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A Systematic Review and Metanalysis on the Use of Hermetia illucens and Tenebrio molitor in Diets for Poultry

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Submitted:

30 November 2023

Posted:

01 December 2023

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Abstract
Insect meal as a protein source has been considered a sustainable way to feed animals. H. illucens and T. molitor larvae meal are considered high protein sources for poultry, also presenting considerable amounts of fatty acids, vitamins, and minerals. However, other potential components in insect meal and insect oil have been more studied nowadays. Chitin, lauric acid, and antimicrobial peptides can present antimicrobial and prebiotic functions, indicating that low inclusions of insect meal can beneficially affect broilers` health and immune responses. This systematic review was developed to study the impact of insect products on health parameters of broilers, and a metanalysis was conducted to evaluate the effects on performance. A database was obtained based on a selection of manuscripts from 2016 to January 2023, following the mentioned parameters. There were positive effects of both H. illucens and T. molitor meal or oil products on poultry health status, especially in microbiota population, immune responses, and antimicrobial properties. The average daily gain was greater in broilers fed T. molitor meal compared to H. illucens meal (p = 0.002). The results suggest that low levels of insect meal were suitable for broilers, without result in negative effects on performance, while the insect oil can totally replace soybean oil without negative impacts.
Keywords: 
Subject: 
Biology and Life Sciences  -   Animal Science, Veterinary Science and Zoology

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1. Introduction

Different vegetable and animal protein sources have been evaluated in diets for poultry, which include dietary inclusions of insect products [1,2,3]. Most of the studies have been conducted to evaluate insect types, and also to elucidate the ideal inclusion of insect meal as an ingredient. There is a large number of insects with economic interest in animal production; however, Hermetia illucens (HI; black soldier fly) and Tenebrio molitor (TM; yellow mealworm) are the ones that can reach an industrial scale of production [4]. Meals generated from these insects contain high protein levels and sufficient quantities of fatty acids, vitamins, fiber, and minerals [5]. Additionally, H. illucens and T. molitor in either meal or oil forms are considered suitable feed ingredients for broilers as they are well accepted for poultry based on a natural behavior [9].
Feeding diets with insect products has also been considered sustainable because insects can be easily reared on a wide range of biological waste streams [6,7,8], using less land and water compared to other protein and energy ingredient sources [9]. Animal production systems based on reduced waste and pollution have become priority, indicating that an increased efficiency of raw material utilization is needed. However, the variability in nutrient composition, scale of production, and ingredient cost and availability are the main challenges for the poultry chain when insect products are intended to be used.
Since more attention has been given to the precision of nutrition and animal health aiming to improve the efficiency of poultry production, H. illucens and T. molitor larvae have been intensively studied to provide accurate information on nutrient composition and digestibility profiles of different products for broilers. Recently, there was an increased interest in better understanding larvae compounds that present functional, prebiotic, or antibiotic functions and antimicrobial properties, reported to benefit broiler immunity and intestinal health [10]. In this context, chitin from the exoskeleton of the insects [11,12], the fatty acid profile with high levels of lauric acid, and the defense mechanisms provided by antimicrobial peptides [13], can label the insect meal and oil also as functional ingredients for animal production. However, there is a lack of information regarding the antimicrobial properties of insect products against intestinal challenges in poultry, and there is limited information available evaluating the inclusion of low amounts of insect meal, the use of insects as functional additives, and their effects on intestinal health.
Therefore, the objective of this study was to review and group the most expressive and recent literature of either H. illucens or T. molitor meal and oil sources for poultry. This study focuses on evaluating the impact of insect products on blood parameters, immune system, gut histomorphology and microbiota of broilers, based on a systematic review. This manuscript was also outlined to present the effects of insect products on broiler performance through a metanalysis.

2. Materials and Methods

2.1. Systematic Review

A literature review was performed using the PRISMA method [14] to select the studies for the database construction. PubMed, Scopus, and Web of Science were used for the PICo framework electronic databases in the systematic review and metanalysis [15]. The following terms were searched: “poultry” or “broiler” or “broilers” or “chicken” or “chickens”, in combination with, “Hermetia illucens” or “Tenebrio molitor”, in addition to “chitin” or “chitosan” or “performance” or “feed conversion” or “feed conversion ratio” or “feed to gain” or “feed : gain” or “feed efficiency” or “gain : feed” or “feed intake” or “average daily gain” or “body weight gain” or “body weight” or “FCR” or “ADFI” or “ADG” or “BW” or “FI” or “health parameters” or “immune system” or “immune response” or “histomorphology” or “histology” or “morphometric” or “morphology” or “intestinal health” or “antioxidant” or “antimicrobial” or “antimicrobial peptides” or “intestinal challenge” or “challenge”.
The systematic review was conducted using published manuscripts and the cited references in the manuscripts were reviewed to identify additional studies that were relevant. All the references were exported to Mendeley software (Mendley Ltd., Elsevier, 2023) and each publication was independently reviewed to be selected for the next step. All the manuscripts selected for this publication were published in scientific journals from January 2016 to January 2023, considering the objective of the systematic review and the possibility of metanalysis.
For this systematic review, manuscripts reporting mainly results on the impact of HI and TM on the intestinal health of broiler chickens were selected, which basically included the effects on intestinal microbiota, histomorphology and histochemistry measurements, and blood parameters. Therefore, all the main observations from the previous studies were grouped into result tables to better demonstrate the effects of dietary HI or TM products on poultry health. In the result tables, the inclusion of insect products was maintained in percentage according to each publication. Percentages of replacement were presented as inclusion levels, when possible.

