RESEARCH ARTICLE

Evaluation of crude protein levels in White Pekin duck diet for 21 days after hatching

Hyun Min Cho1https://orcid.org/0000-0002-9329-8824, Samiru Sudharaka Wickramasuriya2https://orcid.org/0000-0002-6004-596X, Shemil Priyan Macelline3https://orcid.org/0000-0001-6771-3804, Jun Seon Hong1https://orcid.org/0000-0003-2142-9888, Bowon Lee1,*https://orcid.org/0000-0001-5353-8144, Jung Min Heo1,*https://orcid.org/0000-0002-3693-1320
Author Information & Copyright
1Department of Animal Science and Biotechnology, Chungnam National University, Daejeon 34134, Korea
2Department of Animal Science, Uva Wellassa University, Badulla 90000, Sri Lanka
3School of Life and Environmental Science, Faculty of Science, The University of Sydney, Sydney NSW 2006, Australia
*Corresponding author: Jung Min Heo, Department of Animal Science and Biotechnology, Chungnam National University, Daejeon 34134, Korea. Tel: +82-42-821-5777 E-mail: jmheo@cnu.ac.kr
*Corresponding author: Bowon Lee, Department of Animal Science and Biotechnology, Chungnam National University, Daejeon 34134, Korea. Tel: +82-42-821-5777 Email: bowon26@hanmail.net

© Copyright 2020 Korean Society of Animal Science and Technology. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: Jun 04, 2020; Revised: Jun 11, 2020; Accepted: Jun 19, 2020

Published Online: Sep 30, 2020

Abstract

In poultry diets, a requirement of crude protein is one of the most important factors in poultry productivity. Besides, the Pekin duck requirement of crude protein is still not clear. This experiment was conducted to determine the crude protein requirement of Pekin duck on diet formulation by investigation of growth performance, carcass trait, and analysis of blood parameter for a hatch to 21-day (d) of age. A total of 432 male White Pekin ducks were randomly allocated to six levels of crude protein (i.e., 15%, 17%, 19%, 21%, 23%, and 25%) to give six replicate pens per treatment with 12 ducklings per each pen. Body weight and feed intake were measured weekly by calculating feed conversion ratio and protein intake. Two ducklings each pen was euthanized via cervical dislocation for analysis of carcass trait and plasma blood on 21-d of age. Data were applied on both prediction linear-plateau and quadratic-plateau models by estimation of the crude protein requirements. Data were applied on both prediction linear-plateau and quadratic-plateau models by estimation of the crude protein requirements. The level of crude protein requirements of Pekin ducks for 21 days after the hatch was estimated to be 20.63% and 23.25% diet for maximum daily gain, and minimum feed conversion ratio, respectively.

Keywords: Growth performance; Linear-plateau model; Pekin duck; Quadratic-plateau model

INTRODUCTION

Dietary crude protein is known to play a major role in maximizing growth performance. However, it is one of the main factors affecting the cost of Pekin duck diets [1,2]. High protein poultry diets are not only expensive but also cause environmental problems owing to ammonia emissions and nitrogen excretion [3]. However, adverse environmental impacts can be alleviated simply by decreasing the level of protein in poultry diets [48].

Despite the importance of dietary crude protein level on the growth performance of birds, only a couple of studies have demonstrated that feeding birds with a higher dietary crude protein improved their average daily gain and feed efficiency [911]. However, it is often reported that excessive intake of dietary crude protein (i.e., over 22.5%) deteriorates growth performance in birds [12,13]. Conversely, birds fed insufficient dietary crude protein (i.e., under 20.0%), were shown to have compromised growth performance due to amino acid imbalance [14].

