Optimizing Standardized Ileal Digestible Methionine Requirements of White Pekin Ducks in the First 21 Days Post-Hatch

Nuwan C. Chathuranga; Myunghwan Yu; Yu-Bin Kim; Hyun-Min Cho; Shan R. Nawarathne; Elijah O. Oketch; Jung-Min Heo

doi:10.2141/jpsa.2025017

Abstract

The current study investigated the optimal standardized ileal digestible (SID) methionine (Met) requirement for the growth performance of white Pekin ducks from hatching to 21 days of age. A total of 288 one-day-old male white Pekin ducklings were initially weighed and randomly assigned to six dietary groups, with six replicates per group. Eight ducklings were housed in each floor cage, pre-littered with rice hulls. Basal diets (corn-soybean-based) included 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, and 0.55% SID Met, representing the dietary treatment groups. Ducklings were offered unrestricted access to experimental diets and freshwater for the duration of the study. Body weight and feed intake were recorded weekly, and the average daily gain and feed conversion ratios were calculated. Overlapping linear- and quadratic-plateau regression models were employed to estimate SID Met requirements. Final body weight, average daily gain, and feed conversion ratios in white Pekin ducks exhibited significant quadratic growth with increasing dietary SID Met concentrations. In conclusion, estimated SID Met requirements for white Pekin ducks from hatching to 21 days, based on an average of linear and quadratic model responses, were determined to be 0.51% for body weight improvement, 0.51% for average daily gain, and 0.50% for feed conversion efficiency. These findings provided invaluable insight into optimized nutritional strategies for early growth performance in white Pekin ducks.

Introduction

Methionine (Met) was identified as the first feed-grade amino acid (AA) in 1951. It is often the primary limiting AA in corn-soybean-based poultry diets due to its inherently low concentrations in most plant-derived feed ingredients[1,2]. Met plays multiple critical roles in ducks by supporting protein and polyamine synthesis, regulating antioxidant activity, and serving as a precursor for important metabolic intermediates, such as carnitine, homocysteine, cysteine, and taurine[3,4]. These intermediates are further converted into S-adenosylmethionine, a key methyl donor[5,6], which contributes to the balance between Met and Cysteine[4]. In addition, Met is vital for feather growth and affects the carcass quality of broiler ducks[7].

The National Research Council (NRC)[8] recommends dietary levels of 0.4% Met from hatching to two weeks and 0.3% Met from 2–7 weeks for broiler Pekin ducks, based on apparent analyses. These values are questionable because they do not consider endogenous AA losses, urinary AA excretion, or hindgut-derived microbial AAs and proteins[9,10]. Hence, standardized ileal AA digestibility is a more appropriate value as it accounts for endogenous losses, independent of AA intake levels[11].

Although the digestibility coefficients of chickens are widely used for ducks, they may not be perfectly applicable to duck feed formulations due to variations in digestive physiology and genotype[12,13]. Recently, Oketch et al.[10] have evaluated the standardized ileal digestible (SID) coefficients of various feed components. Nevertheless, the SID Met requirements for white Pekin ducks remain unexplored. This study established specific SID Met requirements for white Pekin ducks from hatching to 21 days of age, focusing on the impact of different dietary SID Met levels on growth performance.

Materials and Methods

Ethical statement

The experimental procedures for the current study were reviewed and approved by the Animal Ethics Committee of Chungnam National University, Daejeon, Republic of Korea (202109A-CNU-115).

Birds and housing

The experiment was conducted over two consecutive periods, each involving 192 birds, all within the same research facility owing to spatial limitations. Uniform procedures and environmental conditions were maintained throughout the experiments. A total of 288 one-day-old male white Pekin ducklings were procured from a local hatchery (Charmfre Co., Jincheon, Korea) for these experiments. Upon arrival, the ducklings were weighed and randomly allocated to one of six dietary treatments containing different levels of SID Met (n = 6 replicate pens per treatment). Each pen was stocked with eight birds, with a mean body weight (BW) of 53.20 ± 0.005 g (mean ± standard error of the mean [SEM]), and dimensions of 1.7 m × 1.3 m × 1.0 m. (length × width × height). The floor of each pen was covered with rice husks as litter, based on recommendations of a previous study[14,15]. Each pen was equipped with a corn-type feeder and six nipple drinkers to provide water. The birds had free access to experimental diets and fresh water throughout the 21-day experimental period. The ambient temperature was maintained at approximately 30–32 °C during the first week and gradually decreased to 25 °C at the end of 21 days. Lighting was continuously provided for 24 h throughout the study period.