2.2. Metanalysis

After selecting the manuscripts, a spreadsheet was created based on broiler growth performance, where columns indicate the authorship, feeding phase, ingredient inclusions, average daily feed intake (ADFI), average daily gain (ADG), and feed conversion ratio (FCR). All the data presented in the selected manuscripts was transformed to a daily basis for feed intake and body weight gain, being expressed in g/kg, whereas the FCR was presented in g:g. The obtained information for the metanalysis also includes the type of insect and physical characteristics of the ingredient (meal or oil). Additionally, manuscripts that had live or whole larvae and treatments that did not include insect products (excluding the control diet) were excluded from the metanalysis.
To perform metanalysis, each publication received a sequential code number, which is an inter-code with a sequential code plus a number that represents the treatment. The codes were repeated to indicate different phases of the same treatment (for example, manuscript 10 and treatment 01 for the starter phase = 1001; manuscript 10 and treatment 01 for grower phase = 1001; manuscript 10 and treatment 02 for the starter phase = 1002…). This sequential code allowed us to study the effects of treatments in different growing phases, analyzing values and finding evaluated means. The feeding phases were used for categorical analyzes as: starter (1 to 21 days), grower (21 to 35 days), and finisher (35 to 42 days). Afterwards, the spreadsheet was set and ADG, ADFI, and FCR variables were calculated as a percentage to the respective control in two ways. First, the response for the given performance parameter with the control treatment in each publication, separated by feeding phase, and the control diet was considered 0 (zero). This information was presented as the variation between the control and treatments in percentage. Secondly, the greatest results for ADG and ADFI of each phase were considered 100%; however, for FCR the lowest (best or improved) result was considered 100% for analyses. Results were separated in control treatment or treatments with either HI or TM insect products in low inclusion levels (≤ 100 g/kg for meal and ≤ 25 g/kg for oil) and high inclusion levels (> 100 g/kg for meal and > 25 g/kg for oil). This procedure was used to reduce the variability among studies in the database [16].
In the present manuscript, the metanalysis was performed to combine results from several assays in the database to compare the effects of the two insect products (HI and TM meal or oil) on broiler performance. Graphical analyses are presented to show the results of each manuscript and to obtain an overview of the data heterogeneity. Still, this procedure was divided into type of insect products, meal or oil forms, and feeding phases that were included in the same graphs for better visualization. For the metanalysis, at the end, the 25 selected publications containing information regarding ADFI, ADG, and FCR were used to create 8 graphs with an exploratory analysis, demonstrating the effects of insects as ingredients on broiler performance. Also, the variation on ADFI, ADG, and FCR of broilers fed diets with either insect meal or oil and an analysis of variance to compare both insects were expressed in two tables.

2.2. Statistical Analysis

Data were submitted to analysis of variance to show the effects of inclusion levels of the insect products on growth performance. It was performed using the univariate procedure and the Shapiro-Wilk test of Minitab® Statistical Software. After, performance responses were analyzed for variance-covariance. The model included the code of the manuscript as random effect. Insect meal and oil were fixed effects. Mean differences were considered significant at p ≤ 0.05 using the Tukey test.

3. Results

The literature review resulted in 597 manuscripts that were identified and imported from the database as shown on the PRISMA flow (Figure 1). In the identification, a total of 508 studies were excluded due to inconsistent title, abstract, or duplicates. For the present publication a total of 60 manuscripts were eligible, presenting growth performance information and health impacts in broiler chickens. After full evaluation, 29 publications were removed from the metanalysis due the lack of information on performance data, that precluded the correction for ADFI, ADG, and FCR or were removed due to the missing information on diets description. A total of 25 studies were retained as described in Figure 1 and Table 1. The nutritional and aminoacidic composition of either HI or TM meal are presented in Figures S1–S4, and 16 studies were obtained using insects as ingredients in the diets, also presenting the nutrient composition of the meals. Data were corrected to a dry matter basis when needed.

3.1. Systematic Review

The results of the systematic review of broilers fed diets with HI and the impact on health parameters are shown in Table 2. This table presents authorship, overall information of diet and insects, inclusion levels, and the main observed effects. The publications evaluated HI meal or oil separately, with variable inclusion levels of these products. Few studies replaced soybean meal (SBM) by HI meal or soybean oil by HI oil in different percentages of replacement. On the main effects, previous publications mainly evaluated microbiota, immune responses, intestinal histomorphology, and blood parameters. Results of histomorphology and blood parameters were variable, ranging from no effects to improvements in villus height and blood triglycerides, monocytes, and red blood cell distribution. Some publications demonstrated that there is a potential of using HI meal or oil to improve the relative abundance of beneficial microorganisms and to decrease Clostridium in the gastrointestinal tract (GIT).
Table 3 presents the results of the systematic review of broilers fed diets with T. molitor and the impact on health parameters. Authorship, overall information of diets and insects, inclusion levels, and the main observed effects are shown. Almost all the publications evaluated TM meal and few studies tested TM oil in broiler diets. Also, the majority of the studies was designed to evaluate different inclusions of TM meal in diets for broilers as a protein source, and few studies tested the supplementation of full fat TM meal as a feed additive. The relative abundance of microorganisms was the main studied effect in the previous publications, followed by measurements in immune responses and blood parameters. Interestingly, some publications reported that TM meal inclusion in broiler diets was effective to decrease populations of Escherichia coli, Clostridium, Coprococcus, and Ruminococcus in different trials.
Table 4 shows the effects of H. illucens and T. molitor in broiler diets and the impact on health characteristics based on a systematic review. There are less studies evaluating either HI or TM for broilers in the same experiment compared to experiments evaluating only one insect species. Two studies were developed to evaluate microbiota with different provision of HI or TM products and one publication had supplemented HI or TM. Until the date of this systematic review, there were no found publications evaluating both HI and TM in the same diet.