The National Research Council (NRC) recommended a 16% crude protein level in Pekin duck diets for 14–49 days [15]. However, this study was conducted many years ago and is, therefore, no longer applicable to the formulation of modern diets. It has been reported that feeding 19% crude protein level provided for 15–35 days is suitable for maximizing growth performance and carcass traits without wasting crude protein [16]. However, limited data are available for recommendations for optimal crude protein levels in White Pekin duck diets 21 days after hatching. Therefore, the objective of this study was to examine crude protein level requirements in White Pekin duck diets 21 days after hatching by evaluating growth performance and carcass traits.

MATERIALS AND METHODS

Experimental design

An experiment was conducted using 432 males White Pekin ducklings in a completely randomized design with six levels of crude protein (n = 6 replicate pens per treatment and 12 ducklings per pen). Ducklings were fed their respective experimental diets from the d one to twenty-one.

Birds, housing, and diets

One-d-old male White Pekin ducklings were obtained from a local hatchery (Jang Sung duck farm, Jangseong, Jeonnam, Korea). On the same d, ducklings were weighed individually and randomly allocated to one of six dietary treatments with varying levels of crude protein content (15%, 17%, 19%, 21%, 23%, and 25% respectively). Twelve birds were housed in each pen (1.7 × 1.3 m2), with a mean BW of 55.8 ± 0.31 g (mean ± standard error of mean [SEM]). These ducklings were reared on floor pens littered with rice husk and each pen was equipped with 3 nipple drinkers and a feeder. Birds were offered the experimental diet on an ad libitum basis for the period of the study; the freshwater was available at all times, and lighting was continuous for 24 hours. The ambient temperature was maintained at 32°C from days one to three, and then gradually decreased to 25°C until the ducklings were 21 days of age. Six dietary treatments were formulated to contain a level of crude protein content from 15% to 25% in a 2.0% scale (Table 1). Diets were iso-caloric and formulated to meet or exceed NRC [15] specifications for ducklings 21 days of age. Crystalline amino acids (lysine, methionine, isoleucine, valine, arginine, leucine) also were added to the diet to meet or exceed dietary amino acid requirements in diets. All experimental diets were prepared as mash form.

Table 1. Composition of experimental diets (% as fed)
Item Dietary protein content (%)
15 17 19 21 23 25
Corn 68.98 64.14 59.30 54.45 49.61 44.77
Wheat 10.00 10.00 10.00 10.00 10.00 10.00
Soybean meal (44%) 13.00 17.40 21.80 26.20 30.60 35.00
Fish meal 3.00 3.60 4.20 4.80 5.40 6.00
Vegetable oil 1.00 1.03 1.06 1.09 1.12 1.15
Limestone 1.00 1.00 1.00 1.00 1.00 1.00
Monocalcium phosphate 1.50 1.50 1.50 1.50 1.50 1.50
Vitamin-mineral premix1) 0.10 0.08 0.06 0.04 0.02 -
Salt 0.30 0.30 0.30 0.30 0.30 0.30
Lysine HCl 0.30 0.24 0.18 0.12 0.06 -
L-Arginine 0.25 0.20 0.15 0.10 0.05 -
DL-Methionine 0.15 0.16 0.17 0.18 0.19 0.20
L-Threonine 0.09 0.07 0.05 0.04 0.02 -
L-Tryptophan 0.10 0.10 0.09 0.09 0.08 0.08
L-Isoleucine 0.13 0.10 0.08 0.05 0.03 0.00
L-Valine 0.10 0.08 0.06 0.04 0.02 0.00
Calculated composition2)
 Metabolizable energy (kcal/kg) 3,196 3,197 3,198 3,199 3,200 3,201
 Crude protein (%) 15.43 17.29 19.15 21.01 22.87 24.73
 Calcium (%) 0.80 0.83 0.85 0.87 0.89 0.92
 Phosphorus (%) 0.39 0.40 0.40 0.41 0.42 0.42
 Lysine HCl (%) 0.98 1.08 1.18 1.28 1.38 1.47
 Methionine (%) 0.43 0.47 0.51 0.55 0.60 0.64
 Methionine + Cysteine (%) 0.70 0.77 0.83 0.90 0.97 1.03
 Isoleucine (%) 0.71 0.77 0.84 0.90 0.97 1.04
 Valine (%) 0.79 0.86 0.93 1.01 1.08 1.15
 Arginine (%) 1.08 1.18 1.28 1.38 1.48 1.58
 Leucine (%) 0.68 0.78 0.87 0.96 1.06 1.15
Analyzed composition
 Crude protein (%) 15.67 17.51 19.37 21.25 23.06 24.88

