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. 2024 Dec 21;11(1):e70171. doi: 10.1002/vms3.70171

Effects of Amino Acid Supplementation on the Growth Performance of Broiler Chicks Challenged With Coccidiosis: A Meta‐Analysis

Fatemeh Izadi Yazdanabadi 1,✉, Gholamali Moghaddam 1, Mehdi Abbasabadi 2, Mohsen Akbari 3, Bahram Satlikh Mohammadi 4, Parvin Khosravi 5, Hossein Sabzekar 6, Reza Farrokhi 7
PMCID: PMC11662968  PMID: 39708315

ABSTRACT

This meta‐analysis aimed to evaluate the effects of amino acid supplementation on the growth performance of broiler chicks challenged with coccidiosis. Data were collected on authorship, publication year, study sample characteristics and outcomes of interest related to growth performance. Effect sizes were calculated for both overall effects and the individual effects of each amino acid. The effects of moderator factors, such as supplementation levels and duration, were also assessed, and bias was calculated. Works were obtained from PubMed, Elsevier, ScienceDirect, Wiley, Springer Link and Scopus databases, with the help of search engines like Google Scholar and ResearchGate, covering the period from 2013 to 2023. A random‐effects model was used. Thirteen works were included in the current analysis, examining the effects of arginine (n = 4), methionine (n = 6), threonine (n = 3) and glutamine (n = 3). Amino acid supplementation [0.326, CI 95% (0.297–0.355); p = 0.000], arginine [0.430, CI 95% (0.293–0.568); p = 0.000] and threonine [0.793, CI 95% (0.193–1.38); p = 0.009] significantly increased body weight. Amino acid supplementation [0.052, CI 95% (0.022–0.081); p = 0.000] and arginine [0.317, CI 95% (0.049–0.585); p = 0.000] also significantly increased feed intake. Higher levels of amino acids (≥1.50%) and longer supplementation periods (≥15 days) significantly increased body weight and feed intake, while reducing the feed conversion ratio. Funnel plots, fail‐safe N and Egger tests showed no evidence of bias. In conclusion, arginine supplementation has the potential to increase body weight and feed intake in poultry challenged with coccidiosis. Higher doses of amino acids and longer supplementation periods are recommended in such cases.

Keywords: arginine, broiler chicks, coccidiosis, glutamine, meta‐analysis, methionine, threonine

Amino acid supplementation can improve the growth performance in broiler chciks challenged with coccidiosis.

  • Arginine supplementation can improve body weight and feed intake under challenge with coccidiosis.

  • The results did not show positive effects of methionine and glutamine under challenge with coccidiosis.

  • Supplementation of threonine improved body weight and decreased feed conversion ratio in broiler under challenge with coccidiosis.

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1. Introduction

Population growth has been continuously increasing over the past decades, leading to a greater demand for food (Fatoba and Adeleke 2018). The agricultural sector is responsible for meeting this growing demand. Within agriculture, the poultry industry plays a crucial role in supplying food and serves as a major driving force for the economy (Mottet and Tempio 2017). The poultry industry strives to enhance the growth performance of broiler chicks while maintaining their health in optimal condition. However, the industry faces several challenges, including diseases that affect productivity traits (Fatoba and Adeleke 2018). The prevalence of infectious and parasitic diseases reduces both productivity and economic efficiency in poultry production (El‐Katcha et al. 2018). Coccidiosis is one of the most common diseases affecting poultry worldwide.