3.2. Metanalysis

The exploratory graphical analyses are shown in Figure 2, Figure 3, Figure 4, Figure 5, Figure 6 and Figure 7. The ADFI, ADG, and FCR of broilers fed HI or TM larvae meal are presented in Figure 2, Figure 3 and Figure 4, respectively. The figures allowed us to observe the biological coherence between HI or TM larvae meal inclusion and growth performance parameters of broilers. Also, with the metanalysis it was possible to obtain a general view of the data consistency and heterogeneity as well as to observe data distribution regarding dietary insect levels. Since the feeding phases are within the same graphs in the present manuscript, we can observe the results of different phases observing points that are closer or farther to the Y axis in the graph of each publication.
Figure 2 shows the ADFI from 0 to 200 grams with the HI or TM larvae meal inclusion ranging from 0 to 300 g/kg. It can be seen a decrease in ADFI with the increasing levels of HI meal in 4 manuscripts [19,22,24,72]. On the other hand, increasing inclusions of TM meal does not seem to change ADFI.
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Figure 2. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor larvae meal on the average daily feed intake (ADFI) of broilers.
Figure 2. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor larvae meal on the average daily feed intake (ADFI) of broilers.
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The effects of insect meal inclusions on broiler ADG is shown in Figure 3. For this parameter, the ADG does not seem to change with increasing levels for both insects, but there is a publication [35] demonstrating an increase on ADG in the finisher phase.
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Figure 3. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor larvae meal on the average daily gain (ADG) of broilers.
Figure 3. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor larvae meal on the average daily gain (ADG) of broilers.
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The FCR of broilers according to the insect meal inclusion is presented in Figure 4. This shows that no changes on FCR between the insect sources were observed. The FCR results were, moving from increased FCR using increasing levels of TM meal [34,35] to improvements on FCR [31]. With HI meal inclusions, an increase on FCR was also reported [25,51].
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Figure 4. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor larvae meal on the feed conversion ratio (FCR) of broilers.
Figure 4. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor larvae meal on the feed conversion ratio (FCR) of broilers.
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The effects of increasing levels of HI or TM oil on broiler performance are described in Figures 5 to 7. Figure 5 shows the ADFI from 0 to 200 g when broilers were fed HI or TM larvae oil ranging from 0 to 50 g/kg. Increasing levels of insect oil did not affect ADFI of broiler chickens. One publication was found evaluating TM oil for broilers in floor pens [55] and other in metabolic cages [61].
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Figure 5. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor oil on the average daily feed intake (ADFI) of broilers.
Figure 5. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor oil on the average daily feed intake (ADFI) of broilers.
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In a similar manner to the ADFI results, the ADG of broilers was not affected by increasing levels of either HI or TM oil (Figure 6).
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Figure 6. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor oil on the average daily gain (ADG) of broilers.
Figure 6. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor oil on the average daily gain (ADG) of broilers.
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Figure 7 shows the FCR from 1.0 to 2.5 g:g with HI or TM oil ranging from 0 to 50 g/kg. The insect oils, independent of the source, do not seem to have any effect on this parameter.
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Figure 7. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor oil on the feed conversion ratio (FCR) of broilers.
Figure 7. Exploratory graphs with the effects of increasing dietary inclusions of Hermetia illucens or Tenebrio molitor oil on the feed conversion ratio (FCR) of broilers.
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Since the feeding phases of each publication were included in the already presented graphs, this can imply in a high heterogeneity of results. The ADFI tend to decrease with the inclusion of insect meal in most of the manuscripts, while ADG or FCR were stable throughout the inclusion of insect sources. Using insect oil, the majority of broiler performance results was similar among inclusions.
The dispersion graphs below (Figure 8, Figure 9 and Figure 10) show the percentage of variation in ADFI, ADG, and FCR of broilers fed either HI or TM meal and oil related to the control diets (which is zero in the Y axis) using all selected publications.
Figure 8 presents the variation in ADFI between treatments with inclusion of insect products and the control diet for broilers. The variation between control and treatment diets with HI larvae meal is high and negative. For HI oil, TM meal, and TM oil, the ADFI did not vary from the insect inclusion to the control diet in most of the publications.
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Figure 8. Variation (%) in the average daily feed intake (ADFI) responses between broilers fed control diets (zero in the Y axis) or diets with Hermetia illucens or Tenebrio molitor sources.
Figure 8. Variation (%) in the average daily feed intake (ADFI) responses between broilers fed control diets (zero in the Y axis) or diets with Hermetia illucens or Tenebrio molitor sources.
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The ADG variation between control diets and diets with insect meal sources (Figure 9) indicate high variation. Negative values seem to be more present when TM meal was used. There was no observed variation between the use of insect oil or TM meal compared to the control diets.
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Figure 9. Variation (%) in the average daily gain (ADG) responses between broilers fed control diets (zero in the Y axis) or diets with Hermetia illucens or Tenebrio molitor sources.
Figure 9. Variation (%) in the average daily gain (ADG) responses between broilers fed control diets (zero in the Y axis) or diets with Hermetia illucens or Tenebrio molitor sources.
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Figure 10 shows the variation in FCR of broilers fed diets containing different levels of insect meal or oil compared to control diets. This parameter followed ADFI and ADG results, with most negative variation values for HI larvae meal and higher variation for TM meal. The oil sources did not affect the variation in FCR.
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Figure 10. Variation (%) in the feed conversion ratio (FCR) responses between broilers fed control diets (zero in the Y axis) or diets with Hermetia illucens or Tenebrio molitor sources.
Figure 10. Variation (%) in the feed conversion ratio (FCR) responses between broilers fed control diets (zero in the Y axis) or diets with Hermetia illucens or Tenebrio molitor sources.
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The variance-covariance analysis comparing both insect sources is presented in Table 5 and Table 6. Table 5 shows the variation in percentage of HI and TM inclusion against the control diets and a comparison between the two insects. Significant differences on variance of performance results were observed in ADFI, where there was a difference of -10.70 in ADFI using HI meal compared to TM meal that had +7.20 variance in the meal form. The ADG followed the same premises, as -7.92 was obtained for HI meal and +4.05 for TM meal. For oil sources, there were differences (p ≤ 0.05) in ADFI and FCR. Then, the variance in ADFI was +0.60 for HI oil and -4.25 for TM oil, while +0.41 was found in the FCR for HI oil and -3.54 for TM oil.
Table 6 shows the effects of low or high inclusions of either insect meal or oil, without separating the insect species. For the insect meal, high inclusion of the insect meal decreased the variation of ADFI and ADG of broilers (p < 0.001), without effects on FCR. For the insect oil inclusion, no differences were found.
Table 6. Effects of insect inclusion on broiler performance.
Table 6. Effects of insect inclusion on broiler performance.
Variation, %¹ Meal2 p-value4 Oil3 p-value
Control Low High Control Low High
ADFI 94.42a 95.98a 85.62b <0.001 98.44 97.85 97.17 0.620
ADG 92.46a 94.70a 83.41b <0.001 97.12 97.83 96.85 0.545
FCR 107.1 109.7 107.9 0.647 102.4 101.8 101.7 0.576
a,b Differences were considered significant at p ≤ 0.05. ¹Variation in percentage of each performance parameter with the best performance result; ADFI = average daily feed intake; ADG = average daily gain; FCR = feed conversion ratio. 2 Low (≤ 100 g/kg) or high (> 100 g/kg) inclusion of insect meal. 3 Low (≤ 25 g/kg) or high (> 25 g/kg) inclusion of insect oil. 4 Probability of treatment effects.

