Effect of Different Dietary Concentrations of Amino Acids on the Performance of Two Different Broiler Strains

Four Nutritional Programs (NP) used in the Brazilian poultry industry were tested in two broiler strains (Cobb 500 and Ross 308). NP varied in the concentrations of their main essential amino acids (AA) and were classified as Low, Regular, High and Mixed (high AA concentrations up to 21 days and regular concentrations after that). Minimum digestible Met+Cys/Lys, Thr/Lys, Arg/Lys, Ile/Lys, and Val/Lys ratios were 0.74, 0.64, 1.05, 0.65 and 0.75, respectively, in all NP, and no minimum amount of CP was fixed. There were no interactions between strain and NP for any of the evaluated responses. From 1 to 47 days of age, birds fed the Low NP presented lower average body weight and body weight gain (BWG). The high NP allowed for better feed conversion ratio (FCR), followed by the Regular and the Mixed NP. Ross 308 broilers were heavier, presenting worse FCR due to higher FI. Birds fed the High NP had lower carcass yield than those fed the Low NP. The Low and Regular NP had lower costs per WG when compared with the High NP. Low and Regular NP presented higher gross margin returns compared with the High NP. The Regular and Mixed NP are the most recommended, presenting intermediate performance and higher economic returns.


INTRODUCTION
The accuracy in meeting broiler nutritional protein requirement, as well as the search for an ideal profile of amino acids (AA) to obtain the maximum protein utilization of protein has guided the research in this area.New formulation approaches started to be applied when measuring AA in feeds became feasible, allowing the transition from using crude protein values to the use of total AA.Subsequently, feed formulations for poultry and pigs recommended of digestible (dig) AA values, based on the ideal protein concept; this was aided by the development and availability of synthetic AA.On the other hand, the genetic progress of broilers, including gender and strain, can influence the ideal AA ratio needed; any alteration in the proportion of body protein, feathers and maintenance requirements may result in changes in the ideal AA ratios (Hackenhaar & Lemme, 2005).
During the last decades, broiler average daily weight gain increased from 20 to more than 50 g/day, and the market age was reduced from 12 to six weeks (Silva Junior et al., 2002).The improvement of the genetic potential, the demand for further-processed poultry products and the concern on food quality and safety stimulated the interest on the composition and quality of poultry carcasses, particularly on performance traits and low fat (Araújo et al., 2002).In addition of being an affordable protein source to all social classes, chicken meat is also considered healthy and nutritious.A portion of 100 g of cooked chicken meat contains 239 calories and 27 g of protein, which

Effect of Different Dietary Concentrations of Amino Acids on the Performance of Two Different Broiler Strains
Ebling PD, Ribeiro AML, Trevizan L, Silva ICM da, Kessler A de M, Rubin LL practically satisfies the daily AA demands of human beings (Leeson, 1993).
Due to the contributions that genetic improvements have made to the evolution of the performance of broilers over the years, it is necessary to keep making adjustments or corrections of the recommended nutritional plans (Gous, 2010).Amino acids must be balanced in the diet to avoid energy loss, which can be

Effect of Different Dietary Concentrations of Amino Acids on the Performance of Two Different Broiler Strains
diverted to the synthesis of fat (Leeson et al., 1996).In addition, proper protein balance of diets reduces costs due to higher efficiency of protein utilization, and it also reduces nitrogen excretion in the environment.Therefore, the aim of this study was to evaluate the effects of four nutritional programs used by the Brazilian poultry industry by varying the concentration of the main essential AA on live performance, carcass yield, and economic parameters of two strains of broilers.