Experimental diets

Six experimental diets (Table 1) containing varying levels of SID Met were used. The SID of AAs in corn and soybean meal has been obtained from a previous study[10]. Diets were formulated to contain increasing levels of SID Met, ranging from 0.30–0.55%. All diets were designed to meet or exceed the recommended specifications of the NRC[8], except for Met, which was provided to three-week-old ducks. The concentrations of all indispensable AAs, except Met, in the formulated diets were based on the ideal AA ratios to prevent AA deficiency. All diets were provided in crumbled form.

Table 1. Ingredients and chemical compositions of experimental diets (as-fed basis).

Ingredients	Standardized ileal digestible methionine concentrations, %
Ingredients	0.30	0.35	0.40	0.45	0.50	0.55
Corn	59.30	59.30	59.30	59.30	59.30	59.30
Soybean meal	35.30	35.30	35.30	35.30	35.30	35.30
Cornstarch	2.30	2.25	2.20	2.15	2.10	2.05
Limestone	1.00	1.00	1.00	1.00	1.00	1.00
Dicalcium-phosphate	1.50	1.50	1.50	1.50	1.50	1.50
Iodized salt	0.30	0.30	0.30	0.30	0.30	0.30
Vitamin-mineral premix¹	0.30	0.30	0.30	0.30	0.30	0.30
DL-Methionine	0.00	0.05	0.10	0.15	0.20	0.25
Calculated values²
Metabolizable energy, kcal/kg	3,010	3,010	3,011	3,012	3,012	3,013
Crude protein	21.70	21.70	21.80	21.80	21.80	21.80
Calcium	0.92	0.92	0.92	0.92	0.92	0.92
Non-phytate P	0.35	0.35	0.35	0.35	0.35	0.35
Total Methionine, %	0.34	0.39	0.44	0.49	0.54	0.59
Standardized ileal digestible amino acids, %
Arginine	1.29	1.29	1.29	1.29	1.29	1.29
Histidine	0.53	0.53	0.53	0.53	0.53	0.53
Isoleucine	0.82	0.82	0.82	0.82	0.82	0.82
Leucine	1.68	1.68	1.68	1.68	1.68	1.68
Lysine	1.08	1.08	1.08	1.08	1.08	1.08
Methionine	0.30	0.35	0.40	0.45	0.50	0.55
Cysteine	0.32	0.32	0.32	0.32	0.32	0.32
Phenylalanine	0.96	0.96	0.96	0.96	0.96	0.96
Threonine	0.71	0.71	0.71	0.71	0.71	0.71
Tryptophan	0.23	0.23	0.23	0.23	0.23	0.23
Valine	0.91	0.91	0.91	0.91	0.91	0.91

¹Provided per kilogram of diet: vitamin A, 12,000 IU; vitamin D₃, 2,500 IU; vitamin E, 30 IU; vitamin K₃, 3 mg; D-pantothenic acid, 15 mg; nicotinic acid, 40 mg; choline, 400 mg; and vitamin B₁₂, 12 μg; Fe, 90 mg from iron sulfate; Cu, 8.8 mg from copper sulfate; Zn, 100 mg from zinc oxide; Mn, 54 mg from manganese oxide; I, 0.35 mg from potassium iodine; Se, 0.30 mg from sodium selenite.

²The values were calculated according to the values of feedstuffs in NRC (1994).

Performance measurements and chemical analysis

During the 21-day experiment, BW and feed intake data were recorded weekly (on days 7, 14, and 21). The obtained data were used to calculate average daily gain (ADG), mortality-corrected average daily feed intake (ADFI), and feed conversion (FC) ratios for each pen during the corresponding week of the study. The AA composition of the diets was analyzed using standard procedures[16], and the results are presented in Table 2.

Table 2. Analyzed amino acid composition of experimental diets containing six concentrations of standardized ileal digestible methionine (as-fed basis, %)

Ingredients	Standardized ileal digestible methionine concentrations (%)
Ingredients	0.30	0.35	0.40	0.45	0.50	0.55
Indispensable amino acid
Arginine	1.32	1.35	1.26	1.24	1.34	1.29
Histidine	0.50	0.49	0.49	0.49	0.53	0.50
Isoleucine	0.79	0.83	0.79	0.77	0.85	0.83
Leucine	1.55	1.60	1.51	1.51	1.65	1.58
Lysine	1.02	1.05	1.00	1.01	1.07	1.08
Methionine	0.31	0.34	0.37	0.43	0.53	0.58
Phenylalanine	0.89	0.91	0.86	0.86	0.94	0.89
Threonine	0.62	0.64	0.60	0.58	0.65	0.63
Tryptophan	0.23	0.24	0.23	0.23	0.24	0.23
Valine	0.84	0.86	0.84	0.81	0.90	0.87