4. Discussion

4.1. Impacts of dietary inclusions of insect products on poultry health

Insect-based products are receiving great attention as potential ingredient sources for animals. However, it is difficult to obtain an evidence-based view from the large volume and diversity of information that has been increasingly generated. For this reason, a systematic review with a metanalysis can be a useful method to summarize the findings of all the previous studies. Thus, this manuscript contains all searched studies that explored insect products either in meal or oil forms used in diets for broilers and their effects on growth performance and health parameters.
Insect meals have been evaluated and utilized in broiler diets mainly as dietary protein sources and as functional feed additives. Most of the publications have tested inclusion levels of H. illucens (black soldier fly) and T. molitor (yellow mealworm) to partially replace soybean meal, whereas the studies evaluating insect oil are often designed to replace soybean oil. However, feeding insect products for broilers still generates variable results due to the variability in their composition, the different tested inclusion levels, and production systems as well as the lack of information on digestibility and functional properties of insect products.
The commercial poultry production demands high amounts of ingredients; however, the practical and economical approach of replacing soybean meal by insect meal is still a challenge. For this reason, the benefits of low inclusions of insect products have been recently addressed. Therefore, more data is needed to better understand if insect meal or oil sources can beneficially impact intestinal health, immune system, and antimicrobial functions of broilers. Considering these premises, it is also important to evaluate the effects of insect products in the health status of broilers reared under enteric challenge conditions, which is something that was not already published in the literature. The only published material found through the systematic review had broilers fed HI meal and reared under a Salmonella enteritidis Gallinarum challenge [49].
As an avian species, broiler chickens searching and ingesting insects is a natural behavior. The utilization of scattered larva have enhanced the natural behavior, affecting leg health and welfare of chickens [41,48]. Since poultry have this behavior through their evolution, it has been highlighted that acid chitinases are present on the glandular stomach [62]. Chitin is one important component that constitutes the exoskeleton of the insects and it has been associated to a decrease in nutrient digestibility when present in high inclusions in diets for poultry [57]. However, chitin is also known as a natural antimicrobial component [63,64], and besides chitin, the presence of different antimicrobial peptides identified in both H. illucens and T. molitor [65] can contribute to poultry health. For this reason, chitin composition in different insect meal products and the possible beneficial properties of chitin and antimicrobial peptides on poultry health should be more studied in the future.
The evaluation of poultry health has variable and different approaches and the present review was developed to better understand the effects of the main insect meals and insect oils available for poultry diets. The present systematic review intended to demonstrate the effects of insect products that were already reported on broiler microbiota, gut histomorphology, and blood parameters. The importance of poultry microbiota in gut health is related to its capability to ferment carbohydrates and dispose energy and fatty acids as substrates for the GIT [66]. The most predominant genera of microorganisms in the GIT of broilers are Clostridium, Ruminococcus, Lactobacillus, and Bacteroides [67], which have different relative abundance in each intestine segment [68]. In the current study, it was observed that the population of beneficial bacteria is affected by the dietary inclusion of either insect meal or oil for broilers. The presence of lauric acid in insect meal can be one reason that influences bacteria population in the GIT since this fatty acid affects the proliferation of potentially pathogenic bacteria. Kierończyk et al. [43] reported that increasing levels of butyric and lactic bacteria were observed using the insect oil, which also decreased crop pH and helped to control pathogenic bacteria that usually do not tolerate acidic pH. However, the authors observed increased proliferation of Bacteroides–Prevotella cluster, Enterobacteriaceae and C. perfringens, probably due to the feed retention that was correlated to the antimicrobial effect and the availability of lauric acid in the crop.
Ruminococcaceae and Lachnospiraceae families have been reported to produce butyric acid [69], which is used as an energy source for enterocytes in the gut [70]. Chitin from insects can affect the production of butyric acid [56] and a previous study indicated that low levels of insect full fat meal (0.2%) reduced pathogens as C. perfringens [30]. On the other hand, high doses of HI meal improved the volatile fatty acid profile of the caeca content of broilers [19]; however, the authors only described the correlation between the fatty acid profile of the HI meal in the caeca, without relating chitin with the prebiotic effects. Prebiotic functions provided by chitin from insects were previously described as favorable to improve gut health [71]. The mucin dynamics, when using insect meal, was suggested to beneficially improve histological parameters that were correlated to microbiota due to production of volatile fatty acids [47].
Protein and amino acids that escape from digestion and absorption in the hindgut can be fermented in the caeca being used by bacteria [68]. This can extend the nutritional functions of feeding protein sources once they can be used by the microbiota, impacting the gut health of animals. The caeca microbiome as affected by H. illucens and T. molitor meals was already described [52,54]. Indirect approaches using metabolites can be used as demonstrated by Hartinger et al. [20] and through a principal component analyses [53]. In the present study, it was observed that insect meal affected gut microbiota especially Firmicutes, Lactobacilli, and Bacteroides populations. Positive impacts of insect products in the microbiota can be indicated since lower rates of Bacteroidetes and higher Lactobacilli are correlated with good gut health [47,53]. The Ruminococcaceae family is also important for the intestinal health and it was affected by insect meal [47]. Based on the results, HI and TM probably have different paths in microbiota modulation and the effects differed from each other [37,60]. Also, the region of GIT where microbiota populations were evaluated is variable among the peer-reviewed publications, which can influence the results.
In the present study, we observed that histomorphology findings were not consistent with the inclusion of insect meal or oil in diets for broilers. Some publications that enhanced this affirmation used 50% to 100% replacement of soybean oil by HI oil and did not observe alterations in gut histomorphology [6,32]. However, there are reports using 50% of soybean oil replaced by insect oil where increased villus height of ileum was observed [46], while similar results on jejunum villus height were reported using 50 and 100% oil replacement [20]. There is a publication [34] indicating that 15% inclusion of TM meal decreased villus, deepened crypts, and decreased villus:crypt ratio compared to 5 and 10% for broilers, whereas Biasato et al. [35], evaluating the same TM meal, did not observe any differences on histomorphology parameters.
Higher monocytes and hemoglobin were reported in broilers fed HI meal [17] replacing fish meal. Serum lipids and cholesterol were investigated using HI meal, and decreased cholesterol was found in blood samples, which was associated to the presence of chitin [19], indicating that the chitin could decrease lipid absorption by binding to lipids, and as a result, the plasma cholesterol decreased. Using TM meal for broilers increased albumin:globulin ratio and serum globulin levels [51]. These parameters were also related to the chitin levels that could work as prebiotic and boost the immune response. Increased erythrocytes and decreased albumin and gamma glutamyl transferase (GGT) using TM meal were reported by Biasato et al. [35]. These findings were seen as good results since high GGT levels indicate liver and bile flow disorders.
The inclusion of HI oil as a functional ingredient for poultry diets has been increased because the lauric acid presents antimicrobial properties [6,43]. The impacts of 100% replacement of soybean oil with insect oil were not negative according to our systematic review. Low levels of cholesterol in blood samples demand low bile synthesis, indicating that the animal had a highly efficient fat utilization. Additionally, this result together with low levels of alanine aminotransferase can be related to good liver health. Serum triglycerides reduced when TM oil was compared to poultry fat [55]. The authors also indicated that the high levels of polyunsaturated fatty acid of TM oil could reduce the conversion of acetyl-Coa to triglycerides in the liver, affecting blood triglycerides in broilers.
The use of insect meal has been demonstrated to potentially improve the immunity status in poultry, crustaceans, and fish [72,73,74]. Even though publications with other animal species were not selected in the systematic review, pigs fed HI meal had decreased diarrhea on weaning age and improved intestine homeostasis under the presence of Escherichia coli, by promoting levels of mucin-1 and mucin-2, while regulated the expression of antimicrobial peptides through TLR2-NF-κB/MAKP signaling pathway [75]. Also, the authors observed decreased pro-inflammatory and increased anti-inflammatory cytokines at finishing ages using HI meal on diets [76]. As for dogs and cats, there are reports indicating improvements in the antioxidant status [77], with reduced TNF-α and increased concentrations of superoxide dismutase and glutathione peroxidase in serum of dogs fed diets with HI meal [78]. However more studies are needed to better understand the effects in anti-inflammatory and immunity parameters [79] in companion animals but also in poultry. For the immunology effects in broilers, it shows a decrease in white cells and improved performance [45]. Also, under a viral challenge, there was a reduction in the load of avian infectious bronchitis virus (IBV) of trachea and kidney using 10% HI meal [44], and an increase in the survival rate of broilers with less damage to the trachea tissues. The authors summarized that interferon-gamma (IFN-γ) was activated in mRNA levels and this was involved in the activation of T-cells. Still, the interleukin-2 levels increased and promoted CD8+ lymphocytes responses. Finally, major histocompatibility complex-I (MHC-I) molecules that control CD8+ increased, and with the CD8+ lymphocytes promotion, the elimination of the avian IBV increased when diets had HI meal.
An experimental challenge with Salmonella enteritidis Gallinarum was conducted in broiler chickens fed HI meal [49]. The authors observed an increase on birds’ survival rate followed by a decrease on Gram negative colonies on liver, spleen, bursa of Fabricius, and caeca. However, the mechanism of HI meal against S. enteritidis Gallinarum was not clear. Evaluating a fermented probiotic from TM meal for broilers under Salmonella and Escherichia coli challenge, Islam and Yang [58] reported decreased mortality and improved levels of immunoglobulin (Ig) IgA and IgG. This study showed reduction in the caeca E. coli and Salmonella counts, indicating that the combination of antimicrobial effects of chitin and antimicrobial peptides from larvae could contribute to reduce pathogenic bacteria. The results highlight the possibility of evaluating the effects of insect products at low levels on pathogenic bacteria when broilers are reared under intestinal challenges.