Coccidiosis is primarily caused by parasites of the genus Eimeria and Isospora, which belong to the phylum Apicomplexa. Studies have identified nine Eimeria species, with seven reported as pathogenic in broiler chicks: E. acervulina, E. tenella, E. mitis, E. praecox, E. maxima, E. necatrix and E. brunetti (Perez‐Carbajal et al. 2010). The disease causes an estimated loss of £38 million in the United Kingdom and US$127 million annually in the poultry industry (Castro et al. 2020). Factors, such as poor ventilation, high humidity, overcrowding, impaired immune responses, bacterial enteritis and resistance to anticoccidial drugs, contribute to the prevalence of coccidiosis (Shivaramaiah et al. 2014). Eimeria species destroy the intestinal epithelium in broiler chicks, suppressing growth performance (Quiroz‐Castañeda and Dantán‐González 2015). Coccidiosis primarily affects the intestinal tract in various animals and birds (Peek and Landman 2011), causing malabsorption and diarrhoea in broiler chicks (Lai et al. 2018). In addition to reducing performance, the disease also damages the morphology and function of the intestinal epithelium (Rochell et al. 2017). Studies have shown that coccidiosis increases serum concentrations of pro‐inflammatory cytokines, which lead to decreased growth performance (Yazdanabadi et al. 2020a), disrupts the cecal microbial population (Yazdanabadi et al. 2020b) and increases intestinal damage (Izadi et al. 2020). Challenge with Eimeria damages the structure of cecal tissues and disrupts the gut microbial community, leading to dysbiosis. Yazdanabadi et al. (2020b) demonstrated that coccidiosis increased the population of Escherichia coli (by 7.06%) and decreased the population of Lactobacillus (by 12.35%). Coccidial infections also reduce villi length and width (Nabian et al. 2018). These negative effects of coccidiosis result in economic losses and reduced growth performance in broiler chicks. Nutritional strategies are employed to improve immune responses and mitigate the negative effects of parasitic infestation.

The supplementation of amino acids is one of the most important nutritional strategies for improving growth performance in broilers challenged by coccidiosis (El‐Katcha et al. 2018). Methionine, lysine, glutamine and threonine are the first to third limiting amino acids for broiler chicks fed diets based on corn–soybean meal (Dirain and Waldroup 2002). Methionine is a limiting amino acid that participates in protein synthesis, acts as a methyl donor for normal cellular metabolism and serves as a precursor for the synthesis of cysteine or carnitine (El‐Katcha et al. 2018). Lysine is a precursor for the synthesis of cytokines, which are essential for antibody production and protein synthesis (Geraert and Mercier 2010). Glutamine and arginine promote gut development and enhance gastrointestinal efficiency in broiler chicks (Jazideh et al. 2014; Khajali, Moghaddam, and Hassanpour 2014). Threonine is a major component of intestinal mucin in animals and may have beneficial effects during challenges with coccidiosis (Bortoluzzi, Rochell, and Applegate 2018). Positive effects of other amino acids on growth performance have also been reported during intestinal challenges (Dahiya et al. 2007; El‐Katcha et al. 2018; Rochell 2015).

Given the positive effects of amino acids in mitigating the negative impacts of coccidiosis on the growth performance of broiler chicks, there is a need for a study that investigates the effects of amino acid supplementation on their growth performance during coccidiosis challenges. This study aims to determine the potential effects of different amino acids, identify the most effective amino acid and assess various modulatory factors on growth performance.

2. Methods

2.1. Study Protocol Registration

This study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines (Moher et al. 2009).

2.2. Eligibility Criteria

English‐language works on broiler chicks were included in this study. Studies lacking complete data on growth performance, such as feed consumption, feed conversion ratio, body weight, levels of amino acids, type of amino acids, number of supplementation days, group size and the absence of a control group, were excluded from the current analysis. Additionally, studies involving other poultry species or those not challenged with coccidiosis were also excluded. Unpublished works, review articles and studies with insufficient information were not included. Only studies conducted between 2013 and 2023 were considered for this meta‐analysis.

2.3. Information Sources and Searching Strategies

Keywords searched included the following: coccidiosis, intestinal infection, poultry industry, intestinal challenges, parasitic diseases, parasites, Eimeria, E. acervulina, E. tenella, E. mitis, E. praecox, E. maxima, E. necatrix, E. brunetti, feed consumption, feed conversion ratio, weight gain, growth performance, amino acids, glycine, methionine, lysine, arginine, cysteine, threonine, tryptophan, glutamine and broiler chicks. These keywords were searched in various databases, including PubMed (http://www.ncbi.nlm.nih.gov/pubmed), Elsevier (https://www.elsevier.com/en‐in), ScienceDirect (http://www.sciencedirect.com), Wiley (http://www.onlinelibrary.wiley.com), Springer Link (http://www.springer.co.in) and Scopus (http://www.scopus.com), as well as through search engines such as Google Scholar (https://scholar.google.com) and ResearchGate (https://www.researchgate.net). Duplicate works were excluded, and relevant studies were included in the analysis. The search was finalized on 23 June 2023, after several weeks of searching to obtain the final works.