1) Supplied per kilogram of total diets: Fe (FeSO4 · H2O), 80 mg; Zn (ZnSO4 · H2O), 80 mg; Mn (MnSO4 · H2O) 80 mg; Co (CoSO4 · H2O) 0.5 mg; Cu (CuSO4 · H2O) 10 mg; Se (Na2SeO3) 0.2 mg; I, (Ca(IO3) · 2H2O) 0.9 mg; vitamin A, 24,000 IU; vitamin D3, 6,000 IU; vitamin E, 30 IU; vitamin K, 4 mg; thiamin, 4 mg; riboflavin, 12 mg; pyridoxine, 4 mg; folacine, 2 mg; biotin, 0.03 mg; vitamin B8, 0.06 mg; niacin, 90 mg; pantothenic acid, 30 mg.

2) The values are calculated according to the values of feedstuffs in NRC [14].

Download Excel Table
Growth performance evaluation

Body weight (BW) was recorded at the beginning and on d 7, 14, and 21 of the experimental periods. Pen-based feed consumption was recorded together with BW to calculate average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR).

Post-mortem procedure and sample collection

On d 21, two ducklings (closest to the median BW) were selected from each pen. Individual live BW of the selected birds was recorded and euthanized via cervical dislocation for sample collection after bleeding. Blood samples were collected from the brachial vein into vacutainer tubes coated with lithium heparin (BD Vacutainer, BD SSTTM, Franklin Lakes, NJ, USA). Collected blood samples were quickly transferred to a laboratory for plasma separation. After evisceration, empty bodies were weighed. Drumsticks (skinless) and breast meat were removed from carcasses and weighed. The empty BW, drumstick, and breast meat weight were expressed as proportions relative to slaughter live BW.

Sample preparation and laboratory analysis

Collected blood samples were centrifuged (1248R, GYROZEN, Gimpo, Korea) at 3,000×g for 10 min at 4°C. Plasma samples were separated and stored at −80°C before analysis that the concentrations of total protein (TP), blood urea nitrogen (BUN) were determined using commercial kits (Asan Pharmaceutical, Seoul, Korea) for an automatic biochemical blood analyzer (Model HITACHI 7180 chemistry analyzer, HITACHI, Tokyo, Japan).

Nitrogen Excretion calculation

Average nitrogen excretion was determined using pre-derived equations as shown below according to Belloir et al. (2017).

Nitrogen intake  ( g ) = Feed intake  ( g ) × Crude protein in the diet  ( % ) 6.25 Nitrogen retention = 29 g/kg × Body weight gain  ( g ) 1 , 000 Nitrogen excretion  ( g ) = Nitrogen intake  ( g ) Nitrogen retention
Statistical analysis

Data were analyzed as a completely randomized design, using the general linear model procedure of ANOVA of SPSS software version 24 (IBM Corp, 2016), with a pen used as the experimental unit for growth performance data. Data from selected individual birds for carcass traits and blood metabolites were pooled to get an average value per pen before statistical analysis. When dietary treatment was significant (p < 0.05), means were separated using Tukey’s multiple range test procedures of SPSS software version 24. To determine the optimum crude protein level, linear-plateau and quadratic-plateau regression analysis were conducted using a Nutritional Response Model (Version1.1; [17]) as described previously by [18].