4.2. Metanalysis: exploratory analyses of insect products on broiler performance

Regarding the growth performance of broilers fed diets with the inclusion of insect products, a metanalysis was previous published [80], but did not discriminate the insect products. By the meantime this manuscript was written, another metanalysis was published to predict the metabolizable energy of the HI meal and the effects on performance [81]. In the current manuscript, the metanalysis was conducted to compare results of performance parameters such as ADFI, ADG, and FCR between the insect sources.
The database utilized for the present metanalysis consisted of manuscripts published in scientific journals between January 2016 and January 2023, as presented in the Table 1. Different sources of protein as main ingredients, variable broiler ages and genetics, and insect products were reported, and this could be a reason to the heterogeneity of results reported in Figure 2, Figure 3, Figure 4, Figure 5, Figure 6 and Figure 7. Regardless, the Figure 8, Figure 9 and Figure 10 indicate a greater growth performance of broilers fed TM meal compared to HI meal, and this was confirmed in Table 5 for ADFI (p < 0.001) and ADG (p = 0.002). A different outcome was observed for the oil sources, probably due to the lower number of available publications with TM oil compared to TM meal and HI oil. During the construction of this database, no manuscripts were found evaluating, in the same study, both insects as ingredients on broiler performance. For this reason, further experiments can be performed using different insect sources in the same diet since the availability of insect products can be variable worldwide.
Most of the publications regarding the inclusion of insect products for broilers have been conducted using insect meal to replace soybean meal. The levels of inclusion or replacement of HI or TM meal usually ranged from 5 to 15%. However, this can be not cost-effective for the commercial broiler productions and, for this reason, evaluating lower inclusion of insect products can be highlighted. In the present study, the insect meal at the low inclusion levels had similar growth performance to the control treatment in broilers without any intestinal challenge. No negative effects on performance were reported evaluating low levels of insect meal for broilers [18,21,22,34]. Dietary inclusions of insect meal with levels higher than 1% and lower than 10% should be more studied since this can result in different effects compared to very low or high levels. This evaluation can improve the information on the effects of low inclusions of insect meal on broiler nutrition and health, also allowing results that can be more cost-effective. For the insect oil, no differences were found with low or high inclusion levels, also without presenting any negative effects on broiler performance [38]. No data on full soybean oil replacement with TM meal was found in the literature.
In conclusion, the use of insect products in poultry diets affected broilers` health, demonstrating positive effects in the modulation of microbiota. This can be noticed through the different effects of various phylum, class, family, and genus of bacteria reported in this review that are mostly from caeca content. The reduction in pathogenic bacteria and the enhanced production of short-chain fatty acids are also characteristics of insect inclusions in poultry diets. Nevertheless, the immunology system is indeed improved, and reduced mortality was observed in challenged animals, with positive impacts on immunoglobulins, interleukins, and lymphocytes. To better understand the microbiota mechanism, future studies should be conducted focus on the inclusion levels of insect products and different intestinal challenges that can be found in production systems. For the performance data, T. molitor had better results if compared to H. illucens, also high meal inclusion (>100 g/kg) of insects decreased broiler performance as already reported in some manuscripts. The dietary utilization of insect oil did not affect any performance parameters and it seems that H. illucens oil can be used to completely replace soybean oil, whereas more studies are needed using T. molitor oil. Also, more data is needed to evaluate the effects of insect oil on poultry health aiming to provide more robust conclusions in the presence of an enteric challenge.