2.4. Data Synthesis

The data were collected regarding the authors, publication year, characteristics of the study sample (size and type of amino acid), outcomes of interest for growth performance, and a summary of results. Additionally, data on the number of challenge days were also gathered. Following the eligibility criteria, 13 works were included in the current study. The PRISMA flow diagram is shown in Figure 1. In the initial search using keywords, 212 articles were identified. After an initial review, 175 articles were excluded due to duplication and based on the screening of titles and abstracts. Subsequently, 24 articles were excluded due to incomplete data. Ultimately, as reported in Table 1, a total of 13 articles were included in this study. All authors evaluated the works and consulted each other when differences were observed.

FIGURE 1.

FIGURE 1

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PRISMA flow diagram for included studies.

TABLE 1.

Characteristics of the studies.

Authors AA Levels (%) Period BW (AA) BW (Con) FI (AA) FI (Con) FCR (AA) FCR (Con) N (AA) N (Con) Measurement day Challenge day
Rochell et al. (2017) Arg 1.2 21 473 455 668 649 1.41 1.48 60 60 21 2
Castro et al. (2020) Arg 1.14 26 730 680 1180 1170 1.62 1.71 72 72 26 12
Castro et al. (2020) Arg 1.24 26 740 680 1230 1170 1.67 1.71 72 72 26 12
Castro et al. (2020) Arg 1.34 26 750 680 1230 1170 1.64 1.71 72 72 26 12
Castro et al. (2020) Arg 1.44 26 740 680 1220 1170 1.68 1.71 72 72 26 12
Yazdanabadi et al. (2020a) Arg 1.25 42 1716.12 1615.32 3255 3093.3 1.9 1.92 48 48 42 21
Yazdanabadi et al. (2020a) Arg 1.5 42 1788.57 1615.32 3465 3093.3 1.94 1.92 48 48 42 21
Lai et al. (2018) Met 0.56 42 1221 1187 1838.13 1831.83 2.42 2.33 180 180 42 22
Lai et al. (2018) Met 0.58 42 1212 1187 1820.49 1831.83 2.42 2.31 180 180 42 22
de Souza Khatlab et al. (2019) Met 1.89 20 213 183 420 428 1.98 2.37 64 64 20 14
Xue et al. (2018) Gln 1.07 32 1154 1231 1490 1406 1.21 1.21 153 153 32 9
Mehdipour et al. (2020) Thr 1.12 36 2280.07 1000.67 1318.33 2460.38 1.72 2.15 66 66 36 23
Mehdipour et al. (2020) Thr 1.24 36 2280.05 1000.67 1351.09 2460.38 1.69 2.15 66 66 36 23
Mehdipour et al. (2020) Thr 1.36 36 2281.89 1000.67 1235.26 2460.38 1.85 2.15 66 66 36 23
Wils‐Plotz, Jenkins, and Dilger (2013) Thr 1.8 16 710.4 428.8 1313.6 969.6 1.85 2.26 72 72 16 10
Zhang et al. (2016) Thr 1.8 21 1340 827.2 2632 1927 1.97 2.45 56 56 21 13
Luquetti et al. (2016) Gln 1.2 28 1331 1338 1930 1966 1.45 1.47 100 100 28 1
Teng et al. (2023) Met 0.6 26 506 768 1024 1398 2.02 1.84 72 72 26 14
Teng et al. (2023) Met 0.8 26 868 768 1489 1398 1.73 1.84 72 72 26 14
Teng et al. (2023) Met 1 26 960 768 1528 1398 1.62 1.84 72 72 26 14
Teng et al. (2021) Arg 1.75 28 965 921 1653 1625 1.71 1.77 72 72 28 12
Teng et al. (2021) Gln 1.1 28 936 921 1647 1625 1.76 1.77 72 72 28 12
Teng et al. (2021) Met 1 28 816 921 1490 1625 1.84 1.77 72 72 28 12
Teng et al. (2021) Thr 1.06 28 945 921 1628 1625 1.72 1.77 72 72 28 12
Chen et al. (2022) Met 0.89 27 1534 1482 1984 1909 1.89 1.37 90 90 27 14
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2.5. Statistical Analysis

Comprehensive Meta‐Analysis (CMA) V3 software (Biostat, NJ) was employed to assess effect size and bias. Random‐effects models were applied due to heterogeneity among the groups. The pooled standard error of the mean (SEM) and statistical heterogeneity were evaluated using the Cochrane Q test and I 2 statistics. Fisher's Z was used to assess the effects of weights. The effects of moderator factors, including the levels of amino acids and supplementation duration, were also considered. Additionally, funnel plots, Egger's regression intercept and fail‐safe N were used to evaluate bias.