RESULTS

Growth performance

Health and growth performance were good for all birds over the 21 days of the experiment. BW, ADG, and FCR were higher in White Pekin ducks fed the higher crude protein diet (p < 0.05) on days 7 and 14 than those in White Pekin ducks fed the lower crude protein diet. However, compared to the White Pekin ducks fed higher crude protein diets from days 1 to 21, the ducks fed the diet containing under 21% crude protein exhibited improved BW, ADG, and FCR on d 21 (p < 0.05, Table 2). On days 7 and 14, compared to the ducks fed the lower crude protein diets, White Pekin ducks fed diets with less than 19% crude protein exhibited an increase in ADFI.

Table 2. Effect of different content on body weight, average daily gain, average daily feed intake, feed conversion ratio of male Pekin ducks for 21 days after hatching1)
Item Dietary protein content (%) SEM p-value
15 17 19 21 23 25
Body weight (g/bird/day)
 Day 7 268.1e 280.6d 290.1c 297.4bc 305.5ab 308.0a 2.30 0.001
 Day 14 736.0d 761.2c 793.9b 802.5b 810.9b 837.0a 5.50 0.001
 Day 21 1,329.2c 1,383.4b 1,430.7a 1,465.1a 1,454.9a 1,429.6a 8.90 0.001
Average daily gain (g/bird/day)
 Day 7 30.32e 32.11d 33.44c 34.50bc 35.65ab 36.02a 0.331 0.001
 Day 14 66.84c 68.66c 71.97b 72.17b 72.20b 75.57a 0.531 0.001
 Day 21 84.73c 88.89bc 90.98ab 94.66a 92.00ab 84.66c 0.853 0.001
 Day 1–21 60.63c 63.22b 65.46a 67.11a 66.62a 65.42a 0.424 0.001
Average daily feed intake (g/bird/day)
 Day 7 36.99c 38.16bc 40.48a 38.53abc 39.31ab 37.46bc 0.308 0.008
 Day 14 97.55bc 96.11bc 101.49a 96.18bc 94.91c 99.32ab 0.553 0.003
 Day 21 148.63 151.17 152.17 147.43 148.89 143.07 1.074 0.188
 Day 1–21 94.39 95.15 98.04 94.04 94.37 93.28 0.484 0.070
Feed conversion ratio (g/g)
 Day 7 1.22a 1.19b 1.21b 1.12c 1.10c 1.04c 0.013 0.001
 Day 14 1.46a 1.40ab 1.41ab 1.33c 1.32bc 1.31ab 0.009 0.001
 Day 21 1.76a 1.70ab 1.67ab 1.56c 1.62bc 1.70ab 0.016 0.002
 Day 1–21 1.48a 1.43b 1.43b 1.34c 1.35c 1.35c 0.010 0.001

1) Each value is the mean of 6 replicates (12 birds per cage).

a–e Means in the same row with different superscripts differ in the level of crude protein content (p < 0.05).

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The level of crude protein required to improve growth performance from hatch to 21 d was determined using both linear-plateau and quadratic-plateau models (Figs. 1 and 2). The requirements for attaining maximum ADG were crude protein levels of 19.71% (linear-plateau model) and 21.55% (quadratic-plateau model). Synthetically, there suggested crude protein levels of 20.62% on ADG from hatch to d 21. The maximum proportion of FCR was attained in birds fed diets containing crude protein levels of 21.30% (linear-plateau model) and 25.19% (quadratic-plateau model). Based on both the linear-plateau model and quadratic-plateau model, the suggested crude protein requirement for improving the proportion of FCR was 23.25% fed from hatch to d 21.