Supplementary Materials

The following supporting information can be downloaded at the website of this paper posted on Preprints.org. Figure S1. Nutritional composition of different Hermetia illucens meal. Figure S2. Nutritional composition of different Tenebrio molitor meal. Figure S3. Total amino acids (%) of Hermetia illucens larvae meal. Figure S4. Total amino acids (%) of Tenebrio molitor larvae meal.

Author Contributions

Conceptualization, Y.K.D. and C.S.; methodology, Y.K.D. and C.H.F.; formal analysis, Y.K.D.; data curation, Y.K.D.; writing—original draft preparation, Y.K.D. and C.S.; writing—review and editing, Y.K.D. and C.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

The authors wish to thank Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brasília, Brazil) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brasília, Brazil) for partial scholarships.

Conflicts of Interest

The authors declare no conflict of interest.

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Preprints 91942 g001
Figure 1. Flow diagram of the systematic review process.
Figure 1. Flow diagram of the systematic review process.
Preprints 91942 g001
Table 1. Summary of live production studies used in the metanalysis.
Table 1. Summary of live production studies used in the metanalysis.
Reference Code of publication Insect used1 Feeding phases² Genetic/sex³ Protein/oil source4 n5
Mat et al. [17] 1 HI Str, Grw, Fin Cobb/male FM, SBM 360
Sedgh-Gooya et al. [18] 2 TM Str, Fin Arbor Acres FM, SBM 180
Kim et al. [19] 3 HI Str, Grw Ross/male SBM, CGM 126
Kierończyk et al. [6] 4 HI oil Str, Grw Ross SBM 960
Hartinger et al. [20] 5 HI Str, Grw Ross/male SBM 432
Murawska et al. [21] 6 HI Str, Grw, Fin Ross/male SBM 384
Hartinger et al. [22] 7 HI Str, Grw Ross/mixed SBM 216
Elangovan et al. [23] 8 HI Str Cobb/mixed SBM 90
Kim et al. [24] 9 HI oil Str, Grw Ross/male SBM, CGM 300
Pietras et al. [25] 10 TM Fin Ross/male SBM, LM 64
Dabbou et al. [26] 11 HI oil Str, Grw Ross/male SBM, CGM 200
Mutisya et al. [27] 12 HI Str, Fin Cobb/mixed FM 120
Elahi et al. [28] 13 TM Str, Fin Ross/male SBM 700
Benzertiha et al. [29] 14 TM Str, Grw Ross/female SBM, RS, FM 300
Benzertiha et al. [30] 15 TM oil Str, Grw Ross/female SBM 48
Khan et al. [31] 16 TM Str, Grw Ross SBM, CM, GM, SM 100
Brede et al. [32] 17 HI Str, Grw Ross/male SBM 240
Onsongo et al. [33] 18 HI Str, Fin Cobb/male SBM, FM 288
Biasato et al. [34] 19 TM Str, Grw, Fin Ross/male SBM, CGM 160
Biasato et al. [35] 20 TM Str, Grw, Fin Ross/female SBM, CGM 160
Bovera et al. [36] 21 TM Fin Shaver Brown /male SBM 80
Józefiak et al. [37] 22 HI and TM Str, Grw Ross/female SBM, RS, rye, FM 300
Schiavone et al. [38] 23 HI oil Str, Grw, Fin Ross/male SBM, GLM 150
Schiavone et al. [39] 24 HI oil Fin Ross/male SBM, GLM 120
Kareem et al. [40] 25 HI Str, Grw, Fin Cobb/female SBM, FM 216
¹ HI = Hermetia illucens and TM = Tenebrio molitor in meal form unless indicated as oil. ² Feeding phases = Str: starter; Grw: grower; Fin: finisher. ³ Sex was informed whenever indicated in the manuscripts. 4 Protein sources in the control treatment; FM = fish meal; SBM = soybean meal; CGM = corn gluten meal; LM = lupine meal; RS = rapeseed meal; GM = guar meal; SM = sunflower meal; CM = cottonseed meal; GLM = gluten meal; 5 n: number of birds in the experiment and fed control diets and insect products.
Table 2. Use of Hermetia illucens (black soldier fly) meal or oil as ingredients for broilers and the impacts on health parameters.
Table 2. Use of Hermetia illucens (black soldier fly) meal or oil as ingredients for broilers and the impacts on health parameters.
Reference Overall1 Inclusion Main effects3
Ipema et al. [41] Replacement of 8% of the diet in DM with different provision of HI (meal + oil, live scattered on litter, whole dried in the feeder and whole dried scattered on litter) and impacts on broiler health and behavior 5.76% No difference was found for feather corticosterone, IgG, and IgM against keyhole limpet hemocyanin from plasma. Footpad dermatitis and litter quality were affected by the treatments
Bongiorno et al. [42] HI live larvae for local poultry and the effects on blood parameters 10% live larvae supplementation on the ADFI² HI reduced leukocytes levels and increased monocytes and cholesterol levels. Higher gamma glutamyl transferase in blood samples, indicating improvement on liver health status
Mat et al. [17] Different replacement levels of fishmeal by defatted HI meal for broilers and the effects on blood parameters 4, 8, and 12% Corpuscular volume, monocytes, red blood cells, granulocytes, hematocrits, hemoglobin, corpuscular hemoglobin concentration, red cell distribution width, platelet volume, and lymphocytes were affected by HI meal
Kierończyk et al. [43] HI oil replacing soybean oil and the effects on gut microbiota and immune characteristics 1.67 and 3.34% 100% replacement increased the total number of Clostridium leptum subgroup and Enterobacteriaceae and Lactobacillus groups in crop. No effects in jejunal microbiota. Reduced C. perfringens and all the other microorganisms except Bacteroides with 50% HI replacement. Reduced cholesterol and ALT in plasma. No effects on plasma immunoglobulins and IL
Hartinger et al. [20] HI oil replacing 50 or 100% of soybean oil and HI meal replacing a 15% CP diet for broilers. Evaluated the effects on ileum histomorphology and caeca microbial metabolites 5.2, 4.64 and 4% of HI meal and/or 0.75, 1.5, 0.64 and 1.28% of HI oil HI meal decreased biogenic amines Agmatine, Spermidine, Spermine, and ammonia in caeca contents. Ethanolamine was higher with the HI oil. HI oil increased the concentration of Agmatine in colon contents. HI meal and 50 or 100% oil replacement increased jejunal villus area and width compared to control diets
