenic controls and to commercial reference corn, when fed to growing broilers. For each experiment, a randomized complete block design was used with eight dietary treatments in each of five replicated blocks of pens (eight pens for males and eight pens for females per block). Final live weights and feed conversion were not different (P > 0.05) across all treatments in both experiments. In experiment 1, broilers fed diets containing Roundup Ready corn had similar feed conversion adjusted for mortalities to those fed the non-transgenic control and one of the commercial corn diets. Chill weights and thigh, drum, and wing weights were not affected by diets. Differences (P < 0.05) were noted for breast meat and fat pad weights across treatments. In experiment 2, the adjusted feed conversion and carcass parameters were not affected by diets. Differences (P < 0.05) were noted only for protein content of breast meat. Differences observed in both experiments were consistent with natural variability. Broilers in general performed consistently and had similar carcass yields and meat compositions when fed diets containing Roundup Ready corn or YieldGard x Roundup Ready corn as compared with their respective non-transgenic control and commercial diets supporting similar feeding values among diets.

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.

Threonine requirements of different broiler genotypes

The objectives of this work were to study the responses of one Leghorn and two broiler stocks and sexes to different levels of Thr and to estimate their requirements for this amino acid. All experiments were conducted with birds from 1 to 18 d of age. Body weight gain (BWG) and feed consumption were measured on the eighteenth day, and feed conversion ratio (FCR) was calculated. At Day 18, three birds per replicate were killed, and liver and fat pads were collected and weighed. The data were analyzed by the general linear model and nonlinear model procedures of SAS software, and the broken-line linear model was used to estimate Thr requirements of chicks. Experiment 1 had a 5 x 3 factorial design with five levels of Thr (0.63, 0.70, 0.77, 0.84, and 0.91% of the diet), two broiler genotypes (Arbor Acres Classic and High Yield), and one Leghorn genotype (Hy-line W-36), with three replicate pens of eight male birds each. The basal diet was composed of corn, peanut meal (PNM), poultry by-product meal, poultry fat, DL-Met, L-Lys, and L-Ile (23% CP and 3.2 kcal/g of ME). The Leghorn chicks did not respond to Thr supplementation, indicating their requirement was < or = 0.63%. High Yield birds had better BWG and FCR than Classic. The BWG and FCR were reduced more in Classic than High Yield strains by the lowest Thr level. The percentage of liver was higher in the Classic than High Yield strain broilers with Thr supplementation. The second experiment (2 x 2 x 2 factorial design) was conducted to evaluate the effects of two levels of Thr (0.63 and 0.90%), two levels of Ile (0.72 and 0.90%), and two broiler strains (as Experiment 1). There were no responses to Ile for any parameters measured. Experiment 3 (6 x 2 factorial design, corn, PNM-based basal diet) had six Thr levels (0.63, 0.67, 0.71, 0.75, 0.79, and 0.83%) and two broiler strains (as Experiment 1), with four replicate pens of eight male birds each. The High Yield strain broilers grew significantly better at the lowest Thr level, but performance was similar at the higher Thr levels (significant interaction, P = 0.018). FCR was affected by Thr level but not by strain. The Thr requirement of the Classic strain broilers was 0.69 +/- 0.01% for BWG and 0.68 +/- 0.01% for FCR. The Thr requirement of the High Yield strain broilers was 0.68 +/- 0.01% for BWG and 0.69 +/- 0.01% for FCR. The Thr requirements of male versus female High Yield strain broilers were evaluated in a 6 x 2 factorial design, with six Thr levels (Experiment 4), with four replicate pens of eight birds each. Males and females had the same performance and carcass composition results (P > 0.05), except for percentage abdominal fat pads. The Thr requirement was 0.71 +/- 0.01% for BWG and 0.71 +/- 0.01% for FCR for the males and 0.72 +/- 0.008% for BWG and 0.71 +/- 0.001% for FCR for females. Excellent performance was observed from the corn- and PNM-based diet supplemented to contain 0.72% Thr. The Thr requirements of High Yield and Classic broilers (males and females) were similar and greater than for the Leghorn strain studied.