jast-62-5-628-g1
Fig. 1. Crude protein requirements of Pekin ducks for hatch to 21 d of age for average daily weight gain determined by a quadratic-plateau model was 19.71 [Y = 66.38 – 1.2088(21.55 – x)2, R2 = 94.76] (open line), and by a linear-plateau was 21.55 [Y = 66.34 – 0.1365(21.55 – x)2, R2 = 94.23] (closed line). Data points (°) represent the least-square means of dietary treatment (n = 6). SEM, standard error of mean.
Download Original Figure
jast-62-5-628-g2
Fig. 2. Crude protein requirements of Pekin ducks for hatch to 21 d of age for feed conversion ration determined by a quadratic-plateau model was 21.30 [Y = 1.35 – 0.0215(21.30 – x)2, R2 = 91.19] (open line), and by a linear-plateau was 25.19 [Y = 1.34 – 0.0014(1.34 – x)2, R2 = 87.06] (closed line). Data points (◦) represent least-square means of dietary treatment (n = 6). SEM, standard error of mean.
Download Original Figure
Protein intake

The effect of dietary protein level on the voluntary protein intake of White Pekin ducks is shown in Table 3. Increased protein intake for 21 days after hatching was observed (p < 0.05) with increasing dietary protein levels in White Pekin ducks exposed to a higher protein feed.

Table 3. Effect of different content on protein intake and nitrogen utilization of male Pekin ducks for 21 days after hatching1)
Item Dietary protein content (%) SEM p-value
15 17 19 21 23 25
Protein intake (g)
 Day 7 5.55e 6.49d 7.69c 8.09b 9.04a 9.36a 0.202 0.001
 Day 14 14.63f 16.34e 19.28d 20.20c 21.83b 24.83a 0.498 0.001
 Day 21 22.29f 25.70e 28.91d 30.96c 34.24b 35.77a 0.703 0.001
 Day 1–21 14.16f 16.18e 18.63d 19.75c 21.71b 23.32a 0.46 0.001
Nitrogen retention (g)
 Day 1–21 36.92c 38.50b 39.87a 40.87a 40.57a 39.84a 0.258 0.001
Nitrogen excretion (g)
 Day 1–21 10.65f 15.85e 22.72d 25.49c 32.36b 38.52a 1.383 0.001

1) Each value is the mean of 6 replicates (12 birds per cage).

a–f Means in the same row with different superscripts differ in the level of crude protein content (p < 0.05).

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Carcass trait

No significant differences (p > 0.05) were observed in empty body weight, drumstick, and breast meat of ducks exposed on diverse levels of crude protein, on d 21 after hatching (Table 4).

Table 4. Effect of different content on carcass trait of male Pekin ducks on 21 day of age1)
Item Dietary protein content (%) SEM p-value
15 17 19 21 23 25
Empty body weight (%) 70.51 71.14 71.24 70.85 71.00 71.32 0.171 0.791
Drumstick (%) 7.31 7.45 7.74 7.51 7.74 7.67 0.060 0.204
Breast meat (%) 6.33 6.50 6.86 7.34 6.36 7.22 0.154 0.235

1) Each value is the mean of 6 replicates (1 bird per cage).

Download Excel Table
Urea nitrogen and total protein in the blood

White Pekin ducks exposed to a higher protein diet, showed (p < 0.05) increased blood urea nitrogen and total protein levels on d 21 after hatching (Table 5).

Table 5. Effect of different content on the blood of male Pekin ducks on 21 day of age1)
Item Dietary protein content (%) SEM p-value
15 17 19 21 23 25
Blood urea nitrogen (mg/dL) 0.49c 0.51c 0.59bc 0.59bc 0.73ab 0.81a 0.026 0.001
Total protein (g/dL) 3.44c 3.45c 3.47c 3.51bc 3.71ab 3.86a 0.038 0.001

1) Each value is the mean of 6 replicates (1 bird per cage).

a–c Means in the same row with different superscripts differ in the level of crude protein content (p < 0.05).