3. Results

3.1. Study Characteristics

Table 1 presents the study characteristics of the included works. A total of 13 studies were included in the current analysis, focusing on arginine (n = 4), methionine (n = 6), threonine (n = 3) and glutamine (n = 3). One study examined all the amino acids. The overall analysis involved 3146 broiler chicks, comprising 2041 chicks in the amino acid groups and 1105 control chicks. Additional characteristics are detailed in Table 1.

3.2. The Effect of Amino Acid Supplementation on Body Weight

Figure 2 illustrates the forest plot displaying the effects of amino acid supplementation on body weight. The analyses revealed significant effects of amino acid supplementation overall [0.326, CI 95% (0.297–0.355); I 2 = 98.17; p = 0.000; Q = 132.58], as well as for arginine [0.430, CI 95% (0.293–0.568); I 2 = 81.97; p = 0.000; Q = 38.18] and threonine [0.793, CI 95% (1.93–1.38); I 2 = 98.91; p = 0.009; Q = 45.86] in increasing body weight. The results indicate a higher efficacy of threonine compared to arginine during challenges with coccidiosis. However, no significant effects were observed for methionine [0.079, CI 95% (−0.225 to 0.383); I 2 = 97.51; p = 0.611; Q = 282.58] and glutamine [−0.071, CI 95% (−0.20–0.057); I 2 = 62.53; p = 0.277; Q = 5.33] on body weight. Heterogeneity was high for all amino acids and the overall results. Effect sizes were categorized as insignificant (<0.2), small (0.2–0.5), medium (0.5–0.8) and large (>0.8). The effect sizes for overall, arginine, glutamine, methionine and threonine were 0.326, 0.430, 0.071, 0.079 and 0.793, respectively. Thus, the overall effect and the effect of arginine were considered medium, whereas the effect of threonine was high; the effects of glutamine and methionine were small. The funnel plot (Figure 3) and Egger's statistical test did not indicate any bias in the included articles (p > 0.05). Specifically, Egger's test yielded a p value of 0.0812, confirming the absence of publication bias among the studies. The fail‐safe N was calculated to be 987, suggesting that 987 ‘null’ studies would be needed for the combined two‐tailed p value to exceed 0.050 (Table 2). Because this number is substantial, it indicates that bias is not present.

FIGURE 2.

FIGURE 2

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A forest plot illustrating the effects of amino acid supplementation on body weight. In a forest plot of a meta‐analysis, the terms ‘favours A’ and ‘favours B’ indicate which of the two groups being compared shows better outcomes based on the pooled effect sizes from multiple studies. Specifically, ‘favours B’ means that Group B (amino acids) demonstrates better outcomes compared to Group A (no amino acid supplementation).

FIGURE 3.

FIGURE 3

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Funnel plot a funnel plot illustrating the potential bias among the included studies regarding body weight.

TABLE 2.

The results for bias in Eggers and fail‐safe N tests.

Parameters Funnel plot (CI) Eggers (P) Fail‐safe N Result
Body weight 95% [−0.1 to (0.63)] 0.0812 987 Absence of bias
Feed intake 95% [−0.40 to (0.34)] 0.716 512 Absence of bias
Feed conversion ratio 95% [−0.40 to (0.36)] 0.515 1021 Absence of bias
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3.3. The Effect of Amino Acid Supplementation on Feed Intake