MATERIALS AND METHODS
Birds were reared according to the Brazilian Federal Law Nº 11794 (2008, October 8 th ) and the protocols were approved by the Committee Animal Care and Use of Universidade Federal do Rio Grande do Sul.
The experiment was conducted in an experimental house, where average minimum and maximum temperatures were 19 and 25 ºC, respectively.A total of 1,344 one-day-old male chicks of two strains Treatments consisted of four Nutritional Programs (NP), in which diets were isocaloric with no minimal fixed CP value; however, they contained different concentrations of essential AA.The NP contained Low, Medium, High, or Mixed concentrations of AA.Mixed NP had high AA concentrations until birds were 21 days, followed by regular concentrations (Tables 1 and  2) until the end of the rearing period.The minimum digestible Met+Cys/Lys, Thr/Lys, Arg/Lys, Ile/Lys, and Val/Lys ratios in all NP were 0.74, 0.64, 1.05, 0.65 and 0.75, respectively.These are the ratios typically used by the Brazilian poultry industry.A multiphase feeding regime was applied for all NP, and it was split in five periods: pre-starter (1 to 10 days), starter (11 to 20 days), grower I (21 to 35 days), grower II (36 to 42 days), and finishing (43 to 47 days).Prior to diet formulation, feedstuff AA profile (by high performance liquid chromatography), crude energy and protein were analyzed (AOAC, 2002).The formulated diets were also submitted to the same analyses.Chicken performance was evaluated per period and for the total experimental period relative to body weight (BW), body weight gain (BWG), feed intake (FI) and feed conversion ratio (FCR).
On day 47, three average birds from each replicate were slaughtered to measure carcass, breast, and thigh + drumstick yields.Yield was understood as parts weight or carcass weight without head and feet relative to live weight.Birds were sacrificed by cervical dislocation, followed by scalding, defeathering and evisceration.Carcass parts were cut by a single specialized professional in order to achieve uniformity and precision in the process.
The economic analysis was performed considering feedstuff costs per period multiplied by feed intake during the respective period (feeding cost).This value was divided by 47 days of WG, resulting in cost per kg of BWG.Birds' BW at 47 days was multiplied by live bird price at the time of calculation, feeding cost was subtracted, resulting in gross margin return, considering all other costs as fixed.
Experimental data were submitted analysis of variance (ANOVA).Means were compared by LS means using the GLM procedure of SAS statistical program (Stat Version, 2009).Data were analyzed according to a completely randomized design in a factorial arrangement (4 x 2), in eight treatments with six replicates of 28 birds each.Initial weight, which was used as a covariable in the analysis, was removed from the final model because it was not significant.The statistical model included the effects of NP (Low, Regular, High or Mixed), strain (Cobb 500 or Ross 308) and their interactions on the performance, carcass and parts (breast, thigh + drumstick) yields, and gross margin return.

RESULTS AND DISCUSSION
One-day-old Ross 308 chicks were statistically heavier (48 vs. 44 g; p < 0.05) than Cobb 500 chicks, although breeders were about the same age.None of

Effect of Different Dietary Concentrations of Amino Acids on the Performance of Two Different Broiler Strains
the responses showed any interactions between strain and NP in any experimental phase.Therefore, only the main effects will be discussed.
During the pre-starter period, the High/Mixed NP promoted better BW, BWG, and FCR than the other programs (Table 3).As nutrient concentrations decreased, BW, BWG and FCR progressively worsened.During this period, birds consumed more feed when fed Low and Regular AA concentrations (p < 0.05) were fed, probably in an attempt to supply AA deficiencies.Broiler chickens offered free choice between two diets with different CP and AA levels presented similar performance as the control group (22% CP), by choosing diets with less protein, but rich in essential AA (Kolling et al., 2005).These results indicate that the birds regulated their feed intake according to their protein requirements.
During the starter period, BW, BWG and FCR of the birds fed the Regular NP were similar to those fed the High/Mixed NP, but differed from the birds under Low NP, which promoted the worst results (p < 0.001; Table 3).On the other hand, FI was not different (p > 0.05) among NP, indicating that, during this phase, nutrient differences were not sufficient to increase FI in the birds fed the less concentrated NP.
Between 21 and 35 days, the four NP were applied.The birds fed the High NP presented higher BW and BWG, although BWG was similar to that of birds under the Regular and Mixed programs (Table 4).When Low NP was fed, broilers had lower BW (p < 0.001), but their BWG and FCR were similar (p > 0.05) to those fed the Regular and Mixed NP, in contrast to previous phases that recovered to a certain degree.Between 36 and 42 days, there were no differences in the performance of birds fed the Regular and the Mixed NP.Only BW was statistically different: at 42 days, the broilers fed the High NP were the heaviest (Table 4).
Between 43 and 47 days, broilers from all treatments had the same BW, except for those fed the Low NP (p < 0.001).However, these broilers presented similar BWG and FCR as the High NP birds (p > 0.05; Table 5).The best BWG and FCR during this phase were achieved by the Regular and Mixed NP broilers, possibly indicating AA excess in the High NP.
Evaluating the total period (1 to 47 days), the NP with a low AA concentration was the only one that was different (p < 0.001) and worse than the others for BW and BWG (Table 5).On the other hand, better FCR was recorded for the High NP group (p < 0.001), followed by the Regular and the Mixed NP birds.During the total period, FI was similar among NP (p > 0.05).
During the entire experimental period and in all phases, Ross 308 broilers were heavier (p < 0.001), with higher BWG during the study due to their high FI, and had worse FCR than Cobb 500 broilers (p < 0.01).The lack of significant associations between strains and NP observed in this study differs from previous studies that used 17% CP and 0.6, 0.7 and 0.85% of Lys and two strains.In this study, Cobb chicks had higher BWG and better FCR when fed the lower Lys levels in comparison to Ross 308 chicks, but with high Lys levels, the results were similar (Sterling et al., 2006).Otherwise, no interactions were observed in one experiment when Cobb 500 broilers had higher BW at 21 days and better FCR until the end of the Value within a column with no common superscript differs significantly by LS means at 5% probability.