Download Excel Table

DISCUSSION

In this study, the crude protein requirements for improved growth performance of White Pekin ducks, from hatch to d 21 were evaluated. Although a previous study on the crude protein requirements of White Pekin duck diet exists, it may not be completely applicable to the formulation of new diets due to the evolved genotype of White Pekin ducks. Baéza et al. [19] reported the crude protein requirements for improved FCR in White Pekin duck diet from d 1 to 21% to be 23.2%, which may not apply to diets with varying energy levels (i.e., up to 3,000 kcal/kg metabolizable energy) in feed formulation. Moreover, Jiang et al. [20] recommended crude protein requirements based on only two crude protein levels (17% and 21%). In addition, due to differences in protein digestibility between White Pekin ducks and broiler chickens, the crude protein requirement for broiler chickens cannot be adequately applied to White Pekin ducks [21], as White Pekin ducks have a higher basal endogenous amino acid loss than do broiler chickens. Therefore, it is important to evaluate the crude protein requirements for White Pekin ducks under various conditions.

Protein sources are the most important components of poultry diets after energy sources. Protein is essential in poultry diets because, it supplies amino acids for the growth of muscle and synthesis of egg protein. The synthesis of muscle requires, physiologically, 20 amino acids in poultry diets. Ten of these twenty amino acids cannot be synthesized, while the other ten can be synthesized slowly in the interior of a poultry body. Therefore, sufficient amino acids must be supplied in poultry diets [22]. However, there are limitations in terms of the expense associated with the proportion of the protein source and the environmental contamination resulting from excessive protein diets.

Studies evaluating crude protein requirements have been conducted using a variety of methods (e.g., a statistical model for analysis) to ensure the accuracy of the estimated nutrient requirements [23,24]. Although the statistical model for analysis shows appropriate fit, its output cannot be regarded as the optimal level of nutrient requirement because it does not consider the physiological differences among the individuals in a population [25]. In addition, a broken-line analysis is generally applied by underestimating nutrient requirements [18]. To supplement the analysis of the statistical model method, both the linear-plateau model and the quadratic-plateau model methods have been used in recent studies on the estimation of nutrient requirements [2628]. Consequently, the aforementioned methods (i.e., an average of the linear-plateau and quadratic-plateau models) were used to estimate the crude protein requirements of the White Pekin duck diet for 21 days after hatching, by evaluating the growth performance and carcass traits of the ducks.

In this study, when the level of protein was increased, BW, ADG, and FCR improved over the first 14 days, whereas data acquired on days 14–21 showed different results. The diet containing 21% crude protein elicited a greater improvement in BW, ADG, and FCR of the ducks from d 14–21 than a diet containing 25% crude protein. This result is probably due to higher concentrations of the ratio of amino acids as compared to the ratio before the diet experiments. Based on an average of both the linear-plateau and quadratic-plateau model analysis, the optimum requirements of crude protein for were 20.63% and 23.25%, for maximal ADG and FCR, respectively, for 21 days after hatching. Similarly, Baéza et al. [19] reported that a level of 21% crude protein in the diet could improve feed efficiency; however, crude protein levels higher than 21% may result in an increase in the nitrogen content of White Pekin duck feces. Jiang et al. [29] reported improved ADG in White Pekin ducks in response to the crude protein level of 20.89% in the diet, from d 1 to 21. Moreover, Xie et al. [30] observed that a diet containing 19.58% crude protein improved the BW, ADG, and feed efficiency of White Pekin ducks from d 1 to 19.

According to recent reports, significant differences were observed in the carcass traits exhibited by White pecking ducks in response to different crude protein levels. According to Baéza et al. [19], compared to that with a lower crude protein diet, a higher crude protein diet was observed to increase the breast weight of Pekin ducks, as measured on d 21. However, our results for the carcass trait were not affected by the crude protein requirements probably due to sex, metabolizable energy, and amino acid balance.

CONCLUSION

Crude protein levels of 20.63%, and 23.25% base on both the linear-plateau model and the quadratic-plateau model were respectively recommended to improved ADG, FCR for White Pekin ducks from hatch to 21 days.

Competing interests

The authors declare no conflict of interest related to this work.

Funding sources

This paper was financially supported by the research fund of National Institute of Animal Science (PJ014162032020).