Figure 4 depicts a forest plot showing the results for the effects of amino acid supplementation on feed intake. The analyses revealed significant effects of amino acid supplementation overall [0.052, CI 95% (0.022–0.081); I 2 = 96.80; p = 0.000; Q = 750.37] and specifically for arginine [0.317, CI 95% (0.049–0.585); I 2 = 95.14; p = 0.000; Q = 144.12], indicating an increase in feed intake. The overall effect size is small, whereas the effect size for arginine is medium. Thus, the effects of amino acids are significant, with the most substantial effects associated with arginine. In contrast, no significant effects were observed for glutamine [0.017, CI 95% (−0.327 to 0.293); I 2 = 93.67; p = 0.913; Q = 31.60], methionine [−0.147, CI 95% (−0.381 to 0.086); I 2 = 95.68; p = 0.216; Q = 162.12] and threonine [−0.070, CI 95% (−0.418 to 0.588); I 2 = 98.19; p = 0.778; Q = 277.33] regarding feed intake. Heterogeneity was high for all amino acids and for the overall analysis. The funnel plot (Figure 5) did not indicate any bias in the included studies. Egger's statistical test yielded a p value greater than 0.05 (p = 0.716), confirming the absence of publication bias among the studies. The fail‐safe N was calculated to be 512, indicating that 512 ‘null’ studies would be required for the combined two‐tailed p value to exceed 0.050 (Table 2). Because this number is substantial, it suggests that bias is not present.

FIGURE 4.

FIGURE 4

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Presents a forest plot illustrating the effects of amino acid supplementation on feed intake. In the context of a meta‐analysis, the terms ‘favours A’ and ‘favours B’ indicate which of the two groups being compared demonstrates better outcomes based on the pooled effect sizes from multiple studies. Specifically, ‘favours B’ means that Group B (amino acids) shows superior outcomes compared to Group A (no amino acid supplementation).

FIGURE 5.

FIGURE 5

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Funnel plot illustrating the potential bias among the included studies regarding feed intake.

3.4. The Effect of Amino Acid Supplementation on Feed Conversion Ratio

Figure 6 illustrates the forest plot depicting the effects of amino acid supplementation on the feed conversion ratio. The analysis did not reveal significant effects of amino acid supplementation overall [−0.085, CI 95% (−0.026 to 0.035); I 2 = 93.72; p = 0.166; Q = 383.23], as well as for arginine [−0.052, CI 95% (−0.113 to 0.009); I 2 = 93.21; p = 0.094; Q = 144.30], glutamine [−0.068, CI 95% (−0.148 to 0.009); I 2 = 58.92; p = 0.237; Q = 4.86] and methionine [−0.048, CI 95% (−0.233 to 0.328); I 2 = 97.05; p = 0.738; Q = 237.15]. However, threonine demonstrated significant effects in decreasing the feed conversion ratio [−0.324, CI 95% (−0.480 to (−0.168)); I 2 = 81.29; p = 0.001; Q = 26.73]. This indicates that threonine significantly reduced the feed conversion ratio in broiler chicks challenged with coccidiosis.

FIGURE 6.

FIGURE 6

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Forest plot illustrating the effects of amino acid supplementation on feed conversion ratio. In a forest plot of a meta‐analysis, ‘favours A’ and ‘favours B’ typically indicate which of the two groups being compared (A or B) shows better outcomes based on the pooled effect sizes from multiple studies. There were no significant differences between the groups.

High heterogeneity was observed across all amino acids and the overall analysis. The funnel plot (Figure 7) indicated no bias among the studies included (p > 0.05). The results of Egger's statistical test produced a p value greater than 0.05 (p = 0.515), confirming the absence of publication bias among the studies. Additionally, the fail‐safe N was calculated to be 1021, indicating that 1021 ‘null’ studies would be necessary for the combined two‐tailed p value to exceed 0.050 (Table 2). Because the required number of studies is high, this suggests that bias is not present.

FIGURE 7.

FIGURE 7

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Funnel plot for bias for the included studies in feed conversion ratio.

3.5. The Effects of Moderator Factors on Growth Performance

Table 3 depicts for the effects of moderator factors on the efficiency of amino acids on growth performance. The findings indicated that higher levels of amino acids (≥1.50%) significantly increased body weight and feed intake while decreasing the feed conversion ratio. Additionally, longer supplementation periods (≥15 days) led to increased body weight and a reduced feed conversion ratio.

TABLE 3.

The effects of moderator factors on efficiency of amino acids on growth performance.