Statistical analyses

The collected data were analyzed using a completely randomized design, and a general linear model procedure was employed for one-way analysis of variance (ANOVA) using SPSS software (Version 26; IBM SPSS 2019). Each pen was considered an experimental unit for all growth performance measurements. When the treatment effects were statistically different (P < 0.05), Tukey’s Multiple Range test was used to separate the means. Significant differences in performance parameters were further analyzed using linear and quadratic regression models to estimate the optimal and minimal nutrient requirements to maximize the targeted parameters. To estimate the SID Met requirements, this analysis was conducted using the Nutritional Responses Model version 1.3[17].

Results

White Pekin ducks raised in this study exhibited good health and robust growth performance during the study period. The calculated SID Met values for the formulated diets were comparable to the analyzed values (Table 2). BW, ADG, and FC ratios improved (P < 0.001) in a nonlinear manner as SID Met content increased. However, the ADFI was not influenced by different Met levels (Table 3).

Table 3. Growth performance of white Pekin ducks from 1–21 days of age fed diets containing different dietary standardized ileal digestible methionine concentrations¹.

Item	Standardized ileal digestible methionine concentrations (%)						SEM²	P-value	P-value
Item	0.30	0.35	0.40	0.45	0.50	0.55	SEM²	P-value	Lin³	Quad⁴
Body weight (g)
Day 1	53.20	53.19	53.19	53.20	53.21	53.20	0.005	0.915	0.368	0.617
Day 7	128.75^a	144.39^ab	154.13^b	157.83^b	159.63^b	147.23^ab	1.970	<0.001	0.003	<0.001
Day 14	499.58^a	509.18^ab	529.31^ab	544.03^ab	575.86^b	547.11^ab	6.818	0.030	0.002	0.006
Day 21	1039.53^a	1074.14^ab	1100.31^abc	1130.39^abc	1186.34^c	1151.20^bc	10.143	0.002	<0.001	<0.001
Average daily gain (g/d)
Day 7	10.79^a	13.03^ab	14.42^b	14.95^b	15.20^b	13.43^ab	0.282	<0.001	0.003	<0.001
Day 14	52.98	52.11	53.60	55.17	59.46	57.13	0.781	0.082	0.007	0.028
Day 21	77.14	80.71	81.57	83.77	87.21	86.30	1.197	0.170	0.006	0.023
Day 1-21	46.97^a	48.62^ab	49.86^abc	51.29^abc	53.96^c	52.28^bc	0.483	0.002	<0.001	<0.001
Average daily feed intake (g/d)
Day 7	16.70	17.52	18.05	17.69	17.46	17.46	0.201	0.548	0.432	0.204
Day 14	86.78	82.63	82.34	82.05	83.37	83.12	0.578	0.212	0.181	0.058
Day 21	139.32	139.75	139.08	139.76	139.87	140.41	1.07	0.999	0.758	0.943
Day 1-21	80.93	79.97	79.83	79.83	80.23	80.33	0.423	0.975	0.793	0.697
Feed conversion ratio (g/g)
Day 7	1.57^b	1.35^a	1.25^a	1.20^a	1.18^a	1.30^a	0.019	<0.001	<0.001	<0.001
Day 14	1.65^b	1.59^ab	1.55^ab	1.51^ab	1.42^a	1.46^ab	0.021	0.032	0.001	0.003
Day 21	1.83^b	1.75^ab	1.71^ab	1.68^ab	1.61^a	1.63^a	0.019	0.013	<0.001	0.001
Day 1-21	1.73^c	1.65^bc	1.60^abc	1.57^ab	1.49^a	1.54^ab	0.013	<0.001	<0.001	<0.001

¹Values are the mean of eight replicates per treatment.

²Pooled standard error of the mean

³ Linear

⁴ Quadratic

The data showed a better fit (higher R² values) for the linear-plateau (0.95) model than for the quadratic-plateau (0.87) model. When data were fitted to the linear-plateau model, the SID Met requirements for white Pekin ducks during the initial 21 days post-hatching were determined to be 0.50% for maximum BW, 0.50% for daily weight gain, and 0.49% for enhanced FC efficiency (Table 4 and Figs. 1–3). Conversely, by applying the quadratic-plateau model, the estimated digestible Met requirements were 0.51% for maximum BW, 0.52% for weight gain, and 0.50% to achieve the most efficient FC ratios (Table 4 and Figs. 1–3). Both models demonstrated significantly different results (P < 0.01) for the respective growth parameters. The consolidated means of both models recommended SID Met at 0.51% for maximum BW, 0.51% for ADG, and 0.49% for the minimum FC ratio of white Pekin ducks 21 days after hatching.