Kim et al. [19] Microwave-dried HI meal replacing 25 and 50% of SBM Starter: 7.5 and 15%. Grower: 7 and 14%. Finisher: 6.5 and 13% SCFA in caeca were higher in HI treatments (except butyrate) especially with 50% replacement. Blood triglycerides, monocytes, and red blood cell distribution were higher 50% replacement. Decreased low-density lipoprotein was obtained
Zhang et al. [44] Immune responses using HI larvae meal for broilers experimentally infected with IBV 1, 5, and 10% Reduced IBV symptoms with 10% inclusion. At the tissue level presented reduced IBV infection and lesion. Increased survival rate of chicks. Improved proliferation of CD8+ lymphocytes
Hartinger et al. [22] 0, 15, and 30% of CP from SBM replaced by HI meal 0, 4, 10% No differences on intestine morphology parameters
de Souza Vilela et al. [45] Increasing levels of full fat HI meal for broilers and the effects on immune responses Starter: 2.5, 5, 7.5, and 10%. Grower/Finisher: 5, 10, 15, and 20% Decreased blood lymphocytes at 21 d and decreased cytotoxic T cell CD3+CD8+ in jejunum
Kim et al. [46] Replacement of 50 and 100% of soybean oil by HI oil and the effects on intestinal health and blood profile 1.5% and 3% Higher ileum villus height with 50% replacement. Higher butyrate levels in caeca content with HI oil. Lowered the lipase levels on blood samples
Biasato et al. [47] Use of defatted HI meal for broilers and the impact on gut health 5, 10, and 15% HI did not affect the relative abundance of Firmicutes and Bacteroidetes and Firmicutes:Bacteroidetes ratio, but 15% HI had higher relative abundance of Proteobacteria. L-Ruminococcus (Ruminococcus from Lachnospiraceae family), Faecalibacterium, Blautia, Clostridium, Bacteroides, Roseburia, and Helicobacter genera. Lactobacillus and Ruminococcus improved in 10% HI diet. The mucin staining was not affected by HI
Kierończyk et al. [6] Replacement 25, 50, 75 and 100% of soybean oil by HI oil and the effects on broilers’ gut histomorphology Starter: 0.83, 1.67, 2.34, and 3.34%. Finisher: 1.23, 2.46, 3.44 and 4.92% No effects on histomorphology of duodenum, jejunum, and ileum. The HI oil reduced the jejunum and ileum weights relative to BW
Ipema et al. [48] Use of live larvae and impacts on health and behavior of broilers 5 and 10% of ADFI² in DM with live larvae No effects on hock burns, lameness, cleanliness, thigh scratches, tibia length, tibia fluctuating asymmetry, and tibia breaking strength, only reduced the tibia width with 10% replacement
Lee et al. [49] Immune activity of broilers experimentally infected with Salmonella Gallinarum fed with HI larvae 1, 2, and 3% Higher presence of CD3+CD4+ T lymphocytes in spleen. Amplified spleen lymphocyte proliferation, increased lysozyme activity in serum, and increased survival rate of chicks with 3% inclusion
Dabbou et al. [50] HI defatted meal and impacts on blood traits, gut morphology, and histological features 5, 10, and 15% No effects on hematological and serum parameters. Diet with 15% HI decreased villi height, crypt depth, and V:C ratio compared to the other diets
Schiavone et al. [39] Replacement of 50 and 100% of soybean oil by HI oil for broilers (finisher phase) and effects on blood and gut morphology parameters 3.43 and 6.87% No differences on blood and histomorphology parameters
Schiavone et al. [38] 50 and 100% of soybean oil replaced by HI oil and the effects on blood parameters 2.91 and 5.85 No differences observed in blood analyses
1 HI = Hermetia illucens; SBM = soybean meal; IBV = avian infectious bronchitis virus; CP = crude protein. 2 ADFI = average daily feed intake. 3 IgG = immunoglobulin G; IgM = immunoglobulin M; SCFA = short-chain fatty acids; ALT = alanine aminotransferase; IL = interleukin; BW = body weight; V:C = villus:crypt ratio.
Table 3. Use of Tenebrio molitor (yellow mealworm) meal or oil as ingredients for broilers and the effects on health parameters.
Table 3. Use of Tenebrio molitor (yellow mealworm) meal or oil as ingredients for broilers and the effects on health parameters.
Reference Overall1 Inclusion Main effects2
Sedgh-Gooya et al. [18] Effects on histomorphology of broilers fed full fat TM meal 2.5 and 5% No effects on histomorphology
Sedgh-Gooya et al. [51] Inclusion of TM meal in broiler diets and effects on caeca microbiota and blood parameters 2.5 and 5% Decreased blood albumin:globulin ratio with TM diets. Escherichia coli reduced with 5% TM inclusion
Benzertiha et al. [29] Full fat TM meal supplemented in broiler diets and impacts on bird immune system 0.2 and 0.3% TM meal diets had same IgY, IgM, levels than diets with salinomycin, but increased IL-2 and TNF-α with 0.3% TM inclusion
Biasato et al. [52] TM meal and the effects on broiler intestinal microbiota and mucin 5, 10, and 15% Decreased relative abundance of Firmicutes:Bacteroidetes ratio and the relative abundance of Clostridium, Coprococcus,L-Ruminococcus, and Ruminococcus with 15% TM. Higher mucin staining with 5% TM
Elahi et al. [28] Different levels of dried TM meal and usage of fresh TM meal 2, 4, 8, and 10.48% as fresh matter that correspond to 4% of dried TM inclusion Linear increase of ALT in blood. Reduced total protein. Higher malondialdehyde and lower total antioxidant capacity. Higher uric acid in blood. Decreased levels of lysozyme with fresh TM