Body weight Feed intake Feed conversion ratio
Levels (%) Effect size (CI 95%) Z value (p) Effect size (CI 95%) Z value (p) Effect size (CI 95%) Z value (p)
≤1.00 0.05 (−0.578 to 0.679) 0.157 (0.875) −0.097 (−0.343 to 0.148) 1.44 (0.149) −.123 (−0.143 to 401) −0.931 (0.352)
1.1 −0.40 (0.143–0.942) 1.44 (0.149) 0.013 (−0.138 to 0.163) 0.168 (0.866) −0.106 (−0.235 to 0.024) −1.60 (0.109)
1.2 0.62 (0.051–1.19) 2.13 (0.033) 0.023 (−0.270 to 0.315) 0.152 (0.879) −0.018 (−0.181 to 0.145) −0.214 (0.830)
1.3 1.01 (0.67–1.36) 5.74 (0.001) 0.299 (0.321–0.919) 0.944 (0.345) 0.085 (−0.114 to 0.285) 0.838 (0.432)
1.4 1.59 (1.13–2.05) 6.80 (0.001) 0.145 (0.085–0.871) 0.952 (0.367) −0.123 (−0.143 to 0.401) −1.97 (0.049)
1.5 2.72 (1.02–4.42) 3.14 (0.002) 1.39 (0.034–3.58) 2.36 (0.018) −0.128 (−0.220 to (−.137)) −2.74 (0.006)
≥1.5 1.62 (1.05–2.20) 6.20 (0.001) 1.19 (1.03–1.35) 14.50 (0.001) −0.454 (−0.643 to (−0.265)) −4.71 (0.001)
Period
≤10 0.507 (−0.311 to 0.532) 1.21 (0.224) 0.357 (−0.495 to 1.20) 0.821 (0.412) −0.052 (−0.170 to 0.066) −0.859 (0.390)
10–15 0.111 (−0.213 to 0.435) 0.672 (0.502) −0.042 (−0.237 to 0.152) −0.429 (0.668) 0.025 (−0.102 to 152) 0.392 (0.695)
15–20 0.734 (0.249–1.21) 2.95 (0.003) −0.506 (−0.252 to 0.141) −0.557 (0.558) −0.435 (−0.641 to (−0.174)) −4.402 (0.008)
≥20 3.57 (1.08–6.07) 2.81 (0.005) −0.373 (−0.227 to 0.973) −1.21 (0.223) −0.545 (−0.655 to (−0.435)) −9.71 (0.001)
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4. Discussion

This meta‐analysis aimed to evaluate the effects of amino acid supplementation on the growth performance of broiler chicks challenged with coccidiosis. The results indicated that amino acid supplementation could improve feed intake and weight during challenges with coccidiosis. Although there was a tendency for improved feed conversion ratio (p = 0.166), it was not statistically significant. The findings showed that arginine supplementation improved weight gain and feed intake in broiler chicks facing coccidiosis challenges. The coccidiosis challenge reduces plasma arginine concentration due to increased production of nitric oxide (Allen and Fetterer 2000). Castro et al. (2020) investigated the effects of dietary inclusion of arginine at levels of 1.04%, 1.14%, 1.24%, 1.34% and 1.44%, with a challenge from Eimeria species starting at Day 12 of age. They found that dietary inclusion of 1.44% arginine increased body weight by 8.1% and feed intake by 4.09% compared to broiler chicks fed with 1.04% arginine between 12 and 26 days of age. Yazdanabadi et al. (2020a) examined the effects of dietary arginine inclusion at 125% and 150% of recommended levels in challenged broiler chicks. They reported that the addition of arginine to the diet improved growth performance. The enhanced growth performance resulting from arginine supplementation may be attributed to several factors, including its role in protein synthesis (Emadi et al. 2011), reduction of inflammation (Gottardo et al. 2017), prevention of muscle loss and improvement of recovery during the inflammatory phase (Yazdanabadi et al. 2020a).

In addition, arginine is recognized as an anti‐inflammatory amino acid that enhances immune responses under challenging conditions. The improved immune responses resulting from the addition of arginine can be attributed to its role in the synthesis of antibodies and the increased production of nitric oxide, which acts as a cytotoxic compound (Yazdanabadi et al. 2020a). On the basis of the observed values for immune responses, it can be argued that arginine functions as both an anti‐inflammatory agent and a supportive amino acid for the immune system. This enhanced immune function decreases the body's requirements for amino acids dedicated to immune synthesis, allowing more amino acids to be utilized for growth performance, which, in turn, results in improved growth outcomes. Furthermore, arginine plays a crucial role in intestinal regeneration and can enhance intestinal morphology. Castro et al. (2020) investigated the effects of diets containing arginine on intestinal morphology. Izadi et al. (2020) demonstrated that broiler chicks fed with 150% of the recommended arginine level exhibited significant reductions in lesion scores: 28.57% in the duodenum, 27.14% in the jejunum and 47.54% in the ceca, compared to those receiving only 85% of the recommended arginine. Additionally, Tan et al. (2014) found that although arginine supplementation did not positively affect villus height, villus width or crypt depth, it did lead to an increase in mucosal density. Thus, arginine supplementation improves growth performance through multiple mechanisms, especially when broiler chicks are challenged with coccidiosis.