Table 4. Estimated standardized ileal digestible methionine requirements and recommendations for white Pekin ducks from hatching to 21 days of age based on linear-plateau and quadratic-plateau regression analysis¹.

Item	Requirement (%)²	SE³	R²	P-value	Recommendation (%)⁴
Final body weight (g)
LP	0.50	0.033	0.95	0.001	0.505
QP	0.51	0.081	0.87	0.008	0.505
Average daily weight gain (g/bird/day)
LP	0.50	0.034	0.95	0.001	0.510
QP	0.52	0.084	0.88	0.008	0.510
Feed conversion ratio (g/g)
LP	0.49	0.032	0.95	0.001	0.495
QP	0.50	0.058	0.91	0.003	0.495

¹LP; Linear-plateau regression analysis, QP; Quadratic-plateau regression analysis.

²Standardized ileal digestible methionine requirement based on regression analysis.

³ SE; Standard error.

⁴ Standardized ileal digestible methionine recommendations for each parameter based on both regression analyses.

Fig. 1.

Standardized ileal digestible methionine requirements of white Pekin ducks from hatching to 21 days of age for final body weight determined by a quadratic-plateau model is 0.51 [Y = 1158.19-2951(0.51-x)², R² = 0.87] (open line), and by a linear-plateau model is 0.50 [Y = 1166.77-637.39(0.50-x), R² = 0.95] (closed line). Data points (●) represent least squares means of dietary treatment (n = 8).

Fig. 2.

Standardized ileal digestible methionine requirements of white Pekin ducks from hatching to 21 days of age for average daily gain determined by a quadratic-plateau model is 0.52 [Y = 52.65-128.16(0.52-x)², R² = 0.88] (open line), and by a linear-plateau model is 0.50 [Y = 53.00-30.00(0.50-x), R² = 0.95] (closed line). Data points (●) represent least squares means of dietary treatment (n = 8).

Fig. 3.

Standardized ileal digestible methionine requirements of white Pekin ducks from hatching to 21 days of age for feed conversion ratio determined by a quadratic-plateau model is 0.50 [Y = 1.5219+5.47(0.50-x)², R² = 0.91] (open line), and by a linear-plateau model is 0.49 [Y = 1.515+1.06(0.49-x), R² = 0.95] (closed line). Data points (●) represent least squares means of dietary treatment (n = 8).

Discussion

The present study evaluated the optimal SID Met requirement at 21 days post-hatching in white Pekin ducklings, emphasizing growth performance characteristics. The SID AA values for duck diets were determined by referring to duck SID coefficients and the total AA content of the diet components. Thus, SID AA evaluations are more accurate than apparent AA levels in animal feed formulations[9,12]. Numerous experiments involving Pekin ducks have been conducted at 21 days of age, a critical period marked by rapid growth and heightened metabolic activity[18,19,20]. This stage is particularly crucial, as it substantially influences the subsequent growth performance of ducks. Furthermore, evaluating Met requirements during this phase is essential to ensure adequate dietary levels that support optimal growth, immune function, and feed efficiency[21].

Selection of a nutrient estimation model is critical for feed formulation, particularly for AA determination. The broken-line linear model is widely accepted because it ensures the lowest nutritional requirements and the highest technical efficiency[22]. This model is particularly appropriate when a plateau response is observed beyond a certain point. However, the broken-line linear model often estimates nutritional requirements without accounting for physiological variations within the population, economic considerations, or safety margins[23,24]. To address these limitations, a quadratic-plateau model was introduced. This model is highly accurate and considers the cost of expensive nutrients, although it requires complex and data-intensive analyses[25]. It is particularly useful for assessing AA toxicity when responses increase or decrease after a breakpoint[24]. Thus, by combining both models, the accuracy of SID Met requirement predictions for white Pekin ducks was improved. Furthermore, the linear-plateau model demonstrated a higher R² value than that of the quadratic model for all growth parameters in this study. These data suggest that the linear-plateau approach may be more effective to accurately describe the Met requirements of white Pekin ducks during this growth phase.