Effect of Different Dietary Concentrations of Amino Acids on the Performance of Two Different Broiler Strains
experiment (37 days) while Ross 308 broilers had the highest FI (Vieira et al., 2007).
Results obtained from the present experiment agree with other studies that found that the performance of broilers worsens when low-protein diets are offered (Sklan & Noy, 2005;Lilly et al., 2011).Using data of six experiments, a reduction of more than 3% CP, even when corrected for the main limiting AA, resulted in worse performance (Dean, 2006).Reducing CP (20.8, 19.7 and 17.5%) of diets supplemented with synthetic AA had a negative effect on broiler WG and FCR between 21 and 28 days, indicating that, at this age, protein requirement may be higher than usual (20% CP) due to a higher rate of lean tissue accretion (Viola et al., 2008).It was clear that the increase in AA concentrations in the starter and growing periods improved performance.However, in the present study, the best performance was observed when the High NP was fed during the entire rearing period.Under practical field conditions, where challenges are always stronger than under experimental conditions, the advantages of High NP could last longer.
Some studies show the importance of nutrition immediately after hatching (Halevy et al., 2000;Pophal et al., 2004).In one study, broilers fed CP-deficient diets presented better BWG and FCR when 1% Lys and 0.5% Met were supplemented to the diet containing 15% CP.On the other hand, no FI difference was found when low-protein diets, with or without AA supplementation, were compared (Khan et al., 2011).Cobb 500 broilers fed alternated diets with different AA concentrations (Low-High-High and Medium-High-High) from 1 to 14, 15 to 28 and 29 to 42 days of age, showed the same FI and BWG at 42 d than those fed High-High-High AA concentrations (Corzo et al., 2010).In a similar study, broiler performance was evaluated by feeding three protein profiles, including Medium (similar to those used in the Brazilian industry), High (15% higher) and Low (15% lower), from 1 to 21 and 22 to 42 days (Coneglian et al., 2010).Body weight was similar between Low-High and High-Low programs.
In present study, broilers fed the Mixed NP with high AA concentrations during the starter phase and regular AA concentrations after it did not present any performance differences compared with those fed the Regular and High NP.The Mixed NP is an intermeditate program that prevents excessive dietary AA supply during the finishing phase, when broilers become less efficient and excessive nitrogen may have a negative effect (Kolling et al., 2005).The deamination of AA excess increases nitrogen excretion (Faria Filho et al., 2007) and the carbon chain is stored as fat (Leeson et al., 1996), which is unhealthy for human nutrition (Appel et al., 2005).
Carcass weight was not different between the strains (p > 0.05), but Cobb 500 birds presented higher breast yield than Ross 308 broilers (p < 0.05; Table 6).Birds fed the High NP had lower carcass yields compared with the Low NP (p < 0.05).The other NP showed intermediate values.Breast and thigh + drumstick yields were not different between NP (p > 0.05; Table 6).The higher carcass yield obtained with the Low NP suggests that birds fed this NP maximized body fat deposition, consequently increasing carcass weight.Studies have shown that birds fed diets with low AA concentrations Value within a column with no common superscript differs significantly by LS means at 5% probability.

Table 1 -
Nutritional composition and ingredients of NP in the prestarter, starter and grower I phases.

Table 2 -
Nutritional composition and ingredients of NP in the grower II and finisher phases.

ICM da, Kessler A de M, Rubin LL Effect of Different Dietary Concentrations of Amino Acids on the Performance of Two Different Broiler Strains
(Cobb 500 and Ross 308), with 48 and 44 g of initial weight, respectively, were reared in 48 pens (28 birds/ pen) at a density of 11 birds/m 2 .Chicks derived from broiler breeders of similar age.Mash feed and water were offered ad libitum, and chicks were submitted to a 23-h light regimen during the entire experimental period.

Table 3 -
Performance of broiler chickens at 1 to 10 and 11 to 20 days of age in accordance with each NP(1).Value within a column with no common superscript differs significantly by LS means at 5% probability.

Table 4 -
Performance of broiler chickens at 21 to 35 and 36 to 42 days of age in accordance with each NP(1).

Table 5 -
Performance of broiler chickens at 43 to 47 days of age and the total experimental period (1-47 days) according to each NP(1).