Acknowledgements

Not applicable.

Availability of data and material

Upon reasonable request, the datasets of this study can be available from the corresponding author.

Authors’ contributions

Conceptualization: Heo JM.

Data curation: Cho HM, Wickramasuriya SS, Macelline SP, Hong JS.

Formal analysis: Cho HM.

Methodology: Cho HM.

Software: Cho HM.

Validation: Heo JM.

Investigation: Cho HM.

Writing - original draft: Cho HM.

Writing - review & editing: Lee B, Heo JM.

Ethics approval and consent to participate

The experimental protocol used in this study was approved by the Animal Ethics Committee of the Chungnam National University (CNU-01175).

REFERENCES

1.

Torres-Rodriguez A, Sartor C, Higgins SE, Wolfenden AD, Bielke LR, Pixley CM, et al. Effect of Aspergillus meal prebiotic (fermacto) on performance of broiler chickens in the starter phase and fed low protein diets. J Appl Poult Res. 2005; 14:665-9

2.

Kim CH, Kang HK, Kim HS. Effect of dietary energy levels on growth performance, blood parameter and intestinal morphology of Pekin ducks in low ambient temperature. J Anim Sci Technol. 2019; 61:305-12

3.

Xie M, Jiang Y, Tang J, Zhang Q, Huang W, Hou SS. Starter and subsequent grower response of Pekin ducks to low-protein diets in starter phase. Livest Sci. 2017; 203:92-6

4.

Kerr BJ, Kidd MT. Amino acid supplementation of low-protein broiler diets: 2. formulation on an ideal amino acid basis. J Appl Poult Res. 1999; 8:310-20

5.

Namroud NF, Shivazad M, Zaghari M. Effects of fortifying low crude protein diet with crystalline amino acids on performance, blood ammonia level, and excreta characteristics of broiler chicks. Poult Sci. 2008; 87:2250-8

6.

Attia YA. Possibility of reducing protein level in the broiler finisher diets effects on growth performance, carcass yield and nitrogen excretion. Poult Sci. 2012; 91Suppl:37

7.

Attia YA. Possibility to improve protein utilization in broiler diets with amino acid supplementations. In: Proceeding of 2012 Worlds Poultry Congress. 2012 Salvador, Bahia.

8.

Ospina-Rojas IC, Murakami AE, Duarte CRA, Eyng C, Oliveira CAL, Janeiro V. Valine, isoleucine, arginine and glycine supplementation of low-protein diets for broiler chickens during the starter and grower phases. Br Poult Sci. 2014; 55:766-73

9.

Rezaei M, Hajati H. Effect of diet dilution at early age on performance, carcass characteristics and blood parameters of broiler chicks. Ital J Anim Sci. 2010; 9:e19

10.

Ghazanfari S, Kermanshahi H, Nassiry MR, Golian A, Moussavi ARH, Salehi A. Effect of feed restriction and different energy and protein levels of the diet on growth performance and growth hormone in broiler chickens. J Biol Sci. 2010; 10:25-30

11.

Houshmand M, Azhar K, Zulkifli I, Bejo MH, Kamyab A. Effects of non-antibiotic feed additives on performance, immunity and intestinal morphology of broilers fed different levels of protein. S Afr J Anim Sci. 2012; 42:23-32

12.

Dairo FAS, Adesehinwa AOK, Oluwasola TA, Oluyemi JA. High and low dietary energy and protein levels for broiler chickens. Afr J Agric Res. 2010; 5:2030-8

13.

Laudadio V, Dambrosio A, Normanno G, Khan RU, Naz S, Rowghani E, et al. Effect of reducing dietary protein level on performance responses and some microbiological aspects of broiler chickens under summer environmental conditions. Avian Biol Res. 2012; 5:88-92

14.