Józefiak et al. [53] Full fat TM meal supplemented in broiler diets and effects on caeca microbiome 0.2 and 0.3% Phylum: Decreased relative number of Actinobacteria with 0.2% TM and Proteobacteria in both treatments. Increased Bacteroidetes with TM addition. Class: 0.3% TM decreased Clostridia and 0.2% TM increased Clostridia and decreased Actinobacteria. Order: 0.2% TM increased Clostridiales, but there was a decrease with 0.3% TM, and 0.2% TM decreased Lactobacilales. Family: 0.3% TM reduced Ruminococcaceae, Enterobacteriaceae and Bifidobacteriaceae. Genus: 0.3% TM stimulated growth of Ruminococcus and Bifidobacterium, and 0.2% TM decreased Lactobacillus
Biasato et al. [54] TM full fat meal inclusion in broiler diets and effects on caeca microbiota and health 5 and 15% Higher inclusion of TM meal decreased relative abundance of Firmicutes phylum and Firmicutes:Bacteroidetes ratio. Higher inclusion of TM meal decreased villi mucin staining
Benzertiha et al. [30] Full fat TM meal supplementation in diets and effects on enzyme activity and microbiota 0.2 or 0.3% TM meal at 0.3% decreased the caeca Bacteroides– Prevotella cluster. Also, 0.2 and 0.3% decreased C. perfringens. Salinomycin and TM treatments had the lowest extracellular β-glucuronidase and higher α-glucosidase activity on caeca contents
Benzertiha et al. [55] TM oil and effects on pancreatic enzyme and blood parameters 5% TM oil reduced amylase activity and triglycerides of blood, also triglycerides and total cholesterol of liver
Loponte et al. [56] Total replacement of SBM by full fat TM meal in broiler diets and the effects on caeca VFAs 100% SBM replacement Almost double Mmol/L of all VFAs, increased % of butyrate in total VFAs and decreased the acetate, propionate, and valerianate
Biasato et al. [57] TM meal and effects on intestinal microbiota, histomorphology, and mucin composition of free-range broilers 7.5% Increased Sutterella, Ruminococcus, Oscillospira, Clostridium, Coprococcus, and Firmicutes:Bacteroidetes ratio. Increased mucin staining intensity on ileum
Biasato et al. [35] TM meal and the effects on broilers health 5, 10, and 15% Increased levels of erythrocytes, linear decrease in albumin levels, and quadratically decrease in gamma glutamyl transferase in blood. No differences in histomorphology using TM meal
Islam and Yang. [58] TM probiotic supplementation for broilers experimentally challenge with Salmonella enteritis and E. coli 0.4% of TM probiotic IgG and IgA levels were higher with the probiotic. Lower mortality of birds and lower presence of E. coli and Salmonella spp. in caeca microbiota with the probiotic
1TM = Tenebrio molitor; SBM = soybean meal; VFAs = volatile fatty acids. 2 IgY = immunoglobulin Y; IgM = immunoglobulin M; IL = interleukin; TNF-α = tumor necrosis factor alpha; ALT = alanine aminotransferase; V:C = villus:crypt ratio; IgG = immunoglobulin G; IgA = immunoglobulin A.
Table 4. Use of Hermetia illucens and Tenebrio molitor as ingredients for broilers and their impacts on health parameters.
Table 4. Use of Hermetia illucens and Tenebrio molitor as ingredients for broilers and their impacts on health parameters.
Reference Overall1 Inclusion Main effects
Bellezza Oddon et al. [59] Live TM and HI larvae and impacts on health 5% of ADFI2 with larvae of TM or HI Gut histomorphology index and histopathological alterations were not influenced by HI and TM larvae. No effects on hematological and serum parameters
Colombino et al. [60] Live TM and HI larvae for broilers and effects on mucin, immune response, and caeca microbiota 5% of the expected ADFI TM diets had lower interleukin-2 expression compared to HI diets. Mucin was not affected by live larvae. HI and TM influenced the relative abundance of Victivillaceae family. Saccharibacteria and Clostridium increased HI, Collinsella was more abundant in TM treatment, and Eubacterium increased in both diets
Józefiak et al. [37] TM and HI full fat meal supplementation and impact on microbiota 0.2% supplemented Crop digesta: HI decreased C. leptum and increased C. coccoides–Eubacterium rectale cluster. Lactobacillus spp. and Enterococcus increased in TM and HI groups, while TM reduced Bacteroides–Prevotella. Ileal digesta: both insects increased the number of C. coccoides–E. rectale, Lactobacillus spp. Enterococcus spp. counts decreased in HI and increased in TM groups. Caeca digesta: Bacteroides–Prevotella, Streptococcus spp./Lactococcus spp., C. coccoides–E. rectale cluster, and Lactobacillus spp./Enterococcus spp. count increased with HI
1 HI = Hermetia illucens; TM = Tenebrio molitor. 2 ADFI = average daily feed intake.
Table 5. Variation between control diets and dietary inclusions of HI or TM meal or oil for broilers.
Table 5. Variation between control diets and dietary inclusions of HI or TM meal or oil for broilers.
Variation, %¹ Meal p-value4 Oil p-value
HI2 TM3 HI TM
ADFI -10.70 7.20 <0.001 0.61 -4.25 0.036
ADG -7.92 4.05 0.002 -0.51 0.81 0.888
FCR -1.49 2.46 0.241 0.41 -3.56 0.049
¹ Variation in percentage between control diets (zero) and treatment diets with insect products in meal or oil forms for all feeding phases; ADFI = average daily feed intake; ADG = average daily gain; FCR = feed conversion ratio. ² HI = Hermetia illucens. 3 TM = Tenebrio molitor. 4 Probability of treatment effects, differences were considered significant at p ≤ 0.05.
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