Met is the primary limiting AA in corn-soybean-based diets and affects the AA balance in birds. Accordingly, meeting the Met requirement is critical because it directly influences protein synthesis, AA performance, and feather growth in ducks[24,26]. Its antioxidant activity may also impact gut health and, hence, nutrient assimilation[27]. Therefore, the adequacy of Met levels positively impacts the overall performance and health of the birds. This may explain the improvements in growth performance (BW, ADG, and FC efficiency) in ducks fed diets containing increased SID Met levels. Xie et al.[18] have noted a nonlinear increase in the ADFI as dietary Met levels increase, which is explained by an AA imbalance. Nevertheless, the current study showed no significant effect on the ADFI, further supporting the hypothesis that ducks received sufficient protein and energy through basal diets, with Met being the limiting factor.

In line with the current results, Elkin et al.[26], Xie et al.[18], and Zeng et al.[7] have reported similar quadratic response patterns to dietary Met levels, where ADG increases up to a certain point and then declines in Pekin ducks. Moreover, studies by Elkin et al.[26], Xie et al.[18], Jamroz et al.[28], and Zeng et al.[7] have determined the optimal total Met levels for Pekin ducks to be 0.38–0.45%, 0.48%, 0.40%, and 0.51–0.61%, respectively, to achieve optimal growth performance. Although the current recommended values could not be directly compared to total Met-based studies, inconsistencies in optimal dietary Met levels were evident. These variations may result from differences in genetic lines, diet formulations (e.g., energy and crude protein levels), sex, and growth stages[4].

Despite inconsistencies in outcomes, previous studies have observed a decline in growth performance beyond certain levels of Met supplementation. Xue et al.[29] have studied the effects of excessive DL-Met and L-Met levels (0.49% of total Met in control diets) on the growth performance of white Pekin ducks from days 7–21 of age. That study revealed a significant reduction in ADG and ADFI, regardless of the Met source. Consistent with those findings, the current results demonstrated a decline in ADG when SID Met levels exceeded 0.51%. Additionally, FC ratios deteriorated when SID Met levels surpassed 0.49%. This decline might be attributed to three primary reasons: 1. Excessive Met supplementation may reduce nutrient uptake, including Met itself[3]. 2. An AA imbalance triggers Met degradation, which is then excreted as nitrogen or transformed into non-essential AAs[9]. 3. Met toxicity[7,30].

The current findings indicate markedly higher Met requirements than those recommended by the NRC[8]. This discrepancy might be attributed to several factors. Advancements in genetic selection have enhanced growth rates and production efficiency, thereby increasing the demand for AAs, including Met[31]. Additionally, differences in experimental conditions, such as housing systems, environmental factors, and diet composition, may alter Met utilization[21]. Contemporary feed formulations also differ substantially from those available during the development of the NRC guidelines, affecting both digestibility and bioavailability. Furthermore, NRC recommendations are designed to prevent deficiencies[8], whereas this study aimed to determine the levels that support optimal growth performance. Collectively, this may explain the elevated Met requirements observed in this study.

In conclusion, optimizing the SID Met content enhanced BW, ADG, and FC efficiency of white Pekin ducks. The estimated SID Met requirements for white Pekin ducks from hatching to 21 days were determined by averaging responses from linear and quadratic models, yielding values of 0.51% to optimize BW, 0.51% for maximize ADG, and 0.50% to improve FC efficiency.

Acknowledgments

This research was supported by the Regional Innovation Strategy (RIS) program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (MOE) (grant number: 2021RIS-004) and by the Rural Development Administration of the Republic of Korea (project number: RS-2021-RD009516).

Author Contribution

Conceptualization: Myunghwan Yu, Yu Bin Kim, and Jung Min Heo. Data curation: Myunghwan Yu and Jung Min Heo. Formal analysis: Myunghwan Yu. Methodology: Nuwan Chamara Chathuranga, Myunghwan Yu, and Yu Bin Kim. Software: Myunghwan Yu. Validation: Hyun Min Cho and Jung Min Heo. Investigation: Myunghwan Yu, Yu Bin Kim, Shan Randima Nawarathne, and Elijah Ogola Oketch. Visualization: Myunghwan Yu. Funding acquisition: Jung Min Heo. Project administration: Jung Min Heo. Resources: Jung Min Heo. Supervision: Jung Min Heo. Writing - original draft: Nuwan Chamara Chathuranga and Myunghwan Yu. Writing - review & editing: Nuwan Chamara Chathuranga, Myunghwan Yu, Yu Bin Kim, Hyun Min Cho, Elijah Ogola Oketch, Shan Randima Nawarathne, and Jung Min Heo.

Conflicts of Interest

The authors declare no conflict of interest.

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