Chen X, Murdoch R, Zhang Q, Shafer DJ, Applegate TJ. Effects of dietary protein concentration on performance and nutrient digestibility in Pekin ducks during aflatoxicosis. Poult Sci. 2016; 95:834-41

15.

NRC [National Research Council]. Nutrient requirements of poultry. 9th ed Washington, DC: National Academies Press. 1994

16.

Zeng QF, Cherry P, Doster A, Murdoch R, Adeola O, Applegate TJ. Effect of dietary energy and protein content on growth and carcass traits of Pekin ducks. Poult Sci. 2015; 94:384-94

17.

Vedenov D, Pesti GM. A comparison of methods of fitting several models to nutritional response data. J Anim Sci. 2008; 86:500-7

18.

Wickramasuriya SS, Yoo J, Kim JC, Heo JM. The apparent metabolizable energy requirement of male Korean native ducklings from hatch to 21 days of age. Poult Sci. 2016; 95:77-83

19.

Baéza E, Bernadet MD, Lessire M. Protein requirements for growth, feed efficiency, and meat production in growing mule ducks. J Appl Poult Res. 2012; 21:21-32

20.

Jiang Y, Uzma M, Tang J, Wen ZG, Hou SS, Huang W, et al. Effects of dietary protein on threonine requirements of Pekin ducks from hatch to 21 days of age. Anim Feed Sci Technol. 2016; 217:95-9

21.

Kong C, Adeola O. Comparative amino acid digestibility for broiler chickens and White Pekin ducks. Poult Sci. 2013; 92:2367-74

22.

Ravindran V. Poultry feed availability and nutrition in developing countries. Poult Dev Rev. 2013; :60-3

23.

Pesti GM, Vedenov D, Cason JA, Billard L. A comparison of methods to estimate nutritional requirements from experimental data. Br Poult Sci. 2009; 50:16-32

24.

Nørgaard JV, Pedersen TF, Soumeh EA, Blaabjerg K, Canibe N, Jensen BB, et al. Optimum standardized ileal digestible tryptophan to lysine ratio for pigs weighing 7–14kg. Livest Sci. 2015; 175:90-5

25.

Pomar C, Pomar J, Rivest J, Cloutier L, Letourneau-Montminy MP, Andretta I, et al. Estimating real-time individual amino acid requirements in growing-finishing pigs: towards a new definition of nutrient requirements in growing finishing pigs?.In In: Sakomura NK, Gous RM, Kyriazakis I, Hauschild L, editors.editors Nutritional modelling in pigs and poultry. Wallingford, Oxon: CABI. 2014; p p. 157-74

26.

Heger J, Křížová L, Šustala M, Nitrayová S, Patráš P, Hampel D. Assessment of statistical models describing individual and group response of pigs to threonine intake. J Anim Feed Sci. 2007; 16:420-32

27.

Fan HP, Xie M, Wang WW, Hou SS, Huang W. Effects of dietary energy on growth performance and carcass quality of White growing Pekin ducks from two to six weeks of age. Poult Sci. 2008; 87:1162-4

28.

Xie M, Zhao JN, Hou SS, Huang W. The apparent metabolizable energy requirement of White Pekin ducklings from hatch to 3 weeks of age. Anim Feed Sci Technol. 2010; 157:95-8

29.

Jiang Y, Uzma M, Tang J, Wen ZG, Hou SS, Huang W, et al. Effects of dietary protein on threonine requirements of Pekin ducks from hatch to 21 days of age. Anim Feed Sci Technol. 2016; 217:95-9

30.

Xie M, Jiang Y, Tang J, Wen ZG, Zhang Q, Huang W, et al. Effects of low-protein diets on growth performance and carcass yield of growing White Pekin ducks. Poult Sci. 2017; 96:1370-5

2019 JCR Impact Factor: 1.685

The 2019 Journal Citation Reports (JCR) was announced, and the impact factor of JAST was determined to be 1.685.

We would like to ask for your continued interest and support in our journal.

Thank you.

JAST Editorial Office


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