Supplementation of threonine has been shown to improve body weight and decrease the feed conversion ratio in broiler chicks. As an essential amino acid, threonine plays a vital role, particularly under challenges such as coccidiosis. Mehdipour et al. (2020) investigated the effects of dietary inclusion of threonine on the performance of broiler chicks infected with coccidiosis. In their study, they supplemented diets with 112%, 124% and 136% threonine during the grower and finisher phases, reporting positive outcomes.

Threonine is involved in the production of mucus, which is crucial for maintaining gut integrity. It enhances immune response and mucin synthesis, contributing to improved nutrient absorption. These effects collectively lead to better growth performance. Given that coccidiosis damages the intestinal system, which is essential for antibody production, the role of threonine becomes even more significant. For instance, Ren et al. (2020) reported that a combination of methionine and cysteine increased IgA levels in the intestinal system. Similar to the findings for arginine, threonine significantly affects the immune system, which can be attributed to its protective role in the intestinal system, thereby enhancing growth performance. Moreover, threonine contributes to improved intestinal morphology, further supporting its benefits. In summary, threonine has a notable impact on enhancing intestinal morphology, as evidenced by research conducted by Mehdipour et al. (2020).

The results did not demonstrate positive effects of methionine and glutamine under challenge with coccidiosis. Although some studies have reported benefits of methionine and glutamine on growth performance during coccidial infections, these effects were found to be statistically insignificant. However, longer supplementation periods and higher dosages tended to yield better results. Izadi Yazdanabadi and colleagues indicated that higher levels of arginine significantly enhance growth performance compared to lower levels. Their research showed that dietary inclusion of arginine at a level of 1.50% resulted in increased average daily gain and feed intake while decreasing the feed conversion ratio compared to lower doses. This suggests that broiler chicks may require higher levels of arginine during the finisher period when challenged with coccidiosis to optimize growth performance. Moreover, across all studies, arginine consistently exhibited a greater effect on weight gain compared to feed intake, highlighting its importance in supporting growth during periods of coccidial challenge.

The effects of coccidiosis challenge on the growth performance of broiler chicks were reviewed, revealing that arginine supplementation significantly improves weight gain and feed consumption. Additionally, threonine supplementation was found to enhance weight gain and feed conversion ratio. Therefore, it is recommended to use higher doses (1.50%) of both arginine and threonine for extended periods during coccidiosis challenges. This study is among the first in animal and veterinary sciences to compare groups using quantitative metrics, providing valuable insights into this area of research. However, higher heterogeneity was observed in the results, which may be attributed to variations among the study groups. It is worth noting that there were limitations regarding glutamine, with only three relevant works identified.

In summary, the authors aim to inform readers about the detrimental effects of coccidiosis on broiler growth performance and the potential benefits of amino acid supplementation as a nutritional strategy to combat these challenges. This study highlights the significance of tailored dietary interventions in poultry management to improve overall outcomes.

Author Contributions

Fatemeh Izadi Yazdanabadi: conceptualization, investigation, supervision, funding acquisition, project administration, resources, writing–original draft. Parvin Khosravi: conceptualization and project administration. Gholamali Moghaddam: methodology, supervision, writing–review and editing. Mohsen Akbari: methodology, software, data curation, formal analysis, writing–review and editing. Mehdi Abbasabadi: investigation, funding acquisition, project administration. Hossein Sabzekar: validation, project administration. Reza Farrokhi: validation, project administration. Bahram Satlikh Mohammadi: visualization, funding acquisition, resources.

Ethics Statement

All the principles for care and treatment of broiler chicks were confirmed by the Ethical Committee of Tabriz University (TU, 110254, June 2015).

Conflicts of Interest

The authors declare no conflicts of interest.

Peer Review

The peer review history for this article is available at https://publons.com/publon/10.1002/vms3.70171.

Funding: The authors received no specific funding for this work.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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